Speaker
Prof.
Troy Carter
(University of California, Los Angeles)
Description
Studies of turbulence and transport in the Large Plasma Device (LAPD)
have: documented the role of drift-Alfvén waves and flows in avalanche
events; revealed a new instability in the edge of increased β plasmas;
and demonstrated an interaction between ICRF waves and edge
turbulence, leading to strong modulation of the former and enhancement
of the latter. Intermittent collapses of the plasma pressure profile
(avalanches) are observed with off-axis heating in LAPD and are
associated with unstable drift-Alfvén waves. Flows play a critical
role in the dynamics, in particular in the onset of the drift-Alfvén
waves and avalanches through the interplay of the stabilizing flow
shear and the destabilizing pressure gradient. Active control of the
flows is obtained using biasing; this leads to control over the size and frequency of avalanches. With controlled flows, a regime is found in which avalanches are
absent. Strongly electromagnetic turbulence, identified as being due
to a new instability, the Gradient-Driven Drift Coupling Instability
(GDC), is observed in the edge of increased β plasmas in LAPD. As the
plasma beta is increased (up to 15%), magnetic fluctuations are observed to
increase substantially, with δB/B ~ 1% at the highest β, while density
fluctuations decrease slightly. Parallel magnetic fluctuations are
observed to be dominant at the highest β, with δB∥/δB⊥~2. Comparisons
of the experimental data with linear and nonlinear GENE simulations of
the GDC yield good qualitative and quantitative agreement. An
experimental campaign on the physics of ICRF waves on LAPD has established a correlation between strong modulation of
core coupled fast waves and edge density fluctuations, both of which
increase with antenna power. Strong low-frequency modulation of
coupled fast wave power is observed via direct measurement of the core
RF waves with magnetic probes. This modulation is well correlated with
low-frequency edge density fluctuations associated with drift waves
(measured with Langmuir probes). The amplitude of the RF modulation
and the amplitude of edge density fluctuations in the drift wave
frequency range both grow with increasing RF power, suggesting some
nonlinear coupling between the edge drift waves and large amplitude
fast waves in the core region.
| Country or International Organization | United States of America |
|---|---|
| Paper Number | OV/P-4 |
Primary author
Prof.
Troy Carter
(University of California, Los Angeles)
Co-authors
Bart Van Compernolle
(University of California, Los Angeles)
Prof.
George Morales
(UCLA)
Mr
Giovanni Rossi
(UCLA)
Mr
Matthew Poulos
(UCLA)
Dr
Moritz Pueschel
(UT Austin)
Dr
Patrick Pribyl
(UCLA)
Prof.
Paul Terry
(University of Wisconsin-Madison)
Rory Perkins
(Princeton Plasma Physics Laboratory)
Mr
S.-W. Tsao
(UT Austin)
Dr
Shreekrishna Tripathi
(UCLA)
Dr
Steven Vincena
(UCLA)
Prof.
Walter Gekelman
(UCLA)
