1. ASIPP Magnetic Diagnostics of HT-7U Tokamak Shen Biao Wan Baonian Institute of Plasma Physics, CAS P.O.Box 1126, Hefei, Anhui 230031, P.R.China (e_mail: biaoshen@ipp.ac.cn) HT-7U

2. ASIPP Outline Brief introduce of ht-7u. Principle and purposes of magnetic diagnostics. HT-7U magnetic diagnostic system. Summary. HT-7U

3. ASIPP Main Parameters Main Parameters Toroidal Field, B o 3.5 T Plasma Current, I P 1 MA Major Radius, R o 1.7 m Minor Radius, a 0.4 m Aspect Ratio, R/a 4.25 Elongation, K x 1.6 - 2 Triangularity,  x 0.6 - 0.8 Heating andCurrent Driving: ICRH 3 - 3.5 MW LHCD 3.5 MW ECRH 0.5 MW Pulse length 1000 s Configuration: double-null divertor, single null divertor, pump limiter HT-7U Tokamak HT-7U

4. ASIPP Magnetic Diagnostics Principle Electromagnetism Maxwell’s equations Purposes Equilibrium plasma configuration determination. for real time plasma control. (current, position, shape, current profile, and disruption control). MHD phenomena. Transient electromagnetic phenomena studies.

5. Position/shapeTime resolutionRate of changeAccuracy Rin,Rout1ms100cm/s0.5cm Rx,Zx1ms100cm/s0.5cm Zc1ms100cm/s0.5cm ASIPP HT-7U Ip rangeTime resolutionRate of changeAccuracy 0.1-1MA 1ms5MA/S 2% Beta rangeTime resolutionRate of changeAccuracy 0.01<β p <51ms1mWb/s10 -5 ParameterMax.frequencySpatial resolutionAccuracy MHD>100kHz5cm10%

6. HT-7U ASIPP SensorNumberPosition Two-component Magnetic probe (42+27)*3 pol.*tor. Inner vacuum vessel wall and behind the carbon shield MHD probes (Mirnov coils) 20*3 pol.*tor. Inner vacuum vessel wall Poloidal flux loops31Inner vacuum vessel wall Saddle/locked loops10*3 pol.*tor. Inner vacuum vessel wall In the low field area Voltage loop5Inner vacuum vessel wall Rogowski coil1*3 por.*tor. Inner vacuum vessel Diamagnetic loop1*3 por.*tor Inner vacuum vessel and outer of vacuum vessel Vessel structure current monitor 8*4 behind the divotor

7. HT-7U Magnetic Diagnostic System Magnetic probes are used to measure poloidal magnetic field, and flux loops are for poloidal magnetic flux measurement. ASIPP HT-7U 1. Magnetic probes and Flux/voltage loops 30 magnetic probes on vacuum vessel wall 17 behind carbon shield 39 flux loops on vacuum vessel wall

8. four arrays in different positions. for feedback control of plasma position and shape combine with other diagnostics is used for reconstruction of plasma parameters study the MHD activities one array placed in toroidal direction equably HT-7U ASIPP Magnetic probes

9. Isolation voltage >1000v Inductance: 2.20uh (tangential direction). 1.18uh (Normal direction) Resistance: 4.00 ohm (tangential direction). 2.50ohm Analogue bandwidth: >10kHz (Normal direction) Number of layers: 2 Number of windings per coil: 160 Effective winding area (A*N): tangential direction 1133cm 2 Normal direction 1431cm 2 HT-7U ASIPP

10. HT-7U Flux/voltage loops cover all 16 segments in the horizontal plane (toroidal direction). 31 flux loops are located inside the vacuum vessel expect the horizontal window and upper and down windows near the divertor.

11. ASIPP HT-7U 2. Plasma Current Rogowasky Coil Rogowski coil is a solenoidal coil whose ends are brought around together to form a torus. It is used to measure plasma current One set include 2 Rogowski coils One will be set around plasma inside vacuum wall. Another one will be set outside the vacuum wall. Three sets will be set in different toroidal directions.

12. 3. Saddle/locked-mode coils ASIPP HT-7U One set of saddle/locked-mode coil on the inside vacuum vessel wall

13. ASIPP HT-7U These coils are used to measure poloidal magnetic flux and detect the non-rotating or slowly rotating of magnetic perturbations. The locked-mode coil will be placed on the outer mid-plane inside the vacuum vessel. 5 saddle coils will be placed in the upper and 5 in down positions near the divotors. Six to eight arrays will be installed in different toroidal directions symmetrically.

14. 4. Diamagnetic Loops Diamagnetic loops system includes measurement loops, compensation coils and associated processing electronics. ASIPP HT-7U It is used to measure plasma βp and plasma energy. Three sets are going to be mounted on the inner of the vacuum vessel wall.

15. ASIPP HT-7U Requirement The very small signal need to improve the signal to noise ratio. Position must be vertical direction of the toroidal field strictly to decrease the influence of toroidal field. The diamagnetic loop and compensation coil must be parallel. Both of them set on the same framework. The position of system need to be adjusted to minimize the influence of the poloidal field. Use ceramic or BN as framework.

16. ASIPP HT-7U four sets of Rogowski coils are installed behind the divertor tiles in each toroidal location. The coils are installed to round the roots of the divertor tiles. Four groups of these coils will be set in different toroidal positions 5. Measurement of Halo current A poloidal halo current due to VDE is observed in most large tokamak experiment. During plasma disruptions, a current flow directly into a vacuum vessel from plasma. It will produce an intense electromagnetic force on the in- vessel components.

17. good vacuum Leakage ratio< 10e-6 insulation (Isolation voltage >1000v) heat-resistant >= 300 1. Cables (fiberglass) Special material ASIPP HT-7U

18. 2. framework ASIPP HT-7U ceramic different to machine NB brittleness 3. vacuum feed-through 32 molybdenum conductor pins which gold plated Each pin is fasted and insulated with glass sinter. The leak ratio is litter than 10 -5 Pal/s

19. ASIPP HT-7U Protection and Improve the signal to noise ratio Protection put behind graphite tiles put in a box or behind a sheet Improve the signal to noise ratio output cable need to be twisted each other. stainless steel boxes or tapes could be used as electric-magnetic shield. to avoid ground loops.

20. ASIPP HT-7U Digital Integrator PGA V/F Converter FPGA DSP D 0 ~D 31 Gain ratio digital signals Controler Integrator Digital Signal Processor analog signals

21. ASIPP Summary The progresses of HT-7U project in building, and it is possible to get the first plasma around 2005. Physical design of magnetic diagnostic for HT-7U has been completed. Final engineering design for magnetic diagnostics are under preparation. HT-7U

22. End and thanks ASIPP HT-7U