Symmetric Divertor Research Articles

Mössbauer spectroscopy analysis of plasma-driven carbide formation on graphite limiters in the axis symmetric divertor tokamak experiment

The microstructure and chemical composition of dropletlike deposits formed on the surface of graphite limiters due to plasma discharges in the axis symmetric divertor tokamak experiment were analyzed using 57Fe Mössbauer transmission and conversion electron spectroscopy. It is found that the droplets consist mostly of alloy cementite, (Fe,Cr,Ni)3C, with an admixture of austenite smaller than ≂20%. The amount of cementite and the contribution of austenite depend considerably on the location of the deposits relative to plasma-drift direction, which reflects the varying conditions of metal and carbon redeposition and agglomeration in the tokamak chamber.

Applications of the Integrated-Blanket-Coil Concept to the Compact Reversed-Fi Eld Pinch Reactor

Compact reactors, by their nature, are high-power-density devices. They place a premium on space usage within the system volume, and access to the fusion power core components is limited. The integrated-blanket-coil (IBC) concept relaxes some of these requirements by combining the functions of the breeding blanket with those of the magnet systems. In this paper, the IBC potential is analyzed for the compact reversed-field pinch reactor (CRFPR) coil sets: (a) the toroidal field (TF) system; (b) the polidal field (PF) system; (c) the ohmic heating (OH) subsystem of the PF system; and (d) the divertor coils in the impurity control system. Use is made of the Los Alamos National Laboratory (LANL) RFP systems code with suitable modifications, to estimate ohmic losses, coil masses, and economic (cost of electricity) impact of the different configurations. Preliminary evaluations indicate that a symmetric toroidal divertor would be suitable for the CRFPR. This presents a special attraction for use of IBC divertor coils. Since the minority field (TF) is < 1 T at the plasma edge, the required nulling current is modest. In addition, IBC coils can be placed closer to the plasma, allowing a trade-off between the higher resistive losses and reduced current requirements.more » Perhaps most importantly, use of IBC divertor coils would improve the tritium breeding ratio, which is somewhat marginal with copper divertor coils.« less

A Comparison Study of Toroidal-Field Divertors for a Compact Reversed-Field Pinch Reactor

Two divertor configurations for the Compact Reversed-Field Pinch Reactor (CRFPR) based on diverting the minority (toroidal) field have been reported. A critical factor in evaluating the performance of both poloidally symmetric and bundle divertor configurations is the accurate determination of the divertor connection length and the monitoring of magnetic islands introduced by the divertors, the latter being a three-dimensional effect. To this end the poloidal-field, toroidal-field, and divertor coils and the plasma currents are simulated in three dimensions for field-line tracings in both the divertor channel and the plasma-edge regions. The results of this analysis indicate a clear preference for the poloidally symmetric toroidal-field divertor. Design modifications to the limiter-based CRFPR design that accommodate this divertor are presented.

Aspects of plasma-wall interaction in the ASDEX divertor experiment

ASDEX (Axially SymmetriC Divertor Experiment) is a large tokamak now under construction at IPP Garching. The main parameters are: major radius 1.65 m, plasma radius 0.4 m, toroidal field on axis 2.8 T and plasma current 500 kA. The experiment is scheduled to go into operation in about two years. The first aim of the experiment is to test the divertor action, i.e. plasma stability without material limiter and reduction of impurity influx. Since the divertor will essentially be of the unload-type, the latter problem should be solved by reducing wall bombardment. On the premises of sufficient stability the plasma-wall interaction will occur on the divertor slits, in the main divertor chamber and (with refuelling) on the wall owing to charge exchange neutrals. Plans for surface studies are being discussed.