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

primarily electrostatic, in the case where the ion gyroradius is relatively large, and the direction of
the magnetic field lines changes rapidly within the plasma, (2) control of multiple instabilities in a
plasma surrounded by a metal vessel of finite electrical conductivity, (3) understanding high-pressure
plasmas exceeding stability limits locally or globally, (4) dynamics of magnetic self-organization
in which magnetic reconnection, dynamo, momentum transport, and ion heating occur simultaneously,
and (5) the generic linkage of these phenomena to plasma astrophysics.
Summary of Existing RFP Experimental Facilities and Other available Means
There are four RFP experiments operating in the world. (1) The mst facility at the University of
Wisconsin-madison is the centerpiece of the Us proof-of-principle RFP program. it is physically
large in the RFP context (toroidal minor radius, a=0.5 m, and major radius, R=1.5 m), but has medium
plasma current capability (ip ~ 0.5 ma). The mst program emphasizes the study of plasmas
with high confinement at high pressure made possible by control of the radial profile of the
plasma current density and by auxiliary plasma heating. it also includes investigation of current
sustainment by oscillating Field current drive (oFcd), a low frequency form of magnetic induction.
(2) The world’s largest and highest power RFP facility is RFX-mod in italy (a=0.46 m, R=2.0
m), with an achieved current of 1.5 ma and a design current of 2.0 ma. The RFX program emphasizes
RFP performance at high current and active feedback control of resistive-wall instabilities
with the most sophisticated sensing and feedback system in the world fusion program. a primary
research goal is also optimization of magnetic self-organization to improve fusion performance.
(3) a second, smaller european RFP experiment is extrap-t2R in sweden (a=0.18 m, R=1.24 m). it
also has a sophisticated sensing and feedback system, and this program is focused mainly on advanced
control techniques using this system. (4) a new, small aspect ratio RFP has recently commenced
operation in Japan. The aspect ratio is the major radius divided by the minor radius. The
RelaX device (a=0.25 m, R=0.51 m) aims to understand possible benefits of the low aspect ratio
RFP, including the possibility for substantial pressure-driven “bootstrap” current.
a number of computational tools are available for RFP research. owing to the importance of magnetohydrodynamics
in RFP physics, state-of-the-art nonlinear resistive mhd computation has
long been employed, e.g., the debs code. nonlinear two-fluid (electron and ion fluids) studies are
beginning to use new tools such as nimRod. Gyrokinetic calculations have recently been initiated,
adapting codes developed for tokamak research. similarly, simulation tools developed for
astrophysics studies are being adapted for RFP applications. The last major fusion power system
study (titan) was completed around 1990. The titan codes are still available, but they are outdated
and difficult to use.
Scientific issues and Research Requirements
eight scientific and technical issues for the RFP were identified by taP. The research requirements
for each of these are described below. table 2 at the end of this section summarizes the issues and
connections to theory and modeling, and facility capabilities.
tRanSPORt MECHaniSMS anD COnFinEMEnt SCaLing
key dimensionless parameters for transport mechanisms in the RFP are the lundquist number,
S = tR /ta ~ ipt 3/2
e /ni 1/2 , and normalized ion gyroradius, r* = ri /a. in these expressions, tR is the
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