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First results – H- ion beam extraction in ROBIN
in surface mode
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 1
M. Bandyopadhyay on behalf of
K. Pandya et.al. (ROBIN operational group)
Kaushal Pandya1, Agrajit Gahlaut1, Ratnakar K.Yadav2, Manas Bhuyan2, Mainak Bandyopadhyay2, B.K. Das2, P. Bharathi1, Mahesh Vupugalla1, K.G.Parmar1, Himanshu Tyagi2, Kartik Patel1, Jignesh Bhagora2, Hiren Mistri1,Bhavesh Prajapati1, Ravi Pandey1 and Arun.K.Chakraborty1
1Institute for Plasma Research, Gandhinagar- 382428, Gujarat, India 2ITER-India, Institute for Plasma Research, Gandhinagar-382428, Gujarat, India
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Outline
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 2
• Introduction about ROBIN
• Diagnostic and Monitoring system implemented in ROBIN.
Langmuir probe ( plasma parameter)
Optical Emission Spectroscopy (Cs and plasma impurity trace)
Residual Gas Analyser (Gas impurity)
• Parametric study of ROBIN
• Results from probe study.
• Preliminary results of beam characterization using
thermal differential calorimeter
Doppler Shift Spectroscopy
• Summary
• Future plan
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Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 3
ROBIN
• 1MHz, 100kW, ICP type negative ion source
with 6.5 turn water cooled coiled antenna,
having 3 grid beam extraction and acceleration
system.
• Cs delivery system (1gm Cs ampules) is
attached in the lower side of the expansion
region.
• Source body temperature is maintained @ 40oC.
IPP design; Collaboration under License agreement
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ROBIN Bias plate and PG
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 4
Open Extraction aperture number = 146 out of Total 776;
Open extraction area= 73.38cm2
Plasma grid temperature is maintained at 150°C
Expansion chamber
30cm × 58cm × 19cm
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HVPS System for ROBIN
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 5
High voltage power supply system (APSS: -35kV, 15A DC; EPSS:-11kV35A DC)
commissioned in NNB HVPS Facility
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Typical wave forms of ROBIN
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 6
• Maximum duration of a shot : 4 second shot
• Maximum power couple in surface mode 70kW.
• Maximum HV applied: 24kV (EPSS 10kV, APSS 14kV).
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Diagnostics & Monitoring system
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 7
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Complete system of ROBIN
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 8
Source DSS ports Cryopump RGA
TMP
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Electrical current measurement
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 9
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Source performance in surface mode
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 10
Different RF Power level. Max. beam
current density
~13mA/cm2
Min. e/H- ion
ratio ~ 2
All other parameters are varied.
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Source performance in surface mode
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 11
Different gas pressure level.
Cs conditioning ?
Max. beam
current density
~13mA/cm2
Min. e/H- ion
ratio ~ 2
All other parameters are varied.
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Source performance in surface mode
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 12
RF Power scan in ROBIN
Almost Linear relationship with power
saturation effect ?
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Source performance in surface mode
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 13
Pressure scan in ROBIN
Gas cooling down effect in Electron part ?
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Source performance in surface mode
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 14
Grid bias voltage scan
Optimum PG bias voltage ~ 24V.
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Source performance in surface mode
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 15
Acceleration voltage scan
• Electron current nearly unaffected.
• GG current decreases.
- Is Beam quality getting improved ??
Current in Beam dump has decreasing trend in higher voltage.
- Any other effect (2ndary electron emission) ??
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Source performance in surface mode
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 16
Fixed voltage (HV) ratio scan
• Electron current increases linearly.
• Current in Beam dump has decreasing trend in higher voltage after 5-6kV
extraction voltage.
Is Beam quality getting affected ??
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Beam diagnostics
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 17
Thermal Differential Calorimeter
Beam facing side of the calorimeter
-40 -32 -24 -16 -8 0 8 16 24 32
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Be
am
pow
er
den
sity (
W/c
m2)
position / cm
Vertical profile - data
Horizontal profile - data
Vertical - Gaussian Fit
Horizontal - Gaussian Fit
Shot# 26853
Copper calorimeter centre
Thermal calorimeter used for investigation of beam position, power deposition, beam divergence and beam optics study .
IPP design
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Beam diagnostics
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 18
Preliminary results from calorimeter
Shot# High voltage DC
Beam divergence
26135 EPSS:5kV, APSS: 7kV
5.8°
26137 EPSS:5kV, APSS: 11kV
5.6°
26139 EPSS: 5kV APSS: 15kV
3.7°
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Beam diagnostics
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 19
Specifications EMICON MC
Number of spectrometer channels
1-4
Wavelength range [nm] 200 - 1100
Spectral resolution [nm]
1.5
Signal resolution 16 Bit
Doppler shift Spectroscopy with EMICON MC spectrometer
Light from the
Beam
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Beam diagnostics
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 20
Doppler shift Spectroscopy with EMICON MC spectrometer
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Beam diagnostics
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 21
DSS with high resolution spectrometer
• Preliminary calculation suggests divergence is in the range 4 -5 degree in
beam total operational HV (EPSS+APSS) range 10 – 20 kV..
• Stripping observed
• Further calculation on going.
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Plasma monitoring - Probe
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 22
• Online data analysis during each shot. 1. F.F. Chen, ‘Langmuir probe analysis for high density plasmas’, Phys. Plasmas, 8,3029, (2001).
2. S. Linnane and M. B. Hopkins, Plasma Sources Sci. Technol, 18, (2009) – error estimation.
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Plasma monitoring - Probe
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 23
Plasma parameter variation with bias voltage
RF power: 60kW,
Pressure: 0.6Pa
Plasma non-uniformity
observed ~ one order
difference in density ?
Plasma density
~ (Top)1016 m-3 –
(Bottom) 1017 m-3.
Plasma temp ~ 2 – 4eV.
Cs distribution in the source and its conditioning ?
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Plasma monitoring - OES
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 24
Typical Optical Emission Spectrum
Cs lines
observed.
Impurities like
Oxygen and OH
indicates presence
of moisture or
vacuum leak..
Leak detection
ensures leak rate
< 10-8 mbar l/s
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Gas Monitoring
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 25
Residual Gas Analyser scan • Moisture
level high !
10-7 torr..
• Increases
when H2
gas is
injected.
Gas
quality
Effect on Cs
conditioning ?
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• RF generator and matching circuit is not behaving properly more than 70kW – Improved matching circuit to be connected.
• Cryopump operation (14000l/s) reduces the moisture level 5 times
between the shots compare to only TMP case (effective - 3500 l/s),
- However, beam dump current and DSS signal goes down.
beam blowup ??
• Cryopump operation needs almost double gas throughput to maintain same pressure in the source compare to only TMP case.
• Gas feed starts behaving erratic due to large reflected radiation.
New MFC installed which shows better behaviour.
• PG bias interlock is as reliable as H-alpha interlock for RF generator during the initial plasma breakdown impedance mismatch condition.
See poster - MonP12
Few difficulties & experience
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 26
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• Extraction grid (EG) rise in temp ~ 3oC only in 4 sec shot in spite of with higher e/H ratio – ~ 2 A electron current (42 lpm total flow rate in two grid halves).
– Is it correct ??
• EPSS is riding on APSS, so during breakdown, EPSS voltage shoots up
– To protect special spark gap based arrangement is made.
• Metallic valve bellow leakage in Cs oven (due to Cs corrosion ?)
Valve is removed at present.
• Source is kept in Ar environment when not operational.
– How it affects Cs conditioning ?
Concern over Quality of Cs conditioning in presence of impurities
Few difficulties & experience
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 27
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• Operation with Improved matching circuit to raise the power coupling further.
• Integration of a directional coupler to measure reflected power.
• Use higher purity gas along with a gas purifier in the gas feed line.
• Integration of RF shield around RF coil.
• Integration of a high resolution spectrometer including into DACS.
• Integration with Laser Photo-detachment diagnostics.
• Integration of dedicated Cs absorption line diagnostic system.
Ongoing activities and future plan
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 28
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• ROBIN is upgraded by integration of EPSS, APSS, Cs oven, Cryopump, RGA and a thermal calorimeter.
• Cs oven is integrated and source is operated in Hydrogen in presence of Cs injection.
• Maximum current density is observed as ~ 13mA/cm2
• Minimum e/H- ion ratio observed as ~ 2.
• Needs improvements in many fronts
(RF coupling, Cs conditioning, Gas impurities, Diagnostics).
Summary
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 29
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Thank you
Mainak Bandyopadhyay; NIBS2016, Oxford,UK; 12th-16th Sep 2016 30