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

• develop physics-based, self-consistent, integrated models of startup, with sufficient
predictive capability to permit an evaluation of the most promising startup approaches.
• develop a similar level of predictive capability for ramp-up systems, including
radiofrequency and neutral-beam-based systems.
• implement noninductive (or small-induction, if appropriate) startup, at a toroidal field,
b t , of order 2 tesla, and ramp-up to the multi-megampere current level.
Links to other thrusts: Theme 2, high-performance steady state; auxiliary systems
(Thrust 5)
2. Develop innovative magnetic geometries and first-wall solutions such as liquid metals to accommodate
multi-megawatt per square meter heat loads.
a. Develop and understand innovative magnetic geometries and particle control.
While many of the plasma-material interface issues are common to all high-temperature magnetically
confined plasma devices, the compact geometry of the st and operation at low normalized
density define a unique edge transport regime with much greater demands on divertor and firstwall
particle and heat flux handling. normal and transient heat and particle flux mitigation, and
control strategies beyond those used in present devices, and/or envisioned for near-future devices,
such as iteR, must be developed. These solutions must integrate favorable edge pressure levels
(pedestals) with simplified future remote handling capabilities.
actions:
• develop divertor and first-wall solutions to reduce steady-state peak heat fluxes from
the projected level of 20-60 mW/m 2 to ≥ 10 mW/m 2 and transient loads to ≥ 10 mJ/s
extrapolable to a high-duty cycle nuclear environment. Potential solutions include new
magnetic divertor configurations such as the X, super-X, and “snowflake” divertor,
volumetric momentum and power exhaust, and innovative plasma facing components,
e.g., liquid metal or “pebble” divertors. These configurations should be tested in a lowcollisionality
edge (scrape-off) layer relevant to st applications in existing and upgraded
facilities. however, new st devices may be required for demonstration of integrated longpulse
performance.
• develop efficient impurity, helium and hydrogenic density control at levels 20-30% of
the empirical (Greenwald) density limit, in combination with the proposed heat flux
mitigation techniques. Presently envisioned pumping solutions include cryopumping or
low recycling liquid metal wall and divertor.
• develop efficient plasma refueling techniques, including neutral beam fueling, pellet
and compact toroid injection, and high-density gas jets, for continuous low normalized
density, high confinement mode (h-mode) operation with an appropriate edge plasma
pressure.
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