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A new soft x-ray PHA diagnostic in the HT-7 tokamak

ASIPP. 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. czy1003@ipp.ac.cn. Abstract. A new soft X-ray PHA based on Silicon Drift Detector (SDD) has developed in HT-7

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A new soft x-ray PHA diagnostic in the HT-7 tokamak

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  1. ASIPP 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 czy1003@ipp.ac.cn

  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 (160eV@5.9keV) • First experimental results with SDD PHA in typical ohmic discharge and auxiliary heating discharges are presented

  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 Qualifications of soft x-ray PHA detector • 1. Compact assembly Spatial multi-channel configuration • 2. High input count rate Appropriate time resolution • 3. High energy resolution Impurities transport and concentration measurement

  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

  5. Virtues of SDD detector for PHA • High count rate input count rate >105 cps (0.5 sec shaping time) • High energy resolution FWHM<160eV (@5.9keV, -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

  6. Performance of SDD High detecting efficiency with 8m Be foil in the energy range of 1~20keV Calibration spectra of SDD The energy resolution is about 153eV@5.9keV (0.5sec shaping time, -10 ºC )

  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

  8. SDD for PHA in HT-7 • 15-channel SDD Array • Isolated SDD (6 detectors) Area: 5mm2 Thickness:280µm Be foils:8µm

  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

  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

  11. Experimental Results of Ohmic Discharge Ip=120 kA ne0 =1.43×1019m-3 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 Soft x-ray spectra of horizontal SDD PHA (350~450ms)

  12. Experimental Results of high performance long-pulse discharge LHCD discharge combining with IBW heating Profile at 2.75s in wave heated long pulse discharge by 250ms collecting time The error bars presented ~10% error in fitting • Te 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 Ip=120kA ne0=1.35×1019m-3 LHW~400kW (0.1 s to 5 s ) IBW~200kW(0.2 s to 5.1 s )

  13. Experimental Results of LHCD Discharge Waveforms of LHCD discharge Ip=154kA ne0=1.1 ×1019m-3 LHW: ~275kW Raw spectra from VXPHA in two different phases (200ms) The concentration of iron in core plasma range is about 0.08%

  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 Te profile with moderate time resolution 5. The metallic impurities by SDD PHA diagnostic will be further studied in the next target

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

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