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raman_chi_icc2011_paper.pdf2011-09-12 11:42:21Roger Raman
raman_chi.pdf2011-08-31 10:45:44Roger Raman

Demonstration of Tokamak Inductive Flux Saving by Transient CHI on NSTX

Author: Roger Raman
Requested Type: Consider for Invited
Submitted: 2011-05-25 11:00:26

Co-authors: T.R. Jarboe, B.A. Nelson, D. Mueller, S.C. Jardin

Contact Info:
University of Washington
AERB 352250
Seattle, WA   98195

Abstract Text:
Transient Coaxial Helicity Injection (CHI) initiated discharges in NSTX have attained peak toroidal currents up to 300 kA and when these discharges are coupled to induction, CHI has produced up to 300 kA additional current over inductive-only operation. This is a record for non-inductive plasma startup, and an essential step for developing a fusion reactor based on the spherical torus concept. The method could also reduce the cost of a tokamak reactor. The method was first developed on the Innovative Confinement Concepts experiment HIT-II at the University of Washington, and has now been successfully applied to the much larger NSTX device.

In NSTX, reference inductive only discharges require 50% more solenoid flux than a CHI started discharge to reach 1 MA. These are the first discharges in NSTX that have generated 1 MA of plasma current using only 258 mWb of solenoid flux. In addition, the resulting discharge has low plasma density and normalized internal plasma inductance of 0.35 from the start of the discharge and through the inductive ramp, typical of the type of discharges required for advanced scenario operations.

The Tokamak Simulation Code (TSC) has been used to understand the scaling of CHI generated toroidal current with variations in the external toroidal field and injector flux. These simulations show favorable scaling of the CHI start-up process with increasing machine size and are consistent with the theoretical model for CHI plasma startup. Closed flux in TSC is achieved as result of the decaying CHI discharge that produces an inductive voltage generating the initial closed-flux current. Scaling based on the analysis of experimental results and TSC simulations indicates the possibility for substantial current generation potential by CHI in the upgrade to NSTX.

These exciting new results from NSTX demonstrate that CHI is a viable solenoid-free plasma startup method for future STs and tokamaks.

This work supported by U.S. DOE Contracts DE-AC02-09CH11466 and DE-FG02-99ER54519 AM08

Characterization: A1,A8


University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011