Ion-Optical System with Ballistic Focusing of a Powerful Deuterium Atom Beam Injector for Plasma Heating

Abstract

To heat the plasma in the TCV tokamak (Lausanne, Switzerland), a charge exchange injector of a focused beam of fast deuterium atoms with an energy of 30 keV, a power of 1 MW, and a duration of 2 s has been developed at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences. In the ion source of this injector, a multislit three-electrode ion-optical system with spherical electrodes and an emission region with a diameter of 250 mm is used to form the beam. The angular divergence of the ion beam formed by the multislit ion-optical system is sufficiently small in the direction along the slits, which ensures accurate entry of a focused beam of fast atoms into the narrow injection port of the tokamak. During the formation of the ion beam, the electrodes of the ion-optical system are heated by secondary particles and cooling of the electrodes is required. To increase the transparency of the ion-optical system and ease the manufacture, an inertial version of cooling the electrodes was adopted. During a pulse, the rise in temperature is limited by the heat capacity of the electrodes, and between pulses, heat is transferred to the water-cooled connecting flanges of the electrodes. The performed thermomechanical analysis showed that, in order to achieve acceptable values of the longitudinal deflections of the electrodes arising from thermoelastic stresses, it is necessary to reduce the stiffness of the electrodes at the periphery of the beam formation region. This reduction was achieved by the introduction of cuts—azimuthal for the plasma electrode and radial for the accelerating and grounded electrodes. The article presents the design features and manufacturing technology of multislit electrodes of the ion-optical system.