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

The Us fusion program is well positioned to carry out much of the required work in existing tokamaks,
with modest upgrades to diagnostics and auxiliary systems, but substantial increases in
experimental time and human resources. Further technology development will be required to extend
these techniques to the burning plasma regime in iteR.
Research Elements
transient events such as disruptions and elms must be minimized or eliminated in a burning
plasma. since a disruption is a singular event that terminates the plasma pulse, the conditions
that generate a disruption must be predicted and avoided. techniques to mitigate the effects of a
disruption must also be available, but should only be required in rare instances if avoidance fails.
The transient power loading due to elms must also be avoided in burning plasmas. This impulsive
elm-induced transport is the norm for steady high-confinement mode (h-mode) operation
in present devices, but a burning plasma requires a more continuous process that still allows the
optimum level of heat and particle transport in the plasma edge.
disruptions and elms comprise distinct categories of off-normal transient events and have distinct
research requirements. Research in this area can be organized into four broad elements:
• Prediction of disruptions.
• avoidance of disruptions.
• mitigation of disruptions.
• avoidance of elm-induced impulsive power loads.
many of the tools to achieve these goals are now being developed, and concepts exist for others.
in the next 10 to 20 years, these building blocks must be developed, and integrated into systems
that will ensure reliable, near-steady-state operation of magnetically confined fusion plasmas.
Prediction of disruptions
sustained, full-performance operation of a burning plasma requires that the conditions leading
to a disruption be identified in time to take action to avoid or mitigate the disruption, a challenging
problem even in existing tokamaks. accurate and reliable prediction is necessary to maximize
fusion performance without exceeding stability limits, while minimizing “false positive” results
that may lead to unnecessary retreat from high-performance conditions or shutdown of the discharge.
several levels of prediction must be developed, including empirical characterization of operating
limits, real-time assessment of the plasma operating state including calculation of magnetohydrodynamic
(mhd) stability limits, and identification of plasma “symptoms” indicating that
a disruption could ensue. Reliability requirements motivate a broad portfolio of prediction methods,
and redundancy of detection systems.
key research steps include:
• characterization of disruptions in existing data: cause of disruptions and their relative
frequency, identifiable precursors, electromagnetic and thermal loads.
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