OPERATION OF SECOND-GENERATION HCX DIAGNOSTICS FOR ELECTRON AND GAS EFFECTS IN MAGNETIC QUADRUPOLE MAGNETS

Abstract

We report the successful development and commissioning of new diagnostics for electron cloud and gas desorption studies on the High Current Experiment (HCX) at LBNL. These measure the time-dependent gas density in a 0.03 - 0.2 A 1 MeV K{sup +} ion beam inside of a quadrupole magnet, and the three possible sources of electrons: from ionization of gas, from beam tube walls, and from an end wall where the beam dumps. The accumulation of electrons in the beam is determined by measuring the net charge of the beam with capacitive electrodes, and other diagnostics being developed. These diagnostics are complemented by a suppressor electrode that controls the electron source from an end wall, and clearing electrodes that remove (and measure the current of) electrons from drift regions between quadrupole magnets. Measurements of electron emission coefficients and gas desorption coefficients near grazing angle enable us to infer the magnitude of beam loss needed to produce the measured electron emission and the resulting gas desorption. These new tools provide the capability to explore new areas of electron-cloud effects science, and to make quantitative comparisons with simulation.