Space Charge in Channel Multipliers

Abstract

This chapter discusses the various aspects of the space charge in channel multipliers. The phenomenon of the space charge saturation that occurs in channel multipliers is described, where a cloud of secondary electrons is built up from one electron by the process of electron multiplication. The cloud travels along the tube growing steadily. Within it a space charge potential is created that reduces the time of flight and the gain in energy of the secondary electrons. The space charge density has its maximum value when one secondary electron is emitted from the wall at each impact of an electron from the cloud. The theoretical considerations are based mainly on some assumptions, including the wall potential is a linear function of the axial coordinate and the axial extent of the cloud is large compared to the tube diameter. The theory does not hold in an intermediate range between space charge free and space charge limited operation. It is also assumed that the initial velocities of the secondary electrons exhibit a Maxwellian distribution. The theory predicts the experimental facts to a satisfactory degree provided allowances are made for the respective properties of the tube wall.