Advanced Field-Aligned ICRF Antennas for Improved Breakdown Resistance

To make a viable tokamak reactor concept, efficient, robust steady state current drive is required. RF power is among the leading contenders due to its high efficiency and penetration to the plasma core without density limits. To minimize impact on tritium breeding, high power density RF antennas are desired. At present, electrical breakdown limits the power density to ~10 MW/m2. Recent results at MIT utilizing an Inconel based field aligned ICRF antenna showed significantly increased load tolerance, reduced impurity contamination, and reduced RF enhanced heat flux associated with ICRF antenna operation compared to standard ICRF antennas. However, a field-aligned antenna results in a smaller antenna area compared to a standard antenna due to geometrical constraints. To increase the power density, a field-aligned antenna must have a higher voltage and power limit. Emerging experimental results suggest that materials with higher tolerance to surface fatigue and melting temperature lead to higher breakdown limits. The ability to produce high density, well-bonded refractory metal coatings on Inconel based substrates has recently been demonstrated by Plasma Processes using electroforming (EL-Form) techniques and testing at MIT has confirmed improved breakdown resistance. In addition, the ability to additively manufacture (AM) an ICRF antenna will enable the development of more complex antenna designs that could lead to further improved electrical performance. Therefore, during this investigation, an advanced field-aligned ICRF antenna will be developed by combining additive manufacturing techniques to produce an antenna with complex features such as internal cooling channels and the deposition of innovative EL-Form refractory metal coatings to improve breakdown resistance.