Chan K. Choi

Impurity buildup in tokamak with radial electric fields

Abstract Fusion-product alpha-particle ash in a tokamak is not effectively controlled by a divertor, and hence may represent a limiting impurity in reactors. The capacity of a radial electric field to control ash buildup is investigated. Inward-directed fields of 5 kV/m are shown to result in a 30% enhancement of fusion energy output for a representative ash-fraction-limited burn. This output enhancement is traced to differences between the damping of toroidal rotation and resulting differences in cross-field conductivities for fuel ions and for alphas.

Advanced-fuel pellet approaches to inertial fusion☆☆☆

Inertial confinement fusion (ICF) concepts, as compared to magnetic confinement, provide an attractive approach to burning “advanced-fusion fuels” to achieve fusion. A key advantage of the ICF approach is that the absence of externally imposed magnetic fields avoids large cyclotron radiation losses. An important advantage of advanced-fusion fuels is that advanced fuels provide “cleanliness” due to less neutron production and tritium handling. Present studies focus on the A-FLINT (Advanced-Fuel Layered Ignitor/Pellet Nurturing Tritium) design which consists of a D-T fueled seed surrounded by a D-layer and appropriate tamper. A heavy-ion beam accelerator is proposed to provide adequate input-energy and efficiency. The pellet design minimizes input requirements through shock ignition of the small D-T core, providing a matchhead effect. The surrounding layers provide unburned tritium to fuel subsequent pellets, eliminating the need for a lithium blanket and simplifying the reaction vessel design.

ICF Reactor Using a 3He-Aflint Tritium Self-Sufficient Target

Alternate fuel configurations which enable tritium to be bred within the target itself could provide a significant advantage for ICF reactors since a complicated tritium breeding blanket can be avoided. The present work considers a D-fueled target (termed the “AFLINT” concept) for this purpose. A target design is proposed that achieves an internal Tritium Breeding Ratio (TBR) of ~1.1, sufficient for recycle of tritium for manufacture of subsequent targets in a “closed cycle” fashion. 3He is also recycled to obtain optimum burn conditions. For reactor studies, two driver options of Hg+1 heavy ion beams with the energies of 5 MJ and 20 MJ, and a dual liquid-fall reactor chamber are considered. For both options target gains of about 50 are obtained. The reactor chamber concept employs a thin inner liquid-fall to absorb the × rays and charged-particles energy while a second thin outer fall serves to recondense the vaporized liquid, protect the first structural wall against neutron damage, and absorb the radial momentum transfer from the disintegrating inner fall. These unique features coupled with the tritium self-sufficient 3He-AFLINT concept represent an interesting alternative to the conventional D-T reactor concept.

Effect of alpha drift and instabilities on tokamak plasma edge conditions

Abstract As suprathermal fusion products slow down in a tokamak, their average drift is inward. The effect on the alpha heating and thermalization profiles is examined. In smaller TFTR-type devices, heating in the outer region can be cut in half. Also, the fusion-product energy-distribution develops a positive slope, representing a possible driving mechanism for microinstabilities. Another instability that can seriously affect outer plasma conditions, shear Alfven transport of alphas, is also considered.