M. Placidi

e+e− polarimetry at LEP

Abstract The design of a fast Compton-scattering laser polarimeter for LEP is outlined. Although the design is optimized for LEP at 50 GeV/beam, general considerations are extended to LEP energies up to 100 GeV/beam. Besides a recall of the physics of the polarimeter the study includes considerations on the background and consequent design of the layout, the optimization of the laser-electron beam interaction region, the specifications of the laser to fit the LEP energy range and an overview of the devices to be used as detectors for the high energy backscattered γ-beam. A 50% polarization level is expected to be measured in a few seconds with an accuracy of about 3%.

Development of a detector for bunch by bunch measurement and optimization of luminosity in the LHC

The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the LHC each absorb approximately 1.8TeV of forward collision products on average per pp interaction (~;;235W at design luminosity 1034cm-2s-1). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. Novel segmented, multi-gap, pressurized gas ionization chambers are proposed for sampling the energy deposited near the maxima of the hadronic/ electromagnetic showers in these absorbers. The system design choices have been strongly influenced by optimization of signal to noise ratio and by the very high radiation environment. The ionization chambers are instrumented with state of the art low noise, fast, pulse shaping electronics capable of resolving individual bunch crossings at 40 MHz. Data on each bunch are separately accumulated over multiple bunch crossings until the desired statistical accuracy is obtained. At design luminosity approximately 2x103 bunch crossings suffice for a 1percent luminosity measurement.

An ionization chamber shower detector for the LHC luminosity monitor

The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the Large Hadron Collider (LHC) each absorb approximately 1.8 TeV of forward collision products on average per pp interaction (/spl sim/235 W at design luminosity 10/sup 34/ cm/sup -2/ s/sup -1/). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. A novel segmented, multi-gap, pressurized gas ionization chamber is being developed for sampling the energy deposited near the maxima of the hadronic/electromagnetic showers in these absorbers. The system design choices have been strongly influenced by optimization of signal to noise ratio and by the very high radiation environment. The ionization chambers are instrumented with low noise, fast, pulse shaping electronics to be capable of resolving individual bunch crossings at 40 MHz. Data on each bunch are to be separately accumulated over multiple bunch crossings until the desired statistical accuracy is obtained. At design luminosity approximately 2/spl times/10/sup 3/ bunch crossings will suffice for a 1% luminosity measurement. In this paper we report the first experimental results of the ionization chamber and analog electronics. Single 450 GeV protons from the SPS at CERN are used to simulate the hadronic/electromagnetic showers produced by the forward collision products from the interaction regions of the LHC.

Fast polycrystalline-CdTe detectors for LHC luminosity measurements

Beam diagnostics in future high-energy accelerators will require long lived instrumentation in highly hostile radiation environments. A research program aiming at individuating new solutions and testing them under extreme operational conditions has been launched at CERN in the framework of developments for LHC instrumentation. Its outcome might be used in future accelerator projects, in industry or in physics applications. The detectors which will be adopted for the LHC luminosity monitoring and optimization will be installed close to or inside copper absorbers specifically designed for radiation protection of the accelerator magnetic elements in the interaction regions. These detectors will have to withstand extreme radiation levels and their long-term operation has to be assured without requiring human intervention. Polycrystalline-CdTe detectors have demonstrated their radiation hardness against extreme doses of X-ray exposure in the LEP collider and are considered as good candidates for LHC luminosity monitoring applications. After recalling a series of measurements obtained on CdTe samples exposed to different sources to study their time response and sensitivity we present results on their performance after irradiation at doses of 10/sup 16/ neutrons/cm/sup 2/. This is a preliminary step in the program intended to test the samples during and after irradiation up to levels of 10/sup 18/ neutrons/cm/sup 2/ and 10/sup 16/ protons/cm/sup 2/ comparable to those anticipated at the detector locations over ten years of operation of the accelerator.

Optimization of signal extraction and front-end design in a fast, multigap ionization chamber

This paper discusses the criteria that have been adopted to optimize the signal processing in a shower detector to be employed as a Large Hadron Collider (LHC) beam luminosity monitor. The original aspect of this instrument is its ability to operate on a bunch-by-bunch basis. This means that it must perform accurate charge measurements at a repetition rate of 40 MHz. The detector must withstand an integrated dose of 100 Grad, that is, two to three orders of magnitude beyond those expected in the experiments. To meet the above requirements, an ionization chamber consisting of several gaps of thickness 0.5 mm, filled with a gas that is expected to be radiation resistant, has been designed. Crucial in the development of the system is the signal processing, as the electronics noise may set the dominant limitation to the accuracy of the measurement. This is related to two aspects. One is the short time available for the charge measurement. The second one is the presence of a few meter cable between the detector and the preamplifier, as this must be located out of the region of highest radiation field. Therefore, the optimization of the signal-to-noise ratio requires that the best configuration of the chamber gaps be determined under the constraint of the presence of a cable of nonnegligible length between and detector and preamplifier. The remote placement of the amplifying electronics will require that the front-end electronics be radiation hard, although to a lesser extent than the detector.

Proton extraction from the SPS with a bent crystal

Abstract The RD22 Collaboration has performed several measurements on the extraction of protons from the CERN-SPS by planar channeling in bent silicon monocrystals. Extraction efficiencies of about 10% have been routinely achieved for a bending angle of 8.5 mrad with the SPS running at 120 GeV.