Scrapers are often used in storage rings and accelerators to clean the transverse profile of the beam. When the beam is not exactly midway between the jaws of the scraper the transverse electric and magnetic fields produced by the image charges and currents are asymmetric. For a relativistic beam traveling through a longitudinally uniform tube with infinitely conducting walls the transverse force from the electric field is canceled by the transverse force from the magnetic field. When an off-center particle bunch passes by a longitudinal discontinuity in the beam tube the transverse force from the electric field are no longer cancelled by the transverse force from the magnetic field and particles in the bunch experience a transverse momentum kick which is independent of energy. It is shown that scrapers that pass close by high peak current beams can significantly degrade the beam emittance. A circular scraper was chosen for computer simulation. (LEW)

Expressions are presented for the electric and magnetic fields due to a pulse of charge, which may be oscillating transversely while moving down an infinitely long, highly conducting pipe of circular cross section. The expressions are evaluated at large distances from the pulse and the fields are shown to decrease algebraically in the distance behind the pulse. In the absence of transverse oscillations the longitudinal electric field varies as the inverse three-halves power of the distance; in the presence of oscillations the dominant field component is the transverse magnetic field, which decreases as the inverse one-half power. In the long-range limit the amplitude of the fields is proportional to the square root of the wall resistivity. The phase of the field associated with the oscillating pulse is shown to be the phase of the pulse at the time when it passed the point of observation.

The growth of the quasi-steady-state motion of the coupled bunch oscillations in storage rings has been studied by means of a normal mode analysis to determine the beam stability. In this type of analysis, the initial amplitude displacements of the bunches are first written as a sum of the normal modes of the multiple bunch system, and then the stability of each mode is determined. If the amplitude of all modes decay then the amplitude of all of the individual bunches must eventually decay, and the motion is considered stable. However, if the beat frequency between the different modes is sufficiently high, compared to the decay rate of the modes, it is possible for the amplitude of some of the bunches to grow temporarily before eventually decaying.< >

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.< >

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.< >

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.<>

Relativistic klystrons are being developed as a power source for high gradient accelerator applications which include large linear electron-positron colliders, compact accelerators, and FEL sources. We have attained 200 MW peak power at 11.4 GHz from a relativistic klystron, and 140 MV/m longitudinal gradient in a short 11.4 GHz accelerator section. We report here on the design of our relativistic klystrons, the results of our experiments so far, and some of our plans for the near future. 5 refs., 9 figs., 1 tab.

Two types of beam response measurements were carried out in SPEAR with the aim of gaining understanding of high intensity phenomena. In the first case, the beam was kicked horizontally with the injection kicker magnet and the amplitude of the resulting betatron oscillation was observed as a function of time. This experiment was carried out for different beam intensities. At large currents, the decay of the oscillation is dominated by the “head-tail damping” due to the transverse impedance. It shows the expected dependence on the chromaticity. At small currents, the decay of the excited betatron oscillation is due mostly to Landau damping. Another series of experiments dealt with the longitudinal behaviour of a single bunch. .4 network analyser was used to modulate the phase or amplitude of the RF voltage and thereby excite dipole or quadrupole synchrotron oscillations. The modulating frequency was swept through the dipole or quadrupole frequency and the beam response in phase and amplitude, the longitudinal bunched-beam transfer function, wits observed. The behaviour of the transfer function changed significantly as the beam current was increased. We outline a theoretical framework for the interpretation of these measurements.

I’KI’ has I)crn IISC~ as a. source of synchrol.ron ra.diat.ion with at, 11nd~lat0r beam line operating parasitically tlurirtg particle pllysics runs at 14.5 GeV bca.m energy. ‘I’hc l)ossibi!ltlF. of using PEP in a dcdicntcrl mode for synchr0(1.011 racllat,lon have tenon considered. Since a lower bran1 r~~crgy is preferred in this cast, PEP has hcen succrssfully op~~ratctt at. 8 GeV where I.hr uricc,nplctl l~ra111 ctnittance is 27 null ratl. It is of int.erest to r~lucc this clnit.tance fnrther wit.h a tliffrrent opt,ics ha.ving strongrr horizont~al focnssing. This has I)een (lone by increasing tile horizontal heMron phase aclvauw per cell from 56” 1.0 I 00” resuIt.ing in an cmit,t,ance of about 9 1llJ1 rnd. To keep t,he strc~ngth of the sext 11p0lcs and their crV a l>eam was successfully injected and n.ccn~iiula.led. ‘I’he hol.izontal arid ~.~rtit.nl eniit tanccs were n~easllrc~tl Itsing the photon J)talll of the 58 111 long un(lulator hnnl lint- iI found to be 12.1 ant1 1 2 nnl ~,ntl. This is close to t,hr exp~ct,r~l value of 9.9 11111 ract for the SI~III of the two. The I)ealll lift, t.imr was over 30 110111.S at low cllrrcnts. Diffrrcn! mcltiods of rctliicing this emit.tancr cvcn further are invcst.iRat,e(l. Jncrcasillg tllc horizonl.al tlalnping pal.tition front .J, = rto .r, = 2 looks nlost prornisil.~g. This does uot rquirc new hardware bnl can IJ~ achieved WIllI a. s111nt1 increase of the RF-frequency of about ‘I kHz. Such au operation mode has been co~nputed ant1 tracked. The dyna.mic accrpt.ancr is very large and the expectrtl nnc~onplcd eniitt.ance is ,I.3 *11n rad at 8 (;eV.

We attempt in this note to make plausibility arguments regarding the magnitude of tolerable ground motions for the SSC. A cornpleat, general and quantitative treatment of every conceivable effect awaits far more effort than could have been marshalled for this preliminary study. This note is in three parts: Section 1. A description of the types of motions likely to be encountered on any site and some generally obvious site recommendations. Section 2. Estimates of the consequences of such motions with calculations of only those few types which we consider dominant in the problem. A review of the type and strength of beam position feedback which may be required. Section 3. A summary of suggested tolerances resulting from the calculations and assumptions made. Submitted for Publication * Work supported by the Department of Energy, contract DE AC03 76SF00515.

In large accelerators and low beta colliding beam storage rings, the strong sextupoles, which are required to correct the chromatic effects, produce strong nonlinear forces which act on particles in the beam. In addition in large hadron storage rings the superconducting magnets have significant nonlinear fields. To understand the effects of these nonlinearities on the particle motion there is currently a large theoretical effort using both analytic techniques and computer tracking. This effort is focused on the determination of the 'dynamic aperture' (the stable acceptance) of both present and future accelerators and storage rings. A great deal of progress has been made in understanding nonlinear particle motion, but very little experimental verification of the theoretical results is available. In this paper we describe 'dynamic tracking', a method being studied at the SPEAR storage ring, which can be used to obtain experimental results which are in a convenient form to be compared with the theoretical predictions.

One of the main parameters that determines the next generation of high energy accelerators is the acceleration gradient. Recently there has been interest in the use of plasma density waves for obtaining high acceleration gradients.

Undulators appear to be nearly ideal radiation sources for use in storage rings because of their high brightness and small perturbation on stored beam characteristics. We consider the effects of higher-order magnetic field errors and show how they increase beam size and may lead to unstable growth of betatron oscillations. We have observed such effects in SPEAR at betatron tunes satisfying the equations: 3nu/sub x/ + nu/sub y/ = 21 and nu/sub x/ + 3nu/sub y/ = 21. The widths of these resonances were measured to be GAMMA = 0.008 +- 0.004. They are clearly visible on the synchrotron light monitors with a very dynamic and characteristic beam blow-up pattern (reminiscent of a Miller beer label). A model is developed which predicts the locations of resonances, their widths and the projected shapes observed on the light monitors. By inducing such high-order coupling resonances one could study such things as the beam distribution in electron rings or possibly turbulent motion in proton rings.

Electron linear accelerator technology for high-power, short-wavelength free-electron lasers is reviewed.

A lumped distribution of rf cavities leads to discrete energy gains of the electrons and the positron beams in a storage ring, which in turns leads to a distortion in the closed orbits of the two beams. For PEP, it is found to be a small effect. There is another consequence of having a lumped rf distribution. It comes from a skewness of the synchrotron phase space ellispe and has nothing to do with the net energy gains in the cavities. If the rf cavities are distributed uniformly around the ring, the synchrotron z-delta phase space is an upright ellispe. If the cavities are lumped, however, the ellispe will be slightly tilted. The coupling between the horizontal coordinate x and delta then leads to a small tilting angle theta in the x-z projection of the beam distribution. This small tile must be compared with another small quantity, sigma/sub x//sigma/sub z/, because if theta is not too small compared with sigma/sub x//sigma/sub z/ at the interaction points, there might be some reduction of luminosity. We studied the x-z tilt due to lumped rf distribution and found it is small compared with sigma/sub x//sigma/sub z/ for PEP, hence little loss of luminosity. Our results are presented in this note. 5 refs., 7 figs., 1 tab.