Speaker
Carl Dunlea
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1104.pdf
Magnetic compression at General Fusion -
experiment and simulation with neutral fluid
Carl Dunlea1,2, Ivan Khalzov2, Stephen Howard2, Wade Zawalski2, Kelly Epp2,
Akira Hirose1, Chijin Xiao1, General Fusion Team2
1
University of Saskatchewan, Saskatoon, Canada
2
General Fusion, Vancouver, Canada
*e-mail: cpd716@mail.usask.ca
The magnetic compression experiment at General Fusion was a repetitive non-destructive test to
study plasma physics applicable to Magnetic Target Fusion compression. A spheromak compact
torus (CT) is formed with a co-axial gun into a containment region with an hour-glass shaped
inner flux conserver, and an insulating outer wall. External coil currents keep the CT off the
outer wall (levitation) and then rapidly compress it inwards. The optimal external coil
configuration greatly improved both the levitated CT lifetime and the rate of shots with good
compressional flux conservation. As confirmed by spectrometer data, the improved levitation
field profile reduced plasma impurity levels by suppressing the interaction between plasma and
the insulating outer wall during the formation process. Significant field and density compression
factors were routinely observed. Matching the decay rate of the levitation currents to that of the
CT currents resulted in a reduced level of MHD activity and a higher frequency of long-lived
CTs. We developed an energy and toroidal flux conserving finite element axisymmetric MHD
code to study CT formation and compression. The Braginskii MHD equations with anisotropic
heat conduction were implemented. The code also has the capability to start magnetic
compression from a Grad-Shafranov equilibrium. There are simulated diagnostics for B probes,
q-profile, interferometers, and Ion-Doppler measurements. To simulate plasma / insulating wall
interaction, we couple the vacuum field solution in the insulating region to the full MHD solution
in the remainder of the domain. A plasma-neutral model including ionization, recombination,
charge-exchange reactions, and a neutral particle source, was implemented, primarily in order to
reduce viscous heating of the ions during formation. We see good agreement between simulated
and experimental results.
____________ (EPS 2018)_____________
