In the quasi-gasdynamic high-current ion source described in this work, the plasma is sustained in the CW mode by high-power millimeter-wave radiation under the electron cyclotron resonance condition. The design of the source allows us to achieve high volumetric energy input of up to 250 W cm−3 and obtain proton beams with a minimum amount of impurities and molecular ions. Experiments conducted on Gasdynamic Ion Source for Multipurpose Operation facility demonstrated the proton beam formation with a current of 50 mA and a current density of 700 mA cm−2, 99.9% of which are H+ ions. Such a beam was obtained using 4.6 kW microwave power from a 28 GHz gyrotron. The high proton fraction is explained using global model based on reactions in plasma. According to calculation results, volumetric energy input of 30 W cm−3 at electron density of 6 × 1012 cm−3 is enough to achieve 99% proton fraction in plasma.
Vybin et al. (Sun,) studied this question.