Alpha particle confinement in quasi-helically symmetric stellarators*

Computational modeling is used to determine the confinement of high energy alpha particles in quasi-helically symmetric stellarator configurations. Work is being undertaken to optimize a possible new mid-scale quasi-helically symmetric stellarator experiment, targeting lower neoclassical transport, ballooning stability, and resilience to bootstrap current. Configurations with different rotational transform profiles have been obtained that are able to withstand the addition of bootstrap current at higher beta. That is, the unwinding of the rotational transform due to bootstrap current in quasi-helical configurations does not cause low order rational surfaces to enter the plasma. In this work, alpha particle confinement in these configurations is explored. The code used follows guiding-center orbits of high-energy alpha particles [V.V. Nemov, et al., Phys. Plasmas 21, 062501 (2014)]. This work will test the impact increasing plasma beta, bootstrap current, and different rotational transform profiles have on alpha confinement. Results will be presented for both the confinement of trapped alpha particles as a function of time and the regions of alpha particle losses.