P. L. Morton

Evaluation of Synchrotron Radiation Integrals

Many of the important properties of the stored beam in an electron storage ring are determined by integrals, ’ taken around the whole ring, of various characteristic functions of the guide fielci. Some of the integrals are handled easily, but a few are usually estimated graphically - particularly for alternating-gradient guide fields. This report describes a convenient method for evaluating numerically these recalcitrant integrals. In the usual linear approximation, the integrals we wish to consider are most conveniently expressed in terms of four (somewhat redundant) functions of the azimuthal coordinates: p(s) the radius of curvature of the design orbit, n the field index, F(s) the radial betatro; function andT(s) the off-energy (or “dispersion”) function. The Integrals We restrict our attention to guide fields made up of a number of magnetic segments - magnets or straight sections The functions p and n are assumed to have constant values within a given magnet, but vary abruptly at the entrance and erit boundaries. The integrals of interest are given by:

Computer modelling of bunch-by-bunch feedback for the SLAC B-factory design

A computer model of the storage ring, including the RF system, wake fields, synchrotron radiation loss, and the bunch-by-bunch feedback system, is presented. The feedback system model represents the performance of a fast phase detector front end (including system noise and imperfections), a digital filter used to generate a correction voltage, and a power amplifier and beam kicker system. The combined ring-feedback system model is used to study the feedback system performance required to suppress instabilities and to quantify the dynamics of the system. Results which show the time development of coupled bunch instabilities and the damping action of the feedback system are presented.<<ETX>>

A damping ring design for future linear colliders

The authors present a preliminary design of a damping ring for the TeV Linear Collider (TLC), a future linear collider with an energy of 1/2 to 1 TeV in the center of mass. Because of limits of the emittance, repetition rate, and longitudinal impedance, use is made of combined function FODO cells with wigglers in insertion regions; there are approximately 22 m of wigglers in the 155-m ring. The ring has a normalized horizontal emittance, including the effect on intrabeam scattering, which is less than 3*10/sup -6/, and an emittance ratio of epsilon /sub x/ approximately=100 epsilon /sub y/. It is designed to damp bunches for seven vertical damping times while operating at a repetition rate of 360 Hz. Because of these requirements on the emittance and the damping per bunch, the ring operates at 1.8 GeV and is relatively large, allowing more bunches to be damped at once.<<ETX>>

Spear II Performance

The single beam and colliding beam performance of the SLAC electron-positron storage ring SPEAR II is described. The sevenfold increase in harmonic number in SPEAR II in comparison to SPEAR I has made significant changes in single beam behavior. Strong synchrobetatron resonances and a new transverse instability are observed and our first studies of these phenomena are described, Measurements on current dependent bunch lengthening are presented.

Transverse phase space in the presence of dispersion

A generalized formalism is used to determine the beam ellipse parameters at some location in a transversely uncoupled transport line from a sufficient number of beam size measurements. The authors allow for contributions to the beam sizes from dispersion which can be either transported from some initial point, or generated along the transport line. They derive expressions for the pure betatron emittance in terms of the effective emittance (calculated from the measurements of the total transverse beam sizes) both in the presence and absence of bending magnets. Necessary and sufficient conditions for determining the pure betatron emittance are given and it is shown to be the absolute minimum of the effective emittance. It is shown that dispersion not only directly enlarges the emittance, but also causes a beta -mismatch.<<ETX>>

A Study of Spear as a Dedicated Source of Synchrotron Radiation

We have studied the potential of SPEAR as a dedicated source of synchrotron radiation, based on the expectation that SPEAR will become increasingly available for this purpose as PEP, the 18-GeV colliding-beam storage ring now under construction by LBL and SLAC, becomes operational. A synchrotron radiation research program has been underway since May, 1974. Two beam ports capable of serving 9 simultaneous users are now operational. In single-beam multi-bunch operation high currents are possible (225 mA has been achieved and ¿ 300 mA is expected) and the electron beam emittance can be made smaller, resulting in higher source point brightness. Descriptions aregivenof SPEAR capabilities and of plans to expand the research capability by adding beam runs and by inserting wiggler magnets in SPEAR straight sections.

Accelerator Physics Measurements at the Damping Ring

Besides the optics measurements described elsewhere, machine experiments were done at the SLC damping ring to determine some of its parameters. The synchrotron radiation energy loss which gives the damping rates was measured by observing the RF-voltage dependence of the synchronous phase angle. The emittance was obtained from the synchrotron light monitor, scraper measurements and by extracting the beam through a doublet and measuring its size for different quadrupole settings. Current dependent effects such as parasitic mode losses, head tail instabilities, synchrotron and betatron frequency shifts were measured to estimate the impedance. RF-cavity beam loading and its compensation were also studied and ion collection was investigated. All results agree reasonably well with expectations and indicate no limitations to the design performance.

Transient analysis of multicavity klystrons

A model for analytic analysis of transients in multicavity klystron output power and phase is described. Cavities are modeled as resonant circuits, while bunching of the beam is modeled using linear space-charge wave theory. The analysis has been implemented in a computer program used to design multicavity klystrons with stable output power and phase. The authors present as examples transient analyses of a relativistic klystron using a magnetic pulse compression modulator and of a conventional klystron designed to use phase-shifting techniques for RF pulse compression.<<ETX>>

Operating Results from SPEAR

Initial operating experience with the SLAC electron-positron storage ring SPEAR is described. A luminosity of 1.2 × 1031 cm-2 sec-1 has been achieved and two-beam interaction effects are described. A single-beam coherent instability, which can be suppressed either by control of the ring chromaticity or by feedback, has been observed. Current-dependent bunch lengthening and widening have been observed, and experiments indicate that these phenomena may be associated with an increase in the energy spread of the beam. Procedures to increase the luminosity to the design value are discussed. Plans to increase the maximum beam energy of SPEAR to 4.5 GeV are described.

The SLAC linac as used in the SLC collider

The linac of the SLAC (Stanford Linear Accelerator Center) Linear Collider (SLC) must accelerate three high-intensity bunches on each linac pulse from 1.2 GeV to 50 GeV with minimal increase of small transverse emittance. The procedures and adjustments used to obtain this goal are outlined. Some of the accelerator parameters and components which interact are the beam energy, transverse position, component alignment, RF manipulation, feedback system, quadrupole lattice, BNS damping, energy spectra, phase space matching, collimation, instrumentation, and modeling. The method to bring these interdependent parameters collectively into specification has evolved over several years. The sequence which is sued to turn on the linac from a cold start and produce acceptable beams for the final focus and collisions is reviewed. Approximate time estimates for the various activities are given.<<ETX>>