An electrostatic sweep plate device for simultaneous measurement of angle and energy of low-energy ion beams

Electrostatic sweep plate devices have been used previously to measure the emittance of the beam extracted from an ion source. The devices operate by recording the intensity of the beamlet that passes through a small (∼ mil) entrance and exit slit as the voltage on the sweep plates is swept between preset values. The angular distribution of the beamlet is inferred from the measured intensity as a function of voltage. One of the assumptions of this method is that the energy of the ions is known and is constant. Therefore, any change or miscalculation in the beam energy during the measurement will produce an error in the calculated angular distribution. In this paper, a design change that permits the simultaneous measurement of angle and energy distribution of each beamlet will be described. The change requires multiple slits at the exit of the device and the measurement of the intensity distribution of the beam passing through each exit slit. Each distribution represents a nonindependent measurement of the angle and energy of the beamlet. Multiple measurements permit the separation of the two parameters. A change in the energy of the beam will be immediately apparent. In addition, the absolute beam energy may be independently verified using this method. A discussion of the resolutions and limitations of the method will be presented