HT-7 A new soft x-ray PHA diagnostic in the HT-7 tokamak Zhongyong Chen, Yuejiang Shi,Bo Lv,Baonian Wan, Shiyao Lin,Liqun Hu,Qingsheng Hu, Shenxia Liu,Shiyao Lin ASIPP

HT-7 2 Abstract A new soft X-ray PHA based on Silicon Drift Detector (SDD) has developed in HT-7 The spatial multi-channel SDD PHA has compact configurations. SDD has the virtues of high counting rates (> 100kHZ) and high energy resolution First experimental results with SDD PHA in typical ohmic discharge and auxiliary heating discharges are presented

HT-7 3 PHA diagnostic purposes in HT-7 High spatial resolution profiles of electron temperature Appropriate time resolution of electron temperature Investigating transport and concentration of heavy impurities  1. Compact assembly Spatial multi-channel configuration  2. High input count rate Appropriate time resolution  3. High energy resolution Impurities transport and concentration measurement Qualifications of soft x-ray PHA detector

HT-7 4 Limitation of Candidate soft X-ray Detectors Si(Li) detector High energy resolution Moderate count rate operation Bulk setup (working at LN temperature) Limited the spatial multi-channel configuration APD Working at room temeperture, Low energy resolution, Low absorption efficiency Si-PIN Pelter cooler, Moderate energy resolution

HT-7 5 Virtues of SDD detector for PHA High count rate input count rate >10 5 cps (0.5  sec shaping time) High energy resolution FWHM<160eV -10 ºC) High quantum efficiency suitable for X-ray detecting in range of 1~20keV Integrated FET lower noise, no pickup, no microphony Cooled by peltier element compact assembly, no Liquid Nitrogen SDD very suitable for the set-up of spatial multi-channel PHA in tokamak Characteristics of SDD: 5mm² active surface, 280µm thick Silicon crystal Cooled by a single stage peltier element to -10 ~ -20 ºC High energy resolution at short shaping time The extremely small value of anode capacitance independent of the active area,which allows SDD to gain high energy resolution at short shaping time(0.25~1  sec) The collecting anode is discharged in a continuous mode, thus SDD can be operated with DC voltages only, and the detector has little dead time

HT-7 6 High detecting efficiency with 8  m Be foil in the energy range of 1~20keV Calibration spectra of SDD The energy resolution is about (0.5sec shaping time, -10 ºC ) Performance of SDD

HT-7 7 Layout of SDD PHA in HT-7 tokamak Vertical 15 channel (V-PHA) Measuring range: + 21 cm Spatial resolution : 3 cm Horizontal 6 channels (H-PHA) Measuring range: 0~+24 cm Spatial resolution : 4.8 cm

HT-7 8 SDD for PHA in HT-7  Isolated SDD (6 detectors)  15-channel SDD Array Area: 5mm 2 Thickness:280 µ m Be foils:8 µ m

HT-7 9 Arrangement of vertical SDD PHA Spatial resolution: 3 cm Detecting range: +21cm Unfortunately, five detectors of 15-channel linear array SDD were not operational during the last experiment

HT-7 10 Arrangement of horizontal SDD PHA Spatial resolution: 4.8 cm Detecting range: 0~24cm Unfortunately, the outer SDD measuring 24cm was not operational during the last experiment

HT-7 11 Experimental Results of Ohmic Discharge Ip=120 kA n e0 =1.43 × m -3 Soft x-ray spectra of horizontal SDD PHA (350~450ms) Electron temperature profile of ohmic discharge The measure profile is well described by the analogy parabola form of : 0.86 × (1-(r/a) 2 ) 1.9

HT-7 12 Experimental Results of high performance long-pulse discharge Ip=120kA n e0 =1.35 × m -3 LHW~400kW (0.1 s to 5 s ) IBW~200kW(0.2 s to 5.1 s ) LHCD discharge combining with IBW heating T e increased considerably in half plasma minor radius during wave heated phase Profile was much flat in central region and had a large gradient at 0.52a, showing an ITB-like structure Profile at 2.75s in wave heated long pulse discharge by 250ms collecting time The error bars presented ~10% error in fitting

HT-7 13 Experimental Results of LHCD Discharge Waveforms of LHCD discharge Ip=154kA n e0 =1.1 × m -3 LHW: ~275kW Raw spectra from VXPHA in two different phases (200ms) The concentration of iron in core plasma range is about 0.08%

HT-7 14 Summary 1. The use of SDD has allowed the design of compact spatial multi- channel configurations soft x-ray PHA 2. The level of counting rates improved the time resolution in measurement 3. The high energy resolution is suitable for impurities investigation 4. The SDD PHA successfully measured T e profile with moderate time resolution 5. The metallic impurities by SDD PHA diagnostic will be further studied in the next target

HT-7 15 Further Improvement of SDD PHA  Hardware o Upgrade of Detectors (higher count rate ~200kHZ) o Redesign of machine parts of horizontal SDD PHA (more credible, exchangeable Be foils for every detector) o Improve the shield of vertical SDD PHA o Redesign of pinhole of SDD PHA (Tungsten instead of steel, small aperture:  0.2mm~0.5mm)  Software o Develop the program that can calculate Te automatically o Develop the code about impurities