NSTX presentation

1
NSTX
Supported by
First Test of the X-ray Spectrometer
K. L. Wong, A. L. Roquemore Electronics J.
Dong, J. Wertenbaker Software G. Zimmer
College WM Colorado Sch Mines Columbia
U CompX General Atomics INEL Johns Hopkins
U LANL LLNL Lodestar MIT Nova Photonics New York
U Old Dominion U ORNL PPPL PSI Princeton U Purdue
U SNL Think Tank, Inc. UC Davis UC
Irvine UCLA UCSD U Colorado U Illinois U
Maryland U Rochester U Washington U Wisconsin
Culham Sci Ctr U St. Andrews York U Chubu U Fukui
U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu
Tokai U NIFS Niigata U U Tokyo JAEA Hebrew
U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST
POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP,
Jülich IPP, Garching ASCR, Czech Rep U Quebec
NSTX Physics Meeting LSB318, PPPL Aug 3, 2009
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Purpose of the X-ray spectrometer

• Microtearing modes produce stochastic B, can
  explain ?e in some NSTX discharge
• The old PHA system (from TFTR) saw very few
  photons above 10 keV , much less than one would
  expect in a Te(0) 3 - 4 keV plasma - due to
  stochastic B ?
• The purpose of the spectrometer is to study
  electrons in some NSTX discharges in 5 - 25 keV
  energy range
• - a cheap and quick method to obtain a vital
  piece of info

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X-123 spectrometer (Amptek)Ref Y. Shi et al.,
RSI (2004) - KETEK detectors
4
Specifications

• lt 0.001 counts/s from 2 -150 keV, our range 5 -
  25 keV . Need tangential port ?
• Von Goeler et al. RSI (1994)
• Bremsstrahlung radiation pattern ?
• 2 stage Peltier cooling - ?T80oC
• Thermal noise T ? f, S/N Area /?f.T
• same as old (TFTR) PHA
• Thickness 0.5 mm vs 3-4 mm, less sensitive to
  neutrons, limit not known, NOT INTENDED
  FOR high performance plasmas (1.e14 n/s)
• Shielding Von Goelers PDX X-ray camera has S/N
  1 at 1.e13 n/s with 4 lead 8 polyethelene

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Hardware/Software Modifications for NSTX
Application

• Hardware Add gate input - 4 volts to take data
  (from 404/412 timing module)
• Software Temporal resolution - write software to
  read store up to 10 blocks of data/shot
• Amptek spec time gap DT ti - tsi-1 12 ms,
  
• we measured DT 14 - 15 ms to retrieve data
  overhead(additional dead time)
• For reliable operation, need DT 100 ms gt 50
  ms - decided on 6 blocks of data, 100 ms each

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Sequence of Events

• Mon july 6 finish wiring after 5 pm
• Tues july 7 software not ready, test with manual
  trigger (RF plasma), add shielding in evening
• Wed july 8 test Labview software - see no
  counts, trigger did not work - no gate Vin
• Fix pulse transformer LEMO cable after 5pm
• Thurs july 9 first try with 404/412 trigger -
  see very few counts -
• Saturated by photons ?
  Alignment problem ?
• Fri july 10 try again with smaller aperture
  thicker foil, still no good.
• Wrong parameter settings ? call AMPTEK random
  bits.
• Should read parameter settings with ADMCA
• Mon july 13 Thomson complaint - lead
  reconfigure software
• Tues july 14 read spectrometer parameter with
  ADMCA, read data with Labview,
• ADMCA crashed, power reboot in test cell after
  5 pm.
• Read data from wrong buffer ?
• Wed july 15 control spectrometer with ADMCA,
  read last data files and compare with
• Labview data - they agree - software usable.
  Optimize DT ( 1 pm )
• July 14-15 vary apertures foils, no obvious
  effect, noise creeping up
• Only high power beam shot - No useful data.

7
Spectrum from manual trigger - no temporal
resolution

• HHFW only - triggered a few sec before shot
• - detector noise photon signal
  
  

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Technical problems encountered

• Hard ware
• - no trigger input - LEMO cable problem
• Soft ware
• - late start
• - wrong file loaded or wrong readout data ?
• - Amptek Labview clash
• - read from correct buffer ?
• It was Wed July 15 when software became usable
• - change Al foil aperture - no obvious effect
  
• - only high beam power shots neutrons (
  2.e14 n/s)
• Detector noise creeping up

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Labview Software has 3 parts

• Load a file (from Amptek) to set spectrometer
  parameters
• Read the parameter settings and store in a file
• - needed for data analysis
• Clear buffer, read data file in buffer at
  specified times and transfer data to PC disk and
  store them
• Temporary solution cut out 1 2, just use part
  3

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Parameter settings

• ADMCA (Amptek) Labview
• __________________________________________________
  PUR on PUR 1
• RTD off RTD 10 ?
• gate input active low gate
  input 2
• course gain 106 coarse gain 3
• fine gain 1.0 fine gain
  8192
• 1. Wrong parameter file loaded ?
• 2. Can we read parameter file with ADMCA
  instead of Labview ?
• 3. Read from wrong buffer ( 1 A or B? )

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Spectrometer data time-gtchannel
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Estimation of Neutron Counts

• (A) Detector area 25 mm2, R 4 m, 2.e14
  n/s
• Neutron rate at detector 2.4e7/s
• About 1 of neutrons hitting detector produce a
  current pulse
• ? 2.4e5 counts/s ? saturation
• Note (a). Recommended max. count rate is
  1.2e5/s
• (b). Scattered neutrons ?s not yet
  included (i.e. perfect shielding assumed)
• (B) Ken Hill PILATUS pixel sees up to 320
  counts/s, no shielding
• pixel area 0.172x0.172 mm2, thickness 0.3 mm
  , can count up to 1 MHz
• 0.6 neutrons produce current pulse
• Amptek detector (w/o shielding) should see
  3168 x 320 1.e6 counts/s
• Shielding cuts it down by 4 - reasonable
  agreement.
• ------ Neutrons are NOT the only
  problem ------

13
Detector noise problem bad cooler ?- still
under warranty

• In-situ calibration with 55Fe 2 peaks at 5.9 keV
  and 6.49 keV (7/22/2009)
• Resolution for 2049 was 228 eV (10/06/2008)

14
What did we learn ?

• Use the not-yet-perfected software to do NSTX
  experiments
• - just use the clock cycle to sort out problems,
  never asked a single plasma shot
• X-ray PHA not possible in 2.e14 n/s (not our
  intent, never been done anywhere)
• Highly unlikely in high e13 n/s (do-able for
  Pilatus at 1 MHz count rate)
• Possible in low e13 n/s
• Can we use this spectrometer for microtearing
  mode experiment ?
• - Yes. The experiment has two parts
• 1. HHFW with beam blips - no problem
• 2. Beam heated plasma - needs modification
  
• To avoid neutron saturation, just try to
  inject 1 D-source into a 3.5 kG, 500 kA,
• helium target plasma before consider other
  exotic means
• H-beam, (b) He plasma, (c) Just look at
  afterglow, (d) High ne with HHFW
• Conclusion 1. Spectrometer should work if we fix
  noise problem, move to bottom port
• and add more shielding (on concrete floor),
  improve alignment
• 2. Do we still need this when
  PILATUS becomes operational ?