Ohmic ignition with high engineering beta based on the RFP

The RFP configuration allows the possibility of ohmic ignition for fusion energy, eliminating the need for auxiliary heating~by rf or neutral beam injection. Complex plasma-facing antennas and NBI sources are therefore not required, simplifying the~difficult fusion materials challenge. While all toroidal configurations require a volume-average $\langle B\rangle \ge 5$T, the field strength~at the magnet in the RFP is only B$_{\mathrm{coil}}\approx $3T since plasma current generates almost all of the field. Engineering beta is~therefore maximized. We summarize access to ohmic ignition by examining a Lawson-like power balance for an RFP fusion plasma~comparable to the ARIES-AT advanced tokamak, which generates neutron wall loading $P_{n} /A\approx 5$MW/m$^{\mathrm{2}}$. The required energy confinement~for ohmic ignition in an RFP is similar to that for a tokamak. Confinement in MST is comparable to a same-size, same-field~tokamak plasma, but $\langle B\rangle $ in MST is only 1/20th that required for fusion. While transport could ultimately be dominated by micro~turbulence, extrapolation of stochastic transport using Lundquist number scaling for MHD tearing indicates standard RFP~confinement (not enhanced by current profile control) could be sufficient to access ohmic ignition. This bolsters the~possibility for steady-state inductive sustainment using oscillating field current drive. The high beta and classical energetic ion confinement measured in MST also bolster the RFP's fusion potential. Work supported by U.S. DoE.