H. Schmickler

Diffraction dissociation at the CERN pulsedpp collider at c.m. Energies of 900 and 200 GeV

Cross-sections for diffractive particle production and pseudorapidity distributions of the decay products of diffractive states are presented. The data were obtained with the UA 5 streamer chamber detector at the CERNpp Collider operated in a new pulsed mode yieldingpp interactions at c.m. energies of 900 and 200 GeV. Data recorded with a special trigger designed to select a sample of events enriched in single-diffractive interactions clearly favour apt-limited fragmentation of diffractive states. The cross-section for single-diffractive particle production ϊ was found to be 7.8±0.5±1.1 mb at 900 GeV and 4.8±0.5±0.8 mb at 200 GeV (first error statistical, second systematic). From the pseudorapidity distribution of diffractive states we deduce the average number of charged particles to be 6.5±1.0 at 900 GeV and 4.1±1.1 at 200 GeV. Furthermore we report on our estimates for the cross-section of double-diffractive particle production at both Collider energies.

The UA5 High-Energy anti-p p Simulation Program

Abstract The UA5 Monte Carlo program, consisting of a non-diffractive event generator GENCL, a diffractive event generator DIFFR and a tracking program are described. The inputs to the event generators are explained in detail. Their outputs are compared to available data from the S p pS Collider, and the agreement is shown to be good. The importance of some features of the generators are discussed. It is shown that cluster production and leading baryons are necessary to describe non-diffractive phenomena.

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.

The measurement of chromaticity via a head-tail phase shift

The most common method of measuring the chromaticities of a circular machine is to measure the betatron tune as a function of the beam energy and then to calculate the chromaticity from the resulting gradient. Even as a simple difference method between two machine energies this technique does not allow instantaneous measurements, for instance during energy ramping or beta squeezing. In preparation for the LHC, a new approach has been developed which uses the energy spread in the beams for chromaticity measurements. Transverse oscillations are excited with a single kick and the chromaticity is calculated from the phase difference of the individually sampled head and tail motions of a single bunch. Using this method the chromaticity can be calculated using the data from only one synchrotron period (about 15–50 msec in the case of the LHC). This paper describes the theory behind this technique, two different experimental set-ups, and the results of measurements carried out in the SPS.

Kaon production at 200 and 900 GeV cm energy

Abstract Results on inclusive kaon production at 200 and 900 GeV centre of mass (CM) energy obtained with the UA5 detector at the pulsed CERN SPS antiproton-proton Collider are presented and compared with our earlier data at 546 GeV. The average transverse momentum 〈 p t 〉 of kaons has been estimated to be (0.50±0.04) GeV/ c at 200 GeV and (0.63±0.03) GeV/ c at 900 GeV in the central region and shows an increase with CM energy that is smore rapid than that expected from previous ISR data. The yield of kaons per inelastic p p event is found to be (0.72±0.12) at 200 GeV and (1.31±0.14) at 900 GeV. Finally, the K/π ratio has been found to exhibit a very slow increase with CM energy.

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.

Dynamic effects and their control at the LHC

Tune, chromaticity and orbit of the LHC beams have to be precisely controlled by synchronising the magnetic field of quadrupole, sextupole and corrector magnets. This is a challenging task for an accelerator using superconducting magnets, whose field and field errors will have large dynamic effects. The accelerator physics requirements are tight due to the limited dynamic aperture and the large energy stored in the beams. The power converters need to be programmed in order to generate the magnetic functions with defined tolerances. During the injection process and the energy ramp the magnetic performance cannot be predicted with sufficient accuracy, and therefore real-time feedback systems based on magnetic measurements and beam observations are proposed. Beam measurements are used to determine a correction factor for some of the power converters. From magnetic measurements the excitation of small magnets to compensate the sextupolar (b/sub 3/) and decapolar (b/sub 5/) field components in the dipole magnets will be derived. To meet these requirements a deterministic control system is envisaged.

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.

An interleaved, model-supported system identification scheme for the particle accelerator CLIC

The particle accelerator CLIC is a future linear collider, which is developed at CERN. The quality of the particle-beams produced by CLIC is very sensitive to ground motion. The efficiency of the feedback used to counteract ground motion, relies crucially on the quality of the system knowledge. Therefore, we present a system identification scheme to follow changes of accelerator parameters. The algorithm is based on the well-known RLS (recursive least squares) algorithm with exponential forgetting, but adds modifications to improve the learning speed and to address excitation on-strains given by the system. Parallel-running, interleaved RLS algorithms identify parts of the overall system. The different results are combined by using a priori knowledge. Parts that could not be identified directly, are extrapolated with the help of physical models. The modified algorithm can follow system changes with a factor of approx. 30 improved learning speed, compared to the conventional RLS algorithm. It works robustly, in spite of sensor noise and disturbances acting on the excitation signals. The prize that has to be paid is a minimum permanent error of 13% due to model errors. The scheme can easily be adapted to other linear accelerators. Moreover it should be possible to reduce the steady-state error of the identification for other machines, since the main linac of CLIC is an especially difficult system to model and excite.

LHC beam instrumentation

Six years before the scheduled commissioning of the LHC at CERN, the basic list of beam instruments has been established. This early date is needed due to the impact of the mechanical design of some detectors (mainly the beam position detectors) on the cryogenic part of the machine as well as for other projects due to the long R&D period (emittance measurements, tune and chromaticity diagnostics and control). This paper gives a detailed overview of the basic requirements and specifications of all beam instruments foreseen for transfer lines and main rings.