ECH assisted start up in the Lithium Tokamak eXperiment-β (LTX-β)

The Lithium Tokamak eXperiment β (LTX-β) previously relied on a hot, biased filament to provide seed electrons for plasma breakdown. Breakdown and null formation are complicated by the large eddy currents driven in the shells or conducting walls by the ohmic heating (OH) coil. As a result, at least 25% of the available volt-second capability of the OH can be consumed before and during breakdown. Electron Cyclotron Heating (ECH)-assisted plasma startup can reduce ohmic flux consumption during breakdown resulting in longer and higher performance discharges. Here we describe an ECH system and startup scenarios for LTX-β and the testing performed in preparation for operation. A long pulse (up to 50 msec) 3 kW, 10.36 GHz ECH system has been installed and is being tested. As LTX-β plasma operations resume, startup experiments will be conducted with various magnetic field configurations to determine the breakdown scenario which consumes the least ohmic flux. With analysis of the magnetic field configuration done using PSI-Tri equilibrium reconstructions we will model the ECH-produced plasma, the resulting pressure-driven currents, and the effects on the startup plasma. In the longer term, the use of microwave systems which can provide as much as 25–50 kW of ECH will be considered.