Langmuir Probe Measurements in HIDRA

The Hybrid Illinois Device for Research and Applications (HIDRA) is a toroidal plasma device at the University of Illinois Urbana-Champaign (UIUC). HIDRA's main task is to do plasma material interaction (PMI) studies with different materials including liquid lithium. Currently plasma parameters are measured using a He plasma and He spectrum with a collisional radiative model (CRM) with ne = 2×1018 m-3 and Te = 10-20 eV. When HIDRA operated as WEGA in Greifswald, the device was able to reach electron temperatures up to Te = 20eV and densities ne ~1x1018 m-3. The spectroscopic method does not give radial profiles of the plasma hence Langmuir probe measurements need to be performed to verify and benchmark the spectroscopy and CRM. These measurements are vital to understand results that are seen in experiments with lithium in particular. The HIDRA plasma is heated via ECRH with up to 26 kW of heating power, using two 2.45 GHz magnetrons. In the Fall of 2021, measurements of the plasma parameters will be performed using Langmuir probes. There are two edge Langmuir probes (ELPs) found at the outer radius of HIDRA that will be used to measure the plasma characteristics at the edge, and how they change throughout the course of the plasma. A pneumatically driven reciprocating diagnostic arm can send a Langmuir probe into and out of the plasma in approximately 200 ms. The reciprocating Langmuir probe (RLP) will give measurements of the plasma parameters radially across the plasma. Measurements with the RLP and ELPs will also be done with lithium exposure, to see how lithium effects the electron temperature and density of the plasmas and compare this to the Te and ne measured with the CRM . This presentation will give the results of how magnetron power effects the plasma of HIDRA, including profiles for the edge plasma and throughout the plasma, and how they change with the introduction of lithium.