X.L. Zhang

Tevatron Electron Lenses: Design and Operation

The beam-beam effects have been the dominating sources of beam loss and lifetime limitations in the Tevatron proton-antiproton collider [1]. Electron lenses were originally proposed for compensation of electromagnetic long-range and head-on beam-beam interactions of proton and antiproton beams [2]. Results of successful employment of two electron lenses built and installed in the Tevatron are reported in [3,4,5]. In this paper we present design features of the Tevatron electron lenses (TELs), discuss the generation of electron beams, describe different modes of operation and outline the technical parameters of various subsystems.

Generation and diagnostics of uncaptured beam in the Fermilab Tevatron and its control by electron lenses

In the Collider Run II, the Tevatron operates with 36 high intensity bunches of 980 GeV protons and antiprotons. Particles not captured by the Tevatron RF system pose a threat to quench the superconducting magnet during acceleration or at beam abort. We describe the main mechanisms for the origination of this uncaptured beam, and present measurements of its main parameters by means of a newly developed diagnostics system. The Tevatron Electron Lens is effectively used in the Collider Run II operation to remove uncaptured beam and keep its intensity in the abort gaps at a safe level.

Experimental Demonstration of Colliding-Beam-Lifetime Improvement by Electron Lenses

We report the first experimental demonstration of compensation of beam-beam interaction effects in high-energy particle collider by using space-charge forces of a low-energy electron beam. In our experiments, an electron lens, a novel instrument developed for the beam-beam compensation, was set on a 980-GeV proton bunch in the Tevatron proton-antiproton collider. The proton bunch losses due to its interaction with antiproton beam were reduced by a factor of 2 when the electron lens was operating. We describe the principle of electron lens operation and present experimental results.

The special applications of Tevatron electron lens in collider operation

Besides the Tevatron Electron Lens (TEL) runs as a R&D project for Tevatron Beam-Beam Compensation, it is used daily as a Beam Abort Gap Cleaner for collider operations. It can also serve as beam exciter for beam dynamics measurements and as a slow proton or antiproton bunch remover. This report describes all these applications and related observations.

Commissioning of the second Tevatron Electron Lens and beam study results

In the framework of Fermilabs Beam-Beam Compensation (BBC) project, the 2nd Tevatron electron lens (TEL2) was installed in the Tevatron during Spring 2006 shutdown. It was successfully commissioned and a series of beam studies has been carried out in single bunch and all-bunch modes. The paper describes TEL2 commissioning and beam studies results.

Beam losses at injection energy and during acceleration in the Tevatron

Protons and anti-protons circulate on helical orbits in the Tevatron. At injection energy (150 GeV) the lifetimes of both species are significantly lower on the helical orbits compared to lifetimes on the central orbit but for different reasons. There are also significant beam losses in both beams when they are accelerated to top energy (980 GeV) - again for different reasons. We report on experimental studies to determine the reasons and on methods of improving the lifetimes and losses for both beams.

Beam-beam compensation in Tevatron: status report

The project of beam-beam compensation (BBC) in the Tevatron using electron beams has passed a successful first step in experimental studies. The first Tevatron electron lens (TEL) has been installed in the Tevatron, commissioned, and demonstrated the theoretically predicted shift of betatron frequencies of a high energy proton beam due to a high current low energy electron beam. After the first series of studies in March-April 2001 (total of 7 shifts), we achieved tuneshifts of 980 GeV protons of about dQ=+0.007 with some 3 A of the electron beam current while the proton lifetime was in the range of 10 hours (some 24 hours at the best). Future work will include diagnostics improvement, beam studies with antiprotons, and fabrication of the 2nd TEL.

Tevatron Beam-Beam Compensation Project Progress

In this paper, we report the progress of the Tevatron Beam-Beam Compensation (BBC) project [1]. Proton and antiproton tuneshifts of the order of 0.009 induced by electron beam have been reported in [2], suppression of an antiproton emittance growth in the Tevatron High Energy Physics (HEP) store has been observed, too [1]. Currently, the first electron lens (TEL1) is in operational use as the Tevatron DC beam cleaner. Over the last two years, we have greatly improved its reliability. The 2nd Tevatron electron lens (TEL2) is under the final phase of development and is being prepared for installation in the Tevatron in 2005.

Upgrades of the Tevatron electron lens

This paper will describe the main upgrades of the Tevatron Electron Lens (TEL) during the year 2003. The bending angle of the electron beam entrance and exit to the main solenoid will be decreased from 90 degrees to 53 degrees and three more solenoids will be added to each of the two bends, which will allow us to control the electron beam size more freely. A new gun will also be installed which will give us a Gaussian transverse beam distribution in addition to the flat beam with much smoother edge to minimize the nonlinear effect of the beam-beam force. In addition, a new BPM system will be installed to let us have more precise beam position measurements for proton, antiproton and electron beams. A knife-edge beam profile measurement system will replace the space-consuming scanning wires. We expect that these upgrades will improve the ability to increase the lifetime of the (anti)proton beam during beam-beam compensation operation.

Experimental demonstration of beam-beam compensation by Tevatron electron lenses and prospects for the LHC

Electromagnetic long-range and head-on interactions of high intensity proton and antiproton beams are significant sources of beam loss and lifetime limitations in the Tevatron Collider Run II (2001-present). We present observations of the beam-beam phenomena in the Tevatron and results of relevant beam studies. We analyze the data and various methods employed in high energy physics (HEP) operation, predict the performance for planned luminosity upgrades and discuss ways to improve it.