Download a copy of the latest PSFC Progress Report - Plasma ...

experiments when funding of the project was
terminated by DOE in December 2010.
MReconnection Experiments on the
Versatile Toroidal Facility (VTF)
Magnetic reconnection plays a fundamental role
in magnetized plasmas as it permits rapid release
of magnetic stress and energy through changes
in the magnetic field line topology. It controls
the spatial and temporal evolution of explosive
events, such as solar flares, coronal mass ejections,
and magnetic storms in the earth’s magnetotail,
driving the auroral phenomena. Magnetic reconnection
is studied in the Versatile Toroidal Facility
under the leadership of Professor Jan Egedal, who
leads the effort of half a dozen undergraduate and
graduate students. The magnetic geometry of VTF
is providing insight to what controls the onset of
the explosive magnetic reconnection event observed
in nature. In a recent Physical Review Letter
important details were published about the threedimensional
nature of a magnetic reconnection
event. The spontaneous onset is facilitated by a
global mode, which breaks the axisymmetry that
enables a localized reconnection onset.
In most theories for reconnection, the electrons
are approximated by Maxwellian isotropic distribution.
However, based in part on the VTF experimental
results obtained during the past three
years, members of the VTF group have derived a
new analytic model for the electron pressure tensor
during reconnection. This theory accounts for
the highly anisotropic pressure near the reconnection
region observed by spacecraft and in kinetic
simulations. In fact, the pressure anisotropy is the
driver of the highly structured electron distribution
function that is characteristic of electron jets
observed in the central reconnection region. We
note that a strong collaboration exists between
the VTF group and eminent theorists and computer
modelers at universities and national laboratories
(in particular Bill Daughton at Los Alamos),
who develop some of the largest 3D codes
to properly describe solar coronal mass ejection
phenomena and magnetic reconnection in the
earth’s magnetotail. The VTF group activities are
part of a larger national, and in fact international
effort, to understand the physical processes responsible
for magnetic reconnection and release
of vast amounts of magnetic energy under different
conditions in nature and in the laboratory.
Novel Diagnostics and Collaborations
A. Phase Contrast Imaging on DIII-D and
Alcator C-Mod
This work, by Professor Porkolab on Alcator C-Mod
and Dr. Chris Rost on site at DIII-D, involves strong
graduate student and post-doc participation.
Phase Contrast Imaging (PCI) is a unique interferometer
type of diagnostic utilizing a 50-watt
cw CO 2
laser and a special grooved phase plate
inserted into the CO 2
beam path that ultimately
enables us to image plasma turbulence onto a
liquid nitrogen cooled detector array. The output
of the detectors gives valuable information on
both the phase and amplitude of the turbulent
density fluctuations with extraordinary sensitivity
and fine spatial and temporal resolution. This
diagnostic has been implemented and improved
over the years both on the DIII-D tokamak at
General Atomics in San Diego, and on the Alcator
C-Mod tokamak at the PSFC. The Phase Contrast
Imaging (PCI) diagnostic is able to detect
short wavelength (mm to cm), high-frequency
(up to 5 MHz) modes excited by plasma instabilities
(the so-called ITG, TEM and ETG modes)
which are believed to play a fundamental role
Prof. Jan Egedal (center) works on the Versatile Toroidal Facility with his students: (from
back left )- graduate students Arturs Vrublevski and Air Le; UROP students Jonathan Ng
and Evan Lynch; graduate student Obioma Ohia (right, back) and UROP student Dustin
Katz (front).
PSFC Progress Report 09–11 19