The development of6MeV Heavy Ion Beam Probe

System in LHDA. Shimizu, T. Ido, M. Nishiura, S. Nakamura1, H. Nakano, S. Ohshima2,Y. Yoshimura, S. Kubo, T. Shimozuma, H. Igami, H. TakahashiM. Yokoyama, S. Kato, A. Nishizawa, Y. Hamadaand LHD Group

National Institute for Fusion Science, Toki, Japan1) Graduated School of Engineering, Nagoya University, Nagoya, Japan2) Institute of Laser Engineering, Osaka University, Osaka, Japan

Introduction

1960 1970 1980 1990 2000

History of Heavy Ion Beam Probe (HIBP)

HIBP measurements in cathod arc PlasmaR. L. Hickok

toroidal currentin ST-tokamak (30 keV) T10 (300 keV)

TJ-II (200 keV)TMX ISX-B (160 keV)

NBT (40 keV)

CHS (200 keV)

JIPP-TIIU (500 keV)

TEXT (500 keV) TEXT-U (2 MeV)

LHD-HIBP(6 MeV)

LHD-HIBP should be the most challenging project in plasma diagnostics.

•Highest Probing Beam Energy•Non axis symmetric magnetic field configuration

JFT-2M (500 keV)NIFS Activity

Outline

•Principle of HIBP

•LHD-HIBP*Requirements*Tandem Energy Analyzer

•Results*Potential profile*Temporal change of potential*Fluctuation measurement of potential

•Summary

Principle of HIBPInjected Beam Energy: E0(Primary Beam, Au+)

Detected Beam Energy: Es(Secondary Beam, Au2+)

Energy deference corresponds to plasma potential

Es – E0 = eφ

Secondary Beam Current Intensity~ Plasma density

( path integral effect is included )

Requirements for LHD-HIBP

MrBEbeam /~ 22

1, The acceleration energy of HIBP,

In LHD, Bt ~ 3 T, r ~ 0.6 m

In large sized device, very large acceleration energy and heavy ion is needed

Ebeam ~ 6 MeV for Au+(197)

2, If we would like to measure 1V fluctuation, extremely high resolution(10-6) is required. Parallel 30 degree energy analyzer has been traditionally used, for its second order focusing of injection angle.

3, For the long orbit length inside of plasma, strong beam attenuationis predicted.

B: Magnetic field strengthr: minor radiusM: mass of beam

Is / I0 ~ 10-5, when ne ~ 1 x 1019 m-3As a sensitive detector, MCP is used.

6MeV Tandem Accelerator

LHDTandem energy analyzer

Two sweepersto control 3-dimensional beam orbit in non axisymmetricconfiguration. This concept is tested in CHS

LHD-HIBP system

~5 m

Observable region

Tandem Energy Analyzer

Beamθ1

θ21st stage

2nd stage

Ordinal type of 30 degree parallel plate analyzer requires high voltage of ~1 MV. Not realistic.

We use tandem energy analyzer to reduce required voltage to 120kV.

Second order focusing is realized

Mea

sure

dB

eam

ene

rgy

LHD-HIBP

Incident Angle (Degree)

Y. Hamada, et al., Rev. Sci. Instrm., 68 (1997) 2020

θ1

Ion -root

electron -root

Observed potential profilesDuring ECH,

Er = - grad φ > 0 : electron-root.

As the density increases,Er changes to negative in ρ < 0.4 : ion-rootA

A

B C D E

F

BC

D

E

F

Negative Palsies observed in LHD

0

0.5

1

0 0.4 0.8

φ (k

V)

t (ms)

τ = 26μs

τ = 73 μs

A

B

An expanded view of a pulse

4

3

2

1

0

Pote

ntia

l (kV

)

2.42.22.01.81.61.41.2Time (sec)

0.6

0.4

0.2

0.0

ne (10

19m-3)

NBI#2 NBI#3

ECH

Potential (kV)

ne

4.0

3.5

3.0

2.5

2.0

Pot

entia

l (kV

)

1.901.881.861.841.821.80Time (sec)

Repetitive Transition

Bell Hill

• Potential Fluctuation like pulse is observed in LHD. It is similar to CHS pulsation.

• Typical time constant of potential change is faster than energy confinement time.

• Pulse depth is less than in CHS

4.0

3.5

3.0

2.5

2.0

Pote

ntia

l (kV

)

1.8501.8491.8481.8471.8461.845Time (sec)

τ = 90 μs

τ = 500 μs

Pulsation in CHS

Low Density High Density

Observation of coherent modes

|φ(fGAM)| ~ Several hundreds VIt is considered to be Geodesic Acoustic Mode (GAM) caused by high energy particle driven mode, such as RSAE.

250

200

150

100

50

0

Freq

uenc

y (k

Hz)

2.01.81.61.41.21.00.8Time (sec)

density ~0.1 x 1019 m-3

NBIECH

Radial profile of the coherent modes

The mode corresponds to GAM frequency

These are considered to be RSAE modes

Large coherence with magnetic probe signal

Summary

● The LHD HIBP starts to operate after researches and development of many components and methods,particularly,

- the tandem parallel plate analyzer to analyze the probingbeam with a high energy resolution (~10-4)

- the control method to manage 3-dimensional beam orbit in non-axisymmetric magnetic field configuration

● Thanks to these efforts, several interesting observations have been already made, such as, the potential profile, potential change in microsecond range, coherent mode fluctuations, and their radial profiles in density range of 1018 m-3.

● LHD HIBP can be the most ambitious and challenging trial as diagnostics for large-scale plasma devices.

-5

0

5

10

0.0 0.1 0.2 0.3 0.4 0.5

Er 0.5-0.6sEr 0.8-0.9sEr 1.2-1.3sEr 2.0-2.1sEr 2.4-2.5s

Er

(kV

/m)

rho

#81079 Calc. Result

Comparison between Experiment and Simulation

Experiment Neoclassical Theory

Neoclassical simulation roughly agrees with the experimental results in core region.

-5

0

5

10

0 0.1 0.2 0.3 0.4 0.5

0.4 - 0.5 s0.8 - 0.9 s1.2 - 1.3 s2.0 - 2.1 s2.4 - 2.5 s

Er (k

V/m

)

ρ

#81079 Measured with HIBP

6

4

2

076543210

Time (sec)

-200

-150

-100

-50

0

Ip (KA

)

#81420

Sec

onda

ry

Bea

m C

urre

nt (a

.u.)

Secondary Beam Current

Toroidal Shift

Potential (Vertical shift)

Plasma DSP ON

Sweeper Voltage

Real Time Feedback Control

When the large toroidal current conducts, the beam strongly shifts to toroidal direction, so we cannot detect the secondary current because of exceeding.

Real time feed back control of beam by using sweep system may be required.

Position Sweeping Operation

Real Time Feedback Control with DSP

DSP real time feed back system is now being developed.

•non linear control•real time control•flexible system•C Language programming

In test stand, up to 100 Hz perturbations can be canceled out.Secondary Beam Current

Toroidal Shift

Potential (Vertical shift)

Plasma DSP ON

Sweeper Voltage

P control is used. By using PI control, feed back control will be improved.

Analog Signal Operation

Digital Signal Operation

Can HIBP be installed to ITER?

A. V. Melnikov, L. G. Eliseev, Review of Scientific Instruments 70, 951, 1999

Temporal change of the potential by ECHRax=3.6m, Bt=1.5T,ECH : on-axis heating (1.0 – 1.5 s)The plasma is produced and sustained by NBI.HIBP : Wbeam=1.5MeV , The sample volume is near the magnetic axis.

The increase in the potential tends to related to the increase in Te.

0

2

4

6

2.5 3 3.5 4 4.5

0.945s1.3s

Te(k

eV)

Radius(m)

#70222

0

2

4

6

2.5 3 3.5 4 4.5

0.945s1.3s

Te(k

eV)

Radius(m)

#70224

0

0.5

1

1.5

0 0.5 1 1.5 2

#70220#70222#70224

n e (1019

m-3

)

Time(sec)

-3

-2

-1

0

1

2

3

0 0.5 1 1.5 2

#70220#70222#70224

Pot

entia

l(kV

)

Time(sec)

ECH

NBI

Bt=1.5T,Eb=1.5MeV,Rax=3.6m

Negative Ion source

・Target sputtering Au- ion sourceControl Box

Negative ion source,pre accelerator,sector magnet

Negative ion source

・Au- ion is pre-accelerated to 50kV, and injected to the tandem accelerator

・Produced current is ~ 20μA

Tandem Accelerator

High Voltage Terminal

Column

Chamber of accelerator

Accelerator tube

Au+Au-

High frequency wave generator

・By using tandem accelerator, we can generate 6MeV beam with the voltage of 3 MV・Very stable voltage is needed to measure the plasma potential. (10-5 ~ 10-4)

Gas cell

Beam Control System①③⑨⑪Steerer

②④⑧⑩QuadrupoleLens

⑥Beam Profile Monitor

⑦4.8m Cylindrical Deflector

⑤Charge Separator

Beam Position

Beam Focus

Select Au+ from Aun+

⑬⑭8 pole electrical deflector

Control of injection and ejection angle of beam

Beam Attenuation in LHD

•• Secondary beam intensity Secondary beam intensity attenuates 5 ~ 9 times by attenuates 5 ~ 9 times by neutrals (Hneutrals (H22) in the edge ) in the edge region and impurity ions region and impurity ions (C(C6+6+) in the core plasma.) in the core plasma.

•• But the calculated secondary But the calculated secondary beam intensity is still one beam intensity is still one order of magnitude higher order of magnitude higher than the experimental one. than the experimental one. We found MCP detection We found MCP detection efficiency 0.1~0.5efficiency 0.1~0.5 (Good (Good agreement!!)agreement!!)