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

czy1003@ipp.ac.cn

2

HT-7Abstract

• 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

HT-7

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 resolution3. High energy resolution

Impurities transport and concentration measurement

Qualifications of soft x-ray PHA detector

4

HT-7

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

HT-7Virtues 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 NitrogenSDD 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

HT-7

High detecting efficiency with 8m 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 )

Performance of SDD

7

HT-7Layout 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

HT-7SDD for PHA in HT-7

Isolated SDD (6 detectors) 15-channel SDD Array

Area: 5mm2

Thickness:280µmBe foils:8µm

9

HT-7Arrangement 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

HT-7

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

HT-7Experimental Results of Ohmic Discharge

Ip=120 kA

ne0 =1.43×1019m-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

12

HT-7Experimental Results of high performance long-pulse discharge

Ip=120kAne0=1.35×1019m-3 LHW~400kW (0.1 s to 5 s )IBW~200kW(0.2 s to 5.1 s )

LHCD discharge combining with IBW heating

•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

Profile at 2.75s in wave heated long pulse discharge by 250ms collecting time

The error bars presented ~10% error in fitting

13

HT-7 Experimental Results of LHCD Discharge

Waveforms of LHCD discharge

Ip=154kAne0=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

HT-7

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 investigation4. The SDD PHA successfully measured Te profile with moderate time

resolution5. The metallic impurities by SDD PHA diagnostic will be further

studied in the next target

15

HT-7Further 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