Collider Project Research Articles

Application of M-type cathodes to high-power cw klystrons

Two types of high-power cw klystrons have been widely used at KEK in both TRISTAN and KEKB e +e − collider projects: one is a 0.8 MW/1.0 MW tube, called YK1302/YK1303 (Philips); the other is a 1.2 MW tube, called E3786/E3732 (Toshiba). Normally, the dispenser cathodes of the `B-type' and the `S-type' have been used, respectively, but for improved versions they have been replaced by low-temperature cathodes, called the `M-type'. An Os/Ru coating was applied to the former, whereas an Ir one was applied to the latter. Until now, all upgraded tubes installing M-type cathodes, 9 and 8 in number, respectively, have worked successfully without any dropout. A positive experience concerning the lifetime under real operation conditions has been obtained. M-type cathodes are, however, more easily poisoned. One tube installing an Os/Ru-coated cathode showed a gradual, and then sudden decrease in emission during an underheating test, although the emission could fortunately be recovered by aging at the KEK test field. Once sufficiently aged, the emission of an Ir-coated cathode proved to be very high and stable, and its lifetime is expected to be very long. One disadvantage of this cathode is, however, susceptibility to gas poisoning and the necessity of long-term initial aging. New techniques, like ion milling and fine-grained tungsten top layers, were not as successful as expected from their smaller scale applications to shorten the initial aging period. A burn-in process at higher cathode loading was efficient to make the poisoned cathode active and to decrease unwanted Wehnelt emission. On top of that, the emission cooling, and thus thermal conductivity near the emitting layer could play an important role in such large-current cathodes as ours.

A/sub r/ formulation using edge elements, for the calculation of 3-D fields in superconducting magnets

The Large Hadron Collider (LHC) project is an accelerator for protons and heavy ions, to be installed at CERN. The field distribution in the superconducting LHC main dipoles is dominated by the coil configuration and is very sensitive to the conductor position. Therefore modelling errors on the coil geometry have to be avoided using a method which does not require the meshing of the coil. For the 2-D calculation of iron induced field effects, the reduced vector potential formulation with node-based elements was recently applied. This paper deals with the extension of the method to three dimensions.

The Universality of Science

T he intellectual commerce that has propelled the explosive growth of international science and technology over the past 50 years is threatened. More than at any time since the McCarthy era, our government increasingly has sought to bar the entry of scientists from nations at odds with our foreign policy interests and to prevent the travel of U.S. scientists to many of these same nations. This effort to selectively abridge scientific exchange threatens the vigor of the world's science enterprise. There is perhaps no better rationale for freedom in the conduct of science than that provided by the statutes of the International Council of Scientific Unions (ICSU): “ICSU, as an international nongovernmental body, shall observe and actively uphold the principle of the universality of science. This principle entails freedom of association, expression, information, communication and movement in connection with international scientific activities.” Throughout the darkest days of the Cold War, this statute was accepted by our government and used by the National Academy of Sciences to promote contacts between Soviet and Western scientists. Without such interactions, it was recognized that neither side would be able to fulfill its need to reduce tensions, build confidence, and develop workable schemes for arms control and weapons reductions. Because of Indian and Pakistani ambitions to be nuclear powers, South Asian physicists and other scientists have recently been prevented from attending international scientific conferences in the United States. Within 6 weeks of the first Indian nuclear tests, Rajagopal Chidambaram, chairman of the Indian Atomic Energy Commission and a leading figure in India's nuclear program, was unable to attend a U.S. meeting of the executive committee of the International Union of Crystallography (of which he is a vice president), because, he was told, State Department policy for granting visas to all Indian scientists was under indefinite review. At the same time, a list of Indian and Pakistani institutes presumed to be involved in weapons programs was sent by government officials to Department of Energy laboratories, stating that the visas of visiting South Asian physicists would not be extended beyond the expiration dates. One result was the threatened loss of a productive scientific collaboration by U.S. scientists in the Large Hadron Collider project at the Organisation Europeenne pour la Recherche Nucleaire (CERN). In 1998, then-president of the American Chemical Society, Paul Walter, and the society's administrator of international affairs, John Malin, were denied permission to meet with their counterparts in the Cuban Chemical Society. The Treasury Department concluded that their rationale for travel did not qualify as professional research and education. By early 1999, a more sophisticated application combined with considerable political pressure succeeded, so that a group of U.S. chemists attended a scientific congress in Cuba. In the spring of 1997, five Cuban chemists from the University of Havana were denied visas to attend an important international meeting on quantum chemistry at Sanibel Island, Florida, because they were declare. “government employees,” as are all university professors in Cuba. The State Department later confided that a red flag is raised whenever the wor. “quantum” o. “nuclear” appears in a scientist's application to enter the country. And in a remarkable act of political interference in our intellectual dialogue, eight Department of Energy physicists from Fermilab were denied permission to attend a high-energy physics conference in India in January 1999 despite the scientific consensus that no benefit could possibly accrue to the Indian weapons establishment. One Fermilab physicist did eventually attend the conference after he was granted permission by the lab director to take leave and travel at his own expense. The variegated richness of science is a product of its diversity. In the wake of World War II, the world's scientific talent flocked to U.S. and U.K. research universities and laboratories, thereby vastly enriching science. The efforts of government officials to slow this engine of exchange under the disguise of preventing weapons technology transfers threaten debilitating consequences for science here and abroad.

How engineering data management and system support the main process-oriented functions of a large-scale project

This paper studies the benefits of establishing configuration management procedures and using an engineering data management systems (EDMS) in a large-scale project by dividing theoverall effort into successiveprocesses. Through the identification of the main functional groups who will use the EDMS, the paper outlines the basic motivations and services provided by such a system to each process during the life-cycle of the project. The implications of strict configuration management on the daily operation of each functional user group are also discussed. Themain argument ofthe paper is that each and every user of the EDMS must act in compliance with the configuration management procedures to guarantee the overall benefits from such a system. In truly global projects, special emphasis is placed on the management of distributed opera tions, which sets the flexible and universal access to all engineering and project related documents into a crucial role in the overall success of the project. As an example of the given challenge, this paper documents a World Wide Web-based system to manage documents and interface in-house document vaults and commercial EDM systems. The underlying environment of the case is that of CERN and the ongoing, decade-long, Large Hadron Collider (LHC) project.

Ground vibration measurements for Fermilab future collider projects

This article presents results of wideband seismic measurements at the Fermilab site, namely, in the tunnel of the Tevatron and on the surface nearby, as well as in two deep tunnels in the Illinois dolomite, thought to be a possible geological environment of the Fermilab future accelerators.

Thermohydraulics of quenches and helium recovery in the LHC prototype magnet strings

In preparation for the Large Hadron Collider project, a 42.5 m-long prototype superconducting magnet string, representing a half-cell of the machine lattice, has been built and operated. A series of tests was performed to assess the thermohydraulics of resistive transitions (quenches) of the superconducting magnets. These measurements provide the necessary foundation for describing the observed evolution of the helium in the cold mass and formulating a mathematical model based on energy conservation. The evolution of helium after a quench simulated with the model reproduces the observations. We then extend the simulations to a full LHC cell, and finally analyse the recovery of helium discharged from the cold mass.

Linear Collider Projects and a Polarized Positron Beam

Linear Collider Projects and a Polarized Positron Beam

U.S. Signs On to Collider Project

U.S. Signs On to Collider Project

Politics Meets Technology in Next Collider

While the morale of high-energy physicists, particularly in the United States, was severely dented by the cancellation of the U.S. Superconducting Super Collider project in 1993, they did not dwell on that setback for long. Soon researchers were cooking up plans for an entirely new and truly international venture: the world's longest linear accelerator, or linac, which could stretch as far as 30 kilometers. And late last month, at the 18th International Linac Conference in Geneva, the Next Linear Collider took another step from pipe dream to reality, as five different physics groups unfurled blueprints for the machine.

Adsorption isotherms of H2 and mixtures of H2, CH4, CO, and CO2 on copper plated stainless steel at 4.2 K

Adsorption isotherms in the pressure range 10−11–10−6 Torr have been measured for H2 and mixtures of H2 and CH4, CO, and CO2 on copper plated stainless steel at 4.2 K. The measurements have been focused on the behavior of the isotherms at low surface coverage, up to a few monolayers of adsorbed gas on the cold surface. The isotherms were measured in a static situation with a small amount of gas injected for each point on the isotherm. Coadsorption measurements of H2 with CH4, CO, and CO2 as well as adsorption of H2 on condensates of CH4, CO, and CO2 have been made. A cryotrapping effect of H2 is seen when coadsorbing the gas mixtures, which is especially strong for the mixture of H2 and CO2. The measurements show that CO2 condensed at 4.2 K may have a porous structure that H2 can penetrate, while CO and CH4 have rather dense structures when adsorbed at 4.2 K. The measurements have been done within the framework of the Large Hadron Collider project [The Large Hadron Collider Accelerator Project, CERN/AC/95-05 (LHC), 20 October 1995] at CERN, Geneva, Switzerland, where superconducting magnets will be used to produce a magnetic field of about 9 T around the arcs of the 27 km long quasicircular accelerator. Synchrotron radiation produced by the circulating proton beam in the superconducting magnets will induce desorption of neutral gas molecules, mainly H2, CH4, CO, and CO2, from the inner surface of the vacuum chamber. The desorbed gas molecules will be physisorbed on the cold surfaces in the vacuum chamber and they may induce vacuum instabilities in the accelerator. Hence, it is of importance to have knowledge of the mixed adsorption isotherms of these gases at low temperatures.

The present status of LHC

The Large Hadron Collider (LHC) project was approved by the CERN Council in December 1994. The machine will provide proton-proton collisions with a centre of mass energy of 14 TeV and an unprecedented luminosity of 10/sup 34/ cm/sup -2/s/sup -1/. In order to achieve the design energy within the constraint of the 27 km circumference LEP tunnel, the magnet system must operate in superfluid helium below 2 K, with a dipole field of 8.4 Tesla. In addition, space limitations in the tunnel as well as cost considerations dictate a two-in-one magnet design, where the two rings are incorporated into the same cryostat. The machine will also provide heavy (Pb) ion collisions with a luminosity of 10/sup 27/ cm/sup -2/s/sup -1/ using the existing CERN ion facility. Space will be kept above the LHC for the eventual reinstallation of components of the LEP machine to provide future e-p collisions if the physics case justifies it.

Growth of lead tungstate single crystal scintillators

In this paper we present information on the growth of first-quality lead tungstate PbWO 4 single crystals and their luminescence and absorption properties. In comparison with so far presented PbWO 4 our single crystals show the prevailing blue emission component in radioluminescence at room temperature and fast scintillation decay in the nanosecond range with a very low level of slow processes on the micro-miliseconds time scale. These facts suggest that especially PbWO 4 single crystals with these properties are suitable as scintillating medium for a crystal calorimeter for the Large Hadron Collider project at CERN.

Technological problems related to the cold vacuum system of the LHC

The Large Hadron Collider (LHC) project, now in its design phase at CERN, comprises two proton storage rings with colliding beams of 7 TeV energy. The machine will be housed in the existing LEP tunnel with a circumference of 26.7 km and requires a bending magnetic field of 8.4 T with 14 m long superconducting magnets. The beam vacuum chambers comprise the inner “cold bore” walls of the magnets. These magnets operate at 1.9 K, and thus serve as very good cryo-pumps. In view of reducing the cryogenic power consumption, both the heat load from synchrotron radiation emitted by the proton beams and the resistive power dissipation by the beam image currents have to be absorbed on a “beam screen”, which operates between 5 and 20 K and is inserted inside the vacuum chamber. The design of this beam screen represents a technological challenge in view of the numerous and often conflicting requirements and because of the very tight mechanical tolerances imposed. The synchrotron radiation produces strong outgassing from the walls. The design pressure necessary for operation must provide a beam lifetime of several days. An additional stringent requirement comes from the power deposition in the superconducting magnet coils due to protons scattered on the residual gas which could lead to a magnet quench and, therefore, interrupt the machine operation. Cryo-pumping of gas on the cold surfaces provides the necessary low gas densities but it must be ensured that the vapour pressures of cryo-sorbed molecules, of which H 2 and He will be the most critical species, remain within acceptable limits. In the warm straight sections of the LHC the pumping speed requirement is determined by ion induced desorption and the resulting vacuum stability criterion.

U.S. and Europe Close In on LHC Deal

U.S. and European negotiators have drafted an agreement in which the United States would pump about half a billion dollars into the Large Hadron Collider (LHC) project at CERN, Europe's particle physics laboratory near Geneva. The proposed arrangement, subject to the endorsement of legislators on both sides of the Atlantic, would allow CERN to come closer to meeting its original target date of 2004 to complete construction of the facility. It would also give U.S. physicists a major role in the $2.3 billion accelerator and its two, $1 billion detectors.

High-Energy Physics: U.S. and Europe Close In on LHC Deal

U.S. and European negotiators have drafted an agreement in which the United States would pump about half a billion dollars into the Large Hadron Collider (LHC) project at CERN, Europe9s particle physics laboratory near Geneva. The proposed arrangement, subject to the endorsement of legislators on both sides of the Atlantic, would allow CERN to come closer to meeting its original target date of 2004 to complete construction of the facility. It would also give U.S. physicists a major role in the $2.3 billion accelerator and its two, $1 billion detectors.

CERN to open US talks on collider project

CERN to open US talks on collider project

Decays and production of beauty baryons in pp interactions

We present some physics interests for the study of beauty baryons produced in pp interactions at a center-of-mass energy corresponding to the Large Hadron Collider (LHC) project, √s ≃ 14 TeV. The comparison of beauty-baryon (Nb) production with their charge conjugate particles (N̄b) is discussed as well as the measurement of their polarization. The search for CP violation in the N b, N̄b decays is considered. A possibility for estimating the |Vcb| CKM matrix element is also presented. In order to evaluate the Nb production rates and their detection efficiencies, we utilize the pp luminosity of ℒ = 1033 cm-2 s-1 and the example of the Compact Muon Solenoid (CMS) detector.

95/00444 Superfluid helium cryogenics for the large Hadron Collider Project at CERN

95/00444 Superfluid helium cryogenics for the large Hadron Collider Project at CERN

Abandoned SSC Site can provide underground facility for geoscience research

By the time Congress terminated the Superconducting Super Collider (SSC) project in October 1993, the Department of Energy and the state of Texas had sunk $2 billion into the project. Now closure and remediation of the disturbed surface and subsurface lands are underway with a budget of $22 million, according to a recent agreement between the DOE and Texas. Rather than chalking up the creation of the large, expensive hole in the ground to failure, however, some are hailing the site as an excellent test‐bed for geoenvironmental and geotechnical research (Figure 1). They hope to use the site's tunnel, exploratory shaft, and test wells to identify new and improved methods for investigating subsurface fluid flow and transport processes, to characterize physical properties of weak and fractured rock through geophysics and geomechanical testing, and to test model predictions through large‐scale experiments conducted underground.

Electromagnetic and mechanical design of a 56 mm aperture model dipole for the LHC

The Large Hadron Collider (LHC) project is proposed as the future extension of the CERN accelerator complex. The LHC requires twin aperture superconducting dipoles of highest possible field to guide the proton beams in the existing LEP tunnel of 26.7 km circumference. This paper describes the electromagnetic and mechanical design of a 56 mm aperture model dipole for the LHC.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>