Advanced Scenarios and Control

Leader - Experiment Deputy - Experiment Leader - Theory and Modeling
Stefan Gerhardt Michael Bell Egemen Kolemen
609-243-2823 609-243-3282 609-243-3731

NSTX is the ST world leader in integrating, sustaining, and controlling advanced plasma scenarios with high confinement, high-non-inductive current fraction, and high beta.

Research Priorities:

  • Develop and implement improved plasma control techniques to achieve advanced operating scenarios
  • Develop improved plasma formation and ramp-up techniques for reduced density and collisionality
  • Assess the impact of increased aspect ratio and elongation on the integrated performance of the spherical torus
  • Experimentally realize high non-inductive current fraction plasmas with high-beta under sustained conditions
  • Create and validate models for the integrated plasma performance, with the goal of developing a predictive capability for next-step ST scenario and control design


R(12-3): Assess access to reduced density and collisionality in high-performance scenarios

Responsible TSGs: Advanced Scenarios and Control, Macro-Stability, Boundary Physics

"The high performance scenarios targeted in NSTX Upgrade and next-step ST devices are based on operating at lower Greenwald density fraction and/or lower collisionality than routinely accessed in NSTX. Collisionality plays a key role in ST energy confinement, non-inductive current drive, pedestal stability, RWM stability, and NTV rotation damping. Lower density and/or higher temperature is required to access lower nu*. HHFW is a potential means of increasing electron temperature and reducing nu*, and reduced fueling and/or Li pumping are effective and readily available tools for lowering nu* through lower density. However, while D pumping from lithium has been observed, additional gas fueling is typically required to avoid plasma disruption during the current ramp and/or in the high beta phase of the highest performance (i.e. highest confinement, beta, non-inductive fraction, etc) plasmas of NSTX . The goal of this milestone is to identify the stability boundaries, characterize the underlying instabilities responsible for disruption at reduced density, and to develop means to avoid these disruptions. Possible methods for stability improvement include changes in current ramp-rate (li and q(r) evolution), H-mode transition timing, shape evolution, heating/beta evolution and control, optimized RWM control and error field correction, fueling control (SGI, shoulder injector), and optimized Li pumping. This milestone will also aid development of MISK and VALEN stability models and TRANSP and TSC integrated predictive models for NSTX Upgrade and next-step STs."

ITPA and BPO Participation:

  • IOS-1.2 Study seeding effects on ITER baseline discharges
  • IOS-4.1 Access conditions for advanced inductive scenario with ITER-relevant restrictions
  • IOS-4.3 Collisionality scaling of confinement in advanced inductive plasmas
  • IOS-5.2 Maintaining ICRH coupling in expected ITER regime
  • IOS-6.2 li controller (Ip ramp) with primary voltage/additional heating