Speaker
Description
The Hybrid Illinois Device for Research and Application (HIDRA) is located at the Center for Plasma Material Interactions (CPMI) at the University of Illinois Urbana-Champaign. It is a 5-period classical stellarator with an on-axis magnetic field B0 < 0.5 T. It is capable of true steady state operation with plasma discharge length up to, t < 10,000 s in duration with typical experimental discharges on the order of t = 600 s - 1000 s. HIDRA in conjunction with a mid-plane Material Analysis Teststand (HIDRA-MAT) allows for materials to be exposed to the plasma for great lengths of time. A liquid metal injector allows lithium to be placed on the surface and be exposed to the plasma. Results have shown that lithium operation enhances plasma performance by achieving a low-recycling regime, crucial for future reactor operation. Plasma temperatures increased from Te = 15 eV base pressures to over Te = 100 eV without significant density drop. More over this performance has been shown in helium plasmas and HIDRA has demonstrated the ability to also pump and retain helium, not just hydrogenic fuel species. Langmuir probe measurements show that the plasma profile changes with lithium operation leading to the difference in performance. During operation with hydrogen, evidence of lithium vapor shielding has also been observed where the locking temperature of the surface is similar to that seen on MAGNUM at T = 750 oC. These results have further been verified in other devices such as MAGNUM-PSI where helium experiments with a lithium CPS have been performed and on EAST with a helium plasma and flowing LiMIT plate that was placed different distances from the plasma edge. Long pulse (10,000 s) operation in HIDRA shown evidence that plasma chemistry with the wall and features inside the vessel will play an extremely important role in how future machines will need to deal with impurity formation. RGA studies have shown interesting cyclical effects on the order to 30+ minutes occurring. Thus, flowing liquid lithium systems that can provide a fresh surface will be crucial in handling these impurities and achieving low recycling. Thus, in the future there will be a need for flowing systems to be installed and operated and tested in actual toroidal and 3D magnetic field geometries. This presentation will provide an overview from the last several years with lithium experiments and technology development on HIDRA and at CPMI.