R. DeSerio

Spherical sector electrostatic analyzers for measurements of energy and angular distributions

A method is presented for three‐dimensional trajectory calculations of charged particles in a spherical sector electrostatic analyzer. The particle motion in the entrance and exit fringe fields for particular geometries is included. With the initial conditions as input (the analyzer voltages and the particle position and velocity as it enters the analyzer field), the trajectory calculation provides the following information: (1) the position of the particle as it exits the analyzer; (2) the velocity direction of the particle as it exits the analyzer; and (3) the radial extrema of the particle trajectory within the analyzer sectors. Functions (3) determine whether the particle strikes the analyzer electrodes, while functions (1) and (2) can by used for predicting the particle’s position at any point after exiting the analyzer. Functions (2), here given for the first time, are especially useful for quantifying the response of the analyzer for position‐sensitive detection of narrow angular distributions. The...

Production and transport of convoy electrons in amorphous carbon foils

Abstract The production of free convoy electrons, emitted with velocities near the ion velocity in ion-solid collisions, is not well understood. Experiments concerning thickness-dependent yields have suggested the dominant mechanism for convoy production is electron loss to the continuum (ELC) in the bulk of the solid. Free electrons created in the bulk are subject to multiple elastic and inelastic scattering during transport through remaining layers of the solid. We discuss double-differential measurements of convoy electrons as a function of target thickness for fast O 5+ ion projectiles incident on carbon foils of varied thicknesses. Angular distributions confirm the ELC model for convoy production. From the radial broadening of the convoy cusps we have determined energy and angular spreading parameters due to postcollisional multiple scattering.

Doubly differential emission distributions for electron loss to the continuum from fast heavy projectiles in gas targets

We have constructed an apparatus which utilizes position-sensitive detector technology for the measurement of doubly differential electron emission cross-sections in ion-atom and ion solid collisions at emission angles near the forward direction. The properties of the instrument make it especially well suited for the simultaneous doubly differential measurement of electron emission processes which are centered in the frame of the projectile, and so it is of value for investigations of the well known electron capture and loss to projectile-centered continuum state processes (ECC and ELC) which have received much attention at this symposium. Further, the multichannel nature of the system leads to improved data acquisition efficiency, sometimes an important advantage for the observation of processes which require the use of heavily-subscribed accelerator user facilities. We describe here results of some of the first measurements to be made with this apparatus, specifically for the doubly differential (in velocity and angle) cross s~tion (DDCS) for continuum transfer emission from collisions of 41, 82, and 105 MeV O ~ in helium and argon gas targets. Because the projectiles carry a relatively loosely bound 2s electron into the collision, ELC processes are expected to dominate the emission characteristics.