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

developing steady-state scenarios for iteR is also in line with the research required for a tokamak
demo, since demo operation is foreseen to be steady state. however, the fusion gain of 5 targeted
for iteR’s steady-state mode is well below that required for an economic power plant. Thus,
the thrust toward steady-state research should be aimed not only to enable the iteR steady-state
goal to be reached, but also to establish the basis for a steady-state demo. The difference between
iteR’s needs and those of a demo can be measured by the bootstrap current fraction (with the
remainder of the plasma current driven by neutral beams or radiofrequency waves); in iteR the
bootstrap current fraction is about 50%, whereas in demo a bootstrap current fraction of 80%
or more is projected.
much of the research required for extending the pulse length on iteR can be carried out on the
existing domestic tokamaks with enhanced capabilities. sufficient current drive tools should be
added to ensure that the physics of both hybrid and at scenarios could be adequately investigated.
as a first step, this could be accomplished by doubling the electron cyclotron current drive
power on diii-d, the neutral beam current drive power on nstX, and the lower hybrid current
drive power on alcator c-mod. as different current drive methods have distinct advantages in
their ability to tailor the current profile, future steps may require diversifying the mix of methods
on each facility. additional contributions will be made by the international programs, in particular,
Jet and the new superconducting asian tokamaks with their much longer pulse length.
however, to maximize the prospects for iteR’s success, it is necessary as far as practical to develop
integrated scenarios, i.e., scenarios that simultaneously achieve the high-performance core,
edge, and steady-state conditions as measured by the standard dimensionless parameters (e.g., b,
n*, and r*). achieving such integrated performance and the underlying scientific understanding
may require a new Us facility with lower r* than is currently achievable.
Required facility capabilities. answering these types of burning plasma questions prior to
and during iteR operation will require supporting tokamak research facilities with the tools necessary
to reproduce, study, and control plasma conditions as similar as possible to those in iteR
(with the exception of tritium usage and fusion self-heating). desired attributes for these supporting
facilities include:
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Figure 3. Example of a steady-state advanced tokamak
discharge from DIII-D: (a) normalized beta and
electron cyclotron current drive power, (b) surface
loop voltage, and (c) noninductive and bootstrap current
fractions. (Figure courtesy of Chris Holcomb.)