The UCLA compact 20-MeV/c electron linear accelerators is designed to produce a single electron bunch with a peak current of 200 A, an RMS energy spread of 0.2% or less, and a short 1.2-ps RMS pulse duration. The linac is also designed to minimize emittance growth down the beamline so as to obtain emittances on the order of 8 pi mm-mrad in the experimental region. The linac will feed two beamlines, the first will run straight into the undulator for FEL experiments while the second will be used for diagnostics, longitudinal bunch compression and other electron beam experiments. A description is given of the considerations that went into the design of the accelerating structures and the transport to the experimental areas. (8 References).
The authors explore the use of a large-circumference, high-energy electron-positron collider such as PEP to drive a free-electron laser (FEL), producing high levels of coherent power at short wavelengths. They consider self-amplified spontaneous emission (SASE), in which electron bunches with low emittance, high peak current, and small energy spread radiate coherently in a single pass through a long undulator. The authors also explore various combinations of electron-beam and undulator parameters, as well as special undulator designs and optical klystrons (OKs), to reach high average or peak coherent power at wavelength around 40 AA by achieving significant exponential gain or full saturation. Examples are presented for devices that achieve high peak coherent power (up to about 400 MW) with lower average coherent power (about 20 mW) and other devices which produce a few watts of average coherent power. (22 References).
A collaborative group of accelerator and plasma physicists and engineers has formed with an interest in exploring the use of plasma lenses to meet the needs of future colliders. Analytic and computational models of plasma lenses are briefly reviewed and several design examples for the SLAC Final Focus Test Beam are presented. The examples include discrete, thick, and adiabatic lenses. A potential plasma source with desirable lens characteristics is presented.
UCLA (University of California at Los Angeles) is proposing a compact superconducting high-luminosity (10(32-33)/ cm(-2)/ s(-1)) e+ e- collider for a phi factory. To achieve the required e+ e- currents, full energy injection from a linac with intermediate storage in a positron accumulator ring (PAR) is used. The elements of the linac are outlined with cost and future flexibility in mind. The preliminary conceptual design starts with a high current gun similar in design to those developed at SLAC and at ANL (for the APS). Four 4-section linac modules follow, each driven by a 60-MW klystron with a 1- mu s macropulse and an average current of 8.6 A. The first 4-section module is used to create positrons in a tungsten target at 186 MeV. The remaining three modules are used to accelerate the e+ e- beam to 558 MeV (no load limit) for injection into the PAR. (0 References).
A compact 20-MeV linac with an RF laser-driven electron gun will be used to drive a high-gain (10-cm gain length), 10.6- mu m wavelength FEL (free-electron laser) amplifier, operating in the SASE mode. Saturnus will mainly be used to study FEL physics in the high-gain regime, including start-up from noise, optical guiding, sidebands, saturation, and superradiance, with emphasis on the effects important for future short-wavelength operation of FELs. The primary magnetic flux is provided by C-shaped iron yokes, where between the poles thin blocks of neodymium-iron-boron magnets are placed to provide additional magnetic flux along the undulator axis. (9 References).
We discuss the magnetic lattice design of a high luminosity 510 MeV electron-positron collider, based on high field superconduction bending dipoles. The design criteria are flexibility in the choice of the tune and beta functions at the interaction point, horizontal emittance larger than 1 mm mrad to produce a luminosity larger than 10(32) cm(-2)s(-1), large synchrotron radiation damping rate, and large momentum compaction. The RF system parameter are chosen to provide a short bunch length also when the beam energy spread is determined by the microwave instability. A satisfactory ring dynamic aperture, and a simultaneous small value of the horizontal and vertical beta function at the interaction point, we expect will be achieved by using Cornacchia Halbach modified sextupoles.
Conditions are established for stable single particle motion in a storage ring with very small momentum compaction, and very short bunch length, the quasi isochronous ring. How this condition can be achieved is discussed. Applications of this condition to colliders and synchrotron radiation sources is examined. (2 References).
A 510-MeV electron-positron collider has been proposed at the University of California at Los Angeles to study particle beam physics and phi-meson physics at luminosities larger than 1032 cm/sup -2/s/sup -1/. The collider consists of a single compact superconducting storage ring (SMC), with a bending field of 4 T and a current larger than 1 A. A discussion is presented of the main characteristics of this system and its major technical components: superconducting dipoles and the RF vacuum and injection systems. (6 References).
Laser-driven RF photocathodes represent a recent advance in high-brightness electron beam sources. The author investigates a variation on these devices that was obtained by using a ribbon laser pulse to illuminate the cathode, yielding a flat beam ( sigma /sub x/[right angle bracket][right angle bracket] sigma /sub y/) which has asymmetric emittances at the cathode proportional to the beam size in each transverse dimension. The flat-beam geometry mitigates space charge forces which lead to intensity-dependent transverse and longitudinal emittance growth, thus limiting the beam brightness. The fundamental limit on achievable emittance and brightness is set by the transverse momentum distribution and peak current density of the photoelectrons. (11 References).
An analytical model of the equilibrium approached by the beams, that of a generalized Bennett pinch which develops through collisionless damping due to the strong nonlinearity of the beam-beam interaction is presented. In order to calculate the equilibrium pinched beam size, an estimation of the RMS emittance growth is made which takes into account the partial adiabaticity of the collision. This pinched beam size is used to derive the luminosity enhancement factor, whose scaling is in agreement with the simulation results for both D and thermal factor A= sigma /sub z// beta * large, and explains the previously noted cubic relationship between round and flat beam enhancement factors. (4 References).
A new concept in ion clearing for storage rings, that of resonant removal of ions in dipoles by shaking the beam horizontally near the ion cyclotron frequency is discussed. This method of beam shaking is similar to the variations on ion bounce shaking but has advantages in requiring a narrower bandwidth of shaking frequencies and in much higher achievable ion kinetic energies. The results of analytical theory, and computer simulations are discussed. (7 References).
The transverse emittance in the FNAL (Fermi National Accelerator Laboratory) Booster grows at a high beam intensity, in a time less than 100 turns. An examination is made of the possible contributions to the fast emittance growth from coherent instability of the beam envelope. Theoretical analysis, through the use of envelope equations, is employed to predict the dependence of envelope instability on the peak current of the Booster beam. These predictions are compared to the results of multiparticle tracking calculations. (11 References).