NSTX Supported by First Test of the Xray

NSTX Supported by First Test of the X-ray Spectrometer College W&M Colorado Sch Mines Columbia U Comp. X 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 K. L. Wong, A. L. Roquemore Electronics: J. Dong, J. Wertenbaker Software: G. Zimmer NSTX Physics Meeting LSB 318, PPPL Aug 3, 2009 Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto 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

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 ke. V , much less than one would expect in a Te(0) ~ 3 - 4 ke. V plasma - due to stochastic B ? • The purpose of the spectrometer is to study electrons in some NSTX discharges in 5 - 25 ke. V energy range - a cheap and quick method to obtain a vital piece of info’ NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

X-123 spectrometer (Amptek) Ref: Y. Shi et al. , RSI (2004) - KETEK detectors NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

Specifications • < 0. 001 counts/s from 2 -150 ke. V, our range: 5 - 25 ke. V. Need tangential port ? Von Goeler et al. RSI (1994): Bremsstrahlung radiation pattern • 2 stage Peltier cooling - ∆T~80 o. C • 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. e 14 n/s) • NSTX Shielding: Von Goeler’s PDX X-ray camera has S/N ~ 1 at 1. e 13 n/s with 4” lead + 8” polyethelene Meeting name – abbreviated presentation title (last name) Month day, 20**

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 > 50 ms - decided on 6 blocks of data, 100 ms each NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

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 5 pm 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. NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

Spectrum from manual trigger - no temporal resolution HHFW only - triggered a few sec before shot - detector noise + photon signal NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

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. e 14 n/s) • Detector noise creeping up … NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

Labview Software has 3 parts 1. Load a file (from Amptek) to set spectrometer parameters 2. Read the parameter settings and store in a file - needed for data analysis 3. 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 NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

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? ) NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

Spectrometer data [ time->channel # ] NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

Estimation of Neutron Counts (A) Detector area = 25 mm 2, R ~ 4 m, 2. e 14 n/s Neutron rate at detector: 2. 4 e 7/s About 1% of neutrons hitting detector produce a current pulse 2. 4 e 5 counts/s saturation Note: (a). Recommended max. count rate is 1. 2 e 5/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. 172 x 0. 172 mm 2, 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. e 6 counts/s Shielding cuts it down by 4 - reasonable agreement. ------ Neutrons are NOT the only problem ------ NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

Detector noise problem: bad cooler ? - still under warranty In-situ calibration with 55 Fe: 2 peaks at 5. 9 ke. V and 6. 49 ke. V (7/22/2009) Resolution for #2049 was 228 e. V (10/06/2008) NSTX Meeting name – abbreviated presentation title (last name) Month day, 20**

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. e 14 n/s (not our intent, never been done anywhere) – Highly unlikely in high e 13 n/s (do-able for Pilatus at 1 MHz count rate) – Possible in low e 13 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 k. G, 500 k. A, 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 NSTX Meeting name – abbreviated presentation title (last name) ? Month day, 20**