BUNCHED BEAM CURRENT MEASUREMENTS WITH 100 pA RMS RESOLUTION AT CRYRING

In the 52 m circumference synchrotron CRYRING molecular beams with currents down to 1 nA are often used for experiments. To extend the rms resolution of the bunched beam current measurements down to 100 pA a Bergoz Integrating Current Transformer (ICT) and the sum signal from a capacitive pick-up (PU) are integrated simultaneously. Initially a high current is measured and the ICT signal is then used to calibrate the PU signal. The low noise PU signal can than be used to measure the current. The absolute calibration of the pick-up signal is obtained during 20-60 ms after the acceleration. For both detectors low noise amplifiers and differential input double integrators have been designed. A programmable phase shifter makes it possible to measure the beam current during the acceleration of the ions generating a gate signal for the integrators.