HT-7 Lithium coating and its influence on plasma performance on HT-7 Z. Sun, J.S. Hu, G.Z. Zuo, J.G. Li ASIPP

HT-7 Outline 1.Introductions 2.Lithium(Li) coating system 3.Main Results 4.Comparison with following boronization 5.Summary 2

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

HT-7 Outline 1.Introductions 2.Li coating system 3.Main Results 4.Comparison with following boronization 5.Summary 4

HT 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 meeting Lithium limiter Lithium dropper 5

HT-7  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 500~590 o C ； 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 6

HT-7 Outline 1.Introductions 2.Li coating system 3.Main Results 4.Comparison with following boronization 5.Summary 7

HT 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. 8

HT 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 T e increased 9

HT-7 I p ~150kA, N e ~1.5X10 19 /m 3 ， B t =1.9T Before and after 25 th Li coating Mo impurity was also suppressed by Li coating again and again 10

HT 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 ; 11

HT Control H/(H+D) for various ICRF heating mode I p ~150kA, n e ~1.1×10 19 m -3 ， P ICRF ~750kW ， Phase 180 ° B t ~1.95T Ti>0.8 kev Ti<0.6 kev ~ 20%(No ) mode conversion heating ~7% (No ) minority heating H/(H+D) 12

HT 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

HT Increase plasma reproducibility date Wall condition No Li 1 st Li coating 13 th Li coating 25 th Li coating 28 th 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 14

HT-7 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 discharges. 3.7 Lifetime of Li coating 15

HT-7 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. 16

HT-7 Outline 1.Introductions 2.Li coating system 3.Main Results 4.Comparison with following boronization 5.Summary 17

HT Results of the following boronization Boronization with 3g C 2 B 10 H 12 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% 18

HT Comparison Li coating with boronization MaterialZPriceH contentTechniqueRecyclingRetentionCoatingImpurities Li3 2 ￥ /g Good getter low H/(H+D) Evaporation enhanced by GDC/ICRF Low High due to strong getter Metal vapor poor uniform Good getter for C, O suppress metal impurities C 2 B 10 H 12 5(B) 100 $/g H release high H/(H+D) Require GDC/ICRF High due to H-D exchange Gas more uniform Good 19

HT-7 Summary  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. 20

HT-7 Thank you for your attention!! This research is funded by National Magnetic confinement Fusion Science Program under contract 2010GB and the National Nature Science Foundation of China under contract Acknowledgement 21