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

tion using a central solenoid is also possible by using either mineral insulated cable or retractable
solenoid technology that both require engineering analysis to determine feasibility.
an initiation scenario using electromagnetic waves (electron bernstein wave – ebW) needs to be
developed and quantitatively compared to hi startup in the same facilities. methods for understanding
and controlling the plasma current and density evolution, the influence of plasma density
fluctuations on the wave power coupling, and the levels of plasma current produced as a function
of launched wave power need to be determined. switching from an ebW-based startup to an
alternate sustained heating and/or current drive technique must be shown.
increasing the initially formed plasma current to desired levels requires additional techniques,
including current driven by electromagnetic waves and/or energetic particles (e.g., neutral beam
injection – nbi). Radiofrequency current drive is discussed in the next section. neutral beam current
drive (nbcd) for plasma current ramp-up is largely understood, but the effects of fast-particle
instabilities on current drive efficiency must be determined using existing or upgraded facilities.
development of techniques to control electron transport during nbi current ramp-up is
needed. modeling should be performed to assess the impact on plasma stability of varying levels
of angular momentum input for varying beam conditions. an assessment of the plasma current
rate of rise compared to the plasma duration and the ability of the system to recover from disturbances
that transiently decrease plasma current is required.
RadioFReQUency heatinG and cURRent dRive
many radiofrequency techniques may be applicable in higher toroidal field (1.5 – 3 tesla) sts, such
as a ctF, to heat and/or drive current in the plasma. These include high harmonic Fast Wave
(hhFW) and ebW heating, electron cyclotron heating and current drive (ech/eccd), lower hybrid
current drive (lhcd), mode conversion heating and current drive (mch/mccd), alfvén
wave heating or current drive (aWh/aWcd), as well as other heating and current drive schemes
in the ion cyclotron range of frequencies (icRF).
The requirements of future st devices for radiofrequency heating and current drive need to be
defined.
research requirements
The applicability of various radiofrequency heating and current drive scenarios to higher toroidal
field sts, especially with significant alpha particle populations, has not been modeled with
state-of-the-art radiofrequency codes. Present designs for an st-ctF do not rely on radiofrequency
heating and current drive to sustain the plasma. needs in the plasma current initiation and
ramp-up phase are not fully known. needs for a demo operating at higher toroidal field and very
high plasma pressure are not yet defined.
central plasma heating and current drive (e.g., hhFW) is likely to be useful during both plasma
initiation and ramp-up. The sufficiency of hhFW absorption must be determined for the range
of plasma density and temperature in this period, as well as the operating frequency. The practi-
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