Superconducting Accelerator Research Articles

Passive correction of the persistent current effect in Nb/sub 3/Sn accelerator magnets

Superconducting accelerator magnets must provide a uniform field during operation. However, the field quality significantly deteriorates due to persistent currents induced in superconducting filaments. This effect is especially large for the Nb/sub 3/Sn conductor being implemented in the next generation of accelerator magnets. A simple and inexpensive method of passive correction of the persistent current effect was developed and experimentally verified. This paper describes numerical simulations of the passive correctors and reports the test results.

Studies on the improvement of niobium-sputtered quarter wave resonator supercond ucting cavity

Quarter wave resonator (QWR) is the best choice of the acceleration cavity for heavy ion superconducting accelerator. Using dc bias-voltage sputtering system, w e can sputter niobium films of several microns on the oxygen-free high-conductiv ity copper(OFHC) substrate. Good superconducting properties and acceleration pro perties of the cavity can be obtained. But compared with niobium cavity, it has very low Q and Eacc. Niobium nitride (NbN) is a good superconducto r, and it has a higher superconducting transition temperature (Tc) th an pu re niobium. Through experiments, we find that the Tc transition point of n iobium films rises to about 9.6K by using NbN interlayer between OFHC substrate and niobium films. So using this method can improve the superconducting properti es and thus the acceleration properties.

Peking university superconducting accelerator facility for free electron laser

Peking University Superconducting Accelerator Facility (PKU-SCAF) is to generate high-quality electron beams with high average current. It is mainly composed of a DC-SC photocathode injector and a superconducting accelerator. It will operate in CW mode. The energy of the electrons is 20–35 MeV and the emittance is <15 π mm mrad. PKU-SCAF will be used for Free Electron Lasers.

２１世紀ヘ伝えたい超電導応用技術 ９ 加速器用超伝導マグネットの開発 トリスタン加速器用４極マグネットシステム

Superconducting magnets have become essential components of large accelerators/colliders. Their technology has greatly progressed because of the production of Tevatron, HERA, and RHIC magnets and the intense R&D programs for SSC and LHC. In KEK superconducting quadrupole magnets, which are the first superconducting accelerator magnets in Japan, were developed in the 1980s and installed into the interaction regions of the TRISTAN collider. Since commissioned in February 1991, the magnets had operated five years without serious trouble and contributed to double the luminosity. This paper describes the features and the construction history of the magnet systems.

Quench protection of a high gradient quadrupole for the LHC interaction regions

The energy stored in a superconducting (SC) accelerator magnet is usually dissipated after a quench in the normal zones of the coil, heating the coils and producing a voltage drop between the turns inside the magnet and between coil and ground. This paper presents the results of the analysis of the quench protection problem for a high gradient quadrupole for the LHC interaction regions.

Theoretical sensitivity limits of the SQUID system for measuring the radial position of a beam of electrically charged particles in superconductive accelerators

This paper deals with the problem of implementation of superconductive quantum magnetometers (SQMs) for the measurement of radial deviation of the beam of electrically charged particles in a vacuum waveguide of a superconductive accelerator. The assumed measuring system is essentially based on the measurement of magnetic field induced by a moving electric charge by means of two SQMs with a superconductive differential and cumulative toroidal antennae. Theoretical relations facilitating the optimization of its parameters are derived. The limit of attainable positional spectral resolution of the measuring system given by the noise of SQMs is calculated. From an example, assuming a standard magnetometer with an input energy sensitivity ∼ 1 × 10 −28 J/Hz, the intensity of a beam corresponds to N = 10 7 elem. charges/cycle and an accelerator with a radius of 40 m follows the positional spectral resolution of ∼ 0.1 mm/Hz 1 2 (or resolution of ∼ 0.35 mm at a frequency bandwidth of the transmission path of 10 Hz). The problems of the shielding of the measuring system from operational disturbing magnetic fields are discussed. © 1997 Elsevier Science Limited

Theoretical sensitivity limits of the SQUID system for measuring beam intensities of electrically charged particles in superconductive accelerators

This paper is aimed at theoretical aspects of the application of superconducting quantum magnetometers (SQMs) to measuring the beam intensities of electrically charged particles accelerated in superconducting accelerators. The characteristics of the antenna system picking up the magnetic field which is induced by the unidirectional component of the flux of the accelerated particles, are examined and the influence of the transfer chain element parameters is analysed. On the basis of derived relationships, the antenna parameters have been optimized, from the viewpoint of their sensitivity and reduction of the output signal dependence upon the beam deviation in the transverse direction. The maximum attainable sensitivity of the measuring system, given by its intrinsic noise, has been determined. Theoretical analysis proves that the sensitivity limit for accelerators with a beam trajectory radius of the order of 10 1 m is of the order of (10 2–10 3) elem. charges/cycle. An example of the calculation of measuring system parameters at given accelerator and SQM parameters is also presented. Principles concerning the elimination of disturbing electromagnetic fields by means of superconductive and ferromagnetic shielding are also highlighted.

The determination of an electron beam's longitudinal phase space distribution through the use of phase-energy measurements

Abstract We have been able to measure the longitudinal phase space distribution of the Stanford Superconducting Accelerator's (SCA) electron beam by applying tomographic techniques to energy spectra taken as a function of the relative phase between the beam and the accelerating field. The temporal profile of the beam obtained by projecting the distribution onto the time axis is compared with that obtained from interferometric transition radiation measurements.

Simulations of the Stanford FIREFLY 1 kW free electron laser

A modification of Stanford’s Superconducting Accelerator Free Electron Laser (SCAFEL) has been proposed to increase its average optical power to about 1 kW. The FIREFLY Free Electron Laser (FEL) would be a factor of 100 increase in output power over the most powerful FEL in operation now and would cost about 1 million dollars. Simulations show the evolution of longitudinal modes over many passes and the development of the trapped-particle instability. Power versus desynchronism is studied for

The ATLAS facility at argonne national laboratory

Abstract The Argonne Tandem Linac Accelerator System (ATLAS) is a super-conducting low-energy heavy-ion accelerator [1]. Its primary purpose is to provide beams for research in nuclear structure physics. It therefore seems quite fitting that ATLAS is located in Building 203 at Argonne National Laboratory, the same building where Marie Goeppert-Mayer worked on her Nobel-prize-winning contributions to the nuclear shell model.

An achromat for the ANU 14UD linac

A compact magnetic achromat has been designed and constructed to deliver the horizontal output beam of the ANU 14UD Pelletron tandem accelerator to a superconducting booster accelerator to be located in part of the experimental hall of the laboratory. The achromat provides 90° deflection of the ion beam and is fully achromatic with respect to energy spread in the beam. Due to space constraints in the laboratory, it has been necessary to locate the beam chopping device and bunching cryostat upstream of the 90° bend, thereby requiring that the beam trajectory following the bend be independent of beam energy. The optical performance of the achromat has been investigated in first order using the matrix transfer beam calculation code TRANSPORT, and in high order using the particle tracking code RAYTRACE. In first order, the achromat is shown to have precise achromatism and to be isochronous with the exception of small and predictable time waist shifts. High order calculations lead to an expectation of less than 6% worsening of the transverse beam emittance and less than 9 ps timing degradation for 170 MeV 59Ni 13+, an isotope of interest in accelerator mass spectrometry. The effect on the transmission of this isotope through the subsequent acceleration stages and beam-optical elements is negligible.

JAERI quasi-cw, and high-average power free electron laser driven by a superconducting rf linac

We have developed and constructed a prototype for a quasi-cw, and high-average power free electron laser driven by a superconducting rf linac at the Japan Atomic Energy Research Institute (JAERI), Tokai. We have successfully demonstrated expected performances of the JAERI 250 keV electron gun and bunching system, and completed an extension to an old 5.5 MV electrostatic accelerator building as an FEL accelerator vault in the 1991 Japanese fiscal year. All solid state rf amplifiers, liquid He refrigerators, a hybrid undulator and vacuum pumping stations are ready for use now. The first superconducting accelerator module is now under preparation for a cold rf test, and the other three modules are now under assembly. A description and the latest results of the JAERI superconducting rf linac FEL will be discussed, and reported in detail.

An ultraviolet gas-loaded free-electron laser

By loading the wiggler cavity of a free-electron laser (FEL) with hydrogen gas, it is possible to tune the FEL to below 130 nm, just above the electronic resonance of molecular hydrogen. The change in wavelength results from the refractive index of the gas, which alters the phase velocity of the wave and so modifies the synchronism condition. Using the parameters of the wiggler on the beamline of the Stanford Superconducting Accelerator, this FEL can be tuned from 500 to 130 nm with a pressure ranging from 0 to 55 torr. The calculated electronic gain varies between 5.6 and 11% over this wavelength interval, comparable to the gain in vacuum. >

Recent Advances in the Technology of Superconducting Accelerator Magnets

Recent progress in technology of high-current-density cables for SSC model magnets is summarized. NbTi cable with Jc up to 50% higher than Tevatron cable can be expected. Magnetization effects can be predicted and corrected with several new techniques. Development of Superconductor with 2-3 ?m filament diameter and high Jc is expected.

Superconducting Combined Function Magnets

Superconducting accelerators and storage rings, presently under construction or in the design phase, are based on separate dipole and quadrupole magnets. It is here suggested that a hybrid lattice configuration consisting of dipoles and combined function gradient magnets would (1) reduce the number of magnet units and their total cost and (2) increase the filling factor and thus the energy at a given field. Coil cross sections are presented for the example of the Brookhaven Colliding Beam Accelerator. An asymmetric two-layer cable gradient magnet would have transfer functions of 10.42 G/A and 0.628 G cm-1/A versus 15.77 G/A and 2.03 G cm-1/A of the present separate dipoles and quadrupoles.

Conceptual Magnet Design for an Iron-Free Colliding Beam Accelerator

Superconducting accelerator magnets usually have magnetic iron yokes to obtain maximum magnetic field and to limit stray field. However, the iron is expensive and heavy. The smaller size and weight of an iron-free magnet can result in lower magnet and refrigeration costs. However in a colliding beam accelerator the stray field from one ring produces aberrations in the field in the other. A way to eliminate this mutual interference is to surround each magnet with a coil that exactly cancels the field from the in the other ring magnet. That is expensive in terms of superconductor requirements. However the cancellation of the external dipole field component is unnecessary. Only a small amount of superconductor is required for cancellation of the higher-order field-aberration components. Parameters for the iron-free magnet concept are investigated, and a preliminary conceptual design for an accelerator is presented.

A Four Quadrant Magnet Power Supply for Superconducting and Conventional Accelerator Applications

Modern conventional and superconducting accelerators often require bipolar power supplies capable of operating with high precision from zero to full output. An SCR type power supply comprised of two SCR bridges and operating with circulating current does an excellent job of satisfying this difficult requirement. Power supplies of this type are often called fourquadrant or dual converter power supplies with circulating current. The basic principles and design considerations of this converter are discussed with particular emphasis on the advantages of the converter. Application of the dual converter to high precision bipolar magnet current control within the Fermilab Saver/Doubler project is presented.

Eight-Tesla Synchrotron Dipoles -- Design Alternatives

Superconducting accelerator bending magnets in the 4 to 5 tesla field range have been, or are being, developed for the LBL ESCAR, FNAL Doubler, and BNL ISABELLE projects and can be considered as state-of-the-art. We are now engaged in a program to develop accelerator dipoles with significantly enhanced performance, into the 8-tesla range. Analytical design studies, based on idealized configurations, have been done to trace the dependence of stresses within the coil and overall magnet size on the magnet aperture, coil current density, central magnetic field, structural ring stress, and magnetic induction in the iron flux-return yoke. Our development program includes: 1. Development, and measurement at 4.2°K, of coil structures consistent with the requirements of the analytical design studies. 2. Superfluid helium II at 1.8° K and at atmospheric pressure. Large magnets as well as conductors will be tested. 3. Development and evaluation of aluminum stabilization and various A-15 superconductors. 4. Tests of various model dipoles with instrumentation to measure mechanical motion.

Storage Accelerator Bending Magnet without Median Plane Symmetry

An H-magnet with no median plane symmetry, in which all the current carrying coils lie below the median plane, has been studied using the GRACY magnet program. This magnet was suggested by A. vanSteenbergen and has several possible advantages for use in a super-conducting storage accelerator. The field multipoles violating median plane symmetry were found to be small, and correctable with small correction coils. In addition, it was found possible to reduce these undesired multipoles considerably by shaping the iron pole face.

Progress on RF Electron Superconducting Accelerators

Superconducting rf electron accelerator prototypes have been operated at Stanford University and at the University of Illinois. Many of the beam performance goals for emittance, current, energy resolution and stability have been achieved. Lower-than-expected accelerating gradients have necessitated the reevaluation of the energy objectives. Recirculation of the electron beam through the superconducting linacs will, however, increase the effective accelerating gradient.