Author: Mansfeld, D.
Paper Title Page
The Energy Distribution of Electrons Escaping Minimum-B ECR Plasma in Unstable Mode  
  • I. Izotov, D. Mansfeld, V. Skalyga
    IAP/RAS, Nizhny Novgorod, Russia
  • T. Kalvas, H. A. Koivisto, R.J. Kronholm, O.A. Tarvainen
    JYFL, Jyväskylä, Finland
  Funding: The work was supported by Russian Science Foundation, Grant No. 16-12-10343.
ECRIS plasmas are prone to kinetic instabilities associated with strong microwave emission and bursts of energetic electrons escaping the confinement*. It has been proven** that the instabilities restrict the parameter space available for the optimization of extracted beam currents of highly charged ions. Here we report the measurement of the electron energy distribution (EED) of electrons escaping axially from a minimum-B trap in unstable mode of operation where the Bmin/BECR-ratio exceeds a certain threshold value. The experimental data were recorded with 14 GHz ECRIS at the JYFL accelerator laboratory. The electrons escaping the unstable plasma through the extraction mirror of the ion source were detected with a secondary electron amplifier placed downstream from a dipole magnet serving as an electron spectrometer with 500 eV resolution. It was discovered that the EED is strongly non-Maxwellian. The comparison to EEDs acquired in stable mode, i.e. below the threshold Bmin/BECR-ratio, shows that a "hot" electron fraction with energies in the 200-300 keV range might be responsible for the development of periodic cyclotron instabilities.
* I Izotov et all, Plasma Sources Sci. Technol. 24 (2015) 045017 (9pp)
** O. Tarvainen et all, Review of Scientific Instruments 87, 02A703 (2016)
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