Beam Diagnostics, Wire Scanners
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1 Introduction
It has always been important to measure the profile and the emittance in both planes of the circulating beam in the PS.
The first devices to be installed were fast measurement targets. Small targets are flipped on the side of the beam, their horizontal (or vertical) position is varied and measured until a specified percentage of loss is observed on a beam current transformer. They can give good information on the tails of the beam but not on the heart and they are partially destructive. The precision is reduced at lower energy since the velocity of the mechanism is too low with respect to the beam size variation.
Another development was the Ionization Beam Scanner (IBS). This electron-optical crossedfield device derives its signal from the electrons liberated by the ionization of the residual gas in the beam vacuum chamber. The proton beam is scanned in such a way that the electrons collected at any instant come from a slice of the beam close to the equipotential of the collector. This equipotential is driven through the beam to give, in time, an electrical signal proportional to the projected proton density distribution in a certain plane. It presents the advantage of a faster and repetitive measurement and low interaction with the beam. Unfortunately, several factors perturb the measurement (field imperfections, space charge from the beam etc.) and limit the use of the IBS. In 1978, a proposal was issued to derive the transverse profile of the circulating beam from the interaction between the particles and a thin wire rapidly moving through it [1]. A first version of this device was developed and it came into operation in 1985. The signal from a secondary particles monitor or the secondary emission current of the wire is sampled against the wire position and directly gives the beam profile.
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To read more visit: http://project-ps50.web.cern.ch/project-PS50/Document_draft/wirescanner-v6.pdf
