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

Upgrades to the existing RFP facilities would be useful to demonstrate larger-fraction current
drive by oFcd, in particular agile power supplies capable of producing a wide range of inductive
voltage waveforms. This would permit assessment of critical physics issues and validation of theoretical
models with gradual investment. however, an advanced proof-of-principle facility that
provides access to high plasma current, high lundquist number, and long pulse is necessary to
demonstrate full oFcd sustainment. control of the plasma-material boundary interface beyond
that available in present facilities might be crucial to maintaining high-quality plasmas with low
impurity content.
nonlinear resistive mhd and two-fluid computation is a major research tool needed to understand
oFcd. The magnetic self-organization process that oFcd requires is anticipated to involve
mhd tearing instabilities. Furthermore, the very low frequency of the ac voltages implies that
computation must span a large range of disparate temporal scales. These are demanding needs,
requiring state-of-the-art computational tools that include relevant physics with low dissipation
(s=10 7-8 ). at high temperature, it is also anticipated that two-fluid physics will become important.
exploration of high beta at low aspect ratio is needed. While a specialized concept exploration
RFP experiment might eventually be required, collaboration on existing smaller low-aspect-ratio
devices such as RelaX or ltX should be considered. Present RFP experiments with volume average
beta of 〈b〉 =12% exceed some theoretical limits for pressure-driven instability, indicating a
need for improved understanding.
intEgRatiOn OF CuRREnt SuStainMEnt anD gOOD COnFinEMEnt
current sustainment in the RFP could be (i) steady-state using oFcd, (ii) quasi-steady-state using
a hybrid combination of oFcd and inductive current profile control, or (iii) purely pulsed. achieving
good confinement in at least one of these cases is essential, building on the resolution to the
confinement and current sustainment issues described above. noninductive current drive methods
using radiofrequency or neutral beam injection might be effective for targeted current profile
control, if power requirements are not excessive.
research requirements
The demonstration of 100% current sustainment with oFcd and addressing the scaling of confinement
with oFcd is unlikely to be accomplished in present relatively low-S experiments. numerical
simulations presently do not reach the lundquist numbers specified for the RFP iteRera
goal, nor do they employ the necessary two-fluid physics. equally important, present simulations
do not incorporate transport calculations. This is needed not only to predict transport with
oFcd, but also to understand the effect of varying transport (and plasma temperature and electrical
resistance) on the effectiveness of oFcd. Gyrokinetic simulations are not yet available to
study the compatibility of electrostatic transport and current sustainment.
at least one new facility is needed with capabilities well beyond those of mst and RFX-mod.
This facility would provide higher S as well as longer pulse duration. at least initially, the plasma
current would likely be sustained primarily by conventional induction, followed by substantial
upgrade(s).
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