A. G. Ruggiero

Time and Momentum Exchange for Production and Collection of Intense Antiproton Beams at Fermilab

Antiprotons for the Fermilab p¿p colliding beam project are accumulated by rf stacking of successive 8 GeV antiproton batches in a storage ring using stochastic cooling to reduce both transverse and longitudinal emittance. The rate of accumulation is increased 15-fold by interchange of bunch length and momentum spread of the antiproton bunches in a special purpose debuncher ring. Tightly bunched antiprotons are produced at the target by 120 GeV protons from the Main Ring. From 2.5×1012 protons every 2 seconds the debuncher receives 7×107 antiprotons within a momentum bite ¿p/p=3%. These antiprotons are injected into mismatched stationary rf buckets in the debuncher so that synchrotron oscillation produces bunch rotation. After 90° of rotation followed by adiabatic debunching, the narrow time spread has been converted into a momentum spread ¿p/p=.2%. We describe the rf technique used to shorten the bunches of the primary proton beam in the Main Ring and report test results. We describe the complementary procedures to be used in the Debuncher and demonstrate the expected reduction of the momentum spread by particle tracking simulation.

The Fermilab Tevatron I Debuncher Ring

The Fermilab Tevatron I project includes two rings. One is an Accumulator Ring where subsequent pulses of antiprotons are accumulated by stochastic momentum stacking and the other is the Debuncher Ring. In this paper we describe the design of the Debuncher. The lattice of the Debuncher has been designed with three goals. First, the ring must fit closely around the Accumulator. Second, the lattice must be able to satisfy the primary function of the ring, which is bunch rotation and debunching of an antiproton beam before it is transferred to the Accumulator. Finally, fast betatron stochastic cooling in two seconds must be included to keep the Accumulator aperture as small as possible. In this paper we describe all the features lattice designed to meet these requirements.

Momentum Precooling in the Debuncher Ring for the Fermilab Tevatron-I Project

The design of the antiproton source for the Fermilab Tevatron-I project (TeV-I) incorporates two separate rings. The Accumulator Ring uses a stochastic cooling/stacking system to accumulate a sufficient number of antiprotons for use in the Tevatron collider. The Debuncher Ring rotates buckets and debunches antiproton pulses from the production target. This requires, in the Debuncher, a choice of lattice transition energy very near the beam energy, resulting in very narrow spread in the circulation frequency. If the energy spread could be further reduced in the Debuncher before the beam is transferred to the Accumulator, operational improvements would result in: (1) the reduction of stochastic cooling power in the Accumulator; (2) the acceptance of a larger momentum bite of antiprotons in the Debuncher (thus more antiprotons); and (3) the reduction of momentum aperture in the Accumulator. This note describes a quick investigation of the feasibility of precooling within the framework of technically achievable parameters.

Progress Report on the POPAE Design Study

POPAE (Protons on Protons and Electrons) is a storage ring facility at the Fermilab on a scale suitable to permit the collision of 1000 GeV protons with 1000 GeV protons and with electrons of an energy compatible with that scale. In this paper, we summarize our work thus far on the lattice and layout of the proton storage rings. Though the 1000 GeV physical scale is maintained, the design is developed in a 400 GeV context. The proton rings form a racetrack, the two long straight sections of which are each about 1 km in length. Each long straight section contains a number of matched lattice insertions, as well as uncommitted space for additional development. Depending on the assumptions made concerning the beam-beam limit (as yet unknown experimentally), maximum luminosities are calculated to be in the range from 1033 to 1034cm-2 sec-1.

Deceleration of Antiprotons in the Fermilab Booster

Deceleration has been studied in longitudinal phase space by numerical simulation of the phase motion. Longitudinal acceptances as a function of the antiproton injection momentum, the transition energy and the ramp of the magnetic field are presented. Preliminary deceleration experiments with protons are discussed.

Lattice Insertions for POPAE

Four types of insertions are described for the six 200-m straight sections of POPAE. All have dispersion matched to zero. (1) Injection-ejection insertion - This has proper high-6 values and phase advances for horizontal injection and vertical ejection. (2) Phase-adjust insertion - The phase advance in this insertion is adjustable over a range of ~100°. (3) Generalpurpose insertion - The ß* is adjustable from 2.5 to 200 m and the crossing angle is adjustable from 0 to 11 mrad. (4) High-luminosity insertion - This gives an even lower ß* of 1 meter.

Longitudinal Beam Motion in the Fermilab Booster Accelerator

The intensity of the Fermilab booster accelerator has been limited in part by longitudinal effects. These include longitudinal space charge blowup prior to RF capture, phase space dilution during capture and insufficient voltage to provide bucket area to accelerate the diluted beam. Measurements of beam properties under these conditions, as well as high intensity effects during acceleration, are presented.

Transverse Beam Motion in the Fermilab Booster Accelerator

Measurements are presented of the transverse properties of the booster synchrotron. The principal transverse limitations to operational performance have been due to restricted aperture and improper multiturn injection. In addition to these features, working point, chromaticities, high-intensity effects, and injection matching are discussed.

Correction of Intensity-Dependent Beam Loss in the NAL Booster Synchrotron

At beam currents above 1.5 × 1011 protons/ pulse in the 8-GeV booster synchrotron, part of the beam is lost during a time interval of 2 to 4 msec just before transition. Particles are lost from several of the 84 rf beam bunches while the number of particles in the other bunches does not change. Electromagnetic coupling between the betatron motion and the magnet laminations which are not shielded from the beam by a vacuum chamber may induce the head-to-tail effect and cause the loss. This effect is sensitive to the chromaticity, ? = (??/?)/(?p/p). Changing the chromaticity with dc sextupole magnets at three locations in the ring has eliminated the loss for beam currents as high as 4.5 × 1011 protons/pulse.

Signal Suppression Analysis for the Momentum Stochastic Cooling with a Multiple System

The Tevatron I project at Fermilab depends critically on the momentum stochastic cooling to collect and store antiprotons produced by injecting protons on a target. This project differs from the similar original project at CERN by the fact that it requires greater antiproton flux. Moreover, the stochastic cooling design is made of several systems each with its own pickup, kickers, and chain of amplification. These systems could overlap in the frequency bandwidth as well as in the beam response dynamics. It has been argued, consequently, that the performance of the momentum cooling might have been limited by the signal suppression which one derives when examining the cooling system in closed loop. In this paper an analysis is made of the closed loop system for momentum stochastic cooling. In the closed loop configuration the electronic feedback depends not only on the electronic component characteristics but also on the beam intensity and energy distribution. The results give the interrelation between the signals from the different parts of the system and their mutual enhancement or suppression. The paper goes on to derive the Vlasov equation, to calculate the perturbation force, and to solve a larger number of dispersion relations.