Collider Project Research Articles

New technique for quality factor measurements inundamped and damped cavities

A new method for measuring quality factors in cavities is presented. This method is capable of measuring Q-factors in heavily damped as well as in undamped cavities. In addition, the possibility of separating overlapping modes and measuring their Q-factors is provided. Measurements on HOM (higher order mode) damped cavities for the DESY/THD linear collider project are presented.

Photocathodes tested in the dc gun of the CERN photoemission laboratory

In the framework of the CERN linear collider project (CLIC) the CLIC test facility (CTF) uses a laser driven photocathode in an rf gun as an electron source. Photocathode properties are measured in the photoemission laboratory, which contains a preparation chamber and a dc electron gun, followed by a beam measurement line. Cathodes are illuminated by a nanosecond UV YAG laser. The present note concerns the present installation and summarises different photocathode tests on metallic as well as alkali cathodes. Those used in the rf gun of the CTF are particularly emphasized.

Cryogenic benches for superfluid helium testing of full-scale prototype superconducting magnetsfor the CERN LHC project

The Large Hadron Collider (LHC) project at CERN will make massive use ofhigh-field superconducting magnets, operating below 1.9 K in pressurized superfluid helium. Reception testing of these magnets requires dedicated cryogenic facilities, consisting of an array of single-magnet test benches fed from a common large-capacity refrigeration system. Following installation and commissioning of general. cryogenic infrastructure, we have designed and constructed two such cryogenic benches, and are operating the first one for tests of 10-m long LHC prototype dipole cryomagnets supplied by European industry. We describe system architecture, cryogenic process and constructional features of these benches in the following, and report on test results in a companion paper.

Superfluid helium cryogenics for the large hadron collider project at CERN

The Large Hadron Collider (LHC) at CERN will be the next research instrument of high-energy physics. Colliding protons at 14 TeV center-of-mass energy and high luminosity, it will probe the structure of matter down to an unprecedentedly fine scale, thus allowing to reproduce in the laboratory phenomena which occurred in the very early universe. On the technological side, the LHC makes use of high-field superconducting magnets for guidance and focusing of the particle beams around the 26.7 km circumference of the machine, to be installed in the existing LEP tunnel. The nominal bending field of 8.65 T is produced in some 1300 twin-aperture dipoles, wound with small-filament Nb Ti conductor, and operated below 1.9 K in static baths of pressurized helium II, thus taking advantage of its specific properties as cooling fluid. We present the main technical challenges of the LHC cryogenic system, and review the actions of development and the preparatory work in progress.

A facility to test short superconducting accelerator magnets at Fermilab

The superconducting magnet R&D facility at Fermilab (Lab 2) has successfully tested superconducting dipole, quadrupole, and correction coil magnets less than 2 m in length for the Superconducting Super Collider (SSC) project and the Tevatron D0/B0 Low- beta Insertion. The authors describe the Lab 2 facility and the several upgrades which were developed to accomplish these successful test programs. Several improvements have been made to the facility that have greatly enhanced its magnet testing capabilities. Among the upgrades have been a new rotating coil and data acquisition system for measuring magnetic fields, a controlled flow liquid helium transfer line using an electronically actuated cryo valve, and stand-alone systems for measuring AC loss and training low current Tevatron correction coil packages. Tests are performed in vertical dewars of boiling liquid helium. >

Fabrication and test results of a twin-aperture superconducting dipole model magnet for LHC

In the research and development program for the Large Hadron Collider (LHC) project at CERN the construction of superconducting dipole magnets with a twin aperture plays an important role. The design value of the magnetic field produced by these magnets is 10 T at superfluid helium temperatures below 2 K. One of the 1-m-long model magnets in the program has been built by HOLEC. The behavior of this magnet under cryogenic conditions has been investigated twice: first, after the collaring of the superconducting coils had been completed and, second, after the completion of the magnet, i.e., after assembling the iron yoke and aluminum shrinking cylinder. This procedure has made possible a study of the influence of the iron yoke and shrinking cylinder on the training behavior of the magnet. The test results of this model magnet show that the design value of the magnetic field is feasible and that the mechanical structure can withstand the forces.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comments on the Workshop on techniques to study Cosmic Rays with E&gt;1019eV

Jim Cronin asked me and other colleagues to attend this Workshop to provide a critical point of view from non-expert scientists on the future developments needed to study Cosmic Rays at the highest energy. Being from outside this field, most of my comments will therefore be quite naive. I will take advantage of my involvement in the large Hadron Collider project to make comparisons and try to extract some general comments and guidelines.

Design concept and first experimental validation of the superfluid helium system for the Large Hadron Collider (LHC) project at CERN

The superconducting magnets of the CERN Large Hadron Collider (LHC) project must be kept at their operating temperature of 1.9 K all around the 26.7 km circumference of the machine ring. For this purpose, they are immersed in static baths of pressurized helium II, acting as heat transport medium to a heat exchanger tube running along the magnet string, in which flowing saturated helium II absorbs the deposited heat at constant temperature. Proper operation of this cooling scheme requires stability of the two-phase helium flow and adequate heat transport across the helium II heat exchanger. To investigate these issues, we have conducted tests on heated two-phase flow of saturated helium II in a 24 m long tube simulating the magnet heat exchanger.

Precision heat inleak measurements on cryogenic components at 80 K, 4.2 K and 1.8 K

We have built and are operating a test bench for precision heat inleak measurements and thermal qualification of components for the superfluid helium cryostats of the CERN Large Hadron Collider (LHC) project. The bench features the three temperature levels used for heat interception in the LHC cryostats. The heat loads are measured using both calibrated thermal conductances (“heatmeters”) and standard boil-off methods. After validation of the measurement methods, we compare experimental results with thermal design calculations on a prototype magnet support post.

Enjeux technologiques du LHC, le grand collisionneur de particules supraconducteur en projet au CERN

The LHC lprge superconducting particle collider project is presented, with particular emphasis on its major technological requirements and retums, mostly in the domains of high-field electromagnets, superfluid helium cryogenics, and integration of such advanced techniques in a large machine. The corresponding cooperation and technological transfer to European laboratories and industries and briefly discussed.

Photon‐stimulated desorption yields from stainless steel and copper‐plated beam tubes with various pretreatments

Photon‐stimulated desorption (PSD) from the walls of electron storage rings and associated beamlines imposes serious limits on their beam quality and beam lifetimes. Stainless steel (SS) is the most used material for beam lines and its use has become more dominant for dedicated light sources. Copper‐plated SS beam pipes have been selected for the superconducting super collider (SSC) project. Three‐meter‐long tubes of 3, 8.8, and 10 cm diameter were prepared using the following pretreatments common in storage rings. The samples were chemically cleaned only, vacuum baked to 200 °C, vacuum fired to 950 °C, and argon–oxygen glow‐discharge conditioned. A dedicated beam line at the National Synchrotron Light Source was used to measure PSD from the samples. Desorption was measured as a function of beam current during exposure to white light having a critical energy of 500 MeV. Our results are presented and compared with PSD from previous work on aluminum and SS here and at other laboratories. Glow‐discharged SS ...

A determination of the shear strength parameters of a fine-grained cemented alluvium in the US Desert Southwest

Abstract Laboratory determination of shear strength parameters for alluvial soils in the US Desert Southwest is imprecise at best. These soils contain varying amounts of carbonate cementation and it is extremely difficult to acquire undisturbed samples using conventional soil sampling techniques. Furthermore, even when samples can be retrieved, they are usually not representative of the in situ soil which can demonstrate a wide range of cementation. Therefore, the results of laboratory strength testing may not be representative of the actual in situ behaviour. For these reasons, a simple field test is developed which may be used in conjunction with conventional laboratory testing and analytical procedures to estimate the in situ strength properties of such alluvial deposits. The in situ testing involves a series of plate load tests performed at the crest of freshly cut slopes. A steel plate of known dimensions is loaded by an 89 kN (10 tons) hydraulic jack until the slope fails. The counter weight of a power shovel is used as a reaction support. The failure load and slip surface geometry are measured and recorded. A two-dimensional slope stability procedure (Bishop’s Modified Method) is used to back calculate the value of cohesion associated with failure of the field slopes. The analytical procedure developed by Hovland is used to account for the three-dimensional ‘end effects’ present in the field load tests and to correct the value of cohesion obtained from the Bishop solution. The values of c and φ obtained in this way are used to evaluate the stability of the trench slopes at the State of Arizona’s site for the US Department of Energy’s proposed Superconducting Super Collider (SSC) Project. The determination of a realistic factor of safety during construction is critical to the economical use of open-cut construction techniques for approximately 50 per cent of the 83.7 km (52 miles) circumference of the proposed SSC ring.

Progress on the superconducting magnets for the Large Hadron Collider

After a review of the proposed CERN Large Hadron Collider (LHC) project, the present design of the high-field superconducting magnets is described. One half of each standard cell for the ring of the magnet system under development consists of four ( approximately 10-m long) dipole magnets, a focusing quadrupole magnet, a tuning quadrupole, a combined sextupole/dipole corrector magnet, and a beam observation station. Only the main features of the dipole design are given. Both presently possible routes to high-field/high-current density magnets, using NbTi superconductors at superfluid helium temperatures or Nb/sub 3/Sn at 4.5 K, are summarized. Other major systems such as the vacuum chamber, proton synchrotron, and cavities are also noted. The work then presents the main aspects and the first results of the research and development program that was undertaken in close collaboration with various European industries and laboratories. Emphasis here is on the development of suitable NbTi and Nb/sub 3/Sn wires and cables, and the construction of magnet models (1-m long) and of a 9-m long twin-aperture prototype dipole.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The relativistic heavy ion collider project: A status report

The relativistic heavy ion collider project: A status report

The relativistic heavy ion collider project at Brookhaven

The Relativistic Heavy Ion Collider (RHIC) facility will provide collision energies of 100 GeV/nucleon per beam for heavy ions as massive as gold. RHIC will use the existing Brookhaven AGS and Tandem Van de Graaff as injector. The new accelerator facility, which is a nuclear physics initiative, will utilize the existing facilities of the partially completed CBA project. This report discusses the physics motivation for such a facility, the status of the machine design, R&D work and preparations for experiments at RHIC.

Discovery of the W and 2 bosons

Abstract The experimental discovery of the W and 2 bosons at CERN in 1983 confirmed the detailed predictions of the electroweak theory, which unifies the electromagnetic and weak nuclear forces. After a brief introduction to the most important ideas in this force unification, this account describes the antiproton-proton collider project at CERN. This provided the energetic collisions which enabled the W and 2 bosons, which are around one hundred times heavier than a proton, to be produced for the first time. These heavy particles are produced only very rarely in such collisions and as they decay within 10−-24s, their discovery relied on sophisticated detectors and analysis techniques. This article describes how the evidence for these new particles was extracted from the study of millions of antiproton-proton collisions and includes a first hand account of the exciting experimental runs which led to the discovery of the W−, W+ and Z0 bosons in 1983.

Trends in new collider experiment data acquisition systems

New collider projects such as the SLC and the Tevatron in the States, or LEP in Europe are underway and future generation machines are under consideration for investigation of the TeV domain of high energy physics. Spectrometers at these facilities are of growing size and complexity due to both the increase in energy and the introduction of new detection techniques. The resulting trigger and data acquisition systems have to treat enormous data volumes. New approaches have to be adopted to deal with the collection and filtering of event data. The availability of high performance micro- and specialised processors and of high speed modular bus systems allows the design of data acquisition architectures which are versatile and powerful enough to ensure safe event collection in a form suitable for prompt analysis of new physics processes.

Programmable Synchronization Unit

A Programmable Synchronization Unit (PSU, 135-726) has been designed as an element of the new timing system for the Stanford Linear Collider (SLC) project to provide synchronization signals needed for various apparatus in the SLC Damping Ring, or anywhere it is necessary to monitor longer than the fiducial period (?2.8 ?s). A 119 MHz pulse train derived from the 476 MHz main drive line and superimposed with 360 Hz fiducial signal is the frequency source. Following a programmable delay D of up to 4.4 ?s, the PSU can deliver N pulses of width W (in increments of 8.4 ns) with a pulse period of P (in increments of 58.8 ns, the damping ring half period). The device may be programmed at any time during the interfiducial period.

Nobel Prize to Rubbia and van der Meer for Finding W and Z

Carlo Rubbia and Simon van der Meer of CERN share the 1984 Nobel prize in physics for “their decisive contributions to the large project which led to the discovery of the field particles W and Z, communicators of weak interaction.” In 1976 Rubbia and his collaborators had the idea of converting the Super Proton Synchrotron at CERN into a proton-antiproton collider, where the W and Z particles could be created. In 1968 van der Meer had invented the method of stochastic cooling, which allowed the dense packing and storage of enough antiprotons to make the W and Z in pp̄ collisions. The CERN pp̄ collider project, the largest ever to appear in the context of the Nobel prize, yielded its first collisions in 1981. Two year later, in 1983, both the W and Z were observed by the UA1 detector group led by Rubbia and by the UA2 detector group. The Royal Swedish Academy of Sciences, in announcing the award, said, “Two persons in the CERN project are outstanding—Carlo Rubbia, who had and developed the idea, and Simon van der Meer, whose invention made it feasible.” This year's prize, which is worth about $193 000, is the first to honor work done at CERN.

ＳＳＣ計画の概要

An outline of the Superconducting Super Collider (SSC) project, a 20TeV on 20TeV proton-proton collider, is given. The SSC will have immense potential for major advances in understanding the nature of matter. Background information and specifications for the three different types of superconducting magnet with emphasizing various magnetic fields (low field option 3T, medium field option 5T, high field option 6.5T) are provided. Also discussed are specific R & D needs of the SSC project.