ECR–Driven Negative Ion Sources Operating with Hydrogen and Deuterium

This chapter is devoted to the fundamental principles of electron cyclotron resonance (ECR) sources yielding H− and D− negative ions. Initially, it provides a brief but meaningful overview of the theoretical framework for ECR plasmas along with commonly employed experimental configurations, unveiling thus the distinct features of this special category of high-frequency electrical discharges. It is highlighted that it is not aimed to cover the vast field of microwave discharges (e.g., microwave discharges in waveguides and resonators), nor the vast field of wave-heated discharges (e.g., helicon discharges and surface wave discharges). Such an attempt would be a utopia within the frame of one book chapter. Therefore, Sect. 12.1 of this chapter presents elementary physical quantities of plasmas, related to the ECR idea, and an idealized, simplified concept of the complex wave propagation in ECR plasmas where the wave energy absorption is achieved through collision-less heating mechanism (Firdman and Kennedy, Plasma physics and engineering. New York: Taylors & Francis Books Inc., 2004; Williamson et al., J. Appl. Phys. 72:3924, 1992). The presentation concerns low-pressure, nonthermal, and nonequilibrium plasmas. Then, the core of this review is devoted to the targeted application of ECR heating to negative ion sources operating with molecular hydrogen (H2) and deuterium (D2). Once again, the relatively vast field is impossible to be treated in the context of this chapter, but the authors hope that the cited sources are worthy representatives. Fundamental processes governing the H− and D− ion production (destruction) are summarized in Sect. 12.2, while the extended Sect. 12.3 provides recent experimental results from ECR-driven sources and comments on them in detail. Diagnostic techniques applicable to these sources are also mentioned at the beginning of Sect. 12.3. This chapter closes with Sect. 12.4, where additional ECR sources are touched upon and negative ion-extracted currents from different sources are compared. The review is throughout supported by future-proof classic or up-to-date bibliography for further reading.