Electron Cyclotron Heating (ECH) for Plasma Startup in the Lithium Tokamak eXperiment β (LTX-β)

The Lithium Tokamak eXperiment β (LTX-β) now relies 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 conducting shells 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, and enhance current ramp-up rates. Here we describe an ECH system, launcher geometry, and discuss ECH startup scenarios for LTX-β. A long pulse (up to 50 msec) 3 kW, 10.36 GHz ECH system has been constructed. Following the present maintenance period, startup experiments will be conducted with magnetic field configurations such as Trapped Particle Configuration, field null configurations, and perfect field null configuration, 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.