1 Current State of Omegatron Analyzer in the HT-7 Tokamak HT-7 ASIPP Ling Bi-li a),Wang En-yao b),Gao wei a),Wan Bao-nian a),Li Jian-gang a) a) Institute of Plasma Physics,the Chinese Academy of Sciences b) Southwestern Institute of Physics,Chengdu

2 Content HT-7 (1)The principle and motivation of omegatron (2)Prototype of omegatron (3)Preliminary results

3 The principle and motivation of omegatron The operation principle is based on ion mass separation as ions move in a variable RF electric field normal to an axial magnetic field. The Lorentz force causes ions to circulate at the ion cyclotron frequency. When the RF frequency is set to be resonant with the cyclotron motion of the ions, the ions will receive energy from that electric field and therefore travel in orbits of constantly increasing radius. However, non-resonant ions may initially gain energy, but then experience an energy loss as their velocities become out of phase with the applied RF electric field, forming contracting and expanding spirals of some limited radial extent.. HT-7

4 The principle and motivation of omegatron HT-7 ASIPP The motivation of this diagnostic is to measure ions species in the edge of HT-7 Tokamak and its by-product edge ion temperature.

5 Prototype of omegatron HT-7 Schematic diagram of the plasma omegatron

6 HT-7 Control circuit used for measurement

7 Primary results ASIPP It clearly shows that the fluctuation of the current will reach the minimum when the electron repeller voltage equals about -200volts.

8 HT-7 Primary results Ion temperature has been measured. It is about 7ev where r equals 30cm.

9 HT-7 Primary results The resonant frequency of D + is about 17MHz, corresponding to our calculation, but there exists frequency extension.

10 Primary results HT-7 is also identified in the experiment, whose resonant frequency is 24.4 MHz. 3 He 2+ is also identified in the experiment, whose resonant frequency is 24.4 MHz.

11 Primary results HT-7 The relation between collected current and amplitude of RF wave has been investigated. Arf=9,7,5,3volt Arf=10,8,6,4,2 volt

12 Primary results HT-7

13 Conclusions HT-7 (1)The relation between the current collected at the back plate and the electron repeller voltage and trap voltage was investigated in the experiment. It seems that there exists optimized working point for omegatron operation. (2) The local ion parallel ion temperature of bulk plasma has been measured through fitting. and (3)We have successfully measured the 3 He 2+ and D +

14 HT-7 ASIPP Future work (1) Local acquisition to improve s/n ratio (2) Impendence matching to improve the coupling between RF and ions (3)Grids added to decelerate the ions in two dependent areas

15 THANK YOU. Any suggestion will be appreciated. HT-7 ASIPP

16 Calculations for reference