J. W. Jackson

High Field Iron Magnets for Operation at Cryogenic Temperatures

In various papers by Danby, Allinger, and Jacksonls3 on the properties of a separated function lattice for a large synchrotron it was pointed out that in addition to its advantages in optics and economy it had potential for a specific future improvement using iron core magnets with cryogenic or superconducting coils. The design of room temperature window frame dipoles is dominated by the problem of attaining sufficiently high current densities. The replacement of the exciting coil by a much smaller area high current density cryogenic superconducting or pure metal coil would permit increasing the peak field to about 30 kG with controllable lattice aberration, thus easily obtaining 50% increase in particle energy.

High Precision Superconducting Magnets

Window-frame type superconducting dipole magnets have demonstrated accuracy and predictability of fields which compare well with the best conventional accelerator-type magnets. Precision measurements were made on the two series powered 2 m long 4 T modules comprising the 80 bending magnet at BNL after two years of beam operation including several dozen beam induced quenches. The integral field of the two units is identical to measurement accuracy, ¿ 1 × 10-4 parts at ~ full aperture, for all multipoles except quadrupole. Random quadrupole terms of G/B = 6 × 10-5 cm-1 or 2 × 10-4 parts are present. A 1 m long 6 T model of more advanced design shows pure dipole field, at all field levels, to 1 × 10-4 parts, using a single correction coil with predetermined excitation. The field shape at ~ 0.5 T/sec rise rate is identical to dc. The advantages of the extended current sheet coil construction are discussed. Results will be compared with computer simulations of construction errors. Suitable conceptual designs of compact 6 T dipoles and of quadrupoles applied to a 1 km accelerator lattice will be presented.

AGS Lattice Corrections and Tuning Using Backleg Windings

The excitation of a novel backleg winding system has significantly contributed to increasing the intensity of the AGS. The benefits of the improved magnetic lattice properties at fields in the vicinity of injection were demonstrated, both for future operations and for quantitative study of high intensity phenomena. A record intensity of 3.2 × 1012 protons per pulse was attained when some portions of these windings were activated. This occured approximately two years ago, too late for the previous Conference. The underlying ideas and computations preceded this date by about two years. While many turn backleg windings already existed on the AGS magnets, the appropriate systems connections had to be constructed and installed during a shutdown. It was hoped by now to have experimental studies using all the systems, but time commitments have prevented further work to date. However the ideas used and the particularly simple approach to orbit analysis developed warrants being described.

High-Field Iron Core Magnets

Compact, highly saturated iron window frame dipoles and quadrupoles have been computed with computer programs. Systematic and random aberrations in relation with the saturation have been studied.

Three Dimensional Properties of Magnetic Beam Transport Elements

Analytical and experimental methods to describe precisely, in three dimensions, the magnetic fields of beam transport elements will be discussed. The influence of the fringing field on beam optical properties and magnet design will be presented. With appropriate boundary conditions the field components are expressed in terms of the magnetic potential to arbitrarily high orders with empirical coefficients and are grouped in a form to avoid the divergence of higher order terms. As an accurate description of the true field is obtained, a very precise trajectory can be computed for a known momentum. In addition, the more useful inverse problem of finding the momentum of a particle with known input and output trajectory coordinates is attacked. The trajectory solution is expressed as the sum of an analytical part plus perturbation terms. The first order solution for the momentum is easily obtained and the convergence of the subsequent perturbation calculations is very rapid even for extreme rays. The value of this method, with its precise treatment of fringing fields, is emphasized by treating in detail a wide angle spectrometer (120-in. wide, 36-in. long, 24-in. gap). The perturbation technique shows promise that an accurate instantaneous read-out of the momentum can be obtained by employing a modest number of perturbation corrections stored in the memory of the computer.

Studies of Quench Propagation in a Superconducting Window Frame Magnet

During the testing of a meter long, superconducting window frame magnet, information from many spontaneously generated quenches have been recorded by an on-line computer system. Nearly every layer in an eleven layer dipole had a voltage tap and for some layers this subdivided into two halves. This allowed us to study development of the quenches in some detail. Knowledge of the resistances throughout the magnet also allowed the temperature distributions in the superconducting windings to be determined. A qualitative picture of the quench was developed and quantitative values of quench propagaton velocities were compared to heat transfer calculations.

Large Cost Reductions Made Possible by Reevaluation of Beam Transport Parameters

A detailed study of beam transport hardware for external beams has recently been completed. This study was made from the viewpoint of reducing capital and operating costs of beam components, which could result in a greater number of high quality beams for a given amount of money.