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Development of a new liquid lithium limiter with a re-filling system in HT-7

Development of a new liquid lithium limiter with a re-filling system in HT-7. G. Z. Zuo, J. S. Hu, Z.S, J. G. Li,HT-7 team July 19-20, 2011 Institute of Plasma Physics, Chinese Academy of Sciences, China. HT-7 Data Meeting and Workshop . Hefei, China July 19-20, 2011. Outline. Introduction

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Development of a new liquid lithium limiter with a re-filling system in HT-7

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  1. Development of a new liquid lithium limiter with a re-filling system in HT-7 G. Z. Zuo, J. S. Hu, Z.S, J. G. Li,HT-7 team July 19-20, 2011 Institute of Plasma Physics, Chinese Academy of Sciences, China HT-7 Data Meeting and Workshop . Hefei, China July 19-20, 2011

  2. Outline • Introduction • Design of the new lithium limiter • Main results • Test of re-filling system • Influence on plasma performance • Discussion: Li emission and plasma disruption • Li erosion and deposition • Summary

  3. Introduction • Li is developed as an potential alternative PFM for future fusion devices • Liquid lithium is a self-recovery and renewable PFC material if surface damages due to erosions • Best way to control recycling and H content, also suppress impurities; • Enhance plasma performance. • Main motivation of liquid lithium limiter (LLL) experiment in HT-7 is to provide technical support and data accumulation for future design: • Flowing LLL for HT-7 • Flowing liquid lithium divertor (LLD） after 2014 for EAST • Accumulate data for its application in future fusion reactor.

  4. Lessons from previous Li experiments • Graphite PFCs: • Serious H retention and recycling. • Serious erosion and co-deposition with T in future devices. • Reaction between Li and C, reduce H, D trapping. • Li surface should be confined by CPS to avoid splashing due to MHD. • Heater should be reliable. • It required a re-filling system for lithium: • If lithium plates installed before experiment, it would possible lead to contamination. • No available again, once lithium was used up.

  5. Design of the new lithium limiter • Full metal walls: Change all C tiles to Mo • Using new type SS mesh • Upgrade heater strips with armored structure. • Design a re-filling system outside of HT-7. • Same position, similar area (~400cm2) and same movable system as previous experiment. Re-filling system Sketch of the new designed LLL system with Re-filling system Mo limiters

  6. Structure of LLL New SS mesh With 285*145*2.5 (mm) and pore radius~100μm SS tray with channels for Li reservoir(50cm3) Pipe and heater SS mesh and SS tray

  7. Outline • Introduction • Design of the new lithium limiter • Main results • Test of re-filling system • Influence on plasma performance • Li emission and plasma disruption • Li erosion and deposition • Summary

  8. Successfully test re-filling system • Liquid Li flow could be driven: • In a pipe with 10mm inner diameter • At a low temperature ~250 ℃ • Only by gravity force without pushing by a planed high pressure Ar. • Main problems • Hard to control flow velocity and the amount of injected Li. • Hard to control position of lithium injection • So many lithium flow onto the top of SS mesh After 1st Exp., a lot of liquid lithium was still remained on the top of SS mesh.

  9. Influence on plasma performance With LLL, • High retention (with the same Ne, required more gas puffing). • Reduce recycling. • Reduce total impurities radiations. OH ICRF

  10. Influence on plasma performance Compare some parameters of plasmas before and after using LLL（r=27cm） After 17th lithium coating, total using ~173g lithium

  11. Li emission and plasma disruption • Plasma performance related with LLL position( Mo limiters at r=0.27m). While LLL at r=0.26m, with the same fueling, low density and Vloop than it at r=0.275m. • However, lots of disruptions if LLL at r=27cm and 26cm. • at r=27.5cm, Normal plasmas; • at r=27cm, ~ 2/3 plasmas disrupted； • at r=26cm, ~9/10 plasmas disrupted.

  12. Li emission and plasma disruption • Possibly due to strong Li emission intensity, there are lots of disruptive plasmas if LLL as main limiter at r=27cm and 26cm. Increased lithium emission intensity Disruption Stronger Lithium Ejection

  13. Possible reasons for Li emission • Sputtering (sputtering yield 0.5-1) • Evaporation ~1017s-1 (r=260cm,t~0.8s, OH plasma, calculated Max Temp. of LLL surface in creased to ~360ºC) • Splashing • J×B force (Induced J by plasma, TEMHD, TCMHD, Other MHD instability.) • Possible LLL vibrations during plasma discharge (Lots of Li on top of mesh). Large-scale Droplets Before disruption, Li emission intensity increased and plasma and LLL interaction became strong, then plasma disrupted.

  14. Plasma disruption analysis—Heat flux analysis • Initial Temp. 220ºC(#112357). POH ~200kW , t~1s; If half power loads on LLL, Q0~6.7MW/m2. R B V J1TE • Force (J2TE×B)along radial direction. • Force (J1TE×B)was possible to splash lithium. J2TE Li T1 T2 SS mesh SS tray

  15. Lithium radial flow observed by fast CCD High temp. B 0.29s 0.32s 0.27s • Observed by fast CCD, Liquid lithium flew along radial direction seemed corresponding to the direction of force (J2TExB). • The estimated velocity along radial direction ~0.5m/s

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