Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

Disruption prediction
accurate prediction of an impending disruption is a key element of both avoidance and mitigation
of disruptions and has not been demonstrated to date. in particular, optimizing the reliability
and accuracy of prediction (including minimization of “false-positive” results) will be critical.
Research needs include:
• Real-time mhd calculations for assessment of the approach to stability limits.
• accurate real-time profile diagnostics for input to mhd stability calculations.
• diagnostics for direct detection of stability limits, e.g., real-time mhd spectroscopy to
measure damping rates of large-scale mhd modes.
development of real-time stability assessment and prediction, including diagnostics, stability calculations,
and damping measurements, can be done in existing facilities and with low-power operation
in iteR. two key issues are the accuracy of these diagnostics and analysis techniques to
minimize any loss in plasma performance and the use of diagnostics that are compatible with the
stringent requirements of iteR and demo.
Disruption mitigation
some disruptions are not predictable even in theory, such as those resulting from a sudden influx
of impurities, failure of a power supply, etc. For these and other cases where avoidance fails,
a preemptive rapid shutdown is required. injection of sufficient quantities of gas or other impurities
removes the plasma energy by radiation and raises the particle density to the level needed for
collisional suppression of a runaway electron avalanche. Present experiments have demonstrated
reduction of peak heat loads and electromagnetic forces through gas injection, but sufficient density
for suppression of runaway electrons is a remaining challenge. Research needs in this area
include:
• development and evaluation of options for delivering material to the plasma and improved
predictive capability for the physics of assimilating material into the core plasma.
• assessment of radiation asymmetry during rapid shutdown and of the requirements for
the number of injectors and their location.
• improved understanding of the confinement and loss of runaway electrons, and
development of techniques to suppress or control the position of the runaway electron
beam.
much development of rapid shutdown techniques can be done in existing facilities. The exponential
dependence of runaway electron generation on plasma current indicates a need to include
high-current devices (Jet and Jt-60sa) in these studies. accurate, validated modeling will be
required to extrapolate these results to the quantitatively different size, current, and energy of
iteR. due to its large plasma current, iteR will significantly extend the studies of runaway electron
generation and provide critical data for demo.
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