Measuring the Beam Profile by Counting Ionization Electrons

The principle of non-destructive beam profile measurement with rest gas ionization electrons has remained largely unchanged since the technique was first proposed in the late 1960's. Ionization electrons (or ions) are transported by an electrostatic field onto an imaging detector, where the spatial distribution of detected electrons is a direct measure of the transverse beam profile. The detector typically consists of one or more Micro-Channel Plates (MCP’s) to amplify the signal, followed by either a phosphor screen and camera, or pickup electrodes. A long-standing problem is the ageing of the MCP’s, which limits the accuracy of the beam profile measurement. A new technique to detect ionization electrons has been developed at CERN, which uses a hybrid pixel detector to detect single ionisation electrons. This allows the application of counting statistics to the beam profile measurement. It will be shown that a meaningful beam profile can be extracted from only 100 electrons. Results from the new instrument will be presented, which demonstrate the ability to measure the beam profile of single bunches turn-by-turn, which offers new opportunities for beam diagnostic insights.