Speaker
Suying Jin
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.4012.pdf
Flow control and its impact on avalanche dynamics in a basic transport
experiment
S. Jin1, B. Van Compernolle1, M. J. Poulos1, G. J. Morales1
1
Department of Physics and Astronomy,
University of California, Los Angeles, United States
Results of a basic heat transport experiment1,2 involving an offaxis heat source are
presented. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A
ringfshaped electron beam source injects low energy electrons (below ionization energy)
along a strong magnetic feld into a prefexisting, large and cold plasma. The injected
electrons provide an offaxis heat source that results in a long, hollow, cylindrical region of
elevated plasma pressure embedded in a colder plasma, and far from the machine walls. The
offaxis source is active for a period long compared to the density decay time, i.e. as time
progresses the power per particle increases. Two distinct regimes are observed to take place,
an initial regime dominated by avalanches, identifed as sudden intermittent rearrangements
of the pressure profle, and a second regime dominated by sustained driftfAlfven wave
activity following a global collapse of the density profle. The avalanches are triggered by
the rapid growth of driftfAlfven waves. The data suggest that fows play a critical role in the
dynamics, in particular in the onset of the avalanches through the interplay of the stabilizing
fow shear and the destabilizing pressure gradient. The fows are imposed by the boundary
condition at the ringfsource. This source has now been modifed from previous experiments
to gain active control of the fows by controlling the bias between the emitting ring and
surrounding carbon masks. A regime was found in which avalanches are absent. The new
source also provides some control over the size and frequency of avalanches when present.
Supported by the NSF grant PHY1619505, and performed at the Basic Plasma Science
Facility, sponsored jointly by DOE and NSF.
1
B. Van Compernolle et al. Phys Rev. E 91, 031102 (2015)
2
B. Van Compernolle et al, Phys. Plasmas 24, 112302 (2017)
