Generation Of Tokamaks Research Articles

Normal conducting steady-state toroidal magnet systems for ignited tokamaks

Normal conducting steady-state toroidal magnet systems are investigated, emphasis being placed on applications to large ignited next generation tokamaks. The study is based on water-cooled tape wound D coils. The data for the TF magnet systems are calculated in a consistent manner with a computer program including the plasma, shield, ohmic heating coil system, and geometric requirements for blanket modules, beam ducts, etc. An optimization procedure is used to find those TF coil systems which minimize cost-relevant quantities. The main results are that normal conducting TF coil systems of ignited next-generation tokamaks (following JET, TFTR, etc.) can be operated in a stationary mode and fed from the grid. Cost for electricity is a relatively small portion of the investment cost even in the case of long integral burn times (>107 s).

Description of tokamak discharges in present and future devices at Princeton PPL

The evolution in time and space of plasma temperatures and densities in typical discharges of presently operating tokamak is reviewed. The characteristics of the concomitant bombardment of vacuum walls and aperture limiters by electrons ions, neutral atoms, and photons are described together with the behavior impurities of wall and adsorbed materials in the discharge. The influence of the impurities on the plasma properties is discussed, with special consideration for cumulative effects. The discussion is extended to the extrapolated behavior of the discharges in the next generation of tokamaks at PPL.

Chemical effects of thermonuclear plasma interactions with insulator and metal surfaces

The interactions of chemically reactive ions with insulator and metal surfaces result in specific chemical effects which must be considered in sputtering, blistering, trapping and re-emission processes involving these projectiles. Chemical sputtering and chemical trapping of ion beam flux are examples of chemical interaction effects which are discussed. Bombardment of a niobium surface by oxygen and nitrogen ions results in the formation of sputtered niobium oxide and nitride molecules. The molecular species are identified and characterized by means of their vibrational spectra using isotopic substitution and matrix isolation techniques. Results using matrix isolation spectroscopy for both physical and chemical sputtering studies on materials of CTR interest are presented. Chemical trapping is evaluated as a method of chemically pumping the major fraction of ion beam flux in the divertor of next generation tokamaks.

Radial profile of alpha -particle heating in a Tokamak

An appreciable fraction of the alpha -particles produced by fusion in next generation Tokamaks or in a reactor, will be trapped in the toroidal magnetic field. The radial excursion of their orbits will exceed the width of the production profile. The broadening effect of finite orbit size on the profile of alpha -particle density, and hence of the energy transferred to the thermal plasma, is evaluated. Existing orbit analysis is not valid in the conditions of interest ( epsilon 1/2 rho theta >r, where rho theta is the Larmor radius in the poloidal field) and the orbit characteristics must first be derived. The maximum orbit width is found to be 1.64 R (2q rho /R)2/3, instead of epsilon 1/2 rho theta as predicted by the small rho theta analysis. The broadening of the alpha -heating profile will have a modest effect on the temperature distribution.

Adsorption of simple gases on evaporated boron films

At Forschungszentrum Karlsruhe, a special cryosorption vacuum pump system is being developed for use in the next generation tokamak fusion reactor ITER-FEAT. At the operation temperature of about 5 K, practically all gases can be condensed easily, except of helium and hydrogen. To bind these species as well, the panels are coated with active carbon as cryosorbent. This paper has to some extent overview character and summarises the qualification results of different carbon materials. An experimental programme has been performed to develop an optimum cryopanel set-up with respect to pumping efficiency. Within that framework, material properties were measured (pore-size, sorption isotherms) and the vacuum pumping performance was determined (influence of mixture composition). Judging from these results, the candidate carbon was chosen with which more in-depth studies were made. Strong selectivity effects for the simultaneous sorption of hydrogen and helium were revealed. He sorption, which is very sensitive to temperature fluctuation, was shown to have the predominant influence on the overall pumping speed. The poisoning influence due to the accumulation of air-like and water-like substances was also quantitatively assessed. The observed effects were moderate. To gain a better understanding of cryosorption, a cryocooler-based sorption device which is currently being built, was developed to perform parametric measurements of sorption characteristics in the 5–15 K temperature range.