A Power Accounting Analysis of the Proto-MPEX Linear Device and Target Heat Flux Extrapolations to MPEX-based on Proto-MPEX discharges

Plasma material interaction (PMI) studies are crucial to the successful development of future fusion reactors. Proto-MPEX is a prototype device whose primary purpose is to develop the plasma heating source concepts for the Material Plasma Exposure eXperiment (MPEX), a steady-state linear device being developed to study PMI. Multi-region power accounting studies of Proto-MPEX were performed utilizing an extensive diagnostic suite and software modeling to identify mechanisms and locations of heat loss from the main plasma. Of the 79.4 kW of input power, up to 100% of the power has been accounted for in the helicon region. Extending the analysis to the device from end plate to end plate, 62.4% of the input power was diagnostically verified. The efficiencies of the upstream and downstream regions were 9.7% and 1.9%, respectively. Regions with lower power transport efficiencies have been identified as areas requiring further diagnostic analysis, particularly the sub-region defined between the downstream edge of the helicon region (z = 1.5 m) and the central chamber (z = 2.2 m). The importance of the skimmer plate, located in this sub-region, to the operating performance of Proto-MPEX and design of MPEX has been highlighted. The data acquisition and analysis processes have been streamlined as a working model for future power balance studies of Proto-MPEX. Power-to-target plate efficiencies have been calculated for a variety of plasma production scenarios including helicon power only and helicon power supplemented with electron cyclotron heating (ECH), helicon power supplemented with ion cyclotron heating (ICH), and helicon power supplemented with combined ECH and ICH. These efficiencies are extrapolated to MPEX-level applied power sources to estimate the expected heat fluxes and powers deposited to target plate surfaces for future steady-state PMI studies. In two of the seven operating configurations analyzed, MPEX-extrapolated heat fluxes achieved or surpassed the desired 10 MW/m² target plate heat flux. The desired heat flux can be achieved with helicon + ICH pulses and helicon + ECH + ICH pulses, providing operational flexibility in future MPEX PMI experiments.