ASIPP 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 1 HT-7 Data Meeting and Workshop. Hefei, China July 19-20, 2011
ASIPP Outline Introduction Design of the new lithium limiter Main results Test of re-filling system Influence on plasma performance Discussion: Discussion: Li emission and plasma disruption Li erosion and deposition Summary 2
ASIPP Introduction Li is 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. 3
ASIPP 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. 4 Lessons from previous Li experiments
ASIPP 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 (~400cm 2 ) and same movable system as previous experiment. 5 Re-filling system Sketch of the new designed LLL system with Re-filling system Mo limiters
ASIPP Structure of LLL 6 New SS mesh With 285*145*2.5 (mm) and pore radius~100 μm SS tray with channels for Li reservoir(50cm 3 ) Pipe and heater SS mesh and SS tray
ASIPP 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 7
ASIPP 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 Successfully test re-filling system 8 After 1 st Exp., a lot of liquid lithium was still remained on the top of SS mesh.
ASIPP Influence on plasma performance With LLL, High retention (with the same Ne, required more gas puffing). Reduce recycling. Reduce total impurities radiations. 9 ICRF OH
ASIPP Influence on plasma performance Compare some parameters of plasmas before and after using LLL （ r=27cm ） 10 After 17 th lithium coating, total using ~173g lithium
ASIPP 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 V loop 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. 11
ASIPP 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. 12 Increased lithium emission intensity Disruption Stronger Lithium Ejection
ASIPP Possible reasons for Li emission Sputtering (sputtering yield 0.5-1) Evaporation ~10 17 s -1 (r=260cm,t~0.8s, OH plasma, calculated Max Temp. of LLL surface in creased to ~360 ºC ) 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). 13 Large-scale Droplets Before disruption, Li emission intensity increased and plasma and LLL interaction became strong, then plasma disrupted.
ASIPP Initial Temp. 220ºC(#112357). P OH ~200kW, t~1s; If half power loads on LLL, Q 0 ~6.7MW/m2. Plasma disruption analysis —Heat flux analysis 14 Li SS mesh T1 J 1TE T2 J 2TE V B R Force (J 2TE ×B)along radial direction. Force (J 1TE ×B)was possible to splash lithium. SS tray
ASIPP Lithium radial flow observed by fast CCD Observed by fast CCD, Liquid lithium flew along radial direction seemed corresponding to the direction of force (J 2TE xB). The estimated velocity along radial direction ~0.5m/s 0.27s 0.29s0.32s High temp. B 15
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ASIPP After vent, we have found 1, lots of Li was floated out directly from LLL, possibly due to too much Li filling. 2, Lots of Li droplets around LLL, possibly strong JXB force. 3, SS mesh had no any damage and full of Li, indicating new SS mesh is good for CPS system. Li erosion and deposition 176 After 3rd Exp., thin Li film on mesh, and Li was effectively confined by the CPS.
ASIPP 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 177
ASIPP Liquid lithium was successfully and easily injected into LLL from outside of HT- 7 by re-filling system. Ø10mm pipe, low Temp.~250 C, driven only by gravity. Plasma with a lower recycling and a lower radiation was obtained by using LLL. The new SS mesh was good for CPS system. SS mesh kept no any damage in spite of some disruption shots during LLL Exp. Due to Li emission intensity increase by various reasons, many plasmas was disrupted while as LLL served as main limiter. In alternative, disruption enhanced Li erosion, specially Li ejection directly from LLL. To control Li injection speed and Li splashing during plasma discharge should be considered. Summary and Discussion 178
ASIPP Thanks for your attention! 179 Acknowledgement This research is funded by National Magnetic confinement Fusion Science Program under contract 2010GB and the National Nature Science Foundation of China under contract