Fiscal year 2006 (October 2005 – September 2006)
brought exciting new capabilities and results on
the National Spherical Torus Experiment (NSTX),
very high quality component construction on the
National Compact Stellarator Experiment (NCSX), the
signing of the ITER Agreement at the ministerial level,
strong contributions from theory and advanced computing,
excellent results from the Princeton Plasma Physics
Laboratory’s (PPPL) collaborations on Doublet III-D
(DIII-D), Alcator C-Mod and the Joint European Torus
(JET), as well as a new deeper layer of understanding of
the basic physics of magnetic reconnection. We also contributed
fundamental understanding of how black holes
interact with the plasma that swirls around them and
how intense ion beams can be focused. We continued in
the development of micro-aviation vehicles and tools to
detect rogue radioactive materials for homeland security.
This was an exciting year at PPPL.
This year NSTX, with its improved poloidal-field
coils, produced more strongly shaped plasmas, with longer
pulses, which achieved values of beta and of bootstrap
current fraction representative of an Spherical Torus-based
Component Test Facility. Key diagnostic systems were
upgraded to higher resolution, and entirely new diagnostic
tools were brought on line. The result was the ability
to measure clearly, for the first time in the world, the
effects of low-n instabilities on fast-ion current drive, and
to perform highly localized measurements of electronscale-
length instabilities. Excellent results were achieved
on feedback stabilization of resistive wall modes, while
varying rotation speed using non-resonant perturbations.
Clear evidence was provided that multiple mode overlap
leads to enhanced fast-ion redistribution during Toroidicity-
induced Alfvén Eigenmode (TAE) bursts. Nonlinear
three-wave coupling of modes was clearly demonstrated
as well. Confinement scaling in Spherical Torus plasmas
was convincingly measured, demonstrating a stronger
toroidal-field variation than in other devices. Due to the
excellent diagnostics on NSTX these experiments clarified
that the toroidal-field scaling was mostly in the electron
channel, and the plasma current scaling in the ion
channel. Enticingly, lithium wall coating demonstrated
a ~20% improvement in confinement.
Construction on NCSX proceeded well this year.
Delivery of the modular coil winding forms from industry
began and, after some initial difficulties, accelerated to
the needed pace. Winding of the complex modular coils
themselves was begun and the required very high level of
accuracy was achieved. As more experience was gained
with the procedure, it began to move more rapidly, and
by year’s end four of the eighteen coils were completed.
The manufacture of all three sectors of the vacuum vessel
for NCSX was completed this year as well.
PPPL’s role as a partner in the U.S. Contributions to
ITER Project will be to lead the U.S. diagnostics program
and the development of ITER’s steady-state electrical
power network. The diagnostics task includes both the
design and manufacture of scientific instruments, and also
the development of the complex “port plugs” which provide
the interface between scientific measurement tools
and the fusion nuclear environment of ITER. PPPL will
also support the magnet work and ion cyclotron transmission
lines for ITER. PPPL is strongly engaged in scientific
preparations for ITER through the International
Tokamak Physics Activity, the U.S. Burning Plasma Organization,
and ITER Design Review Working Groups.
Access to the most powerful nonclassified computers
has allowed substantial advances in plasma theory this
year, supporting, for example, global-scale turbulence calculations
showing that ion thermal transport in NSTX
should be relatively immune to the ion-temperature-gradient
modes that are believed to cause much ion thermal
transport in conventional tokamaks. On the other hand,
in more conventional configurations this turbulence is
not only important in transport, but it can spread from
unstable to stable regions, causing transport in regions
that are not predicted, in local models, to have turbulence.
Advanced nonlinear calculations of beam-driven
modes in NSTX show the experimentally observed chirping
down in frequency and the evolution of mode structure
as the fast-ion distribution evolves self-consistently
under the impact of the mode. Continuum damping of
Toroidicity-induced Alfvén Eigenmode modes was calculated
accurately, and found to agree with experiments on
C-Mod, resolving a long-standing discrepancy between
theory and experiment. The Theory Department has also
supported the Compact Stellarator Program by providing
guidance for the placement of magnetic detection coils for
equilibrium reconstruction, and finding operating modes
with even higher symmetry than those planned during
the machine design. The Computational Plasma Physics
Group has helped implement PPPL’s codes on the fastest
computers and both sped up and increased the availability
of PPPL’s TRANSP transport analysis code, with the
result that more than 2,500 production runs were performed
for the world research community this year on
PPPL’s cluster.
The Off-site Research Department continued to perform
leading-edge research on major devices not available
at PPPL. By working on both DIII-D and JET, PPPL
scientists demonstrated that Alfvén eigenmodes can be
driven unstable even by thermal ion gradients, so these
modes are far more prevalent than previously understood.
To do this required the application of advanced internal
diagnostics, as begun on the Tokamak Fusion Test Reactor
(TFTR), to measure these modes. On C-Mod, PPPL’s
major contributions to the lower-hybrid wave launcher
began to bear fruit, as current drive was convincingly
demonstrated on C-Mod this year.
The Plasma Science and Technology Department
scored some major successes this year. The Magnetic
Reconnection Experiment measured, for the first time
in a laboratory plasma, the fine-scale electron diffusion
region that is created by the Hall effect, and where
the final reconnection process takes place. Furthermore
intense magnetic fluctuations are found localized
in the reconnection zone, correlating in time and
space with reconnection events. While the results are
not fully in place, it appears that the long-standing scientific
controversy over whether anomalous reconnection
is caused by the Hall effect or by turbulent resistivity
may be resolved by the proverbial “you are both
right.” Another very exciting piece of basic physics this
year was uncovered using a rapidly rotating pair of coaxial
cylinders that produced sheared flow analogous to
the Keplerian flow of plasma orbiting a black hole or a
planet-forming star. It was shown that even at very high
speeds there is no instability in the absence of magnetic
field effects. This has strong implications for theories of
star and planet formation. Another very exciting result
was provided closer to the area of fusion energy. One of
the main challenges for fusion using heavy ions to heat
and compress fuel capsules, is to make a beam of ions
that is highly localized both parallel to and transverse
to its direction of motion. Numerical calculations that
this could be achieved using a background plasma to
neutralize the space-charge of the ion beam were confirmed
using a long intense plasma source developed by
PPPL and applied at the Lawrence Berkeley National
Laboratory.
Applications research activities have been successful
this year as well, with PPPL contributing practical tiny
micro-aviation vehicle prototypes to the Naval Research
Laboratory’s Micro Air Vehicle Program, and with our
Miniature Integrated Nuclear Detection System being
deployed for field testing.
In sum, FY2006 was an exciting year of scientific progress
on all fronts. With NSTX producing key results,
NCSX construction demonstrating high quality, signing
of the ITER agreement at the ministerial level, advances
in theory and in Off-site research, we continue to bring
fusion energy closer to practical reality.
Robert J. Goldston's Resume
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