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

alpha particles (ash removal). mode-converted ion bernstein waves, alfvén waves, and acoustic
waves have been suggested as possible avenues for this energy transfer. another mechanism, related
to channeling, is to generate, in a controlled manner, phase-space “buckets” that spontaneously
sweep in frequency as they transfer energy from the alphas to the background plasma.
While the specific mechanisms and required wave spectra to facilitate alpha channeling remain
somewhat speculative, the potential benefits motivate the inclusion of this area in the control
component of this Thrust. as simulation tools and diagnostic methods improve, it is expected
that more specific alpha channeling approaches can be identified and tested.
Conclusion
The achievement of dominant self-heating by fusion-produced alpha particles is a primary goal
of the upcoming iteR and eventual demo projects. it is essential to monitor by active or passive
measurements the properties of the alpha particle distribution function. moderate alfvénic instability
can be tolerated and can, by itself, aid in the determination of the alpha particle distribution
function. The redistribution of alpha particles within the plasma is tolerable, but significant
loss of alphas is not. methods of external control of the alpha particle build-up need to be developed,
and the beneficial exploitation of the tendency of alpha particles to spontaneously transfer
wave energy directly to the plasma should be investigated. numerical transport and simulation
tools, validated with results from present-day experiments, will be crucial for burning plasma experiments
to predict the desirable range of operation and to assess the extent to which burn control
techniques are feasible.
This ReneW Thrust has overlap and close connections to a number of other thrusts. The development
of new energetic particle and neutron-hardened diagnostics for the burning plasma environment
is central to Thrust 1 and much of the diagnostic development described here will be
done jointly between Thrusts 1 and 3; results from Thrust 1 will be critical to understanding alpha
physics issues in future d-t plasmas. Thrust 5 will develop methods to control and sustain fusion
plasmas; control techniques specifically for alpha physics should factor significantly into Thrust 5.
improvements in theory, simulation, and diagnostics for alpha-driven instabilities and transport
should be coupled into Thrust 6, which has the goal of making overall advances in theory, simulation
and measurements. Progress in alpha transport simulations will also be of use for Thrust
8, which addresses the integrated dynamics of burning plasmas. alpha particle loss rates to plasma
facing components are relevant to Thrusts 9–11, which cover various aspects of the scrape-off
layer and plasma-material interfaces. Finally, although the primary focus of the present Thrust is
iteR, the methods developed for simulating and measuring alpha-driven instabilities will have
application to energetic ion phenomena in reduced-aspect-ratio tokamaks (Thrust 16), stellarators
(Thrust 17), and configurations with minimally applied magnetic fields (Thrust 18).
256