Calibration of the Fermilab Booster ionization profile monitor

Abstract

The booster ionization profile monitor (IPM) obtains transverse beam profiles by measuring the distribution of ions resulting from interaction of the proton beam with background gas in the beam chamber. The challenge of the IPM operation is that the measured ion distribution is not an exact representation of the beam distribution, since the ion trajectories are influenced by the electromagnetic field of the beam. We have developed a new model for the dependence of the IPM measurement on the beam parameters, assuming a Gaussian beam distribution. Our model of the ion dynamics in the detector was constrained by making independent measurements of the horizontal beamwidth at injection and extraction and comparing these to data taken from the IPM at the same time. Our calibration results in the formula σ_{measured}=σ_{real}+C_{1}Nσ_{real}^{p_{1}}, where N is the number of protons in the machine, in units of 10^{12}, C_{1}=(1.13±0.06)×10^{-5}, in units of (meters)^{1-p_{1}}/10^{12}, and p_{1}=-0.615±0.013; the subscript “measured” indicates the raw IPM measurement, the subscript “real” the true beamwidth. This result is the first detailed calibration of the response of the booster IPM based on experimental data.