E. D. Courant

Commissioning the Polarized Beam in the AGS

After the successful operation of a high energy polarized proton beam at the Argonne Laboratory Zero Gradient Synchrotron (ZGS) was terminated, plans were made to commission such a beam at the Brookhaven National Laboratory Alternating Gradient Synchrotron (AGS). On February 23, 1984, 2 ..mu..A of polarized H/sup -/ was accelerated through the Linac to 200 MeV with a polarization of about 65%. 1 ..mu..A was injected into the AGS and acceleration attempts began. Several relatively short runs were then made during the next three months. Dedicated commissioning began in early June, and on June 26 the AGS polarized beam reached 13.8 GeV/c to exceed the previous ZGS peak momentum of 12.75 GeV/c. Commissioning continued to the point where 10/sup 10/ polarized protons were accelerated to 16.5 GeV/c with 40% polarization. Then, two experiments had a short polarized proton run. We plan to continue commissioning efforts in the fall of this year to reach higher energy, higher intensity, and higher polarization levels. We present a brief description of the facility and of the methods used for preserving the polarization of the accelerating beam.

On Improving the Chromatic Effects of Storage Rings with Antisymmetric Insertions

High luminosity storage rings require good chromatic behavior for beams with large momentum spreads. This requires that the effects of half-integer structure resonances for off-momentum particles be minimized. We show that a lattice with antisymmetric insertions can be so designed that the driving term for the half-integer structure resonance is suppressed by cancellation of successive pairs of highbeta multiplets. Hence, even though the periodicity is half that of a lattice with symmetric insertions, the chromatic properties are similar.

SSC Test Lattice Designs

Simple test lattices for a 20 TeV superconducting super collider have been designed based on each of the major dipole designs, 3, 5, 6, and 6.5 Tesla. These lattices have been made as nearly identical as possible. The reason for different lattices is to be able to evaluate equally the different magnet designs, with associated multiple distributions and persistent current errors, through analytical and tracking programs without the complications of different lattice designs. It should be noted that while these designs are typical of a 20 TeV SSC, they are meant only for study and do not represent a machine which would be built. Thus, they do not have crossing magnets or utility insertions. However special phase shifting sections called Phase Trombones are included, a feature not present in most of the previous SSC lattice designs.

The RHIC Lattice

An antisymmetric lattice for the proposed Relativistic Heavy Ion Collider at Brookhaven National Laboratory is presented, which has been designed to have (1) an energy range from 7 GeV/amu up to 100 GeV/amu; (2) a good tunability of ß* and betatron tune; (3) freedom in the choice of crossing angle between beams; and (4) capability of operating unequal species, for example, proton on gold. Suppression of structure resonances is achieved by a proper choice of the phase advances across the insertion and the arc cells.

Enhanced Resistive Wall Instability for off-Centered Beams

Beam occupation of a large fraction of the available vacuum chamber, typical of high energy proton storage ring designs, results in an enhancement of the resistive wall instability. The effect is considered for ISABELLE during the current stacking procedure. Results for the coasting stack in its initial phase as well as for the injected bunches are presented.

Depolarizing 'beat' Resonances in the Brookhaven AGS

While accelerating polarized protons in the Brookhaven AGS we found a variant of the standard imperfection and intrinsic depolarizing resonances which has some of the properties of both types. Imperfection resonances occur at G¿ = k, when the number of spin precessions per revolution, G¿, equals a harmonic of the depolarizing field, k. Intrinsic resonances occur at G¿ = nP±¿Z, when the AGS gradient periodicities, nP, modulate free vertical betatron oscillations to create the sum and difference frequencies. The variant resonance is a beat between nP and an imperfection driven betatron oscillation of periodicity k. These occur at G¿ = nP±k, and are strongest when the driven betatron oscillation is largest. The effect was most dramatic at the strong G¿ = 27 resonance. Since ¿Z = 8.8 for the AGS, and there is a major nP = 36 AGS periodicity, a strong beat resonance should exist at G¿ = 36-9 = 27. Applying a 27th harmonic correction directly was unsuccessful, but a 9th harmonic correction removed the depolarization.

Status of ISABELLE Lattice

ISABELLE, a facility for colliding protons with center of mass energies between 60 and 800 GeV, is presently under construction at Brookhaven National Laboratory. The device consists of two identical rings for the accumulation, acceleration and storage of proton beams, shaped and interlaced in the horizontal plane to intersect in six so-called crossing points where the beams that rotate in opposite directions in the two rings are exposed to each other. The overall dimensions of the facility are kept relatively small because advantage is taken of the large fields and gradients that are possible in superconducting magnets; the associated saturation effects in the magnet iron make a separated function lattice practically inevitable. The rings are to be filled from the AGS, using synchronous beam transfer; this forces their circumference to an integer multiple of the rf wavelength in the AGS (=67.26 m). The integer chosen is 57, about the lowest value possible, thus the circumference of each ring is 3833.85 m. The charge in each ring is expected to be about 6.4 x 10/sup 14/ protons, which requires about 250 AGS charges of 2.75 x 10/sup 12/ protons per pulse if the injection efficiency is 100%.The actual efficiency is unlikelymorexa0» to be better than 50%, so that in excess of 500 AGS pulses may be needed per ring. The beam is to be accumulated in synchrotron phase space by means of an injection and stacking procedure similar to one developed for the ISR at CERN; this leaves the betatron emittance of the circulating beams independent of its intensity and equal to that in the AGS just before extraction while its momentum spread increases with intensity.«xa0less

Effects in Low Periodicity Lattices Resulting from Low ß Insertions

In intersecting proton storage rings such as the existing ISR and the proposed ISABELLE, the beams are stacked in momentum space and occupy a momentum bite of 1-3%. The chromaticity of the rings reflects a dependence of the betatron tune as well as the structure function,2 p, on momentum. Correction of these effects can at least in part be accomplished by a distribution of sextupole magnets. The momentum spread within which the variations of the tune and the P-function with momentum can be eliminated or tolerated is the momentum aperture.

Injection into the ISA

Three modes of injection into the ISA storage accelerators are discussed. The three are: 1) Energy stacking in the ISA. 2) Acceleration of 12 bunches in the AGS followed by single bunch transfer to the ISA. Application of a moving bucket technique then allows the transferred bunch to be brought closer to the bucket train circulating in the ISA. 3) Acceleration on the first harmonic in the AGS. The single bunch is then transferred directly to the ISA into a matched bucket.

Experimental Insertions for the ISA

The general design features of experimental insertions for the ISA storage accelerators are presented. Various insertions which satisfy the requirements for specific high energy particle experiments are discussed. Some consideration is given to a) the distribution of the insertions in the lattice; b) the separation of experimental areas from those used for injection and protective extraction; c) the subject of beam crossing; d) the implications of high s, high quadrupole gradient conditions required in the insertions; and e) general characteristics, including luminosity and beam momentum spread.