  The measurement of the electron energy distribution (EED) of electrons
escaping axially from a minimum-B electron cyclotron resonance ion source
(ECRIS) is reported. The experimental data were recorded with a
room-temperature 14 GHz ECRIS at the JYFL accelerator laboratory. The electrons
escaping 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
in the range of 5 - 250 keV is strongly non-Maxwellian and exhibits several
local maxima below 20 keV energy. It was observed that the most influential ion
source operating parameter on the EED is the magnetic field strength, which
affected the EED predominantly at energies less than 100 keV. The effects of
the microwave power and frequency, ranging from 100 to 600 W and 11 to 14 GHz
respectively, on the EED were found to be less significant. The presented
technique and experiments enable the comparison between direct measurement of
the EED and results derived from bremsstrahlung diagnostics, the latter being
severely complicated by the non-Maxwellian nature of the EED reported here. The
role of RF pitch angle scattering on electron losses and the relation between
the EED of the axially escaping electrons and the EED of the confined electrons
are discussed.
