Proposal for Relative Calibration of ECE Diagnostic System in HT-7 Tokamak.

BY

S. Sajjad

2007-04-13

Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, China.

HT-7

Outlines EC Emission in Tokamaks. Accessibility and Absorption Conditions. Radial Profiles of ECE Radiation in HT-7. Process for Relative Calibration.

• ECE Emission in Tokamaks• For a tokamak of major radius and toroidal field ,the

harmonic n of the ECE frequency emitted at radius r , in the equatorial plane, is given by

• where and are respectively the electron charge and mass. The relativistic factor γ , for the usual temperatures found in tokamaks can be considered as unity.

• The transport of the electron cyclotron radiation in a thermal plasma is given by

• where I(ω), the intensity of radiation, and is the radiative power per unit area per unit solid angle per unit of angular frequency, τ(ω) is the optical depth given by

0R 0TBnf

0 0

02e T

ne

n B Rfm R r

eme

1BI I e

0

L

ds

• where α(ω) is the absorption coefficient and is the Rayleigh-Jeans approximation for the blackbody radiation given by .

• For an optically thick plasma τ(ω) >1 substantial absorption occurs and which gives the results

• Therefore, for a given frequency, the detected radiative• power is proportional to the electron temperature.

BI

2 3 2/ 8B eI kT c

2

3 28e

BkT

I Ic

Accessibility and absorption conditions • The conditions for accessibility and absorption for a radial profile of the following

frequencies can be given as:• The first and the second harmonics of the electron cyclotron frequency

• The right and left-hand cutoff frequencies

• The upper-hybrid resonance frequency

• and the plasma frequency

0 0

02T

cee

eR Bfm R r

12 2

, 2

41 1

2pece

R Lce

ffff

1

2 2 2uh ce pef f f

12 2

0

0

12pe

e

n efm

2 2 112 20

102 2 1 2

nnpeX X Xt

n n nnce

f v Rnn f c

2

3 22

212 1

peX nn

ce

fnn f

/t e ev kT m 0 /c f

Optical DepthTo determine absorption conditions of the plasma, the most important parameter is the optical depth τ(ω) .For the extraordinary mode ( n ≥ 2 ) and perpendicular propagation ( θ = π/2 ) parallel to the equatorial plane of the torus τ(ω) is given as,

and

Where

Radial Pofiles of : Fundamental ECE frequency ( ), second ( ) and third ( ) harmonics of ECE radiation, Plasma frequency. = 2 T ,

= and = 700 eV .

Radial Profiles of ECE Radiation in HT-7 Tokamak

cef2 cef

pef 0TB

0eT0en

0

5E+10

1E+11

1.5E+11

2E+11

2.5E+11

-30 -20 -10 0 10 20 30

Radius (cm)

Freq

uenc

y (H

z)

19 32.0 10 m

3 cef

3 cef

cef

2 cef

pef

Process for ECE System Calibration It is proposed that the relative calibration of ECE

signals can be done by small change in the toroidal field in consective shots at same plasma conditions.

Where the magnetic field varied a little in each shot to make a superposition for measured frequency points or channels on ECE resonant positions.

Electron temperature profiles and plasma conditions are supposed to be changed very little in these shots.

In this way, relative calibration factors for each measurable ECE frequency points of the receivers can be easily obtained.

Schematic of HT-7 ECE Diagnostic System

Pre Amp

ECE Channels VS Position

Channel sFrequencyPos. 2T(cm)Pos. 1. 99T(cm)Pos. 1. 98T(cm)Pos. 1. 97T(cm)ECE01 98.501 16. 6366 15. 9434 15. 2503 14. 5571ECE02 100.433 13. 9697 13. 2899 12. 6100 11. 9302ECE03 102.366 11. 4022 10. 7352 10. 0682 9. 4011ECE04 104.299 8. 9298 8. 2751 7. 6205 6. 9658ECE05 106.232 6. 5474 5. 9047 5. 2619 4. 6192ECE06 108.165 4. 2501 3. 6189 2. 9876 2. 3564ECE07 110.098 2. 0336 1. 4134 0. 7932 0. 1731ECE08 112.031 -0. 1065 -0. 7160 -1. 3255 -1. 9349ECE09 111.501 0. 4729 -0. 1395 -0. 7519 -1. 3642ECE10 113.502 -1. 6863 -2. 2879 -2. 8894 -3. 4910ECE11 115.501 -3. 7686 -4. 3597 -4. 9509 -5. 5421ECE12 117.501 -5. 7810 -6. 3621 -6. 9432 -7. 5243ECE13 119.501 -7. 7261 -8. 2975 -8. 8688 -9. 4402ECE14 121.501 -9. 6071 -10. 1691 -10. 7311 -11. 2930ECE15 123.501 -11. 4272 -11. 9801 -12. 5330 -13. 0858ECE16 125.501 -13. 1893 -13. 7334 -14. 2774 -14. 8215

Plasma parameters for Experiment

BT = 2.0 T, 1.99T, 1.98T, 1.97T, 1.96T, 1.95T.

(ΔBT =0.01T)= 100 Gauss

I p = 180-200 kA ne = 2.0-3.0*1019 m-3

R = 122 cm a = 27 cm

谢谢