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Current State of Omegatron Analyzer in the HT-7 Tokamak

HT-7

ASIPP

Ling Bi-lia),Wang En-yaob),Gao weia),Wan Bao-niana),Li Jian-ganga)

 a)Institute of Plasma Physics,the Chinese Academy of Sciences

b)Southwestern Institute of Physics,Chengdu 610041

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Content HT-7

(1)The principle and motivation of omegatron

(2)Prototype of omegatron

(3)Preliminary results

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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..

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The principle and motivation of omegatron

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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.

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Prototype of omegatronHT-7

Schematic diagram of the plasma omegatron

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HT-7Control circuit used for measurement

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Primary results

ASIPP

0.0 0.5 1.0

0.00.51.00.00.51.00.00.51.00.00.51.00.00.51.00.00.51.00.00.51.00.00.51.0

time(s)

v1=0v

v1=-50v

v1=-100v

back

plat

e cu

rrent

(uA)

v1=-120v

v1=-150v

v1=-175v

v1=-197v

v1=-220v

-250 -200 -150 -100 -50 00

0.05

0.1

0.15

0.2

0.25

0.3

0.35

The first stage biasing voltage (V)

STD

of c

urre

nt (A

U)

It clearly shows that the fluctuation of the current will reach the minimum when thIt clearly shows that the fluctuation of the current will reach the minimum when the electron repeller voltage equals about -200volts.e electron repeller voltage equals about -200volts.

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

0.0 0.5 1.0-0.010.000.010.020.03-0.010.000.010.020.03-0.010.000.010.020.03-0.010.000.010.020.03-0.010.000.010.020.03-0.010.000.010.020.03-0.010.000.010.020.03-0.010.000.010.020.03

time(s)

v2=120v

v2=130v

v2=140v

v2=150v

v2=160v

curre

nt co

llecte

d at

the

back

plat

e(uA

)

v2=170v

v2=180v

v2=190v

0 50 100 150 200-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

baising voltage (V)

LnI Ti=7.8740eV

LnI= 20.0167 -0.1270 *V

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

0.0 0.5 1.00

20406080

100120140160

0.0 0.3 0.5 0.8 1.0

16

18

20

22

240.0 0.3 0.5 0.8 1.0-0.002

0.000

0.002

0.004

IP (

KA

)

time(s)

Fre

qu

en

cy(M

Hz)cu

rre

nt(

uA

)

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Primary results

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3He2+ is also identified in the experiment, whose resonant frequency is 24.4 MHz. is also identified in the experiment, whose resonant frequency is 24.4 MHz.

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Primary results

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The relation between collected current and amplitude of RF wave has been investigated.

Arf=9,7,5,3voltArf=10,8,6,4,2 volt

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Primary results

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Conclusions

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(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. (3)We have successfully measured the 3He2+ andand D+

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HT-7

ASIPPFuture 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

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THANK YOU.Any suggestion will be appreciated.

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Calculations for referenceCalculations for reference