Space charge effect in the Multi-ionization chamber response signal

Abstract

The ionization of the gas molecules by X-rays results in electron-ion pair production. The positive ions need several milliseconds to move from the generation position to the cathode. Conversely, the electrons require few microseconds to reach the anode plates. The accumulation of the positive ions inside the active volume, according to their slower drift, leads to space charge effect which has an influence on the signal amplitude. The Multi-channel ionization chamber is a beam monitor which is developed to measure the intensity of the incoming synchrotron radiation exposing the object and the fluctuation in the beam as a function of time. The measurements were carried out at the EDR synchrotron beam line at BESSYII. The chamber was filled with a mixture of 90% Argon and 10% Methane with a pressure of (5.7 and 10) bar. The applied electric field has been tuned from 400v/cm up to 2500 v/cm at which the space charge effect is clearly observed.