Solenoid-Free Start-up and Ramp-up

Leader - Experiment Deputy - Experiment Leader - Theory and Modeling
Roger Raman Dennis Mueller Steve Jardin
609-243-2855 609-243-3239 609-243-2635

NSTX is unique in the world program investigating coaxial helicity injection (CHI) plasma startup and fast-wave assisted current ramp-up.

Research Priorities:

  • Minimize reliance on central solenoid flux to achieve 0.8-1MA plasma currents using early NBI/HHFW heating and by reducing impurities
  • Assess heating and current drive in inductive low plasma current discharges using HHFW
  • Determine maximum achievable closed flux currents with CHI start-up
  • Start CHI discharges with a pre-charged central solenoid


R(12-2): Assess confinement, heating, and ramp-up of CHI start-up plasmas

Responsible TSGs: Solenoid-Free Start-up, Wave-particle Interactions, Advanced Scenarios and Control

"Elimination of the ohmic heating (OH) solenoid is essential for proposed ST-based nuclear fusion applications. Coaxial helicity injection (CHI) is a leading candidate method for plasma initiation without an OH solenoid. Understanding CHI plasma confinement is important for projecting non-inductive start-up and ramp-up efficiency to next-steps. CHI initiated plasmas have been successfully coupled to induction H-mode plasmas with Neutral Beam Injection (NBI) heating. While these results are favorable, the confinement properties of CHI start-up plasmas have not been characterized. High-Harmonic Fast Wave (HHFW) and more recently NBI heating of low-current ohmic targets has been demonstrated and will be further developed. HHFW and/or early NBI heating will be applied to CHI targets coupled to induction to compare the confinement and heating versus non-CHI plasmas. Early NBI and HHFW heating and CD will be applied progressively earlier in the target to assess non-inductive sustainment, and the degree to which the OH flux consumed can be reduced will be quantified. Utilization of an all metal divertor could further improve CHI start-up and will also be characterized if such a divertor is present in NSTX. TRANSP and/or TSC will be used to both analyze and simulate the CHI experiments. This milestone informs the early auxiliary heating requirements for non-inductive start-up for NSTX Upgrade and for next-step ST facilities."