Speaker
Mr
Bart Van Compernolle
(UCLA)
Description
Results of a basic heat transport experiment$^{1,2}$ involving an off-axis heating source are presented. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A ring-shaped electron beam source injects low energy electrons (below ionization energy) along a strong magnetic field into a pre-existing, large and cold plasma. The injected electrons provide an off-axis heating 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 source is active for a period long compared to the density decay time, i.e. as time progresses the heating power per particle increases. Two distinct regimes are observed: 1) an initial regime dominated by avalanches, identified as sudden intermittent rearrangements of the pressure profile; 2) a state dominated by sustained drift-Alfven wave activity following a global collapse of the density profile. The avalanches are triggered by the rapid growth of drift-Alfven waves. The data suggest that ambient flows play a critical role in the dynamics, in particular in the onset of the avalanches through the interplay of the stabilizing flow shear and the destabilizing pressure gradient. The flows are a consequence of the boundary conditions at the ring-source. Recently a new configuration has been implemented that allows active control of the flows by changing the bias between the emitting ring and surrounding carbon masks. A parameter regime has been found in which avalanches are absent. The new source configuration also provides some control over the size and frequency of avalanches when present.
This work is supported by the NSF grant PHY1619505, and is performed at the Basic Plasma Science Facility, sponsored jointly by DOE and NSF.
**References:**
$^{1}$ B. Van Compernolle et al. Phys Rev. E **91**, 031102 (2015)
$^{2}$ B. Van Compernolle et al, Phys. Plasmas **24**, 112302 (2017)
Primary author
Mr
Bart Van Compernolle
(UCLA)
Co-authors
Prof.
G. J. Morales
(UCLA)
Mr
M. J. Poulos
(UCLA)
Ms
S. Jin
(UCLA)
