Ficker, Ondrej

Imrisek, Martin

Mlynar, Jan

Paprok, Richard

Varavin, Mykyta

Varju, Josef

Vlainic, Milos

Weinzettl, Vladimir

English

Ghent University Academic Bibliography

5. CONCLUSIONThe purpose of the poster is to show potential of new HXR diagnostic for RE studies. The difficulties regarding the CsI(Tl) semiconductor detector presented are limiting factors for their performance on tokamaks.OUTLOOK: Optimize the shielding!REFERENCES[1] http://www.eurorad.com/probes.php[2] http://www.eurorad.com/PDF/UG_CSI_1010_1515_1530_2525.pdf[3] Z. Zelenka, Technical report TZ_CSOD_2015_01, 20151st EPS Conference on Plasma Diagnostics14th-17th Apr 2015, Frascati, Italy1. INTRODUCTIONBackground: - runaway electrons (RE) can reach a few MeV- RE hit the plasma facing components- radiation in Hard-X Ray (HXR) region of the electromagnetic spectrumMotivation: - toroidal asymmetry of the RE losses- toroidal asymmetry of kinetic loads- ECONOMIC AND FAST DETECTORSPossibilities: - toroidal propagation of the Parail-Pogutse instability- bremsstrahlung from the in-flight REDetectors [1,2]: - EURORAD (commercial) detectors- “Solid State Scintillation Probe SC2525”- 4 CsI(Tl) scintillators with Si photodiode- diameter = 3.5 cm, length = 7 cm- input +/- 12V- integrated preamplifier- scintillations in ~100 keV to 1 MeV range- Aluminum encapsulation2. TECHNICAL SOLUTIONS2.1 Modification of Temporal Characteristics- Too long decay time- The detector had to be opened- Tested in the same position4. CsI(Tl)+Photodiode vs NaI(Tl)+PMTCsI(Tl) Semiconductor Detectors for Hard X-Ray Diagnostics at COMPASS TokamakRichard Paprok1,2, Milos Vlainic1,3, Jan Mlynar1, Vladimir Weinzettl1, Mykyta Varavin1,Jozef Varju1, Ondrej Ficker1,4, Martin Imrisek1,2 and the COMPASS Team1Institute of Plasma Physics AS CR, v.v.i., Prague, Czech Republic 3Department of Applied Physics, Ghent University, Ghent, Belgium2Faculty of Mathematics and Physics, Charles University in Prague, Prague, Czech Republic 4Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech RepublicPARAMETER VALUEMajor Radius 0.56 mMinor Radius 0.23 mToroidal Magnetic Field 0.9-1.25 TPlasma Current < 400 kADischarge Length < 0.4 sElectron Density 1019 - 1020 m-3Plasma Facing Material C-limiter & Inconel-625COMPASS tokamak parameters:Experimental setup of diagnostics used for RE loss detection during the 2nd COMPASS RE campaign.2.2 Relaxation Time Issue- Artificial negative values- Tested in the same places- Higher peaks2.3 Radiation Effect- Manufacturer's threshold ~1 Gy:- 2nd campaign (unshielded): ~7.36 mGy [3]- RE discharge (unshielded): ~100 μGy- Shielding with Pb-bricks needed:- 5 cm enough for non-RE experiments- 10 cm NOT ENOUGH for RE experimentsADVANTAGES DISADVANTAGES- Compactness - Switches off in high gamma fluxes- No need for high voltage (safer) and photomultiplier tube (cheaper)- Space usage increases with the amount of the Pb-bricks- Better quantum efficiency relative to the output signal- Makes studies of the dedicated RE experiments in COMPASS difficult- More stable control of the multiplication factor- Temporal characteristics were too slow for the required application- Weaker or none integration of consecutive detections- Artificial negative signal still appears for strong peaks- Better signal-to-noise ratio - After modification: lower sensitivityThickness of single Pb brick ~5 cm3. OBSERVATIONS OF TOROIDAL ASYMMETRIES ON COMPASSThe behavior or three detectors verifiedto be consistent before and aftermodification.Details of discharge #8953:- D-shaped L-mode plasma- el. density ~4x1019 m-3- plasma current 150 kA- disruption at 1229 ms- HXR detectors toroidally distributed- NBIs shielding North-East andNorth-West detectors- South-East has the strongest signals- South east only without signal beforedisruptionACKNOWLEDGMENTThis work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

CsI(Tl) semiconductor detectors for hard X-ray diagnostics at COMPASS Tokamak

https://biblio.ugent.be/publication/6862839/file/6862844.pdf

CsI(Tl) semiconductor detectors for hard X-ray diagnostics at COMPASS Tokamak

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Ghent University Academic Bibliography