Investigation of hot electrons in electron-cyclotron-resonance ion sources

Abstract

The hot electrons in the plasma of an electron-cyclotron-resonance ion source are investigated by three passive diagnostics: bremsstrahlung, electron cyclotron emission, and diamagnetism. For this type of plasma the feasibility of the second diagnostic is an innovative development, as is the simultaneous use of two independent plasma diagnostics for either steady-state or transient experiments. In the steady-state experiments the bremsstrahlung and the electron cyclotron emission are interpreted by comparing the experimental spectra with simulated spectra calculated for the first time from a non-Maxwellian electron distribution. The ‘‘perpendicular temperatures’’ obtained by the two diagnostics are in good agreement. In the transient experiments the electron cyclotron emission and the diamagnetic signals are recorded to study the electron density and the electron lifetime. All these experiments performed using the Minimafios ion source working at 18 GHz with oxygen gas demonstrate trends and saturation effects when the gas injection pressure and the radio-frequency power are varied.

Electronic temperatures, densities, and plasma x-ray emission of a 14.5 GHz electron-cyclotron resonance ion source

“…We have shown that the temperature is weakly dependent on the microwave power and has, in normal operating conditions of the plasma source, a value ranging from 39 to 50 keV, independently of the injected gas. Even though the plasma volume of such a permanent magnet ECRIS is necessarily small, the electronic temperature of this source is four times larger than what has been found on a 10 GHz, R = 3.7 source (T around 11 keV) [13], and at the lower edge of the range mesured on a 18 Ghz , R = 2.6 ECRIS (T between 35 and 100 keV) [3], as expected.…”

“…[3,7], we observed no particular dependence on the injected pressure value in the range p = 1 − 10 × 10 −5 mbar. We did not observe either any dependence on the injected gas composition.…”

“…The high-energy component has a typical temperature of several tens of keVs [3] while the low-energy component has a much lower value, around 1 keV. Measured temperatures for the high energy electron population range from 5 to 13 keV for an ECRIS operated at 2.45 GHz [6,7], 40-60 keV for a CAPRICE source operated at 10 GHZ [13], and up to 100 keV for an ECRIS operated at 18 and 28 GHz [3,10]. As in the measurements cited above, our study is sensitive to the high-energy electron component due to our detection energy range of ∼ 20 − 120 keV.…”

“…The electron Bremsstrahlung spectra have been used for measuring electronic temperature in the ECRIS plasma [3][4][5][6][7][8][9][10], and high-resolution X-ray spectroscopy has been applied to characterize charge state distribution and electronic density [11][12][13][14]. Results on accurate X-ray spectroscopy, from Ref.…”

Limitation of the ECRIS performance by kinetic plasma instabilities (invited)

“…7,8 The warm electron population is responsible for electron impact ionization of highly charged ions and together with the "run-away" hot electron component carries most of the plasma energy content. 9 Only the perpendicular energy of the electrons increases in the resonance and, hence, the electron velocity distribution (EVD) is strongly anisotropic, i.e., ⟨v ⊥ ⟩ ≫ ⟨v ∥ ⟩, where the symbols ⊥ and ∥ refer to the external magnetic field.…”