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Lithium coating and its influence on plasma performance on HT-7

Z. Sun, J.S. Hu, G.Z. Zuo, J.G. LiASIPP

2011-7-20

 

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Outline

1.1. IntroductionsIntroductions

2.2. Lithium(Li) coating system Lithium(Li) coating system

3.3. Main ResultsMain Results

4.4. Comparison with following boronizationComparison with following boronization

5.5. SummarySummary

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Li has good properties, such as low Z, strong getter of C, O and H isotopes.

Li coating is a better way to reduce impurities, control recycling and H content.

Controlling H content is useful for the different mode of ICRF heating.

Li coating is beneficial for plasma performance enhancement.

On the Mo wall Li coating maybe increase its effect on plasma performance.

1 Introductions

3Changed graphite limiter to Mo limiter in HT-7 in this campaign

HT-7HT-7

Outline

1.1. IntroductionsIntroductions

2.2. Li coating system Li coating system

3.3. Main ResultsMain Results

4.4. Comparison with following boronizationComparison with following boronization

5.5. SummarySummary

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HT-7HT-72.1 Configuration of Li coating system Two oven system for pre-coating:

•Two ovens were shifted from EAST in 2010 for uniform coating;•Deeply movable to the center of inner vessel for enlarge coating surface.

One lithium dropper for active Li coating from PPPL . Movable liquid lithium limiter.

Lithium oven

Two lithium oven systems

Lithium limiter

Lithium dropper

Reported by Dr. Zuo in this meetingReported by Dr. Zuo in this meeting

Lithium limiter Lithium dropper 5

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Li coating 28times ~350g Li injection 3 times Liquid Li limiter Exp. 5 times Boronization 3g

2.2 Techniques of Li coating in HT-7

• By evaporation, associated by He-GDC or He-ICRF discharge；

• Evaporated at 500~590oC；• 1~2Hr./coating;• 5~30g/coating;• 1~2 times coating/day;• GDC: 3A• ICRF: 5~20kW

Red discharge zone during ICRF Li coating in HT-7

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Outline

1.1. IntroductionsIntroductions

2.2. Li coating system Li coating system

3.3. Main ResultsMain Results

4.4. Comparison with following boronizationComparison with following boronization

5.5. SummarySummary

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3.1 Main results of Li coating

Reduce impurity radiation;Decrease H/(H+D) to below 10%; Lower particle recycling； Fast plasma recovery after leaks; The lifetime of Li film is 60~100shots; Improve plasma performance； Control H/(H+D) to convert ICRF heating mode, and to improve ICRF minority heating efficiency；

Increase plasmas reproducibility.

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HT-7HT-73.2 Reduce impurities and recycling

By Li coating,C and O impurities decreased step

by step;

Mo impurity also was suppressed;

Low Recycling plasma was easily

obtained;

Li emission intensity increased

every time;

Improve plasma performance

Radiation decreased 

significantly

 Te increased

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Ip~150kA, Ne~1.5X1019/m3 ， Bt=1.9T

Before and after 25th Li coating

 

Mo impurity was also suppressed

by Li coating again and again

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HT-7HT-73.3 Decrease H/(H+D) ratio

Control H/ (H+D) ratio for converting different ICRF heating mode H/ (H+D)  could be controlled in the range of 5-10% for improvement of

ICRF minority heating efficiency;

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HT-7HT-73.4 Control H/(H+D) for various ICRF heating mode

Ip~150kA, ne~1.1×1019m-3  ， PICRF~750kW ， Phase 180 ° Bt~1.95T

Ti>0.8 kevTi<0.6 kev

~ 20%(No.113388) mode conversion heating

~7% (No.113527) minority heating

H/(H+D)H/(H+D)

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3.5 Fast plasma recovery after leak

When the HT-7 vessel leaked air to 100Pa, repeatable plasma could be got just using 30g Li coating.

impurities radiation didn’t increase.H/(H+D) recovered to previous ratio via 100 shots

Air leaked to 100Pa on about 330g Li coated walls is not a serious problem.13

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3.6 Increase plasma reproducibility

 date 4-23 4-25 5-6 5-22 5-25 5-26

Wall condition

No Li 1st Li coating

13thLi coating

25th Li coating

28th Li coating boronization

Ratio* 33.3% 41% 75% 89% 90.7% 89.5%

Lithium coating increased the percentage of effective plasmas step by step.

*the ratio of normal to total plasma discharges

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Possibly due to Li consumption (depended on Li coating and plasma operation)

LiI emission intensity decrease shot by shot after Li coating;Impurities, include CIII, OII, MoI emission increase with LiI emission intensity decreasing;Plasma performance decrease

Normally, the lifetime of Li film is for about 60-100 discharges. 

3.7 Lifetime of Li coating

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The Li film on the movable Mo limiter

3.8 Distribution of Li film

Before li-coating

After li-coating

With suitable arrangement of ovens and liquid lithium limiter

It seemed Li was coated on all limiters and Liners after exposure.

The Li film near oven seemed thicker than other surface.  

contribution from liquid lithium limiter. 

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Outline

1.1. IntroductionsIntroductions

2.2. Li coating system Li coating system

3.3. Main ResultsMain Results

4.4. Comparison with following boronizationComparison with following boronization

5.5. SummarySummary

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HT-7HT-74.14.1 Results of the following boronizationResults of the following boronization

Boronization with 3g C2B10H12 was carried out by ICRF discharge after 28 Li coatings.

After boronization on the Li wall: The Li emission intensity reduced 

significantly CIII and OII emission intensity  

reduced.   MoI emission intensity didn’t change 

obviously H/(H+D): ~90%40%

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HT-7HT-74.2 4.2 Comparison Li coating with Comparison Li coating with

boronizationboronization

Material Z Price H content Technique Recycling Retention Coating Impurities

Li 32

￥ /g

Good getter

lowH/(H+D)

Evaporationenhanced

by GDC/ICRF

Low

High due to strong getter

Metal vaporpoor

uniform

Good getter for

C, Osuppress

metal impurities

C2B10H12 5(B)100$/g

H release high

H/(H+D)

RequireGDC/ICRF

High

High due to

H-D exchange

Gas more

uniformGood

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SummarySummary   We have carried out Li coating successfully and good results were

obtained in HT-7.

Li coating reduced impurity radiation significantly

By the Li coating, H/(H+D) can be controlled below 10%(Min. ~5%).

Li coating is useful for plasma recovery after vessel leak.

Lower particle recycling even if high fuel retention after Li coating;

The lifetime of 10-30g Li coating is about 60~100shots;

With Li coating contribution, various ICRF heating mode were easily achieved;

After 28 times Li coating, uniform and thick lithium film was found;

The boronization following 28 Li coatings also have good results.

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Thank you for your attention!!

This research is funded by National Magnetic confinement Fusion Science Program under contract 2010GB104002 and the National Nature Science Foundation of China under contract 11075185

Acknowledgement

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