Stability and transport in compact quasi-axisymmetric stellarators

The potential performance and flexibility of a compact, quasi-axisymmetric (QAS) stellarator design, has been addressed by studying the effects of varied pressure and rotational transform profiles on the global, ideal magnetohydrodynamic (MHD) stability and the energetic particle transport. The CAS3D and TERPSICHORE code packages were used in the MHD studies while the ORBITMN/ORBIT3D code package was used for the transport simulations of the three field period QAS. To assess robust performance in a medium-size experiment, the VMEC code was used to obtain magnetic flux surfaces for 30 equilibria near the design point, while keeping the boundary shape and the average beta fixed at 3.8%. The plasma equilibria obtained were designated P0X/I0Y as follows: P00/I00 was the baseline configuration. P01, P02 and P03 were defined so that P01 was similar to P00, P02 was more peaked than P01, while P03 was broader than P01. P04 was a very broad, parabolic pressure profile and P05 was the pressure profile used in helias reactor studies based on the W7-X design. The iota profiles were chosen as follows: I01 was linear, maintaining i(0) and i(a) the same as in I00. I02 and I03 were based on I01 and also kept i(0) and i(a) as in the baseline case, but with edge shear increased by a factor of 1.5 and 2. I04 was a linear iota profile with i(0) as for the other profiles, but i(a) higher than 0.5, similar to I01. The pressure and iota profiles are shown in Ref. [2]