Investigation of ion trapping in high-power electron beams for electron coolers

Abstract

Electron coolers utilize high-current electron beams to counteract emittance blow up of hadron beams circling in storage rings with equal velocity, by enveloping the hadrons and transferring their momentum to the electrons in a dedicated cooling section of the accelerator. To achieve effective cooling, electron beams with currents in the Ampere regime are required. Diagnostics of such high-current electron beams is crucial for effective operation. In this thesis, the possibility of using beam induced fluorescence (BIF) of residual gas as a means of beam diagnostics was investigated. At the electron cooler test bench located at Helmholtz-Institute Mainz the BIF signal, which is caused by ionized residual gas particles trapped in the electromagnetic potential of the electron beam, indicated the center of charge and the boundary of said electron beam. A simple model, describing the intensity distribution of the BIF, could be established. Brief beam interruptions were used to significantly suppress the BIF, while preserving a large duty cycle. It also became evident, that the residual gas in the ultra-high vacuum vessel of the test bench is infused with barium, evaporating from the dispenser cathode, which in turn influences the BIF. This type of cathode is commonly used in most applications that rely on high DC beam currents. In addition, the electron source was improved to be more robust against Penning discharges for certain electromagnetic field configurations, allowing for an electron beam current of 1A.