Historical research guide · 0564 · 2012
Imposed-dynamo current drive
T.R. Jarboe · B.S. Victor · B.A. Nelson · C.J. Hansen · C. Akcay · D.A. Ennis · N.K. Hicks · A.C. Hossack · G.J. Marklin · R.J. Smith
In one minute
Thomas Jarboe’s group at the University of Washington runs HIT-SI, a machine that makes a spheromak — a self-organised ring of plasma that holds its own magnetic shape. The hard part of any such machine is keeping a large electric current running inside the plasma with nothing touching it. The old answer was to let the plasma go unstable and let the resulting churn, a dynamo, push the current around; instabilities of that kind also break the magnetic surfaces a fusion reactor needs. Jarboe and his co-authors report a different mechanism. The wiggles that drive the current are not grown by the plasma at all: steady inductive injectors impose them from outside, and shear in the flow of the electron fluid twists those imposed wiggles into current. Their model predicts the measured toroidal current as it evolves, how the injector impedance scales, and the profile the machine produces. That means a stable equilibrium can be sustained efficiently, and the current profile shaped on purpose.
Connection
Chapter 12 needs a route to fusion a reactor can actually hold steady, and this is one: current driven by fluctuations you impose rather than by instabilities you have to tolerate. For chapter 9 it is the same physics the site follows in plasmoids — a self-organised magnetic object that can be steered from outside — and the same group carried it straight into a reactor design, the dynomak, at /library/stm-45bcd277ce.
From the source
A mechanism for steady inductive helicity injection current drive has been discovered in which the current-driving fluctuations are not generated by the plasma but are imposed by the injectors.Abstract, sentence 1
Sheared flow of the electron fluid distorts the imposed fluctuations, and that distortion is what drives the current.Abstract, sentence 2
The model accurately predicts the time-dependent toroidal current, the injector impedance scaling, and the profile produced in the HIT-SI experiment.Abstract, sentence 3
A stable equilibrium can be efficiently sustained with imposed fluctuations, and the current profile can in principle be controlled — which the authors call two large steps for controlled fusion.Abstract, sentences 4 and 5
Some of the effects of the imposed fluctuations on confinement in tokamak and spheromak reactors are assessed, and the degradation may be tolerable.Abstract, sentence 6
The mechanism is of interest beyond current drive: to plasma self-organization, to fast reconnection, and to plasma physics in general.Abstract, final sentence
The way in
https://doi.org/10.1088/0029-5515/52/8/083017How to cite it
T.R. Jarboe, B.S. Victor, B.A. Nelson, C.J. Hansen, C. Akcay, D.A. Ennis, N.K. Hicks, A.C. Hossack, G.J. Marklin, R.J. Smith (2012) Imposed-dynamo current drive doi:10.1088/0029-5515/52/8/083017