|raman_icc_07.pdf||2007-03-28 15:44:09||Roger Raman|
Solenoid-free Plasma Start-up in NSTX using Transient CHI
Author: Roger Raman
Requested Type: Poster Only
Submitted: 2006-12-18 15:13:24
Co-authors: T.R. Jarboe, B.A. Nelson, D. Mueller, M.G. bell, M. Ono
University of Washington
Seattle, WA 98195
Elimination of the central solenoid is a consideration for the design of toroidal confinement devices which will then require alternative methods for initiating the plasma current. A method of plasma current generation known as Coaxial Helicity Injection (CHI) has been successfully applied in the National Spherical Torus Experiment (NSTX) to form closed, nested magnetic surfaces carrying a plasma current up to 160 kA. In some discharges the generated current persists for a surprisingly long ~400 ms. While the CHI method has previously been studied in smaller experiments, such as the Helicity Injected Tokamak (HIT-II) at the University of Washington, the significance of these results are (a) demonstration of the process in a vessel volume thirty times larger than HIT-II on a size scale more comparable to a reactor, (b) a remarkable multiplication factor of 60 between the injected current and the achieved toroidal current, compared to six in previous experiments, and (c) for the first time, fast time-scale visible imaging of the entire process that shows discharge formation, disconnection from the injector and the reconnection of magnetic field lines leading to closed flux. These significant results indicate favorable scaling with machine size. These significant results, which were obtained on a machine designed with mainly conventional components and systems, indicate favourable scaling with machine size. Near term plans are to further increase the plasma current and to couple the CHI produced plasma to induction from the central solenoid. This would be followed by the application of up to 200 kW of microwave power to increase the electron temperature for coupling to other non inductive current drive methods. Experimental results from these experiments in HIT-II and NSTX will be presented.
*Work supported by US DOE contracts DE-FG03-9ER54519 and DE-AC02-76CH03073.
Workshop topic: A.5