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The effect of alleviating the heat load The effect of alleviating the heat load of of

the first wall by impurity injectionthe first wall by impurity injection

B.Shi, J. Huang, X.Z. Gong, X.D. Zhang

Institute of Plasma Physics, Chinese Academy of Sciences P.O.Box 1126, Hefei, Anhui 230031, P.R.China

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OutlineOutline

• Motivation

• Background

• Preliminary observation in HT-7

• Experimental setup plan

• Desired Results and Analysis

ASIPPASIPPHT-7HT-7The RI mode advantages

•It is characterized by a large radiation emission from the injected impurities,up to 90% of the total input power, this strongly alleviating the heat load problem on the first wall materials.

•It can be maintained up to density limit with good confinement, and in some case also beyond this limit.

•It can be free of MHD instabilities, when ß is below the critical value, and thus is not transient. (it last many energy confinement times on TEXTOR)

•It is compatible with the H-mode, since it even improves the H value in this regime.

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Motivation for Radiation Improved(RI) modes

•Impurity seeding helps power exhaust problems especially during long pulse operation .•The solution is valid both in limiter and divertor configuration and in the different heating.•Inexpensive and efficient tool for density peaking and higher Te.•Operation close to Greenwald limit is possible at good confinement level.•Possible ELM mitigation in H-mode.

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• Impact of impurities on plasma-wall interaction especially for high performance and long pulse discharge

• Effect of impurities on transport• Turbulence studies • Impurities transport and screening • Multi-machine program needed

Involved physics

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RI-mode was demonstrated in TEXTOR with steady state conditions, t RI-mode / E > 100 (P.R. Weynants)

RI-mode in TEXTOR

ASIPPASIPPHT-7HT-7RI-mode in ASDEX Upgrade

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Preliminary observations in HT-7

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Preliminary observations in HT-7

•The neon gas puffing for the production of a radiative layer near the plasma edge has been investigated in HT-7. In spite of increased radiation losses, the plasma with the performance improvement has been obtained. The peaked electron temperature and the broadened density profiles was formed, the central electron temperature was increased by nearly 50%. These discharges also exhibited a relatively higher plasma inductance compared with the reference discharges without the neon gas puffing.

•Future experiments are planned to extend operation to higher densities, including extending RI–mode to higher normalized parameters, for long pulse higher performance discharges in HT-7. It is characterized by a large radiation emission from the injected impurities, creating a cold radiating mantle at the plasma boundary, thus strongly alleviating the heat load problem the first wall materials, impurity seeding can help power exhaust problems, it is important for future tokamak such as EAST, ITER.

ASIPPASIPPHT-7HT-7Preliminary observations in HT-7

0.0 0.2 0.4 0.6 0.8 1.0 1.20

100

200

300

400

T(0 C)

Time(s)

81423 81425 81426 81427 81428

Shot 82909 (td~200s, Ip~60KA, ne~0.5, PLHCD~150KW)

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Experimental setup

Figure1.Impurity seeding system

2D IR

Camera

(320*240pixels)

A sample with two thermocouples

Figure2. Observe the temperature of a limiter sample with a IR camera

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Experimental setup

Figure 3.Size and geometry of the sample.

The surface temperature of the sample is observed with a IR camera.

Figure 4.Two thermocouples mounted 5mm and 25mm behind the surface without water-cooling.

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Experimental plan

• Clean plasma required(Radiation losses below 40%,see the effect of Boronization).

• Possibly consider Argon and other impurities. • Optimize of the control for the Gas puff rate and plasma.• First approach will be in OH discharges at Bt=1.6-

2T,Ip=120-180KA, Line density about 1.0-3.0x10 19 m-3 .• Study the combination with additional electron heating

(IBW&LHW), to obtained higher Te with good confinement.• Move to high confinement under the state steady operation.

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Requirements for System and DIA

IBW (27MHz, 150~250KW),LHW(2.45GHz,300KW~600KW).

• The stable control of plasma and density. • The profile of Te/Ti (SXS,ECE,NPA,CER,TS). • The behaviors of radiation and density(XUV,HCN).• The transport and behaviors of impurities (Spectrum).• Bremsstrahlung profile(Zeff).• MHD&We(Magnetic Measure).• The behaviors of edge plasma (Probe)• The power deposition of LHW (HX)

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Desired Results and Analysis

• Compare the temperature of first wall before and after impurity-seeding.

• Calculate heat flux on limiter surface.• Compare ne (r), Ti®, Te , Zeff before and after impurity-

seeding.• Analysis of the radiating power profile. • Analysis of the transport and behaviors of impurities.