Collider Project Research Articles

Simon Peter Rosen

Simon Peter Rosen

Mechanical Properties of High RRR Niobium With Different Texture

High purity bulk niobium RRR ~ 300 is the standard material used for SRF cavities since this has been the most promising material for over 10 years. Mechanical properties of the high RRR niobium play a critical role in the physical integrity of these structures. It is well known that the mechanical properties of polycrystalline high RRR niobium are affected by a variety of possible contributors: crystallographic texture, grain size, and impurity concentration. Tensile tests were carried out using three groups of niobium samples from MSU SRF cavity and Fermi International Linear Collider projects with different texture and grain size, which came from two different manufacturers. For some of the groups the tensile tests were done with different orientations with respect to the sheet. Orientation Imaging Microscopy (OIM) data were collected in these samples. The relationships between mechanical properties, texture, and grain size in these samples are analyzed.

The Search for New Physics Phenomena using e-e- Collisions in the CLIC Energy Range

The International Linear Collider project, now no longer on the back burner, finds its natural sequel in the several-TeV realm by relying on CLIC technology. We briefly home in on a few of those physics processes initiated by e-e- collision where the extension to that higher energy region is likely to be of major importance.

Angular distributions of 7 TeV protons axially channeled through the thin bent 〈1 0 0〉 Si crystal

We have studied theoretically angular distributions of relativistic protons axially channeled through the thin bent 〈1 0 0〉 Si crystal. The proton energy is 7 TeV, the thickness of the crystal is 1 mm, which corresponds to the reduced crystal thickness, Λ, equal to 2.1, while the bending angle, α, is varied from 0.002 to 0.020 mrad. The angular distributions of axially channeled protons are generated by the computer simulation method using the numerical solution of the ion equations of motion, with the Lindhard’s expression for the continuum interaction potential of the ion and the crystal. Uncertainness of the scattering angle of the proton caused by its collisions with the electrons of the crystal and proton (electronic) energy loss are taken into account. The results of the analysis show that the two additional maxima appear in the angular distributions, for the bending angles α ⩽ 0.006 mrad. They originate from four areas in the impact parameter plane located in between atomic strings defining the channel that correspond to the saddle points of the continuum potential. The obtained deflection efficiency curve has an inflection point, which can be attributed to the disappearing of the two additional maxima in the angular distribution. We have also studied the dependence of the deflection efficiency on the length of the crystal when the deflection angle is equal to 0.1 mrad, regarding the possible application of the crystal channeling for halo collimation of the proton beam in the Large Hadron Collider (LHC) project, at the European Organization for Nuclear Research (CERN).

CCD-based vertex detector for GLC

As a charged particle tracking device, CCD pixel sensors are expected to have very high performance because of the excellent spatial resolution and the very thin material thickness of the sensitive layer. We have been executing R&D of a CCD vertex detector for Global Linear Collider (GLC) project. In this article we mainly present recent results of radiation damage tests of CCDs irradiated with low-energy β -rays and with a high-energy electron beam.

CERN Large Hadron Collider projects to improve the radiation hardness of ionizing radiation detectors: The role and control of defects in Si and potential of GaN

J. Vaitkus , A. Blue , W. Cunningham , E. Gaubas , J. Grant , K. Jarasiūnas , A. Kadys , V. Kalendra , V. Kažukauskas , P. Pobedinskas , V. O’Shea , K. Smith , J. Storasta , and A. Žukauskas a a Institute of Materials Science and Applied Research, Vilnius University, Saulėtekio 10, LT-10223 Vilnius, Lithuania E-mail: juozas.vaitkus@ff.vu.lt Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland, UK

The discovery of the W and Z

We briefly discuss the genesis of the CERN antiproton–proton collider project aimed at discovering the intermediate vector bosons W and Z, describe the main features of the UA1 and UA2 experiments, as well as the initial search and discovery of the W and Z. We also review the subsequent improvements in the determination of the basic electroweak parameters of the W and Z and of their QCD production properties as they evolved over the ten years of operation of the CERN antiproton–proton collider.

The Large Hadron Collider project: historical account

This article gives a historical account of the origin and the development of the design of the Large Hadron Collider, the low-temperature superconducting collider being built at CERN. The basic choices of the superconducting technology, based on NbTi cables cooled at 1.9K by superfluid helium, and of the magnet structure, the twin-aperture configuration, are reviewed in some details. The centre-of-mass energy is 14TeV for protons and 1148TeV for lead ions (2.76TeV/u). The expected luminosity is 1034cm-2s-1 for protons and 1027cm-2s-1 for lead ions. After a long phase of construction and testing of magnet models and prototypes, the industrial production of all components is well under way, with hundreds of magnet dipoles and tens of quadrupoles on site, ready for installation in the tunnel, which was constructed and used for LEP.

Surface superconductivity in niobium for superconducting RF cavities

A systematic study is presented on the superconductivity (SC) parameters of the ultrapure niobium used for the fabrication of the nine-cell 1.3 GHz cavities for the linear collider project TESLA. Cylindrical Nb samples have been subjected to the same surface treatments that are applied to the TESLA cavities: buffered chemical polishing (BCP), electrolytic polishing (EP), low-temperature bakeout (LTB). The magnetization curves and the complex magnetic susceptibility have been measured over a wide range of temperatures and DC magnetic fields, and also for different frequencies of the applied AC magnetic field. The bulk superconductivity parameters such as the critical temperature T c = 9.26 K and the upper critical field B c 2 ( 0 ) = 410 mT are found to be in good agreement with previous data. Evidence for surface superconductivity at fields above B c 2 is found in all samples. The critical surface field exceeds the Ginzburg–Landau field B c 3 = 1.695 B c 2 by about 10% in BCP-treated samples and increases even further if EP or LTB are applied. From the field dependence of the susceptibility and a power-law analysis of the complex AC conductivity and resistivity the existence of two different phases of surface superconductivity can be established which resemble the Meissner and Abrikosov phases in the bulk: (1) “coherent surface superconductivity”, allowing SC shielding currents flowing around the entire cylindrical sample, for external fields B in the range B c 2 < B < B c 3 coh , and (2) “incoherent surface superconductivity” with disconnected SC domains for B c 3 coh < B < B c 3 . The “coherent” critical surface field separating the two phases is found to be B c 3 coh = 0.81 B c 3 for all samples. The exponents in the power law analysis are different for BCP and EP samples, pointing to different surface topologies.

Design Study of a Normal Conducting Helical Snake for AGS

A new normal conducting snake magnet is being fabricated for the alternate gradient synchrotron (AGS) at Brookhaven National Laboratory (BNL). In the Relativistic Heavy Ion Collider (RHIC) project, a superconducting type helical dipole magnets had been developed and it performed successfully in high-energy polarized proton acceleration. The new AGS helical snake has the same basic magnetic structure but is more complicated. To achieve no beam shift and no beam deflection in one magnetic device, helical pitches and rotating angles were carefully calculated. Compared to a superconducting magnet, a normal warm magnet must have a large cross-sectional area of conductors which make it difficult to design a magnet with large helical pitch. We developed a modified window frame structure to accommodate the large number of conductors. Its three dimensional magnetic field was simulated by using OPERA3D/TOSCA.

LHC Cable Production in Japan

Supply of the dipole outer layer and the quadrupole superconducting cable (cable 2) is one of the major contributions by Japanese firms to the Large Hadron Collider (LHC) project. In April 2003, after 57 months since the contract agreement, the production of cable 2 was successfully completed at the Japanese firm in charge, the Furukawa Electric Co., Ltd. (FEC). The amount of the produced cable 2 was 92 ton by weight and 575 km in length, which corresponds to one octant ( 1/8 ) of the cable 2 required for the LHC. In this production many new management schemes were tried and introduced based on the close collaboration between the customer (CERN) and the supplier (FEC) in order to achieve the overall uniformity of the cable 2 performance. The author presents the cable 2 performance obtained and the procedures employed for the control of quality, delivery rate and production efficiency. The author believes that such an experience is useful as the measurements for an on-time production of uniform superconducting wire and cable with a highly demanding specification in a future project.

A GEM-TPC prototype with low-noise highly integrated front-end electronics for linear collider studies

Connected to the linear collider project, studies on the readout of time projection chambers (TPCs) based on the gas electron multiplier (GEM) are ongoing. Higher granularity and intrinsically suppressed ion feedback are the major advantages of this technology. After a short discussion of these issues, we present the design of a small and very flexible TPC prototype, whose cylindrical drift volume can be equipped with endcaps of different gas detector types. An endcap with multi-GEM readout is currently set up and successfully operated with a low-noise highly integrated front-end electronics. We discuss results of measurements with this system in high intensity particle beams at CERN, where 99.3 /spl plusmn/ 0.2 % single-pad-row efficiency could be achieved at an effective gain of 2.5 /spl times/ 10/sup 3/ only, and spatial resolutions down to 63 /spl plusmn/ 3 /spl mu/m could be demonstrated. Finally, these results are extrapolated to the high magnetic field in a linear collider TPC.

A Vector Hysteresis Model for Superconducting Filament Magnetization in Accelerator Magnets

Magnetic field changes in the coils of superconducting magnets are shielded from the filaments' core by so-called persistent currents which can be modeled by means of the critical state model. This paper presents a semianalytical two-dimensional model of the filament magnetization due to persistent currents for changes of the magnitude of the magnetic induction and its direction while taking the field dependence of the critical current density into account. The model is combined with numerical field computation for the calculation of field errors in superconducting magnets. The filament magnetization and the field errors in a nested orbit corrector magnet for the large hadron collider project at CERN have been calculated as an example.

Achievement of [formula omitted] in the superconducting nine-cell cavities for TESLA

The Tera Electronvolt Superconducting Linear Accelerator (TESLA) is the only linear electron–positron collider project based on superconductor technology for particle acceleration. In the first stage with 500 GeV center-of-mass energy an accelerating field of 23.4 MV/ m is needed in the superconducting niobium cavities which are operated at a temperature of 2 K and a quality factor Q 0 of 10 10. This performance has been reliably achieved in the cavities of the TESLA Test Facility (TTF) accelerator. The upgrade of TESLA to 800 GeV requires accelerating gradients of 35 MV/ m . Using an improved cavity treatment by electrolytic polishing, it has been possible to raise the gradient to 35– 43 MV/ m in single cell resonators. Here we report on the successful transfer of the electropolishing technique to multi-cell cavities. Presently 4 nine-cell cavities have achieved 35 MV/ m at Q 0⩾5×10 9, and a fifth cavity could be excited to 39 MV/ m . In two high-power tests it could be verified that EP-cavities preserve their excellent performance after welding into the helium cryostat and assembly of the high-power coupler. One cavity has been operated for 1100 h at the TESLA-800 gradient of 35 MV/ m and 57 h at 36 MV/ m without loss in performance.

Field Instrumentation and Numerical Analysis of an Elliptical Shaft Constructed for the Texas Superconducting Super Collider Project

This paper focuses on the field data interpretation and numerical analysis of an elliptical shaft constructed for the Texas Superconducting Super Collider Project. The instrumentation program consisted of measurements of lateral deformation, heave and pore pressure within the undoweled and predoweled reaches of the advancing shaft. The field measurements point to a blocky, post-peak response of the clay shale beneath the advancing shaft invert and indicate the importance of predoweling reinforcement in controlling progression of the blocky failure. The numerical analysis was performed based on an understanding of the rock mass response to excavation developed through analysis of field instrumentation data. The technique developed for simulating the impact of the blocky, post-peak response of the shale on the redistribution of stresses around the shaft opening was successful in describing the pore pressure response recorded beneath the shaft invert and has proven to be a useful tool in studying the redistribution of stresses in blocky materials.

CCD-based vertex detector for JLC

The Charge Coupled Device (CCD) based vertex detector is being studied for the Joint Linear Collider (JLC) project. One of the main goals is the operation of CCDs at near-room temperature in order to reduce the amount of materials between the interaction points and outer detectors, and minimize the thermal distortion of CCD wafers. In this paper, we describe some of the aspects about the operation at near-room temperature with the results of radiation immunity and spatial resolution studies for the JLC project.

Past, present and future of data acquisition systems in high energy physics experiments

Data Acquisition (DAQ) systems for large high-energy physics (HEP) experiments in the eighties were designed to handle data rates of megabytes per second. The next generation of HEP experiments at CERN (European Laboratory for High Energy Physics), is being designed around the new Large Hadron Collider (LHC) project, and will have to cope with gigabyte-per-second data flows. As a consequence, LHC experiments will require challengingly new equipment for detector readout, event filtering, event building and storage. The Fastbus and VME-based tree architectures of the eighties run out of steam when applied to LHC's requirements. New concepts and architectures from the nineties have substituted rack-mounting backplane buses for high speed point-to-point links, abandoned centralized event building, and instead use switched networks and parallel architectures. Following these trends, and in the context of DAQ and trigger systems for LHC experiments, this paper summarizes the earlier architectures and presents the new concepts for DAQ.

Design and evaluation of a 10-ma dc current reference standard

A new DC current reference standard has been developed for high-current power converter calibration in the large hadron collider (LHC) project at the European Organization for Nuclear Research (CERN). This standard provides a near ideal 10-mA DC current with long-term drift of one part in 10/sup 6/ per year. The paper describes the requirements and the detailed design and evaluation of the unit. Since similar 10-V standards are commercially available, the paper concentrates on the unique current output capability of this device.

Short‐term solubility of eight alloys circulating in mercury at room temperature

Because mercury is a dense liquid at room temperature, it has found application in particle-accelerator targets with high energy-deposition rates such as proton spallation targets. Such targets usually require an active heat-removal system to remove the energy deposited by the particle beam, energy deposition rates that can be as much as several megawatts Ž. Weeks, 1996 . Solid targets generally require a water-cooling system that can introduce significant complexities into the system. However, a mercury target has several advantages over a solid target, one of which is that the mercury itself can be circulated to remove the deposited heat. Although the service lifetime of a mercury target container may be limited by corrosion or erosion caused by the flowing mercury, the present authors found it difficult to retrieve clear guidance from the literature for our application on the compatibility of various alloys with circulating mercury and even less guidance on the effects of radiation. Although one approach to a potential mercury incompatibility problem could be to schedule periodic removal of a target assembly for examination and possible replacement, it would be useful to have experimental evidence of the performance of a material under representative conditions prior to actual service. In order to be useful for application in a mercury-wetted environment, a material should form no solid alloys with Ž. mercury Weeks, 1967 . Since nickel is known to form intermetallic compounds with mercury as well as with lead and bismuth, it has been recommended that austenitic steels or other alloys with more than a trace of nickel be avoided for Ž. use with mercury Weeks, 1997 . Also, chromium is soluble in heavy liquid metals. Therefore, chromium depletion at surface grain boundaries of seasoned steels can be a concern when in contact with mercury. In spite of these concerns, the Spallation Neutron Source project under construction at the Oak Ridge National Laboratory is using 316L Stainless Steel for the mercury target container, and no such difficulties have been observed in laboratory and proton irradiation experiments with 316L Stainless Steel vessels containing mercury Ž. National Spallation Neutron Source, 1997; Haines, 2002 . The muon collider project is also proposing to use mercury Correspondence concerning this article should be addressed to G. A. Greene. for their production target in the configuration of a free jet; in very limited tests conducted to date, no mercury incompatŽ. ibility issues have been encountered Simos et al., 2001 . Although the potential exists for the mercury to become saturated with an alloying constituent, it has been suggested that the soluble components could precipitate or plate out in the cold sections of a flowing loop, thereby promoting the continued dissolution process. It has been suggested that molybdenum, tantalum, or carbide coatings may protect underlying Ž. alloys from corrosion by mercury Weeks, 1997 ; however, the subject of coatings is beyond the present scope.

CERN collider project back on track.

CERN collider project back on track.