Modified Thomson spectrometer for the detection of low energy (1 keV) high power ion beams
Summary form only given. The Thomson parabola spectrometer with the CR-39 nuclear track detector as detection plate has been widely used in the detection of mass and energy spectra of pulsed high power ion beams in a wide energy range from 30 keV to more than MeV. However, its application to even lower energy ion beam detection, say 1 to several keV, is limited by the threshold energy for the particle track formation of the detection plate which is usually higher than 30 keV. The pulsed high power and low energy ion beams, such as N/sup +/, C/sup +/ and B/sup +/ and so on, with energy of about 1 keV in the high energy density plasma streams generated by the coaxial plasma gun are of special interest in materials surface modification and film deposition. To solve the detection problem, we designed an after-acceleration electric field near and cross the detection plate to accelerate the ions, after deflection by the electric and magnetic fields of the spectrometer, to high enough energy for effective registration by the detection plate. The acceleration field is formed by a front grounded planar metal mesh electrode 3 mm in front of the detection plate and a back electrode applied to a pulse voltage of 50 kV behind the plate.