Plans for Neutral Beam Injection on HSX

A neutral beam injector on loan from the MST group is being refurbished for use on HSX (1.2 ms, 20 keV, 40A). Initially the beam will be used to produce a population of fast ions so that the confinement can be studied as a function of the magnetic field geometry (quasisymmetric or with introduced changes to the spectrum). Confinement will be measured through neutron production rates from deuterium beams injected into a deuterium plasma. This has been successfully done under similar parameters in the CHS device [1]. The HFREYA and GNET [2] codes have been used to look at fast-ion birth profiles, confinement and thermalization. Under attainable conditions a geometrical restrictions 15-25 % of the beam energy can be coupled to the plasma in the QHS mode, including charge exchange losses. To improve efficiency of NBI, an upgrade to HSX is under consideration to increase plasma density, reduce neutral population, and increase ion temperature. The magnetic field will be increased to 1.25 T to be able to utilize a 1 second 500 kW 70 GHz gyrotron for plasma heating.

[1] M. Isobe et al. Rev. Sci. Instrum. 68 (1) 1997

[2] H. Yamaguchi and S. Murakami, Plasma and Fusion Research, 9 (2014) 3403127