Abstract: Realizing controlled fusion as a commercial energy source is faced with many challenges, with one of the main challenges being the development of Plasma Facing Components (PFC) that can survive the extreme environment encountered in a fusion reactor. To expedite the testing and development of PFCs Oak Ridge National Laboratory (ORNL) is building the Materials Plasma Exposure eXperiment (MPEX), which is a linear device purposed specifically for studying Plasma Material Interactions (PMI). Current linear devices cannot produce plasmas with fusion divertor relevant electron and ion temperatures and instead rely on electrostatic biasing of the target to simulate the relevant ion energies. This methodology inhibits studying the interaction of the eroded material and recycled neutral gas with a fusion relevant divertor plasma and does not properly simulate the angular energy distribution of the ion fluxes, therefore, PMI studies on these linear devices omit a vast amount of rich physics important to PFC development. MPEX will enable the study of fusion relevant PMI by producing fusion divertor relevant plasma conditions in front of a target station using RF technology. Proto-MPEX is the device that is currently operating at ORNL, where the viability of this RF technology is being demonstrated. The electron density, electron temperature, and ion temperature of the target plasma will be controlled independently with separate RF heating systems. This thesis focuses on the electron density production system and the ion heating systems on Proto-MPEX and their viability for MPEX.
The electron density production on Proto-MPEX is accomplished by a helicon plasma source. Efficient electron density production by the helicon plasma source is hypothesized to be enabled by strong core power deposition when the plasma conditions allow for the formation of fast-wave normal modes. An electromagnetic full-wave simulation coupled to volume averaged particle power balance is used to predict and optimize the electron density production from the helicon plasma source. Next, the viability of direct ion heating on Proto-MPEX is explored. Direct ion heating is accomplished by ion cyclotron heating which is expected to increase ion temperatures on Proto-MPEX to values of Ti = 20 eV or more. Although this technique has been demonstrated previously on other devices, Proto-MPEX’s high electron density creates a novel environment for this ion heating scenario complicating the access of RF energy into the core plasma. In this thesis, the Alfvén resonance’s presence in the plasma column is exploited to allow RF energy access to the Proto-MPEX core plasma. Numerical simulations and experimental demonstrations of core ion heating in Proto-MPEX are presented to demonstrate the viability of this direct ion heating method in the high-density plasmas expected in MPEX
