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

• evaluate the effectiveness of fueling and pumping — including core pellet fueling — in
the presence of 3-d fields used for pedestal density reduction and elm control.
• identify the underlying mechanisms responsible for the modification of edge transport
and stability in elm-free regimes such as the quiescent h-mode (Qh mode) and the
enhanced d-alpha (eda) h-mode.
• identify and test other means of edge profile control — e.g., shallow pellet injection,
radiofrequency-based methods, recycling control (lithium wall), or external rotation
shear modification.
• in improved confinement regimes with a low-confinement mode (l-mode) edge,
assess whether the reduced edge pressure gradient is compatible with the required
high confinement, and assess any possible reductions in the global stability limits and
achievable bootstrap fraction.
• identify and test elm-tolerant wall concepts — e.g., liquid walls.
Scale of effort
a Us research thrust to establish the basis for reliable operation, free of elms and disruptions,
could make a major contribution to the world fusion program. The output from this research
thrust would include:
• development of mhd stability measurements and calculations for real-time execution,
as well as detailed, physics-based models of disruptions, elms, and their control.
• incorporation of validated models into simulations suitable for prediction, avoidance,
and mitigation of transient events in iteR and future burning plasmas.
• development and assessment of solutions for detection, avoidance, and mitigation of
transient events, including diagnostics and actuators suitable for burning plasmas.
• implementation of the techniques of disruption prediction, avoidance, and mitigation in
iteR and assessment of their effectiveness.
• confidence that a sufficiently low rate of transient events can be routinely achieved in
future devices.
virtually all of the research needed for disruption prediction and elm control, and a large proportion
of the research for disruption avoidance and disruption mitigation, can and should be done
in existing short-pulse facilities (c-mod, diii-d, and nstX in the Us, plus international facilities
such as Jet and asdeX-Upgrade). at most, modest upgrades to diagnostics, actuators, and
control systems would be required. existing facilities have several major advantages over iteR
and other future burning plasma devices: greater tolerance for elms and disruptions, which is
necessary for the “learning curve” in avoiding them; greater flexibility for modification of the facility,
which allows testing of multiple control techniques; and more complete diagnostic sets, facilitating
the physics understanding and benchmarking of predictive models.
in addition, the emerging generation of superconducting tokamaks (east, kstaR, sst-1, Jt-
60sa) will be crucial for demonstrating stable operation, free of elms and disruptions, in iteR-
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