MHD Modeling of Current Drive in HIT Devices with Extended Validation of HIT-SI3*

The Helicity Injected Torus – Steady Inductive 3 (HIT-SI3) uses Steady Inductive Helicity Injection (SIHI) to drive current within a spheromak plasma via Imposed Dynamo Current Drive (IDCD)[1]. SIHI sustainment and the IDCD model are used as founding principles for a proposed new HIT experiment, the Helicity Injected Torus- Technology Demonstration (HIT-TD), which aims to sustain toroidal current in a closed-flux spheromak using SIHI. HIT devices are modeled using the NIMROD MHD code. The most recent design of HIT-TD is modeled in NIMROD and driven to high enough current gain for closed flux surfaces to form. The properties of the resultant closed flux equilibrium are presented and analyzed with emphasis on scaling to fusion reactor operation. Simulations of recent HIT-SI3 plasma pulses are also presented to validate new experimental results gained from a recently-installed 3D electron density tomography system. Experimental and synthetic density profiles are examined alongside profiles of current-driving terms using simulation results to determine the fidelity of the simulation model and study the effects of three-dimensional density fluctuations on current drive and sustainment.

[1]B. S. Victor et al., Phys. Plasmas 21, 082504 (2014)