SPS Accelerator Research Articles

The ZEUS forward plug calorimeter with lead–scintillator plates and WLS fiber readout

A Forward Plug Calorimeter (FPC) for the ZEUS detector at HERA has been built as a shashlik lead–scintillator calorimeter with wave length shifter fiber readout. Before installation it was tested and calibrated using the X5 test beam facility of the SPS accelerator at CERN. Electron, muon and pion beams in the momentum range of 10–100 GeV/ c were used. Results of these measurements are presented as well as a calibration monitoring system based on a 60Co source.

Deuteron production in central Pb+Pb collisions at 158A GeV

Experimental results on deuteron emission from central Pb+Pb collisions ( E beam=158A GeV, fixed target), obtained by NA49 at the CERN SPS accelerator, are presented. The transverse mass m t distribution was measured near mid-rapidity (2.0< y<2.5) in the range of 0< m t − m 0<0.9 GeV/ c 2 (0< p t <2.0 GeV/ c) for the 4% most central collisions. An exponential fit gives an inverse slope T d =(450±30) MeV and a yield dN d / dy=0.34±0.03. The coalescence factor B 2( m t = m 0)=(3.5±1.0)·10 −4 GeV 2 and its m t -dependence are determined and discussed in terms of a model that includes the collective expansion of the source created in a collision. The derived Gaussian size parameter R G of the emission volume is consistent with earlier HBT results on the source of pion emission.

The NA48 LKr calorimeter readout electronics

The NA48 experiment at the CERN SPS accelerator is making a measurement of the direct CP violation parameter /spl epsiv/'//spl epsiv/ by comparing the four rates of decay of K/sub S/ and K/sub L/ into 2/spl pi//sup 0/ and /spl pi//sup +//spl pi//sup -/. To reconstruct the decays into 2/spl pi//sup 0/ the information from the almost 13500 channels of a quasi-homogeneous liquid krypton electromagnetic calorimeter is used. The readout electronics of the calorimeter has been designed to provide a dynamic range from a few MeV to about 50 GeV energy deposition per cell, and to sustain a high rate of incident particles. The system is made by cold charge preamplifiers (working at 120/spl deg/K), low-noise fast shapers followed by digitizer electronics at 40 MHz sampling rate that employs a gain switching technique to expand the dynamic range, where the gain can be selected for each sample individually (i.e. every 25 ns). To reduce the amount of data collected the system contains a zero suppression circuit based on halo expansion.

Electromagnetic Dissociation of Au Targets by Relativistic Pb Projectiles

Electromagnetic Dissociation (ED) occurs in collisions of relativistic heavy ions involving impact parameters larger than the nuclear interaction radius. In such collisions strong electromagnetic fields acting at the nucleus can produce, for high charges and ultrarelativistic energies, cross sections much larger than the total nuclear interaction cross section. In ED collisions absorption of a virtual photon generally leads to excitation of a nuclear giant resonance. The NA53 experiment studied ED by bombarding Au targets with 158 GeV/nucleon Pb projectiles from the SPS accelerator. Preliminary values of σED for the one- and two-neutron removal processes were determined to be 26.4 ± 4.0 and 4.6 ± 0.7 barns, respectively. Theoretical predictions for σED were calculated including the effects of both the E1 and E2 giant resonances. The calculations are extended to energies planned for heavy ion collisions at the RHIC and LHC colliders.

Electromagnetic dissociation of Au targets by relativistic Pb projectiles

Electromagnetic Dissociation (ED) occurs in collisions of relativistic heavy ions involving impact parameters larger than the nuclear interaction radius. In such collisions strong electromagnetic fields acting at the nucleus can produce, for high charges and ultrarelativistic energies, cross sections much larger than the total nuclear interaction cross section. In ED collisions absorption of a virtual photon generally leads to excitation of a nuclear giant resonance. The NA53 experiment studied ED by bombarding Au targets with 158 GeV/nucleon Pb projectiles from the SPS accelerator. Preliminary values of σ ED for the one- and two-neutron removal processes were determined to be 26.4 ± 4.0 and 4.6 ± 0.7 barns, respectively. Theoretical predictions for σ ED were calculated including the effects of both the E1 and E2 giant resonances. The calculations are extended to energies planned for heavy ion collisions at the RHIC and LHC colliders.

Study of the πpi-system with the GAMS-4000 spectrometer at 100 GeV/c

The πpi-system produced in the charge exchange π−p-reaction at 100 GeV/c has been studied. The experiment was performed at the CERN SPS accelerator with the multiphoton hodoscope spectrometer GAMS-4000. A partial wave analysis was carried out in the mass range from 0.8 GeV to 3.0 GeV at −t < 0.2 (GeV/c)2 with the S, D, G and J waves. The S-wave exhibits rather complicated behaviour with a series of four bumps separated by three dips, at 1 GeV, 1.5 GeV and 2 GeV, which give the evidence for several scalar resonances. Clear peaks corresponding to the f2(1270), f4(2050) and f6(2510) mesons are seen in the higher waves. All the three mesons are produced via a dominating one pion t-channel exchange. The parameters and production cross sections of these mesons are measured.

The NA48 data acquisition system

NA48 is a CP violation experiment that is starting its period of data taking at the CERN SPS accelerator. The expected average data rate of a few thousand events/s (with the possibility to go up to 10 kHz), a data volume up to 100 MB/s sustained over the beam burst, and the necessity to handle different subsystems with very wide variation in the number of channels have lead to the design of a modular pipelined data acquisition system with a sampling rate of 25 ns.

A threshold imaging Cherenkov detector with CsI photocathodes

A Threshold Imaging Cherenkov (TIC) detector, in conjunction with a tracking device and a time-of-flight system, has been developed to allow pion, kaon and proton identification in the 3–8GeV/c range of momenta. The system allows spatial identification of the photons of particles above the Cherenkov threshold and their correlation to a particular track. The TIC detector uses a MWPC detector with a CsI coated photocathode for photon conversion. The results obtained in ultrarelativistic lead–lead collisions at the CERN SPS accelerator are presented.

The trigger system for K0→2π0 decays of the NA48 experiment at CERN

A fully pipelined 40MHz “dead-time-free” trigger system for neutral K0 decays for the NA48 experiment2Cagliari, Cambridge, CERN, Dubna, Edinburgh, Ferrara, Firenze, Mainz, Orsay, Perugia, Pisa, Saclay, Siegen, Torino, Warszawa, Wien Collaboration.2 at CERN is described. The NA48 experiment studies CP-violation using the high intensity beam of the CERN SPS accelerator. The trigger system sums, digitises, filters and processes signals from 13 340 channels of the liquid krypton electro-magnetic calorimeter. In 1996 the calorimeter and part of the trigger electronics were installed and tested. In 1997 the system was completed and prepared to be used in the first NA48 physics data taking period.

On the energy dependence of proton beam extraction with a bent crystal

Proton beam extraction from the CERN SPS by means of a bent silicon crystal is reported at three different energies, 14 GeV, 120 GeV and 270 GeV. The experimental results are compared to computer simulations which contain a sound model of the SPS accelerator as well as the channeling phenomena in bent crystals. The overall energy dependence of crystal assisted proton beam extraction is understood and provides the basis to discuss such a scheme for future accelerators.

Stopping and radial flow in central58Ni+58Nicollisions between1Aand2AGeV

The production of charged pions, protons. and deuterons has been studied in central collisions of Ni-58 on Ni-58 at incident beam energies of 1.06A, 1.45A, and 1.93A GeV. The dependence of transverse-momentum and rapidity spectra on the beam energy and on the centrality of the collison is presented. It is shown that the scaling of the mean rapidity shift of protons established for between 10A and 200A GeV at the Brookhaven AGS and the CERN SPS accelerators energies is valid down to 1A GeV. The degree of nuclear stopping is discussed ; quantum molecular dynamics calculations reproduce the measured proton rapidity spectra for the most central events reasonably well, but do not show any sensitivity between the soft and the hard equation of state. A radial Bow analysis, using the midrapidity transverse-momentum spectra, delivers freeze-out temperatures T and radial flow velocities beta(r) which increase with beam energy up to 2A GeV ; in comparison to the existing data of Au on Au over a large range of energies, only beta(r) shows a system size dependence.

Measuring the Resonance Structure of Accelerator Impedance with Single Bunches

We describe a new method used in the CERN SPS accelerator to measure the longitudinal impedance in the frequency range 100 MHz to 4 GHz. Single high intensity proton bunches were injected and their spectrum observed during slow debunching. The presence of different resonant impedances leads to line density modulation at the resonant frequencies. This instability reaches some maximum modulation amplitude which was recorded as a function of frequency for many bunches. Using sufficiently long bunches the SPS impedance structure was observed and previously unknown sources were identified.

Atomic collisions with 33-TeV lead ions

Recent availability of relativistic and ultrarelativistic beams of heavy ions has permitted the first controlled studies of atomic collisions at energies sufficient to measure effects of several new basic phenomena. These include measurements substantiating recently predicted finite nuclear size effects resulting in a reduction in the total electronic energy loss of heavy ions in matter, and measurements of Coulomb collisions in which electrons are excited from the Dirac negative energy continuum. Measurements of total energy loss, free electron-positron pair production, and electron capture from pair production have been recently performed using 33-TeV Pb82+ ions from the CERN SPS accelerator in Geneva. Results of these studies are presented, along with comparisons with relevant theory.

Resistive Plate Chambers in ATLAS

The ATLAS first level muon trigger is based, in the rapidity region | η| ≤ 1.05, on fast and finely segmented gaseous detectors, Resistive Plate Chambers (RPCs). A prototype of a small scale RPC trigger tower has been assembled and tested. We present results on efficiency, time resolution, cluster size and collected charge. The detectors, filled with a non-flammable and environment-safe gas mixture, have been operated in avalanche mode. The measurements have been made at the CERN SPS accelerator in the H8 test-beam area with muon fluxes up to 900 Hz/cm 2. A 14 mCi 60Co radiactive source has been used to illuminate the chambers with a flux of low energy photons, simulating LHC background conditions.

An accurate telescope for beam position monitoring and spatial resolution studies

A telescope designed for the study of position sensitive detectors has been used for beam position monitoring. The telescope consists of eight silicon strip detectors and it is installed in the RD5 experiment at CERN. The telescope was tested with pion and muon beams in the energy range between 30 and 300 GeV/c in the North Area of the SPS accelerator. The best impact point errors were 2.5 μm in the vertical and 2.9 μm in the horizontal direction. The signal-to-noise ratios of the detectors were around 40 and the efficiencies above 96%. The alignment of the telescope was very accurate and the correction for possible tilts did not essentially improve the performance.

Evolution of the SPS and LEP communication control network for the SPS and LEP accelerators

From its startup in July 1989, LEP continues to be the largest accelerator in operation in the world. At the present time, the controls networks cover a very large site (more than 200 km 2) integrating LEP and the SPS accelerator and interconnecting more than 1000 hosts. This paper describes the evolution of the network architecture from the commissioning of LEP until now and future trends, taking into account our experience of supporting more user requests, higher bandwidth, and greater reliability. The commercial availability of higher performance technology and market trends are considered.

Installation and management of the SPS and LEP control system computers

Control of the CERN SPS and LEP accelerators and service equipment on the two CERN main sites is performed via workstations, file servers, Process Control Assemblies (PCAs) and Device Stub Controllers (DSCs). This paper describes the methods and tools that have been developed to manage the file servers, PCAs and DSCs since the LEP startup in 1989. There are five operational DECstation 5000s used as file servers and boot servers for the PCAs and DSCs. The PCAs consist of 90 SCO Xenix 386 PCs, 40 LynxOS 486 PCs and more than 40 older NORD 100s. The DSCs consist of 90 OS-968030 VME crates and 10 LynxOS 68030 VME crates. In addition there are over 100 development systems. The controls group is responsible for installing the computers, starting all the user processes and ensuring that the computers and the processes run correctly. The operators in the SPS/LEP control room and the Services control room have a Motif-based X window program which gives them, in real time, the state of all the computers and allows them to solve problems or reboot them.

Innovative aspects of the controls for the helium cryoplants in the CERN SPS accelerator

For the cooling of superconducting accelerating cavities in the CERN SPS, two identical helium refrigerators of 400 watt at 4.5 K have been required. The first one has been in operation since 1992 and the second one was commissioned at the beginning of 1994. Both refrigerators are equipped with an industrial process control system which allows fully automatic remote operation of the entire cryoplant from ambient to liquid helium temperatures. This achievement was obtained by combining the suppliers knowledge of the refrigerators and the CERN operational experience with the capability of a modern control system. The logic of the cryoplant and its integration in the state of the art software concept, based on an object-oriented approach, are presented.

Long-term operational experience and upgrade of the cryogenic system for the superconducting cavities in the CERN SPS accelerator

Cryogenics at liquid helium temperature has been requested in the SPS for testing and operating superconducting accelerating RF cavities: in 1988 and 1989 a single LEP prototype cavity made of bulk niobium, in 1990 two cavities made of niobium sputtered copper and finally, in 1991, a single niobium sputtered cavity. To cope with the various cooling needs, we used the same refrigerator (120 watt at 4.5 K) and the associated cryosystem has been optimized to reduce the thermal load. The original transfer line has been replaced by a flexible and thermally shielded one made of six coaxial bellows. The achieved thermal performance for the various combination of superconducting cavities, the long-term behaviour and operational experience of the cryosystem are given. While the first cryosystem is maintained in operation, a new one (using a refrigerator of 400 watt at 4.5 K) is now being tested to increase, in 1992, the SPS accelerating field by means of two additional superconducting cavities. A description and the preliminary results of the new cryogenic facility are presented.

The CERN LEP-SPS Librarian system

The complexity of a software working environment, such as the control system for the SPS and LEP accelerators, requires a considerable management effort. The software needed to run the machines is continuously evolving, as new releases of application and system programs are introduced rather frequency. Ideally the management effort must coordinate all the different software developers and their users (the machine operating team). A software tool, the Librarian, has been written to help them in performing this task. Its ultimate goal is to enable the accelerator operators to retain control of all the software running in the control system. All the source files needed to produce a piece of running software (a “product”) are saved together, and can be retrieved either individually or as a whole. Management of the different versions of a product is also implemented, as well as a scheme for protections and access rights depending on the type of user (Librarian manager, application manager or software developer). The data base ORACLE has been used to maintain logical links between files saved under the Librarian.