Ignition Physics in Multiscale Plasma Turbulence

Abstract

Tokamak machines designed to reach ignition during a transient pulse driven by the transformer action of the primary voltage applied with coils in a central solenoid have a long history. Such tokamaks, however, are yet to be built on the scale required to test the ignition hypothesis. Tokamaks designs in this class include the Compact Ignition Torus CIT, Fusion Ignition Research Experiment FIRE and IGNITOR. The compact high-field IGNITOR design is the most extensively developed design. In this chapter we show the performance projections for the IGNITOR machine made with the multiscale transport codes called JETTO and the MMM model. The parameters and characteristics of that typical high-field tokamak design are given in this chapter. Currently, there are plans to built a version of this compact high-field tokamak machine in Troisk under an agreement between Italy and Russia. The general description of IGNITOR is found at http://www.frascati.enea.it/ ignitor/.The basic plan for this type of tokamak is to use the natural ohmic heating to the maximum extent that technology will allow. As shown in Chapter 15 the energy confinement time scaling law is most favorable for the intrinsic plasma heating produced by Coulomb collisions relaxing the transformer driven plasma current I p driven by the toroidally symmetric voltage V loop . When auxiliary power P aux from neutral beams or radio frequency antennas is applied the energy confinement time degrades, as detailed first in the Kaye-Goldston scaling law in PLT. The confinement time is found to decrease with applied P aux as τ E ∼ 1/(P 1/2 aux ). The reason for this degradation, as explained in Chapters 13-15, is that as the auxiliary power P aux increases, the level of the drift wave turbulent transport rapidly increases.The issue with using the natural ohmic heating of ηj 2 to reach the temperature required for ignition, which is at least 10 KeV, is that the plasma resistivity η decreases with increasing temperature and thus the plasma temperature reaches a plateau for a given geometry and toroidal magnetic field strength. To reach the ignition temperature with ohmic heating alone, the plasma current density j must 420 Turbulent Transport in Magnetized Plasmas Downloaded from www.worldscientific.com by NANYANG TECHNOLOGICAL UNIVERSITY on 08/23/15. For personal use only.