Behaviors of Electron Heat Transportation in HT-7 Sawtoothing Plasma

HT-7 ASIPP

Behaviors of Electron Heat Transportation

in HT-7 Sawtoothing Plasma Liqun HU, Yi XU, Baonian WAN, Yuejiang SHI Xiangj

un ZENG and HT-7 Team

Institute of Plasma Physics

Chinese Academy of Sciences

Shushanhu Road 350, Hefei 230031, P. R. China

E-mail contact of main author:lqhu@ipp.ac.cn

HT-7 ASIPPIn HT-7 ohmic plasma, main energy loss comes from

electron heat conduction, electron thermal transportation plays a crucial role in determining achieved plasma parameters and their spatial distribution, which is very closely associated with the plasma confinement. Based on the heat pulse propagation originating from the sawtooth activity on the soft x-ray intensity signal, some data processing methods, including average of tens of sawteeth, has been tried to experimentally determine electron heat diffusivity on the HT-7 tokamak. As a result, methods of time to peak and sawteeth averaging have been adopted finally to get stable and reasonable electron heat diffusivity value. Based on preliminary understanding of the measured electron heat diffusivity, performances of different high confinement target plasmas are presented and discussed.

HT-7 ASIPP

Experimental apparatus HT-7 Experimental apparatus HT-7 superconducting Tokamaksuperconducting Tokamak

R = 1.22 m, a = 0.27 m

Ip = 100~250 kA

BT = 1~2.5 T

ne = 1~8x1013 cm-3

Te = 1~5 KeV

Ti = 0.2~1.5 KeV

Limiter:

graphite limiter with poloidal and toroidal configuration

ICRF:

f = 15~30MHz, P = 0.3MW

f = 30~110MHz, P = 1.5MW

LHCD:

f = 2.45GHz, P = 1.2MW

Main Goal:

Advanced Steady-state operation and related physics

Vertical array with 37 detectors of SBDs

Horizontal array with 37 detectors of SBDs

Slot-aperture with a movable slider covered with Be foils

Au-Si detector

Au-Si detector

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Soft X-Ray Diagnostic Arrays

High spatial

resolution and

time resolution

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Mathematical description of the heat pulse propagation

General electron-heat-balance equation:

Qr

trTrrrn

rrt

trTrn e

eee

e

]

),()()([

1),()(

2

3

Ignoring all heat sources and sinks, and assuming constant Ne (r) and e (r):

]),(

[1),(

)(2

3~~

r

trTrn

rrt

trTrn eee

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Time-to-peak analysis

Fourier transform:

sensitive to the shape of heat pulse

high and better periodical sawtooth

Dipole Model: e

p

rt

9

2

p

e t

r

9

2

Monopole

Model: ep

rt

8

3 2

p

e t

r

8

3 2

1. Time-to-peak analysis 2. Fourier transform based techniques 3. Time-domain modeling: data fitting by a model

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The dipole model: applied, more ideal and more suitable

for HT-7 than the monopole model for good mathematical

reasons and carrying zero total heat content.

Time-to-peak analysis

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Data Processing Method for determining electron thermal diffusivity e

1. Function fitting

Difficult to find suitable function for the data

2. Superposing of sawteeth heat pulse

Good ratio of signal to noise, but sensitive to the initial point choice of each sawtooth, suitable for platform stage of the discharge.

3. Averaging of sawteeth

Relatively simple, better for widely practical use

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Averaging of tens of sawteeth

pe t

r

8

3 2

mttt jro

m

j

jripi /)(

1

ri

tPi

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1. Asymmetry of the spatial electron heat transport

Ip=200kA, BT=2.0T, ne=1.51019 m-3, PLHW=400kW, PIBW=230kW

Preliminary analyses of HT-7 electron heat transport

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Improvement of heat transport in LHCD plasma

Ip=220kA, BT=2.0T, ne=1.51019m-3, PLHW=260kW, f=2.45GHz

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Dependence of electron heat transport on LHW power

Ip=125kA,BT=1.8T,ne=1.51019m-3

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Dependence of electron heat transport on IBW power

Ip=150kA, BT=1.9T, ne=1.51019m-3, f=30MHz

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Dependence of electron heat transport on density in the synergy of LHW+IBW heated plasma

Ip=200kA,BT=1.8T, PIBW=230kW(27MHz),PLHW=540kW

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Dependence of electron heat transport on density in the synergy of LHW+IBW heated plasma

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Ip=200kA,It=1.95T,ne=1.71019m-

3,PIBW=230kW

Dependence of electron heat transport on LHW power in the synergy of LHW+IBW heated plasma

HT-7 ASIPPDiscussion

Dependence of RF power on electron heat transport

HT-7 ASIPPDiscussion

Dependence of RF power on electron heat transport in the synergy of LHW +IBW

Preliminary analyses on HT-7 electron heat transport indicates:• Asymmetry of the spatial electron heat transport• LHW can not only drive plasma current and plasma

temperature, but also improve plasma particle confinement and electron heat transport. As increase of the LHW power, electron heat transport decreases apparently.

• In IBW heated plasma, the electron electron heat transport decreases obviously as the IBW power increase after the IBW power launched over a power threshold.

• In the synergy of LHW and IBW plasma, the electron heat transport improves as the density increase, however, over a certain value, deteriorate as the power increase.

• More deep and systematic analyses will be done to find detailed relations among the electron heat transport and plasma parameters.

Summary

HT-7 ASIPP