Probing the limits on beta and density in the RFP

RFP-record values of total beta and normalized density have been achieved in MST plasmas with inductive current profile control combined with pellet and neutral beam injection. Total beta reaches 28{\%} and appears to be limited by transport. The density has thus far reached 2.0*n$_{\mathrm{Greenwald}}$, limited only by the size of pellet that can be ablated inside the MST plasma. Current profile control is used routinely in MST to reduce current-gradient-driven tearing fluctuations and stochastic transport. Beta is thereby increased but is well below pressure-related stability limits due to a concomitant reduction in P$_{\mathrm{Ohmic}}$. With edge-deposited fueling based on gas puffing, the density is also necessarily low, typically at or below 0.2*n$_{\mathrm{Greenwald}}$, in order to avoid edge-resonant instability. With direct pellet fueling of the plasma core, a substantially larger density is possible, and this leads to a substantially larger P$_{\mathrm{Ohmic}}$ and beta. NBI further augments beta with modest heating and a population of 25 keV fast ions. The beta limit is probed with a three-fold variation in P$_{\mathrm{Ohmic}}$ brought about with a density scan. Magnetic fluctuations increase with density, likely leading to increased transport and the observed saturation of beta.