iwep2017 02 web - djs · international workshop on electric probes in magnetized plasmas (12 ; 2017...

Book of Abstracts12th International Workshop on

Electric Probes in Magnetized Plasmas 2017

Naklo 2017

IWEP 2017September 4 - 7N A K L OS L O V E N I A

12th International Workshop on Electric Probes in Magnetized Plasmas

Book of Abstracts

12th International Workshop on Electric Probes in Magnetized Plasmas

2017

Naklo 2017

Organizers: Nuclear Society of Slovenia

and Jožef Stefan Institute

Reactor Physics Department

Jamova cesta 39 SI-1000 Ljubljana

Slovenia

www.nss.si/iwep2017/

Book of Abstracts 12th International Workshop on Electric Probes in Magnetized Plasmas 2017 Naklo 2017 Editor: ddr.Tomaž Gyergyek Published by: Nuclear Society of Slovenia Jamova cesta 39 SI-1001 Ljubljana Web: www.djs.si E-mail: [email protected] Printed 50 copies. Printed by DEMAT d.o.o.. Not for sale.

CIP - Kataložni zapis o publikaciji Narodna in univerzitetna knjižnica, Ljubljana 533(082) INTERNATIONAL Workshop on Electric Probes in Magnetized Plasmas (12 ; 2017 ; Naklo) Book of abstracts / 12th International Workshop on Electric Probes in Magnetized Plasmas, [also] IWEP 2017, September 4-7, Naklo, Slovenia ; [organizers Nuclear Society of Slovenia and Jožef Stefan Institute Reactor Physics Department ; editor Tomaž Gyergyek]. - Ljubljana : Nuclear Society of Slovenia, 2017 ISBN 978-961-6207-41-6 1. Gyergyek, Tomaž 2. Društvo jedrskih strokovnjakov Slovenije 3. Inštitut Jožef Stefan (Ljubljana). Reaktorski center (Podgorica) 290715136

Previous meetings organized by the Nuclear Society of Slovenia • First Meeting of Nuclear Society of Slovenia, Bovec, Slovenia, June 1992 • Regional Meeting: Nuclear Energy in Central Europe, Present and Perspectives,

Portorož, Slovenia, June 1993 • PSA/PRA and Severe Accidents ‘94, Ljubljana, Slovenia, April 1994 • Annual Meeting of NSS ‘94, Rogaška Slatina, Slovenia, September 1994 • 2nd Regional Meeting: Nuclear Energy in Central Europe, Portorož, Slovenia, September 1995 • 3rd Regional Meeting: Nuclear Energy in Central Europe, Portorož, Slovenia, September 1996 • 4th Regional Meeting: Nuclear Energy in Central Europe, Bled, Slovenia, September 1997 • Nuclear Energy in Central Europe `98, Čatež, Slovenia, September 1998 • Nuclear Energy in Central Europe `99 with Embedded Meeting Neutron Imaging Methods to

Detect Defects in Materials, Portorož, Slovenia, September 1999 • 20th International Conference on Nuclear Tracks in Solids, Portorož, Slovenia, August 2000 • Nuclear Energy in Central Europe 2000, Bled, Slovenia, September 2000 • Nuclear Energy in Central Europe 2001, Portorož, Slovenia, September 2001 • Nuclear Energy for New Europe 2002, Kranjska Gora, Slovenia, September 2002 • Nuclear Energy for New Europe 2003, Portorož, Slovenia, September 2003 • Nuclear Energy for New Europe 2004, Portorož, Slovenia, September 2004 • Nuclear Energy for New Europe 2005, Bled, Slovenia, September 2005 • Nuclear Energy for New Europe 2006, Portorož, Slovenia, September 2006 • Nuclear Energy for New Europe 2007, Portorož, Slovenia, September 2007 • Nuclear Energy for New Europe 2008, Portorož, Slovenia, September 2008 • Nuclear Energy for New Europe 2009, Bled, Slovenia, September 2009 • Nuclear Energy for New Europe 2010, Portorož, Slovenia, September 2010 • Nuclear Energy for New Europe 2011, Bovec, Slovenia, September 2011 • Nuclear Energy for New Europe 2012, Ljubljana, Slovenia, September 2012 • Nuclear Energy for New Europe 2013, Bled, Slovenia, September 2013 • Nuclear Energy for New Europe 2014, Portorož, Slovenia, September 2014 • Nuclear Energy for New Europe 2015, Portorož, Slovenia, September 2015 • Nuclear Energy for New Europe 2016, Portorož, Slovenia, September 2016

Committees

Members of the committees are listed in alphabetic order.

International Scientific Committee

Michael LAUX, Germany, Chair

John ALLEN, UK Gheorghe DINESCU, Romania Åshild FREDERIKSEN, Norway

James Paul GUNN, France Tomaž GYERGYEK, Slovenia

Carlos HIDALGO, Spain Mark KOEPKE, USA

Emilio MARTINES, Italy Hans Werner MÜLLER, Germany

Tsviatko POPOV, Bulgaria Jens Juul RASMUSSEN, Denmark Roman SCHRITTWIESER, Austria

Carlos SILVA, Portugal Reiner STENZEL, USA

Organizing Committee

Tomaž Gyergyek, Chair

and Editor of Book of Abstracts

Saša Bobič Mateja Južnik Jernej Kovačič Urška Turšič

Nina Udir Bojan Žefran

Welcome

International Workshops on Electric Probes in Magnetized Plasmas (IWEP) take place every second year since 1993. They are devoted to understanding and solving problems associated with electric probes in either magnetized or unmagnetized plasmas. The 12th International Workshop on Electric Probes in Magnetized Plasmas 2017 (IWEP 2017) takes place in Hotel Marinšek in Naklo, Slovenia from 4th to 7th of September 2017 and is organized by the Nuclear Society of Slovenia. This Society has a long tradition of successful organization of scientific conferences and workshops. The organizers have received 18 abstracts. All the abstracts were approved by the International Scientific Committee and are published in this book of abstracts.

Place and time of Workshop

The Workshop will take place in Hotel Marinšek in Naklo, Slovenia. Address: Hotel Marinšek d.o.o. Glavna Cesta 2 4202 Naklo Slovenija, EU From: Monday, September 4, at 12:00 To: Thursday, September 7, at 12:00

Registration

Registration desk opening hours: Monday, September 4: 12:00 to 18:00 Tuesday, September 5: 9:00 to 12:00

Social Activities

Welcome Reception: Monday, September 4 Workshop Lunch: Tuesday, Wednesday and Thursday. Lunch is included in the registration fee and will be served from 12:00 - 13:30. Workshop Trip: Wednesday, September 6 Workshop Dinner: Wednesday, September 6

Workshop Program

Monday, September 4

12:00-16:00 Arrival and registration 16:00 Opening Ceremony Paper no. 101 16:15 – 16:45

Measurements with cold and emissive probes in a High Power Impulse Magnetron Sputtering discharge (HiPIMS) R. Schrittwieser

Paper no. 102 16:45-17:15

Design and Status of the Electrostatic Probe System for the SPIDER Experiment M. Spolaore

Paper no. 103 17:15 – 17:45 Electric Probe Measurements in Uniform and Strongly Magnetized Plasma Produced by Glow-Discharge in Halbach Array S. Costea

19:00 Welcome cocktail

Tuesday, September 5 Paper no. 104 9:00 – 9:30

Slabbing Model for Kinetic Description of ion Thrusters Plasma Plumes: Propagator Integral Method Solutions J. M. Donoso

Paper no. 105 9:30-10:00

Kinetic Analysis of Weakly ionized Plasmas in presence of collecting and emissive walls J. Gonzales

Paper no. 106 10:00-10:30

A Study of the Electron Energy Probability Function in the Plume and Channel of a low-power Hall Thruster M. Tichy

10:30-11:00 Coffee break Paper no. 107 11:00-11:30

Multiprobe Characterization of Plasma Flows for Space Propulsion J. Damba

Paper no. 108 11:30-12:00

Langmuir Probe Measurements in the Early Hydrogen Discharge of GLAST-III Tokamak A. Qayyum

Lunch Paper no. 109 16:00 – 16:30

Measurements of Densities of Gas Constituents in a Discharge Device with a Large Wall Probe I. P. Kurlyndskaya

Paper no. 110 16:30-17:00

Spatial Distribution of Plasma Parameters in Gas Aggregation Nanocluster Source A. Kolpakova

Wednesday, September 6 Paper no. 111 9:00-9:30

Determination Of Anisotropic Ion Velocity Distribution Function In Intrinsic Gas Plasma. Theory A. Grabovskiy

Paper no. 112 9:30 – 10:00

Determination Of Anisotropic Ion Velocity Distribution Function In Intrinsic Gas Plasma. Probe Method A. Grabovskiy

Paper no. 113 10:00 – 10:30

Feasibility, Strategy, Methodology, and Analysis of Probe Measurements in Plasma under High Gas Pressure V. Demidov

10:30-11:00 Coffee break Paper no. 114 11:00 – 11:30

Current-Voltage and Floating Potential Characteristics of Cylindrical Emissive Probes from a Self-consistent Full-Kinetic Model X. Chen

Paper no. 115 11:30 – 12:00

Current Density Distribution Along the Cylindrical Probe in Magnetized Plasma G. Popa

Lunch 15:00 – 18:30 Workshop trip 20:00 Workshop dinner

Thursday, September 7 Paper no. 116 9:00 – 9:30

Disturbances of ICP Plasmas by Langmuir Probes with Uninsulated Protecting Shields V. Riaby

Paper no. 117 9:30-10:00

The Radial-Motion-Only (RMO) and Orbital-Motion (OM) Methods for Calculating Velocity Distribution Functions in a Spherical Probe Scenario S. Kuhn

Paper no. 118 10:00-10:30

Some Experiments with the Tunnel Probe in a Low-Temperature Magnetized Plasma J. Kovačič

10:30 Closing ceremony

Abstracts

Disclaimer The content of abstracts published in the book of abstracts is the responsibility of the authors concerned. The organizer is not responsible for published facts and technical accuracy of the presented data.

101.1

Measurements with cold and emissive probes in a High Power Impulse Magnetron Sputtering discharge (HiPIMS)

Roman Schrittwieser

Institute for Ion Physics and Applied Physics, University of Innsbruck

Technikerstr. 25

A-6020 Innsbruck, Austria

[email protected]

Bernd S. Schneider, Stefan Costea, Ovidiu Vasilovici, Codrina Ionita

Institute for Ion Physics and Applied Physics, University of Innsbruck

Technikerstr. 25


[email protected], [email protected], [email protected],

[email protected]

Tiberiu Minea, Daniel Lundin

Laboratoire de Physique des Gaz et des Plasmas, LPGP, Université Paris-Sud, Université Paris-

Saclay

Bat. 210, rue H. Becquerel,

F-91405 Orsay Cedex

[email protected], [email protected]

A combination of two Cold Langmuir Probes (CLP)

and one Electron Emissive Probe (EEP) was used for local

measurements of plasma (ion) density ni, plasma potential

pl and electron temperature Te, with high temporal resolu-

tion, only limited by the data acquisition system (see Fig. 1).

The ion density was determined as usual from the ion satura-

tion current Iis:

eB

i

p

is

i

Tk

m

eA

In

7,0

, (1)

with Ap being the effective probe area for ion collection, mi

the ion mass and kB the Boltzmann constant. The relation be-

tween pl and the floating potential Vfl of a CLP is given by:

e

TV

I

I

e

TV

e

fl

is

ese

flpl

ln (2)

Here Ies is the electron saturation current. By means of an EEP we have

the possibility to estimate pl (notwithstanding the pending discussions

on the reliability of EEP for measuring pl). Combining an EEP and a

CLP, Te can be derived by converting Eq. (1):

flpleV

e

T (3)

Probe measurements of pl and Te were carried out in two differ-

ent plasma discharges mounted in the same vacuum chamber (Fig. 2).

The first discharge consisted of an inductively coupled plasma using a

radio-frequency (RF) power supply. Good agreement between the new

probe and a commercial "Smart Probe" was found. In the second case,

similar measurements were carried out in a High Power Impulse Magne-

tron Sputtering discharge (HiPIMS) (Fig. 2 shows the probes' positions).

We also measured the full time-traces of pl and Te during a 40 µs

HiPIMS and evidence for a possible ion acoustic wave launched at the

onset of the discharge pulse were found.

Fig. 1: The probe with two cold and one emissive

sive Langmuir probe.

Fig. 2: Position of combined probe

and the Smart Probe in the HiPIMS)

mailto:[email protected]







101.2

Proceedings of the 12th International Workshop on Electric Probes in Magnetized Plasmas 2017

102.1

Design and Status of the Electrostatic Probe System for the SPIDER Experiment

M. Spolaore

M. Brombin, R. Cavazzana, G. Serianni, R. Pasqualotto, N. Pomaro, C. Taliercio

Consorzio RFX (CNR, ENEA, INFN

Università di Padova, Acciaierie Venete SpA) Corso Stati Uniti 4

35127 Padova, Italy

The neutral beam injector, an additional heating system for the ITER project, will be optimized in the NBI

test facility under construction in Padova. The facility includes the SPIDER ion source representing the full size

prototype for the production of negative ions, based on RF plasma with expected beam 100kV energy and 50A

current. The source will be equipped with a system of 84 electrostatic probes for the investigation of the

homogeneity of plasma parameters, such as plasma density, electron temperature, and plasma potential and

possibly of the Electron Energy Distribution Function. Measurements will be performed in the extraction region

of the ion source, where most of the extracted negative ions are produced. The system consists of 2D arrays of

different sensors, covering the Plasma Grid (PG) surface and the Bias Plate (BP), which are the components facing

the plasma in the extraction region. The probe system design accounts for the constraints related to the need of

embedding the sensors within the PG and BP. It has been carried out with the aim of providing sensors easy

maintenance and enough robustness to withstand the experimental operation of SPIDER. A special machining of

the insulating part has been adopted in order to avoid sensor short circuit due to deposition of metals such as

caesium or copper on the BP and PG surfaces during the operation of the SPIDER source. Given the RF plasma,

a particular attention is paid to the RF conditioning of the current collected by the probes in order to minimize the

spurious effects on the voltage-current characteristic of the sensors. In order to test in advance the electrostatic

sensor and to check possible weak points in the design, prototype sensors were manufactured and successfully

tested in plasma conditions as similar as possible to the plasma which will be produced in the SPIDER source.

The system is presently being installed on the SPIDER grids. In this contribution the overall system

description and status will be provided, including the in-vessel and ex-vessel parts, following the path from the

sensors up to the conditioning electronics and the acquisition system.

102.2


.

103.1

Electric Probe Measurements in Uniform and Strongly Magnetized Plasma

Produced by Glow-Discharge in Halbach Array

Stefan Costea Institute for Ion Physics and Applied Physics, University of Innsbruck

Technikerstraße 25b/3


[email protected]

Ovidiu Vasilovici, Bernd S. Schneider, Roman Schrittwieser, Codrina Ionita

Institute for Ion Physics and Applied Physics, University of Innsbruck Technikerstraße 25b/3


[email protected], [email protected], [email protected], codri-

[email protected]

For many experiments and applications, plasma is confined using magnetic fields, especially in fusion-

relevant devices. There are two ways of producing external magnetic fields: by strong electric currents in coils or

by permanent magnets. Coils have the advantage of varying the magnetic field strength by changing the electric

current flowing through them but for high currents a cooling system has to be implemented. Permanent magnets

can deliver magnetic fluxes into the gap of a magnetic circuit without continuous consumption of energy. We

present a way to produce highly-magnetized plasma using a special magnet assembly, known as the Halbach ar-

ray, able to produce a homogeneous magnetic flux density across a cylindrical gap region. Electric probes were

used to characterise this highly magnetized plasma.

An ideal Halbach array is a ring magnet where the po-

larization direction varies continuously along the circumfer-

ence such that the magnetic flux increases in the enclosed

space and reduces or cancels outside it. In practice, typical

Halbach cylinders are built using discrete permanent magnets

each with its own magnetization direction, approximating the

Halbach magnetic distribution [1]. Choosing the orientation of

each segment appropriately, the fields will all add at the centre.

We simulated the magnets’ positions in order to obtain a

uniform and homogenous magnetic field and the optimum cyl-

inder bore diameter, using Quick Field v6.1 Student Edition

(Figure 1). The input parameters for the magnetic material

were set according to the technical datasheet of the magnets.

For our experimental device, 8 identical 50×15×15 mm

Nd2Fe14B cubic bar magnets were used to produce a 0,5 T

magnetic field. The plasma was produced inside the 22×22×45

mm magnetized region by a glow discharge. Two electrodes were placed in such a way that the electrical field is

parallel with the magnetic field lines, one electrode was grounded and the other was biased with negative voltag-

es of a few hundreds of volts.

REFERENCES

[1] C.K. Chandrana, J.A. Neal, D. Platts, B. Morgan, P. Nath, "Automatic alignment of multiple magnets into

Halbach cylinders", Journal of Magnetism and Magnetic Materials, 381, 2015, pp. 396-400.

Figure 1: Magnetic flux simulation of exper-

imental Halbach array.

y x







103.2


104.1

Slabbing Model for Kinetic Description of ion Thrusters Plasma Plumes: Propagator Integral Method Solutions

José Manuel Donoso Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (ETSIAE), Technical University of Madrid

Plaza del Cardenal Cisneros, 3 28850, Madrid, Spain

[email protected]

Jorge González, Luis Conde Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (ETSIAE), Technical University of Madrid



The comprehension of the phenomena involved in plasma thrusters devices, where ions can be

accelerated to high velocities, is of relevant importance to improve the efficiency and designing of these engines,

as well as to ensure a correct interpretation of plasma diagnostics measurements [1,2]. Usually, fluid model

equations mislead upscaling diffusive kinetic effects that remains to mesoscopic or fluid scales. We present an

extension of the previously stated one-dimensional collisional velocity-space kinetic model [3,4], for weakly

ionized plasmas, to describe a plasma plume column in physical space. We propose a slabbing model to compute

the transient ion distribution function by including elastic collisions and charge-exchange contributions. The

plasma is spatially sectioned into a set of contiguous interconnected slabs, transversal to the direction of the

flows carried from the ionization chamber to the exhaust area. For each plasma slab, the kinetic nonlinear

equation is solved by the semi-analytical stable Integral Propagator Method, which allows the computation of the

non-local energy and mass flows of the analysed plasma species. This firstly offered global kinetic treatment

does not require the local thermodynamic equilibrium hypothesis and it establishes a feasible tool able to detect

and describe phenomena, as the merging of two distinguishable ions populations with high and low energy, in

accordance to several experimental results [1,5].

REFERENCES

[1] Zun. Zhang, H. Tang, J. Ren, Zhe. Zhang, J. Wang, Rev. Sci. Instrum. 87, 2016 pp. 113502

[2] J. C. Adam, A. Héron, and G. Laval, “Study of stationary plasma thrusters using two-dimensional fully

kinetic simulations”, Phys. Plasmas, 11, 2004, pp. 295-305

[3] J. M. Donoso and J. J. Salgado, “Nonlinear Fokker–Planck–Landau integral propagator (II): Transport far

from equilibrium,” J. Phys. A, Math. Gen. 39, 2006, pp. 587–600

[4] J. Gonzalez, J. M. Donoso, and S. P. Tierno, ”Three species one-dimensional kinetic model for weakly

ionized plasmas”, Phys. Plasmas, 23, 2016, pp. 062311

[5] J. Gonzalez, S. P. Tierno, J. M. Donoso, "Comparison between experimental Langmuir probes and three

species one-dimensional kinetic simulations", Phys. Plasmas, 23, 2016, pp. 103514

104.2


105.1

Kinetic Analysis of Weakly ionized Plasmas in presence of collecting and emissive walls

Jorge González Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (ETSIAE), Technical University of Madrid


[email protected]

José Manuel Donoso Escuela Técnica Superior de Ingeniería Aeronáutica y del Espacio (ETSIAE), Technical University of Madrid


[email protected]

Plasma-wall interaction is an unavoidable phenomenon in plasma science that is always under theoretical

and experimental consideration. This interaction essentially involves charge emission and collection processes

that may perturb the whole plasma inside a device [1]. A wide range of processes appears when a plasma

interacts with a wall, such as the thermionic emission, discharges, that may govern the plasma dynamics and the

confinement. Many fluid [2] and kinetic [3] models attempt to describe this scenario, accounting for various

phenomena under different time and spatial scales. In this work, some kinetic models to describe the dynamics of

Weakly Ionized Plasmas in front of a metallic flat wall are presented. In these plasmas elastic collisions between

charges and neutrals play a relevant role to properly describe the dynamics of the system [4]. Kinetic

descriptions provide an excellent tool to deal with the processes of disparate intensities, time scales and origin

that appear in the plasma-wall system. Phenomena such as the self-consistent electric field and electric density

currents, or the interaction between charges and neutrals, can be deeply analysed at kinetic scale to determine its

relevance in the system dynamics. It is found that a proper description of this complex system is only possible

with a self-consistent study that includes significant possible microscopic effects to elucidate and to understand

macroscopic measurable effects.

To solve the proposed models, the Propagator Integral Method [5] is employed. Since this method

provides a physically meaningful time evolving solution, as a semi-analytical method, it allows to accounting for

many phenomena of disparate time and spatial scales simultaneously, without affecting the method consistency.

REFERENCES

[1] M. Campanell, "Entire plasmas can be restructured when electrons are emitted from the boundaries", Phys.

Plasmas, 22, 2015, pp. 040702

[2] T. Gyergyek, B. Jurčič-Zlobec, M. Čerček, J. Kovačič, "Sheath structure in front of an electron emitting

electrode immersed in a two-electron temperature plasma: a fluid model and numerical solutions of the

Poisson equation", Plasma Sources Sci. Technol., 18, 2009, pp. 035001

[3] J. Sheehan, I. Kaganovich, H. Wang, D. Sydorenko, Y. Raitses, N. Hershkowitz, "Effects of emitted

electron temperature on the plasma sheath", Phys. Plasmas, 21, 2014, pp. 063502

[4] J. Gonzalez, S. P. Tierno, J. M. Donoso, "Comparison between experimental Langmuir probes and three

species one-dimensional kinetic simulations", Phys. Plasmas, 23, 2016, pp. 103514

[5] J.M. Donoso, A. Jimenez, J. Gonzalez, L. Conde, "Integral propagator method as a kinetic operator to

describe discontinuous plasmas", J. Phys. Conf. Ser, 768, 2016, pp. 012004

105.2


106.1

A Study of the Electron Energy Probability Function in the Plume and Channel of a low-power Hall Thruster

Milan Tichý1 1Charles University, Faculty of Mathematics and Physics

Ke Karlovu 3

121 16 Praha 2, Czech Republic

[email protected]

Aude Pétin2, Pavel Kudrna1 and Stéphane Mazouffre2 2Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), CNRS

1C Avenue de la Recherche Scientifique

45100 Orléans, France

[email protected], [email protected], [email protected]

The local properties of the electrons in the plasma emitted by a thruster such as the electron density, the

electron temperature and the electron energy distribution function are studied most effectively by electric probes.

Since the power deposition on the probe is high when measuring inside the channel of a Hall thruster, one type

of plasma thruster for spacecraft propulsion, the probes are as a rule fixed on a fast moving translation stage [1].

The electron energy distribution function (EEDF) or the electron energy probability function (EEPF)

belong among the most interesting electron properties, since it describes both the electron density as well as the

electron mean energy also in the case when the EEDF deviates from Maxwellian. Several groups have attempted

the measurements of the EEDF in the thruster channel and plasma plume using the Langmuir probe, e.g. [2,3].

The studied Hall thruster is a 200 W class thruster able to deliver a thrust of 10 mN when operated at

250V and 1.0 mg/s xenon mass flow rate [4]. The thruster was placed inside a 1.8m long and 0.8m in diameter

stainless-steel vacuum chamber. The associated pumping system is composed of a large dry pump (400m3/h), a

200 l/s turbomolecular pump to evacuate light gases and a cryogenic pump with a typical surface temperature of

35 K (8000 l/s) to get rid of the propellant gas. A background pressure of 2×10−5 mbar was achieved in the

working conditions - xenon mass flow rate of 1.0 mg/s and input power of 250W. The Langmuir probe used in

this work was made of a 0.2 mm in diameter tungsten wire. The non-collecting part of the wire was insulated by

a 100 mm long and 2 mm in diameter alumina tube. The length of the collecting part was 1 mm.

The measured EEPF’s confirm the idea that the EEPF near the thruster exit plane is composed of two

groups of electrons [2,5]: The first group is extracted from the hollow cathode by the electric field having a

component along the magnetic field near the cathode region. On arriving at the channel exit, these electrons are

deflected by the strong radial magnetic field in the vicinity of the thruster exit and become involved in a E B

drift motion. This magnetized beam of electrons has in our Hall thruster an energy around 120 eV. The second

group consists of slower electrons produced by ionization inside the thruster channel and accelerated by the

electric field at the channel exit. The EEPF’s measured downstream of the thruster give a logical picture on how

the magnetized beam of electrons merges into the EEPF body. At large distances the EEPF becomes Maxwellian

and one can observe a decrease in both the electron temperature and density due to the expansion process.

REFERENCES

[1] K. Dannenmayer and S. Mazouffre, “Compact high-speed reciprocating probe system for measurements

in a Hall thruster”, Rev. Sci. Instrum. 83, 2012, 123503.

[2] V. Yu. Fedotov and A. A. Ivanov, G. Guerrini, A. N. Vesselovzorov, and M. Bacal, “On the electron

energy distribution function in a Hall-type thruster”, Physics of Plasmas 6, 1999, 4360.

[3] K. Dannenmayer, S. Mazouffre, P. Kudrna and M. Tichy, “The time-varying electron energy distribution

function in the plume of a Hall thruster”, Plasma Sources Sci. Technol. 23, 2014, 065001.

[4] A. Leufroy, T. Gibert, A. Bouchoule, “Characteristics of a permanent magnet low-power Hall thruster”,

Proc. of the 31th International Electric Propulsion Conference (Ann Arbor), IEPC-2009-083, 2009.

[5] F. Taccogna, “Monte Carlo Collision method for low temperature plasma simulation”, J. Plasma Physics

81, 2015, 305810102.

106.2


107.1

Multiprobe Characterization of Plasma Flows for Space Propulsion

Julius Damba

Department of Applied Physics. ETSI Aeronáutica y del Espacio. Universidad Politécnica de Madrid

Plaza Cardenal Cisneros 3, 28040 Madrid, Spain

[email protected]

P. Argente1, P.E. Maldonado2, A. Cervone2, J. L. Domenech-Garret1 and L. Conde1 1 Department of Applied Physics. ETSI Aeronáutica y del Espacio. Universidad Politécnica de Madrid

Plaza Cardenal Cisneros 3, 28040 Madrid, Spain 2 Department of Space Engineering. Delft University of Technology.

Kluyverweg 1, 2629HS Delft. The Netherlands

Plasma engines for space propulsion generate plasma flows (also denominated plasma plumes) having

supersonic ion groups with typical speeds in the order of tens of kilometres per second. The mapping of the

plasma potential, electron and ion densities and temperatures as well as the ion energy distribution function

(IEDF) are important ground tests to study the plasma

expansion process and also the performance of plasma

engines. Diagnostics of plasma streams using a four-grid

retarding potential analyzer (RPA) [1], emissive probe (EP),

Langmuir probe (LP), and Faraday cup (FC) mounted on a 3-

D displaced multiprobe stand is discussed.

The response of such electric probes in relation with

the presence of supersonic ions in the plasma stream will be

explored, specifically the existence of secondary electron

emission due to impact of energetic ions with the RPA

internal surfaces on the voltage–current characteristic curves.

Spatial profiles of the plasma potential and charged

particle densities obtained with LP and EP probes

characterize the length and radial collimation of the plasma plume. The two-peaked IEDFs shown in the figure

above are characteristic of a mesothermal plasma flow [2–4] and can be seen as superpositions of two ion

populations. The low-energy group is constituted by ions with low random speeds whereas fast ions reach

supersonic velocities along a fixed direction. The reduction in peak heights and fast-ion energy losses observed

in the figure provide information concerning the energy relaxation [5–8] length along the engine axis of

symmetry. Furthermore, the relation between the observed energy relaxation lengths and mean free paths

corresponding to the different collisional processes will be discussed.

Finally, we examine the connection between the plasma stream properties and the space propulsion

performance of our ALPHIE (alternative low power hybrid ion engine) plasma thruster.

REFERENCES

[1] C. Bohm, J. Perrin, Rev. Sci. Instrum. 64 (1) (1993).

[2] Zun. Zhang, H. Tang, J. Ren, Zhe. Zhang, J. Wang, Rev. Sci. Instrum. 87 113502 (2016).

[3] Y. Hu, J. Wang, IEEE Transactions on Plasma Science 43 (9) (2015).

[4] M. Merino, E. Ahedo, IEEE Transactions on Plasma Science 43 (1) (2015).

[5] M. Capitelli et al., Chemical Physics Letters 316 (2000) 517–523.

[6] Z. Wang et al., Phys. Plasmas 21, 072703 (2014).

[7] U. Hohenester et al., Eur. Phys. J. B 5, 143–152 (1998).

[8] M. Shihab et al., Appl. Phys. B (2016) 122:146.

107.2


108.1

Langmuir Probe Measurements in the Early Hydrogen Discharge of GLAST-III Tokamak

A. Qayyum, F. Deeba, S. Ahmad, S. Hussain

National Tokamak Fusion Program, 3329 Islamabad, Pakistan

[email protected], [email protected], [email protected], [email protected]

Triple Langmuir probe has been developed and successfully applied for time resolved measurements in

the first hydrogen discharge of GLAST-III spherical tokamak started with electron cyclotron heating (ECH).

Diagnostic measurements provide insights into expected and unexpected physics issues of the initial discharge.

Triple Langmuir probe (TLP) has the ability to give time-resolved measurements of floating potential (Vfloat),

electron temperature (Te), and ion saturation current (Isat ne√kTe). The evolution of ECH-assisted pre-ionization

and subsequent current formation phases in one shot are well envisioned by probe measurements. Probe data

seem to correlate with microwave absorption and subsequent light emission. Intense fluctuations in the current

formation phase advocate for efficient equilibrium and feedback control systems. A noticeable change in the

profile's shape of floating potential, electron temperature, ion saturation current (Isat) and light emission is

observed with changing hydrogen fill pressure and vertical field.

Plots show the effect of vertical field on electron temperature measured by triple Langmuir probe during

the evolution of two phases in one shot. It is clear from probe signals that two region of electron temperature

corresponding to ECH pre-ionization and plasma current formation can be easily recognized. Moreover, plasma

stays for longer time with vertical field corresponding to 40 V charging voltage.

REFERENCES

[1] A. Qayyum, N. Ahmad, S. Ahmad, Farah Deeba, Rafaqat Ali, S. Hussain," Time-resolved measurement

of plasma parameters by means of triple probe", Rev. Sci.Instrum.,84, 2013,pp. 123502

[2] C. Theiler, I. Furno, A. Kuenlin, Ph. Marmillod, A. Fasoli, "Practical solutions for reliable triple probe

measurements in magnetized plasmas",Rev. Sci. Instrum. 82, 2011, pp.013504

0 1 2 3 4 5 6

0

5

10

0

5

10

0

10

20

300

20

40

0

20

40

0

20

40

t[ms]

VF(100V)

Dependence of electron temperature on Vertical field

VF(80V)

VF(60V)

VF(40V)

VF(30V)

Te[e

V]

VF(20V)

Photographic image of GLAST-III Spherical Tokamak

108.2


109.1

Measurements of Densities of Gas Constituents in a Discharge Device with a Large Wall Probe

I. P. Kurlyandskaya, A. A. Kudryavtsev

INTEPH Technologies LLC

Springboro, OH 45066, USA


S. F. Adams, J. A. Miles

Air Force Research Laboratory

WPAFB, OH 45433, USA


V. I. Demidov, M. E. Koepke

West Virginia University

Morgantown, WV 26501, USA


An approach leading to the development of gas analytical detectors has been previously reported [1,2].

This approach is based on the use of a large electric wall probe to measure fine structures associated with atomic

and molecular plasma processes at the high-energy portion of the electron energy distribution function (EEDF)

in the near-cathode plasma. The large-area wall probe provides increased sensitivity of the gas detector.

However, the additional potentials that are necessary to apply to the probe during the measurements can

significantly change the properties of the entire plasma in the discharge [3], thus altering the EEDF, which the

probe is attempting to measure. As a result, each measured EEDF can be associated with a different plasma for

different energies (probe potentials). This is not an issue, though, as the exact knowledge of the undisturbed

EEDF is not really important for measurements of densities of gas constituents. The result of the measurements

can be corrected by calibrating with known gas mixtures. Even though the ratios of the high-energy electron

features in the EEDF change with probe potential, the presence of a specific target gas component can still be

monitored from the measured EEDF.

In this work, a short (without positive column) dc discharge with cold cathode and conducting walls was

used in experiments at gas pressures of a few Torr [1]. For the investigated conditions, the plasma is collisional

and one might expect that maxima corresponding to arising energetic electrons are proportional to the first

derivative of electron current with respect to the probe potentials (collisional probe theory) [4]. However, it is

experimentally shown that the maxima are proportional to the second derivative of electron current with respect

to the probe potentials (as in collisionless theory [4]). The reason for this discrepancy is unknown and still

should be investigated. Measurements have been conducted in Helium-Argon gas mixtures with content of

Argon from 0.002 to 5% and calibration of the device has been demonstrated.

REFERENCES

[1] V. I. Demidov, S. F. Adams, J. Blessington, M. E. Koepke M. E., J. M. Williamson, “Short dc discharge

with wall probe as a gas analytical detector”, Contributions to Plasma Physics, 50, 2010, 808-813.

[2] V. I. Demidov, S. F. Adams, J. A. Miles, M. E. Koepke, I. P. Kurlyandskaya, “Suprathermal Electron

Energy Spectrum and Nonlocally Affected Plasma-Wall Interaction in Helium/Air Micro-Plasma at

Atmospheric Pressure”, Physics of Plasmas, 23, 2016, 103508.

[3] S. F. Adams, E. A. Bogdanov, V. I. Demidov, M. E. Koepke, A. A. Kudryavtsev, I. P. Kurlyandskaya,

“Control of Plasma Properties in a Short Direct Current Glow Discharge with Active Boundaries”,

Physics of Plasmas, 23, 2016, 024501.

[4] V. A. Godyak, V. I. Demidov, “Probe Measurements of Electron Energy Distributions in Plasmas: What

Can We Measure and How Can We Achieve Reliable Results? (Invited review)”, Journal of Physics D:

Applied Physics, 44, 2011, 233001.







109.2


110.1

Spatial Distribution of Plasma Parameters in Gas Aggregation Nanocluster Source

Anna Kolpaková

Dept. of Surface and Plasma Science

Faculty of Mathematics and Physics, Charles University

V Holešovičkách 2

18000, Prague 8, Czech Republic

[email protected]

Artem Shelemin, Pavel Kudrna, Milan Tichý, Hynek Biederman

Charles University

V Holešovičkách 2

18000, Prague 8, Czech Republic


Gas aggregation cluster sources (GAS) are widely used for production of nanoparticles (NPs) ranging from

metallic to plasma polymer ones. The special version of GAS based on planar magnetron as a plasma source [1]

has become more popular recently. GAS usually work with pressures at least one order of magnitude higher than

what are typical for magnetrons optimized for deposition [2]. At sufficiently high pressure the material sputtered

from the target creates nanoparticles within the aggregation chamber. These nanoparticles are dragged by the flow

of a carrier gas downstream and transported through an orifice to the substrate located in the deposition chamber

with reduced pressure, where they are physically cooled by adiabatic expansion. For better understanding of

nucleation, formation, and electric charge of NPs there is an urgent need to determine plasma parameters inside

the aggregation chamber.

For that purpose the special “diagnostic GAS” with axially movable magnetron has been constructed [3].

This system is equipped with optical emission spectroscopy, quadrupole mass spectrometry, quartz crystal

microbalance, and probe diagnostic. The last mentioned technique may provide plasma parameters with spatial

resolution in two dimensions by means of radially movable probe.

Different plasma-based methods have been developed that enabled deposition of plasma-polymerized

nanoparticles using RF plasmas. In our case nylon-sputtered nanoparticles were prepared by means of gas

aggregation cluster source based on a planar RF magnetron that involves a low-temperature plasma in the process

of production of nanoparticles. GAS was equipped with a nylon target which was sputtered in pure Ar. Aggregation

chamber pressure was varied, which resulted in two studied situations: (1) discharge without nanoparticles and (2)

discharge with production of nanoparticles in pure argon.

The spatial profiles of plasma parameters were obtained by means of heated probe. Such construction

minimizes the deposition of polymer layer on the probe surface. Heating current kept the probe clean of insulating

nylon films that would otherwise depreciate the probe data.

REFERENCES

[1] H. Haberland, M. Mall, M. Moseker, Y. Qiang, T. Reiners, Y. Thurner, "Filling of micron-sized contact

holes with copper by energetic cluster impact", J. Vac. Sci. Technol. A, 12 (5), 1994, pp. 2925-2930.

[2] P. J. Kelly, R. D. Arnell, "Magnetron sputtering: a review of recent developments and applications",

Vacuum, 56, 2000, pp. 159-172.

[3] A. Shelemin, O. Kylián, J. Hanuš, A. Choukourov, I. Melnichuk, A. Serov, D. Slavínska, H. Biederman,

"Preparation of metal oxide nanoparticles by gas aggregation cluster source", Vacuum, 120, 2015, pp. 162-

169.

110.2


111.1

Determination of Anisotropic Ion Velocity Distribution Function in Intrinsic Gas Plasma. Theory

Aleksandr Mustafaev, Artem Grabovskiy, Oscar Murillo

Saint Petersburg Mining University

21 line of the Vasilievskiy Island, h. 2

199106, Saint Petersburg, Russia

[email protected]

Vladimir Soukhomlinov

Saint Petersburg State University

Universitetskaya emb., h. 7-9


[email protected]

Ion velocity distribution function (IVDF) researches are vital for a wide range of modern applications:

plasma technologies, ion surface treatment, technology of selective etching and creation of relief by ion

bombardment, new generation of nanoelectronics (single-electron transistors, spintronics, etc) [1, 2]. In this

context, the development of reliable theories for IVDF in different discharges, in particular, in DC self-sustained

discharge plasmas are of special interest.

This paper deals with development of theory for IVDF, based on the analytic solution of the Boltzmann

kinetic equation for ions in the plasma of their parent gas under conditions, when the resonant charge exchange

is the predominant process, and an ion acquires on its mean free path a velocity much higher than the

characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is

taken into account. It is shown that the ion velocity distribution function is determined by two parameters and

differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift

velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the experimental data shows their conformity. The

results of the IVDF calculation correctly describe the experimental data on its measurements.

Analysis of the result shows that in spite of the presence of the strong field, the IVDF’s are isotropic for

ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution

becomes more and more extended in the direction of the electric field.

REFERENCES

[1] H. Abe, M. Yoneda and N.Fujiwara. Jpn. J. Appl. Phys. 2008. Vol.47. P. 1435.

[2] Michael A. Lieberman. Bull. of the APS. 2010. Vol. 55. N 7. P. 105.

111.2


112.1

Determination of Anisotropic Ion Velocity Distribution Function on Intrinsic Gas Plasma. Probe Method

Aleksandr Mustafaev, Artem Grabovskiy

Saint Petersburg Mining University

21 line of the Vasilievskiy Island, build. 2


[email protected]

Vladimir Soukhomlinov

Saint Petersburg State University

Universitetskaya emb., build. 7-9


[email protected]

The ion velocity distribution function (IVDF) is of interest in cases, associated with the study of

plasmachemical reactions occurring with the participation of ions, the determination of ion mobility in the

plasma object, processes of heating of the neutral plasma component, and a series of others. Among technical

applications, we note modern plasma nanotechnologies, fine ion purification of the surface of products, and the

technology of creating reliefs on the surface owing to selective etching during bombardment by ion fluxes. In

this context, the development of reliable probe methods for IVDF measurements in different discharges, are of

great importance.

Despite the significant amount of theoretical works [1-4], the experimental investigations of IVDF are

almost absent, except paper [5], where IVDF in the plasma of DC discharge was determined. The Doppler shift

of ion lines in the argon discharge was measured spectroscopically at the observation along the discharge axis in

[5], and, judging by its value, a conclusion was made about the average ion velocity, which was on the order of

104 сm/s under the conditions of experiments.

In this paper a new probe method for the IVDF determination was proposed. For the first time, the ion

distribution function over energies and directions of the motion for Hg+ ions in Hg, He+ in He and Ar+ in Ar has

been measured at the arbitrary value of the electric field using the plane one-sided probe. The experiment is

carried out under conditions when the ion velocity, acquired at the mean free path, is on the order of and larger

than the average thermal velocity of atoms and resonance recharging is the dominating process in plasma. The

main requirement, limiting the region of the applicability of the method, is the small thickness of the near-probe

Debye layer in comparison with the probe sizes.

The obtained results make it possible to conclude that, in independent gas discharge plasma, even at

moderate fields, where E/P=10-20 V/(cm∙Torr), the ion distribution function can have noticeable anisotropy and

can strongly differ from the Maxwellian distribution.

REFERENCES

[1] Smirnov B.M., Zh. Tekh. Fiz., 1966, vol. 36, p. 1864.

[2] Perel’ V.I., Zh. Eksp. Teor. Fiz., 1957, vol. 32, p. 526.

[3] Fok V.A., Zh. Eksp. Teor. Fiz., 1948, vol. 18, p. 1048.

[4] Golant V.E., Zhilinskii A.P., Sakharov S.A., Osnovy fiziki plazmy (Fundamentals of Plasma Physics),

Moscow: Atomizdat, 1977.

[5] Frish S.E. and Kagan Yu.M., Zh. Eksp. Teor. Fiz., 1947, vol. 17, p. 577.

112.2


113.1

Feasibility, Strategy, Methodology, and Analysis of Probe Measurements in Plasma under High Gas Pressure

Vladimir Demidov


White Hall

26501, Morgantown, USA

[email protected]

Mark Koepke, Mikhail Malkov


White Hall

26501, Morgantown, USA

[email protected], [email protected],

At present, most published probe measurements of electron energy distribution function (EEDF) f() and

electron density n are conducted by using a Langmuir probe and interpreted by using the Langmuir formula [1]

𝑰(𝑽) =𝟐𝝅𝒏𝒆𝑺

𝒎𝟐 ∫ 𝒇(𝜺)(𝜺 − 𝒆𝑽)𝒅𝜺,∞

𝒆𝑽 (1)

where I is the probe current, e is the elementary charge, S is the probe surface, m is the mass of electron, V is the

probe potential and is the electron energy. From Eq. 1 it is simple to obtain the Druyvesteyn formula with

double differentiation over probe potential [1]

𝒇(𝜺) =𝒎𝟐

𝟐𝝅𝒏𝒆𝟑 ×𝒅𝟐𝑰

𝒅𝑽𝟐. (2)

In practice, the application of Eq. 1 and 2 is restricted by an important requirement: the mean free path of

electrons is assumed to be much greater than the probe radius r and Debye length rd. As a result, in noble gases,

the probe method is inapplicable for gas pressure higher than 10 Torr. For the last 50 years, a number of theories

and methods have been developed to extend probe measurements of EEDFs to higher gas pressure [3,4].

However, analysis using most of these theories and methods seldom appears in the literature.

This talk will review existing theories and previous probe measurements of EEDFs at higher gas pressure.

An explanation of whether or not the measurements are realizable and reliable, an enumeration of the most

common sources of measurement error, and an outline of proper probe-experiment design elements that

inherently limit or avoid error will be presented. Additionally, we describe recent EEDF-measurement

developments in higher-pressure plasma conditions, including electron spectroscopy analysis. This summary of

the authors’ experiences gained over decades of practicing and developing probe diagnostics is intended to

inform, guide, suggest, and detail the advantages and disadvantages of probe application in plasma research.

REFERENCES

[1] H. M. Mott-Smith, I. Langmuir, “The Theory of Collectors in Gaseous Discharges”, Phys. Rev. 28, 1926,

pp. 727-763.

[2] M. J. Druyvesteyn, “Der Niedervoltbogen”, Z. Phys. 64, 1930, pp. 781-798.

[3] J. D. Swift and M. J. R. Schwar, Electrical Probes for Plasma Diagnostics, Iliffe Books, London, 1970.

[4] Y. B. Golubovsky, V. M. Zakharova, V. I. Pasunkin, and L. D. Tsendin, “Probe measurements of the

electron energy distribution under diffusion conditions”, Sov. J. Plasma Phys. 7, 1981, pp. 340-344.




113.2


114.1

Current-Voltage and Floating Potential Characteristics of Cylindrical Emissive Probes from a Self-consistent Full-Kinetic Model

Xin Chen

Universidad Carlos III de Madrid

Escuela Politécnica Superior, Avd. de la Universidad 30

28911, Leganés (Madrid), Spain

[email protected]

G. Sánchez-Arriaga

Universidad Carlos III de Madrid

Escuela Politécnica Superior, Avd. de la Universidad 30

28911, Leganés (Madrid), Spain

[email protected]

To model the sheath structure around a cylindrical emissive probe (EP), difficulties arise due to the space-

charge effects and the possible non-monotonic character of the potential profile. For instance, in space conditions,

where probe radius can be comparable to the Debye length (R ≈ λDe) due to low plasma density and the ion

temperature is not negligible compared to electron temperature, it is essential to include the orbital effects and to

solve the non-monotonic potential profile without ambiguity. A full-kinetic model based on Orbital Motion Theory

(OMT) was not available until very recently [1]. The OMT takes advantage of three conserved quantities,

distribution function f, transverse energy E, and angular momentum J, to transform the stationary Vlasov-Poisson

system into a single integro-differential equation. For a stationary collisionless unmagnetized plasma, this equation

describes self-consistently the probe characteristics. A numerical scheme can solve this equation and find the radial

profile of the electrostatic potential for arbitrary parameters. Then, the current versus voltage characteristics and

the floating potential versus probe temperature curves can be computed. The goal of this work is to make extensive

parametric analysis in order to determine the I-V characteristics and the floating-potential-versus-probe-

temperature curves and to analyse their dependence on key dimensionless parameters, for instance, the probe-to-

Debye-length ratio, the probe-to-electron-temperature ratio, the ion-to-electron-temperature ratio, and the work-

function-to-electron-temperature ratio. As shown by the results, the floating potential - at which a cylindrical

emitter collects/emits zero net current – can be positive relative to the plasma potential and depends on the probe

radius, instead of being about one electron temperature below the plasma potential as predicted by the classical

planar theory. The results from the extensive parametric analysis have been used to obtain fitting laws for both I-

V characteristics and the floating potential curves. The former can provide the probe potential at which the

transition between operational regimes (e.g, OML collection, SCL emission) occurs. The latter can be useful for

determining the plasma potential by using the EP floating-potential technique. Besides probe theory and plasma

diagnostics, the results of this work can also benefit space applications and technology such as Low Work function

Tethers (LWTs) for space debris removal [2] and spacecraft charging.

REFERENCES

[1] Xin Chen, G. Sanchez-Arriaga, “Orbital Motion Theory and Operational Regimes for Cylindrical Emissive

Probes”, Phys. Plasmas 24, 2017, pp. 023504.

[2] G. Sanchez-Arriaga, Xin Chen, “Modelling and Performance of Electrodynamic Low-Work-Function

Tethers with Photoemission Effects”, to be published in J. Propul. Power.



114.2


115.1

Current Density Distribution Along the Cylindrical Probe in Magnetized Plasma

Gheorghe Popa

Alexandru Ioan Cuza University, Faculty of Physics

Blvd. Carol I, 11

700506, Iasi, Romania

[email protected]

Claudiu Costin1, Ilarion Mihaila2 1Alexandru Ioan Cuza University, Faculty of Physics

2Alexandru Ioan Cuza University, Integrated Center of Environmental Science Studies in the North-Eastern

Development Region (CERNESIM)

Blvd. Carol I, 11

700506, Iasi, Romania [email protected], [email protected]

Cylindrical probes are frequently used for magnetized plasma diagnostic, being one of the most

affordable tools. Extensive analysis of both theoretical model and experimental technique were published in

many textbooks [1] and general review articles [2]. The presence of a magnetic field induces a strong anisotropy

of the plasma, making the probe characteristic strongly depend on the probe orientation with respect to the

direction of the magnetic field lines. There are two main orientations: along and perpendicular to the magnetic

field lines, but intermediate angles are also possible. The reported experimental results showed that probe

characteristics exhibit different shapes for the two main orientations, even if the same plasma volume was

investigated. In some experimental conditions, even a negative slope might appear in the electronic part of the

probe characteristic when the cylindrical probe is parallel to the magnetic field lines [3]. On the other hand,

Stamate & Ohe showed that the space charge sheath may cause particular focalization of the ions collected by a

negatively biased probe, demonstrating a non-uniform distribution of the current density at the probe surface in

an unmagnetized plasma [4]. To the best of our knowledge, there are no published results concerning the

distribution of the current density along the probe length, when the probe is parallel to the magnetic field lines.

Consequently, the present work reports experimental and simulation results of the distribution of the local

current density along the probe, having the probe bias and the magnetic field strength as parameter. A cylindrical

probe (tungsten wire of 0.5 mm in diameter) was placed in a magnetized plasma column produced in a

previously described experimental device [3]. The probe length was modified by moving the wire along a

ceramic tube, which assures the insulation of the rest of conducting wire within the supporting shaft. The basic

idea is to record the probe characteristic for different probe lengths in an axially uniform plasma region and the

same stationary conditions (typically Ar pressure of 1 mTorr, discharge current intensity of 0.5 A, but variable

magnetic field strength up to 0.45 T). The probe was placed along the axis of the magnetized plasma column,

aligned with the magnetic field lines. Probe characteristics were recorded starting with a plane probe, when only

the top cross section of the W wire is exposed to plasma, followed by cylindrical probes with different lengths

(up to the total length of 5 mm). Under the hypothesis that the local plasma potential does not change along the

probe length, the current density at the probe surface was calculated for each segment of the probe.

REFERENCES

[1] O. Auciello, D.L. Flamm, Plasma Diagnostics: Discharge Parameters and Chemistry, Acad. Press, 2013.

[2] G.F. Matthews, “Tokamak plasma diagnosis by electrical probes”, Plasma Phys. Control. Fusion, 36,

1994, pp. 1595–1628.

[3] I. Mihaila, M. L. Solomon, C. Costin, G. Popa, “On Electrical Probes Used in Magnetized Plasma

Diagnostics”, Contributions to Plasma Physics, 53(1), 2013, pp. 96-101.

[4] E. Stamate, K. Ohe, “On the Surface Condition of Langmuir Probes in Reactive Plasmas”, Appl. Phys.

Lett., 78, 2001, pp. 1-3.

https://www.researchgate.net/researcher/85227445_I_Mihaila

https://www.researchgate.net/researcher/2014283429_M_L_Solomon

https://www.researchgate.net/researcher/74642725_C_Costin

https://www.researchgate.net/publication/258770672_On_Electrical_Probes_Used_in_Magnetized_Plasma_Diagnostics?ev=prf_pub

https://www.researchgate.net/publication/258770672_On_Electrical_Probes_Used_in_Magnetized_Plasma_Diagnostics?ev=prf_pub

115.2


116.1

Disturbances of ICP Plasmas by Langmuir Probes with Uninsulated Protecting Shields

Valentin Riaby

Research Institute of Applied Mechanics and Electrodynamics (RIAME) of the Moscow Aviation

Institute (National Research University), 5 Leningrad Rd., 125080 Moscow, Russia

[email protected]

Valery Godyak Electrical Engineering and Computer Science Dept., University of Michigan, Ann Arbor, 48109

Michigan, USA and RF Plasma Consulting, Brookline, 02446 Massachusetts, USA

[email protected]

Benjamin Alexandrovich

Plasma Sensors, Brookline, 02446 Massachusetts, USA

[email protected]

Pavel Masherov

RIAME

[email protected]

Vladimir Savinov and Valery Yakunin

Moscow State University named after M.V. Lomonosov, Physical Dept., 119991 Moscow, Russia

[email protected]; [email protected]

Probe diagnostics of xenon inductively coupled plasma (ICP) has been carried out using two cylindrical

classic Langmuir probes. One of them was straight and could move radially and the other, L-shaped one could

move along plasma area and revolve around its axis. The purpose was to study plasma “tablet” 146 mm in

diameter and 39 mm thick at pressure 2 mTorr by measurement of its plasma parameter spatial distributions.

This “tablet” represented one half of gas discharge space that was located in front of an ion extracting grate

(IEG) of an ion thruster model in which an external planar antenna coil enhanced with ferrite core was used.

Such measurements were necessary for correct calculations of IEG accelerating cells and subsequent

manufacturing of this system. Probe measurements were arranged with the automated VGPS-12 probe station of

Plasma Sensors Co., USA that provided accurate plasma diagnostics due to the most advanced achievements of

nowadays’ experimental physics included into its control program and circuit engineering of the VGPS-12 probe

station. Measurements with probes 0.15 mm in diameter and of different lengths resulted in the selection of

probe tip’s length lp=10 mm that practically excluded local plasma perturbations caused by the first probe holder.

Diagnostic results for spatial plasma parameter distributions in the common cross-section showed

noticeable differences of both probe readouts. Their analysis based on the previous authors’ research of large

uninsulated metallic bodies’ behaviour under floating potential in contact with plasmas showed that the said

measurement discrepancies could be caused by use here of grounded, uninsulated externally probe shields that

protected probe circuits against RF interferences. Physical consideration of the grounded probe shields and the

ones under floating potential in contact with plasmas proved that they both behaved as short-circuited,

asymmetrical double Langmuir macro-probes that caused disturbances of the discharge structure decreasing

plasma or discharge currents and plasma ionization level and providing electrical power loss in the probe shields.

So this phenomenon could be considered as the reason for qualitative error fields of probe measurements. Beside

that a combination of two probe forms in the present experiments allowed for determination of quantitative scale

of measurement errors caused by L-shaped probe. In the common plasma “tablet” cross-section a point was

found at its periphery where only L-shaped probe caused disturbances lowering electron temperature and

concentration by up to 15% and plasma potential by about 30%. Besides from the axis to periphery of plasma

“tablet” it decreased plasma floating potential from positive area to zero level and then made it negative.

According to physical essence of this phenomenon, thus found discharge structure damage and plasma

parameter perturbations can be eliminated by deposition of dielectric layer upon probe shields.




116.2


117.1

The Radial-Motion-Only (RMO) and Orbital-Motion (OM) Methods for Calculating Velocity Distribution Functions in a Spherical Probe Scenario

Siegbert Kuhn

Institute for Theoretical Physics, University of Innsbruck

Technikerstrasse 21A


[email protected]

Alif Din

Theoretical Physics Division, PINSTECH

P.O. Nilore, Islamabad

44000, Islamabad, Pakistan

[email protected]

We consider the time-independent collisionless plasma-probe transition (PPT) region around a negatively

biased non-emissive spherical probe, extending from the probe radius p

r to the presheath-entrance radius p s

r .

The particle species involved are thermal electrons and cold ions entering the PPT region at p s

r . Their velocity

distribution functions (VDFs) are denoted by , ,s

r tf r v v , with ,s e i the respective species index and

,r t

v v the radial and tangential velocity components, respectively.

The VDF of a particle species essentially moving in the radial direction can be calculated in the “radial-

motion-only (RMO)” approximation ( 0t

v ), whereas that of a particle species with a non-negligible

tangential velocity spread requires application of the full “orbital-motion (OM)” method. While the former is

fairly straightforward, the latter is based on the concept of “trajectory integration” [1], structurally represents a

boundary-value problem and turns out to involve some tricky mathematics.

In this paper, the general formalism and the ensuing equations for the RMO and OM methods will be

presented and discussed in detail. Then, these methods will be specifically applied to calculating the VDFs of the

cold ions and the thermal electrons, respectively, in the entire PPT region. Ultimately, the Poisson equation

appropriate for the scenario considered will be set up and solved numerically [2] to obtain the potential profile in

the sheath and presheath regions at moderate negative values of the probe bias.

REFERENCES

[1] S. Kuhn, “The Physics of Bounded Plasma systems (BPS's): Simulation and Interpretation”, Contrib.

Plasma Phys., 34 (4), 1994, pp. 495–538.

[2] A. Din and S. Kuhn, “Numerical Matching of the Sheath and Presheath Solutions for a Spherical Probe in

Radial-Motion theory”, Phys. Plasmas, 21, 2014, pp. 103509-1–6.

117.2


118.1

Some Experiments with the Tunnel Probe in a Low-Temperature Magnetized Plasma

Jernej Kovačič

Reactor Physics Department, Jožef Stefan Institute

Jamova cesta 39

SI-1000, Ljubljana, Slovenia

[email protected]

Tomaž Gyergyek

University of Ljubljana, Faculty of Electrical Engineering

Tržaška cesta 25

SI-1000, Ljubljana, Slovenia

tomaž[email protected]

James P. Gunn

CEA, IRFM

F-13108 Saint-Paul-Lez-Durance, France

[email protected]

Experiments were performed using a Tunnel Probe (TP) inside the weakly-ionised plasma of the Linear

Magnetized Plasma Device (LMPD). The TP is designed as a concave probe, which annihilates the problem of

sheath expansion in the ion branch of the I-V characteristic. As the ion saturation current is consequently well

defined, the plasma density can be more accurately calculated and the ratio between the ion saturation currents on

the two collectors (ring and the back-plate) can be used to derive the electron temperature. The TP has repeatedly

been used with success on the former Tore-Supra tokamak and will be used on its upgraded version – the WEST

tokamak – as well [1, 2], however it was never used in a low-temperature plasma.

We studied the feasibility of the TP use in a low-temperature plasma for direct measurements of plasma

temperature and density. The various probe characteristic dimensions, such as the distance between the two

collectors, the aperture size and the probe radius were varied to see influence of the individual probe feature. We

also varied the level of magnetization of the charged particle species, the background gas pressure (which

influences the electron energy distribution function), the plasma density (important for the ratio between the λD

and the ion Larmor radius). The sensitivity of the probe alignment to the magnetic field lines was also studied. We

found, that the ion saturation current does not necessarily saturate and that the probe works according to

expectations only in a limited amount of regimes.

.REFERENCES

[1] J. P. Gunn et al, "Tunnel Probes for Measurements of the Electron and Ion Temperature in Fusion Plasmas

", Rev. Sci. Instrum., 75, 2004, pp. 4328-4330

[2] J. P. Gunn et al, “Simultaneous DC Measurements of Ion Current Density and Electron Temperature Using

a Tunnel Probe”, J. Phys.: Conf. Series, 700, 2016, 012018


mailto:tomaž[email protected]


118.2


Authors index

Adamas S. F. 109.1 Popa G. 115.1 Ahmad S. 108.1 Qayyum A. 108.1 Alexandrovich B. 116.1 Riaby V. 116.1 Argente P. 107.1 Sánchez-Arriaga G. 114.1 Biederman H. 110.1 Savinov V. 116.1 Cervone A. 107.1 Schneider B. S. 101.1, 103.1 Chen X. 114.1 Schrittwieser R: 101.1, 103.1 Conde L. 104.1, 107.1 Shelemin A. 110.1 Costea S. 101.1, 103.1 Soukhomlinov V. 111.1, 112.1 Costin C. 115.1 Spolaore M. 102.1 Damba J. 107.1 Tichy M. 106.1, 110.1 Deeba F. 108.1 Vasilovici O. 101.1, 103.1 Demidov V. I. 109.1, 113.1 Yakunin V. 116.1 Din A. 117.1

Domenech-Garret J. L. 107.1

Donoso J. M. 104.1, 105.1

Godyak V. 116.1

Gonzáles J. 104.1, 105.1

Grabovskiy A. 111.1, 112.1

Gunn J. P. 118.1

Gyergyek T. 118.1

Hussain S. 108.1

Ilarion M. 115.1

Ionita C. 101.1, 103.1

Koepke M. E. 109.1, 113.1

Kolpaková A. 110.1

Kovačič J. 118.1

Kudrlyandskaya I. P. 109.1

Kudrna P. 106.1, 110.1

Kudryavtsev A. A. 109.1

Kuhn S. 117.1

Lundin D. 101.1

Maldonando P. E. 107.1

Malkov M. 113.1

Masherov P. 116.1

Mazouffre S. 106.1

Miles J. A. 109.1

Minea T. 101.1

Murillo O. 111.1

Mustafaev A. 111.1, 112.1

Pétin A. 106.1

w w w . n s s . s i / i w e p 2 0 1 7

iwep2017 02 web - djs · international workshop on electric probes in magnetized plasmas (12 ; 2017...

Documents