High-Intensity Thermionic Alkali Ion Sources for Plasma Diagnostics

The beam probing is widely used for the investigations of hot plasmas in thermonuclear devices. This diagnostic provides not disturbing local measurements of several plasma parameters such as the plasma density, the electron temperature, the plasma potential, and the magnetic field distributions. The atomic or ionic beams are injected into the plasma, and the secondary fluxes of ions of higher charge states or excited light radiation created during collisions with plasma particles are detected outside the plasma device. The physical characteristics of these secondary fluxes present the data for the plasma-parameter measurements. The injectors of probing beams should provide the beams of high intensity for clear discrimination of secondary signals. The ion source is the heart of any diagnostic injector. Among a variety of ion sources, the sources with solid-state thermionic emitters are commonly used in a heavy ion beam probe (HIBP) and different beam emission spectroscopy (BES) diagnostics due to their advantages in operation, such as simplicity, high enough emissivity, and capacity. This paper summarizes the results of development and investigations of the alkali (Li⁺, Na⁺, K⁺, and Cs⁺) and alkalilike (Tl⁺) thermionic ion sources with the beam current densities up to 4 mA/cm² and the emitter capacities up to 5-6 mA ldr h/cm². These ion sources are in use on currently operating injectors of HIBP (tokamaks: T-10, TUMAN-3M, and ISTTOK; stellarators: TJ-II and WEGA) and BES (ASDEX-U tokamak) diagnostics.