High resolution RTE measurements at 0 degrees using a hemispherical analyser with lens and 2-D PSD

First high resolution measurements using a new electron spectrograph at 0 d egrees to the beam direction are reported. The new apparatus consists of a hemispherical analyser with a mean radius of 101.6 mm, a 4-element focusing lens and 40 mm diameter 2-D position sensitive detector (PSD). Electrons a re decelerated and focused in the lens prior to analysis to improve the ene rgy resolution. As a test of the apparatus in deceleration mode, we measure d the differential cross section of the F7+(2p(2))D-1 state produced by Res onance Transfer Excitation (RTE) in collisions of 21.78 MeV F8++ H-2. An ef fective energy resolution of 0.25% was obtained using a deceleration factor of 4. Good agreement with known cross section Values was found. Presently, our spectrograph with a maximum count rate of about 4 kHz (limited by dead -time considerations) is more than 15 times faster than the conventional ta ndem zero-degree spectrometer at Kansas State University, while using a fac tor of 20 lower intensity beams. (C) 1999 Elsevier Science B.V. All rights reserved.