in search of alternative propellants for ion...

In Search of Alternative Propellants for Ion Thrusters

Kristof Holste

I. Physikalisches Institut

Justus Liebig Universität Gießen

Justus Liebig University Giessen ̶ Proprietary 2016-03-16 In Search of Alternative Propellants for Ion Thrusters - Kristof Holste

Outline

• General aspects

• Atomic propellants

• Molecular propellants

• Experimental setups

• Outlook

2


General aspects General aspects

How is thrust generated in a gridded ion thruster?

1

𝑇 = −1

2𝜀0(𝐸𝑎𝑐𝑐𝑒𝑙

2 − 𝐸𝑠𝑐𝑟𝑒𝑒𝑛2 )

Thrust is generated by electrostatic forces between the ions and the grids

+

E

Fel

PH

V

NH

V

T

plasma

How does the mass come into play?

Electrostatic forces are mass independent

plasma

region

ion beam region


General aspects General aspects

How is thrust generated in a gridded ion thruster?

1

+

E

Fel

PH

V

NH

V

T

plasma

plasma

region

ion beam region


2

Comparison of xenon and protons as propellant:

+

E

Fel

PH

V

NH

V

T

plasma

𝑇 = 1 𝑚𝑁

Propellant Mass (amu) vex (ms-1) t (ns) dmi/dt (kgs-1) I (mA) P/N (WmN-1)

Xenon 131.3 4.7E4 42.6 2.13E-8 15.65 23.5

Proton 1.0 5.4E5 3.7 1.87E-9 179.0 268.5

𝑈 = 1500 𝑉 𝑑 = 1 𝑚𝑚

Higher propellant mass reduces the

power-to-thrust ratio

89% less power required

General aspects


General aspects 3

• High mass

• Easy handling

• Efficient ionization

• No energy loss channels

• Availability

• Cheap


3

Atomic Propellants


Atomic Propellants 4

Element Mass

(amu)

Ii (eV) Tb (K)

Li 6.939 5.390 1603.0

Kr 83.800 13.996 121.1

Cd 112.400 8.991 1038.0

I 126.900 10.440 457.2

Xe 131.300 12.127 165.2

Cs 132.905 3.893 963.2

Hg 200.590 10.434 630.2

Tverdokhlebov & Semenkin, AIAA 2001-3350

Material properties for some elements:

0 5 10 15 20 25 30 35 400

300

600

900

1200

1500

1800

2100

2400

2700

Cro

ss s

ection [M

b]

Electron-impact energy [eV]

lithium

cesium

tin

cadmium

iodine

krypton

xenon

Computed electron-impact ionization

cross-sections for various propellants:

Los Alamos National Laboratory Physics

Code (LANL) using a configuration average

of ionic states



How about xenon?

Pros Cons

High mass Gaseous

Non-reactive High ionization potential

Gaseous Average cross section

High price

400 ppb mass fraction 1000 t air provide 400 g xenon



RIT-22 consuming 50 sccm xenon

4.915×10-6 kg/s 155 kg/year

price for xenon: ~ 1300 €/kg

200,000.00 €

lifetime test


12

Molecular Propellants


13 Molecular Propellants 13

P. Ehrenfreund & S. B. Charnley, Organic Molecules in the Interstellar Medium, Comets, and Meteorites: A Voyage from

Dark Clouds to the Early Earth, Annu. Rev. Astrophys. 2000. 38:427-89



• 720.11 amu

• solid at room temperature

• heating required (400 °C – 800 °C)

• plasma quenching due to anion formation

Leifer & Saunders, IEPC 91-154

Anderson & Fitzgerald, IEPC 93-003

Torres & Martinez-Sanchez, AIAA 93-2494

Takegahara & Nakayama, IEPC 93-032

Scharlemann, Acta Astronautica 51 (2002)

FULLERENES



• solid with high density (4.94 gcm-3)

• 0.3 Torr at room temperature

• IP(eV): I2 9.4 eV, I 10.45 eV

• I2: 253.8 amu

• corrosive

• negative ions

Dressler et al., AIAA-2000-0602

Tverdokhlebov & Semenkin, AIAA-2001-3350

BUSEK 3cm RF Ion Thruster

IODINE



IODINE

Modelling done by Konstantinos Katsonis

(DEDALOS Ltd.)



IODINE


Diamondoids 18

• sp3-hybridized carbon clusters

• superimpose diamond lattice

• very few vibrational channels

• adamantane C10H16

• solid at room temperature

• sublimation at low temperature

• cheap IP = 9.23 eV

M =136 amu

adamantane


Diamondoids 19

! Storage has to be designed carefully with respect to sublimation rate

40 50 60 70 800

1

2

3

4

5

6

7

8

experiment

theory

pre

ssure

[m

bar]

Temperature [°C]


Diamondoids 20

Lenzke et al., J. Chem. Phys. 127 (2007)

IP = 9.23 eV


Diamondoids 21

RIT-10 in operation with adamantane


Diamondoids 22

0.1 0.2 0.3 0.4 0.5 0.6 0.7

15

20

25

30

35

40

45

50

7.5 mA Xenon

7.5 mA Adamantan

10 mA Xenon

10 mA Adamantan

RF

-po

we

r [W

]

Mass-flow [sccm]

performed with a RIT-4

flow for adamantane in arb. units


Diamondoids 23

Problematiken

Gewollte Kaltstelle


Diamondoids 24

Problematiken


25

Experimental setups


Mass spectrometry of diamondoids 26

magnet

test chamber

slits

slits

Faraday-cup



0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

-C8H

x

-C7H

x

-C6H

x -C5H

x

-C4H

x

-C3H

x

-C2H

x

Ion c

urr

en

t [n

A]

Mass-to-charge ratio [amu/q]

1000

1

2

3

18

26

39

5067

79

93

107 121

136

Adamantane

-CHx

plasma biased with 7 kV; ECR ion source for highly charged ions




0 20 40 60 80 100 120 1400

5

10

15

20

25

30

C2H

x

C3H

x

C4H

x

C8H

x

C9H

13

C5H

x

C6H

x

C7H

x

C10

H15

Io

n c

urr

ent [n

A]


C10

H16

Source parameters show strong

influence with respect to fragmentation



Argon-Adamantane-Mixture (5 sccm-Ar + some C10H16)

20 40 60 80 100 120 140 160

0.0000

0.0005

0.0010

0.0015

0.0020

Adamantane

reference peak: Argon

Io

n c

urr

ent [n

A]


Almost no fragments

RIT-10

peak distortion in inductively

coupled rf-plasmas under

investigation



132 133 134 135 136 137 138 139 140 141 142

0

5

10

15

20

25

30

35

40

Experiment

Natural isoptope distribution

(C10

H16

+ C10

H15

)

Ion c

urr

en

t [n

A]

Mass [amu]

132 134 136 138 140

1E-4

1E-3

0.01

0.1

1

10



Electron-Impact Cross Section 31

Electron-impact ionization cross sections needed:

New setup to perform cross-section measurements is planned.

PSD

Faraday cup

Repeller

Electron gun

x,y-steerer

collimator

Gold grid

Position sensitivedetector (2 MCPs,1 resistive anode)

𝜎𝑛+ = 𝑁𝑖

𝑛+

𝑁𝑒𝑛𝑙


32

Calculation by Chris Volkmar

Electron-Impact Cross Section


33

0 500 1000 1500 2000

0

1

2

3

4

5

6

7

8

TT

L [V

]

Time [ns]

e-

ions3 - 5 kV

t10-90%

= 40 ns50 V

t10-90%

= 1 ns

e--pulsing ion pulsing

-150 -100 -50 0 50 100 150

0

100

200

300

400

500

x

Ion c

urr

ent [n

A]

Deflection voltage [V]

|1st derivative|

Gaussian fit

FWHM = 13.31 V FWHM = 15.08 V

~ 3 mm diameter


1 eV – 2000 eV


34

Straub et al. J. Chem. Phys. 106 (11) 1997


Ar I cross section


Conclusion and outlook 35

• Diamondoids and iodine are promising candidates as propellants for ion thrusters

• EP team at Giessen university developed a gas feed line

• Calibration of mass flow can be done in Giessen

• Performance of propellant will be measured by:

• Modification of diamondoids for optimization possible with chemical methods

• Electron-impact cross-sections of diamondoids will be measured

• Extended setup to measure excitation cross sections is under development

1. RF-power vs. massflow mapping

2. Optical emission spectroscopy

3. Mass spectrometry of extracted ion beam

in search of alternative propellants for ion...

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