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

• Reduction of spheromak magnetic turbulence has improved confinement. best
confinement has been obtained by tailoring the current profile to avoid low-order
rational surfaces. This was accomplished by edge direct current injection at a level
slightly below the sustainment value. The result was core electron energy confinement
consistent with tokamak l-mode scaling. (ssPX experiment).
• Whole-device, resistive mhd simulations (nimRod code) agreed well with experiments
(ssPX) and improved understanding of the coupling between transport and nonlinear
3-d magnetic evolution.
• spheromaks have been formed and sustained by the continuous injection of magnetic
helicity from an inductive source. This theoretically predicted method has achieved a 34
ka toroidal plasma current, which is nearly double the injected current. (hit-si)
• new experiments have begun to explore innovative startup and current-drive
techniques. (PbX, lanl-dRX experiments).
• basic physics experiments have advanced the understanding of the high-speed dynamics
intrinsic to helicity injection (caltech) and the understanding of magnetic reconnection
and relaxation processes (ssX, RsX experiments).
Research Requirements
The research requirements associated with each of the toroidal alternates are described. a more
detailed discussion of the scientific issues is included in the Fesac toroidal alternates Panel Report.
thE StEllaRatoR
introduction
The stellarator is a toroidal device that nominally produces all of the confining magnetic field
through use of external coils. an immediate advantage of the configuration is intrinsically steadystate
operation because there is no need for a pulsed transformer to drive a plasma current. stellarators,
having no need for noninductive current drive, could prove to be very efficient fusion
systems. Plasma startup is on existing magnetic surfaces and positional control is not needed. sophisticated
plasma control to avoid discharge-terminating current-driven instabilities is largely
eliminated.
Production of the confining fields with external currents requires that the stellarator be an inherently
3-d configuration. The 3-d shaping of the plasma provides for a broader range in design
flexibility than is achievable in a 2-d system. also, in a steady-state 3-d system there is no need
to design for large transient thermal and mechanical loads on the vacuum vessel and supporting
structure associated with abrupt confinement termination (major disruptions). however, as
shown for example in Figure 2, coil systems are more highly shaped than simple toroidal and poloidal
field coils.
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