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

PLaSMa bOunDaRy intERaCtiOnS
The existing RFP facilities are not well equipped to investigate advanced control of the plasma
boundary. such control is important to prevent damage to the device wall, and to prevent influx
of impurities into the plasma. although some knowledge is transferable from research in other
concepts, there are challenges unique to the RFP. existing RFP devices employ basic material limiter
structures to protect the wall from plasma interaction, and particle control is maintained by
fueling adjustments and limiter conditioning. existing devices are also not easily modified to investigate
magnetic divertors, which allow heat flux from the edge plasma to be spread over a large
area, rather than be concentrated on a limiter. components for other strategies like pumped limiters
or a liquid wall might be testable in present devices. This is a critical area of need, and the
compatibility of boundary control solutions with confinement, sustainment, and global stability
challenges must be determined. significant boundary control capability should be considered for
any new device.
research requirements
new devices or major upgrades will be required to adequately address the plasma-boundary issue.
This research could begin in smaller devices at the concept exploration level. Possibilities for
investigation are a toroidal magnetic divertor or liquid lithium boundary. The effect of plasma
cross-sectional shape could be simultaneously investigated. since ohmic heating for smaller RFP
plasmas is substantial, it is relatively simple to efficiently attain heat flux levels relevant to future
devices in small concept exploration experiments.
some progress can be made in existing RFP facilities by improving diagnosis of the edge and core
with the goal of increasing understanding of the 3-d nature of the edge plasma, impurity influx
and production, and impurity transport. This will require a variety of probe and spectroscopic instrumentation,
and may use active techniques such as impurity injection. Going forward, a key
component of the effort to understand and control the plasma boundary will be modeling of the
edge plasma, boundary interactions, and impurity transport. This modeling effort should be coordinated
among present RFP experiments and should take advantage of the substantial tools
and understanding available in the larger fusion community. it should also be integrated with the
broader scope modeling and simulation effort that will be required to understand RFP physics.
EnERgEtiC PaRtiCLE EFFECtS
The confinement of energetic particles (especially ions) and their affect on stability are largely unexplored
for the RFP. although some knowledge, both experimental and theoretical, is transferable
from other configurations, unique physics is also expected. While particle orbits are more
nearly classical in poloidal-field-dominated plasmas like the RFP, concerns include direct orbit
losses at lower magnetic field and nonclassical loss associated with magnetic turbulence. The
planned installation of ~1 mW neutral beams in mst and RFX-mod will provide first-time assessment
of energetic particle effects in the RFP with the ion speed comparable to alfvén speed,
and with the energy content comparable to that of the plasmas.
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