F. E. Mills

Intermediate Energy Electron Cooling for Antiproton Sources Using a Pelletron Accelerator

It has been shown at FNAL that the electron cooling of protons is a very efficient method for reaching high luminosity in a proton beam. The emittance of the 120 KeV electron beam used at Fermilab corresponds to a cathode temperature of 0.1 eV. In order to apply cooling techniques to GeV proton beams the electron energies required are in the MeV range. In the experiment reported in this paper the emittance of a 3-MeV Pelletron electron accelerator was measured to determine that its emittance scaled to a value appropriate for electron cooling. The machine tested was jointly owned and operated by the University of California at Santa Barbara and National Electrostatics Corporation for research into free-electron lasers which also require low emittance beams for operation. This paper describes the thermal emittance of the beam to be the area in phase space in which 90% of the beam trajectories lie and goes on to describe the emittance-measurement method both in theory and application.

Electron Cooling Experiments at Fermilab

A 115 MeV proton beam has been successfully cooled in the Electron Cooling Ring at Fermilab. Initial experiments have measured the longitudinal drag force, transverse damping rate, and equilibrium beam size. The proton beam was cooled by a factor of ~50 in momentum spread in 5 sec, and by a factor of 3 in transverse size in 15 sec. Long term losses were consistent with single scattering from residual gas, with lifetime ~1000 sec. Using the measured electron beam temperature Te= 0.8(2) eV, the observed cooling agrees well with expectations from cooling theory.

Progress Report on Construction and Testing of a 3 MeV, DC, Ampere Intensity Electron Beam Recirculation System

Construction is underway on a 3 MV electrostatic accelerator designed to recirculate D.C. electron beams with intensities up to 4 amperes. The test facility includes a 3 MV, SF6 insulated vertical accelerator with parallel accelerator and decelerator tubes, diagnostic equipment, and vacuum and beam line components to bend the beam 180° and return it to the terminal. Special consideration has been given to cathode, electron gun, electron collector, and optical design to allow beam recovery efficiency of better than 99.99% at currents up to 4 amperes.

The Electron Beam for the Fermilab Electron Cooling Experiment

We describe the design and construction of the electron beam for the Fermilab Electron Cooling Experiment. Important parameters are (1) 110 keV kinetic energy; (2) 26 A current; (3) 0.5 eV rest frame temperature; (4) space charge neutralization; (5) beam modulation; (6) efficient energy recovery at the collector. The 5 m overlap region between the electron beam and the storage ring orbit represents 4% of the total ring circumference.

Azimuthal Redistribution of Beam in the Fermilab Main Ring

A technique is described by which the proton beam in the Fermilab main accelerator can be relocated from its original uniform distribution into a much smaller azimuthal region. This allows fast extraction of the entire beam in such a way as to allow single turn injection into a much smaller ring. The technique is applicable to generation, capture, and subsequent cooling of antiprotons. Experimental results are presented.

6D Cooling of a Circulating Muon Beam

We discuss the conceptual design of a system to reduce the 6D emittance of a circulating muon beam. This system utilizes ionization cooling to achieve 6D phase reduction of the beam. Our design is based on a hydrogen gas filled ring which incorporates optics consisting of weak‐focusing dipoles and 200 MHz rf cavities which restore the ionization energy loss due to the muons traversing the hydrogen gas.

Beam Envelope Solution of a Finite Emittance Beam including Space Charge and Acceleration

The intermediate-energy electron-cooling effort at the University of Wisconsin began as a collaboration with the University of California - Santa Barbara free electron laser group to measure the emittance of their test device. The measurement indicated that the optics of the FEL test device were extremely good; there was no emittance degradation throughout the system. For this reason, the electron gun for the electron-cooling effort has been designed to be optically identical to the UCSB gun designed by Hermannsfeldt of SLAC. The optics program used to investigate the gun behavior is EGUN, written by Hermannsfeldt. Because of the complicated problem of electron optics at the start of the Pelletron accelerating column, the first 120 kV of acceleration in the Pelletron is included in the gun optical study. At that point in the Pelletron, the electric field no longer has any significant radial component and the following optical treatment of the device is done.

Active Filter for High Current dc Magnets

Thyristor type regulated power supplies operated from 3 phase power lines are sensitive to phase unbalance, voltage fluctuations, line impedance and to other loads connected to the same line. At Fermilab, the large variety of pulsed equipment provides such perturbations in a wide frequency domain. A description is given of active filters used to stabilize magnet power supplies for a storage ring against fast fluctuations.

Electron cooling for the fermilab p source

Electron cooling will be used to cool and accumulate antiprotons in the Fermilab p source. Successive p production cycles will be injected into the cooling ring with offset momentum, and coalesced into the stack using longitudinal electron cooling. The stacking performance of electron cooling is evaluated. It is shown that optimum p accumulation rate is obtained by increasing the cooling energy until the cooling time just matches the cycle time T0, for p production. For Fermilab Tevatron I this corresponds to Tp = 1.5 GeV, Te = 750 keV. The main features of the electron beam design are described. For a primary electron beam current Ie = 10A, we expect a loss current (to ground) Il ≲ 10mA and a transverse temperature T⊥ ˜0.25 eV.

Injection, Magnet, and Vacuum Systems for the Fermilab Antiproton Cooling Ring

This paper gives construction details of the dipole and quadrupole magnets, a brief description of the proton injection line, and a short report of the vacuum system design for the existing Fermilab Cooling Ring.