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

Figure 7. Simulation of an ITER discharge. The current ramp-up, flattop, and ramp-down phases are illustrated
in the upper left panel. Fueling is added during the ramp-up and flattop phase to bring the density up
to slightly over 1×10 20 m -3 during the flattop phase. The alpha power trace in the right panel indicates that
the total fusion power is 425 MW. Careful programming of the auxiliary power is required to produce a stable
burn and a “soft landing” at the end of the discharge. (Figure courtesy of C. Kessel.)
waves, the bootstrap current points the way toward steady-state non-inductive tokamak operation.
From this viewpoint, the theoretical prediction and subsequent experimental verification of
the bootstrap current is considered to be one of the most significant and important results from
the international tokamak research effort.
SCiEnCE CHaLLEngES, OPPORtunitiES, anD RESEaRCH nEEDS
Evaluation of ITER performance capabilities in non-DT phases
an extended period of operation in hydrogen and helium, followed by operation in deuterium, is
planned before full d-t operation in iteR. The pace at which Q = 10 operation can be achieved
in the d-t phase will be strongly influenced by the research that can be done during the preceding
non-dt phases. For example, achieving robust h-mode operation during the non-dt phases
would enable the development of techniques to handle critical issues (such as elms and stabilization
of neoclassical tearing modes) early in the research program.
each fuel presents special issues relative to the baseline d-t operation for which iteR was designed.
For example, access to the reference elmy h-mode is generally more difficult to obtain in
hydrogen than in heavier fuels such as deuterium or a mixture of deuterium and tritium. similarly,
ion cyclotron resonance heating scenarios that are based on heating a minority helium-3 component
and/or tritium at the second harmonic of the cyclotron frequency must be adapted to the
conditions of the initial operating phase. Research on the requirements for developing h-modes
for the early operating phase of iteR is required, preferably resulting in a validated theoretical
model for the l-mode to h-mode transition. This is particularly important since present empirical
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