High Energy Physics Accelerators Research Articles

Progress with Nb/sub 3/Sn conductors at oxford instruments, superconducting technology

Oxford Instruments, Superconducting Technology (OI-ST) produces Nb/sub 3/Sn wires by two major process routes: bronze and internal Sn, including modified jelly roll (MJR). Each process has its own strengths for particular applications. We report on MJR wire designed for prototype high energy physics accelerator magnet studies which achieved short sample non-Cu critical current density at 12 T, 4.2 K exceeding 2000 A/mm/sup 2/. We also report recent results from wires fabricated by other internal Sn methods, the bronze process, and powder-in-tube processes.

Development of a Nb/sub 3/Sn conductor containing Ga and Mg dopants

Future high energy physics accelerators and fusion machines will require superconducting magnets generating fields of 12 T and above. These magnets will most probably utilize Nb/sub 3/Sn superconductor, since Nb/sub 3/Sn-based conductors are a proven technology. The high-field performance of Nb/sub 3/Sn-based conductors can be improved through the use of dopants. Among the elements that have been investigated as potentially beneficial dopants for Nb/sub 3/Sn are Ga and Mg. Ga has been shown to increase both the critical temperature and upper critical field of Nb/sub 3/Sn, while Mg has been reported to provide grain refinement, which is essential for high critical current density. Supercon has recently investigated a method for improving high field critical current density in bronze-route Nb/sub 3/Sn through the simultaneous addition of Ga and Mg dopants. The results of the investigation, including critical current density and critical temperature data, are presented and the performance of the doped conductors is evaluated in comparison to an un-doped control.

Regeneration of irradiated optical fibres by photobleaching?

Optical fibres that are permanently installed in nuclear reactors (fission or fusion) or at high energy physics accelerators can accumulate considerable long-lived radiation-induced loss. Four different fibre types were irradiated up to dose values from 10/sup 3/ to 10/sup 6/ Gy and an attempt was made to reduce the residual loss /spl ges/28 h after the end of irradiation by injection of high intensity laser light (40-100 mW) of 672, 830 and 980 nm wavelength. The radiation-induced loss of undoped silica core fibres could not be reduced by photobleaching, whereas the loss of Ge-doped fibres could only be reduced after lower dose values and in the wavelength region of lowest loss increase (800-1200 nm) where it is tolerable anyhow.

Magnet insulation with resistance to high levels of radiation

Large, capital intensive magnets, superconducting or resistive, are essential components of fusion devices and high energy physics (HEP) accelerators. Magnets built for these applications need to be reliable, possess long mean time between failures (MTBF), and be able to be manufactured using cost-effective materials and fabrication processes. Electrical insulation is often the weak-link in the design of magnets, due to its sensitivity to high radiation doses, embrittlement at cryogenic temperatures, and limitations in fabricability. Current magnet insulation materials provide sufficient electrical insulation, suitable mechanical properties at magnet operating temperatures, flexible processing for cost-effective coil fabrication and assembly, and reasonable cost. However, they degrade to unacceptable levels of performance when exposed to high levels of radiation. Recent work performed by CTD studied the hybridization of insulation chemistry. The goals of this work was to increase radiation resistance of the insulation while maintaining suitable properties and enable cost-effective processing techniques. Hybrids of different organic polymers including epoxies, polyimides, bismalimides (BMIs), and other aromatic based polymers were successfully demonstrated. Furthermore, hybridization of inorganic with organic materials was also demonstrated. The former materials are well suited for magnets manufactured from resistive conductors or NbTi, while the latter materials are well suited for Nb/sub 3/Sn and potentially HTS conductors because these materials enable a wind, insulate, and react fabrication scenario. A discussion of new hybridized radiation resistant insulation materials will be presented. Data will include anticipated end-of-life performance after exposure to high levels of radiation.

次世代応用超伝導技術とＮｂ３Ａｌ導体

R & D for the next generation superconducting magnets of high-energy physics accelerators, MHD generators, SMES, nuclear fusion reactors, and higher resolution NMRs needs advanced superconductors. The conductors of Nb3Al are the possible candidates because of the higher magnetic field properties of critical current density, the excellent critical current density at lower- and medium-field ranges, and the higher strength against mechanical stress. The R & D of jelly-roll processed Nb3Al has given already well-qualified conductors. Newly proposed rapid heat, the rapid quench process for Nb3Al, is also attractive from an economic aspect because of the superconductive characteristics of conductors. However, further developments are needed for the choice of stabilizer metal, cross-section configuration design, insulation materials, reinforcement and impregnant, n-value, joint technology between the two conductor; thus a prompt start of R & D is being requested.

Thomas Gerald Pickavance, 19 October 1915 - 12 November 1991

Thomas Gerald Pickavance was a leading authority on the design of particle accelerators for high-energy physics and was responsible for the construction of the most powerful accelerator built in this country, at the Rutherford Laboratory of which he was Director. He is chiefly remembered for the skilful, unselfish and unsparing way he made research facilities available for his fellow nuclear physicists and helped them to solve the problems of using large accelerators away from their universities. While Director for Nuclear Physics at the Science Research Council he played a major part in ensuring that the 300 GeV proton synchrotron at CERN was supported by this country and thus made available for the continued pursuit of high-energy physics here. He was elected to the Fellowship in the first year of his Suspension.

Measurement of neutron yield for a tungsten target irradiated with 70-GeV protons

The yield of neutrons emitted by an extended tungsten target irradiated with 70-GeV protons from the Institute of High Energy Physics accelerator (Protvino) is measured. The target was an assembly of tungsten plates with an overall size of 160 x 160 x 300 mm. The measurements were carried out on the 23rd channel with an intensity {approximately}10{sup 11} protons per pulse and on the 21st channel with {approximately}10{sup 5} protons per pulse. In the former case the protons were recorded with a copper foil placed before the end of the target. The positions of the proton beam in the front and back ends of the target were determined with photographic paper in experiments without the target.

Physics design of the high brightness linac for the advanced free-electron laser initiative at Los Alamos

Abstract Free-electron lasers and high energy physics accelerators have increased the demand for very high brightness electron-beam sources. This paper describes the design of an accelerator that can produce beams of greater than 7×10 11 A/m 2 (brightness equal to 21/ϵ 2 , with ϵ = 90% normalized emittance, equivalent to four times the rms emittance). The beam emittance growth in the accelerator is minimized by: producing a short electron bunch in a high gradient rf cavity, using a focusing solenoid to correct the emittance growth caused by space charge, and designing the coupling slots between accelerator cavities to minimize quadrupole effects. The simulation code PARMELA was modified for this design effort. This modified version uses SUPERFISH output files for the accelerator cavity fields, MAFIA output files for the 3-D perturbation fields caused by the coupling slots in the accelerator cells, and POISSON output files for the solenoid field in the gun region. The results from simulations are, at 2.3 nC, a peak current of 180 A and a 90% emittance of 6.4π mm mrad, and, at 4 nC a peak current of 300 A and a 90% emittance of 9.4π mrad. The exit energy from the linac is 20 MeV for both cases. A magnetic pulse compressor can be used to further increase the peak current.

Heavy-Ion Fusion: Setting the Stage

The purpose of this paper is to establish the context on which the rest of this session will be based. Several papers will report work inspired by the Heavy-Ion Fusion Systems Assessment (HIFSA) Project. This is a small project that is about 2 years old. It is a small fraction of the Heavy-Ion Fusion (HIF) Program, which is itself very small compared to virtually any other fusion effort. Certainly, part of the basis for HIFSA lies in the history of HIF. The program was invented in high-energy physics accelerator laboratories in about 1975. In the past decade, work at several U.S. laboratories and universities, and in Japan and Europe, has resulted in fundamental understanding of the phenomena involved in the stable transport and acceleration of space charge limited beams. HIF is the approach that is, more than any other, most suited to the high energy (multi-megajoule), high repetition rate, and high efficiency required of a power plant driver. There have been seven international conferences devoted to HIF (most recently in May 1986) and numerous independent reviews. All of these confirm the promise of HIF for eventual use for commercial power production. Perhaps the best overall systems study for inertial fusionmore » to date, certainly the best for HIF, is the HIBAll-II study. In this study, the authors arrive at a power plant scenario in which they project a cost of electricity that is somewhat lower than that found for various magnetic fusion scenarios. Certainly it is competitive with magnetic fusion.« less

Computer Modelling of Two- and Three-Dimensional Cavities

The rf accelerating system is the heart of many low, medium and high energy particle accelerators and in many cases, it is also a major drain of investement money and operational costs. In order to increase efficiency, many computer codes have been developed in the last few decades. Recently, it has been realized that parasitic collective effects can also present serious problems in the most expensive front line high energy physics accelerators. Nowadays, cavity design is no longer only a question of optimizing the shunt impedance but also of optimizing the overall effect of the system. Also, all other non-rf cavities in an accelerator are found to cause many problems. For cylindrically symmetric structures well tested computer codes are in widespread routine use as design tools. Fully three dimensional codes are just coming into common operation. At the present time, we are able to solve almost every two or three dimensional cavity problem either by mode computation or by transient wake field computation.

Basic Research in the East and West: A Comparison of the Scientific Performance of High-Energy Physics Accelerators

This paper presents the results of a study comparing the past scientific performance of high-energy physics accelerators in the Eastern bloc with that of their main Western counterparts. Output-evaluation indicators are used. After carefully examining the extent to which the output indicators used may be biased against science in the Eastern bloc, various conclusions are drawn about the relative contributions to science made by these accelerators. Where significant differences in performance are apparent, an attempt is made to identify the main factors responsible.

Radiation stresses of the proton synchrotron at the institute of high-energy physics and the stability of structural materials

surement results of the dosages in individual performances. A description of these distributions for a single beam of protons interacting with a target (target region), and a beam of protons incident on unit running length of the vacuum chamber (quiescent region), has permitted the radiation stresses in the plant of the circular electromagnet units to be calculated, by taking into cons [deration all variations of the beam intensity, and we shall use this calculation for other similar accelerators. As applicable to the calculated and measured radiation stresses, the analysis is carried out of the radiation stability of the structural materials irradiated in a reactor, in a ~/facility and at the Institute of HighEnergy Physics accelerator at a dose intensity of 2800, 250, and 2.5 rd/sec, respectively. The observed difference s in the results of irradiation of the materials in the reactor, the 7 facility and the accelerator, is explained by the nonidentical component-energy constitution, the radiation dose intensity, and by comparison of the data obtained with the handbook data for foreign materials of similar type, with the noncorrespondenc e of their structural characteristics. All this points to the necessity for taking account of the irradiation conditions when determining the radiation stability of materials. The data obtained in this paper allow the radiation stresses and the stability of materials to the effect of radiation to be assessed, not only for any unit of the Institute of HighrEnergy Physics accelerator electromagnet, but also for similar accelerators.

Suppression of Multipactoring in Superconducting Cavities

Future application of superconducting cavities to accelerators for high energy physics will probably require cavities designed for the UHF region. Experience has shown that vacuum electronic phenomena, particularly multipactoring, play an important role in limiting performance of cavities in this frequency domain. We report here work aimed at the suppression of multipactoring by deposition of superficial films on superconducting surfaces.

New accelerators for high energy physics

New accelerators for high energy physics

EPIC as a window on the forces of nature

A proposal has been made to the Science Research Council for the construction of a new high energy physics accelerator called EPIC: electron positron intersecting complex. Because of recent experimental discoveries which have challenged earlier theoretical ideas, there is a general expectation that a major advance in our understanding of the basic forces of nature is imminent. EPIC, if constructed, will open up a new energy regime that will provide vital information to guide this advance.

First results of working with beams of separated particles in the institute of high-energy physics accelerator

The initial results in forming beams of separated particles on the IHEP accelerator for the Mirabelle bubble chamber from Saclay (France) are presented. The parameters of the beam of particles and high-frequency separator are given. The characteristics of the beam Optical system and rf separator are given. These systems can provide the chamber with pure kaon and antiproton beams in the momentum interval 17 to 40 GeV/c and pion beams with momenta up to 50 GeV/c. Preliminary analysis of the pictures obtained in the kaon beam with p = 32 and 34 GeV/c, has exhibited the fact that impurity of other particles in the beam is not more than 2%. (auth)

Superconducting Magnets for High-Energy Physics

Superconducting magnets have established themselves as useful tools in solid-state physics, magneto-optical experiments, NMR, MHD, plasma, and other areas of physics. In high-energy physics only the bubble-chamber physicist has shown ample interest in using superconducting magnets. Reasons why there is a reluctance against large superconducting magnets in combination with high-energy physics experiments and accelerators are discussed. However, in various areas of high-energy physics superconducting magnets may be utilized, such as accelerator, beam-transport, and experimental magnets. This paper summarizes physical properties of superconducting systems for experimental and beam transport magnets in quantitative form. Charging time, field uniformity, resolution, acceptance, solid angle, improvement in optical measurements accuracy, and first- and second-order optics for superconducting magnets, with and without ferromagnetic return paths, will be compared to room and cryogenic magnets. Summary of experiences with superconducting magnets (energies > 106 J) will be given, as well as irradiation properties of superconducting type II materials and systems. Expected irradiation doses in accelerators and their effect on superconducting systems will be discussed. Lifetime expectancy, economy of operation, and effect of power failures are treated. A short section is devoted to possible design of superconducting magnets with and without ferromagnetic return paths.