Session 8W - Circular Electron Colliders, Linear Colliders (Beam Dynamics), Other Accelerators and Storage Rings.
POSTER session, Thursday afternoon, May 15
Waddington Room,

[8W.01] An e^+e^- Top Factory in a 50+50 TeV Hadron Collider Tunnel

We have begun to look at the parameters of an e^+e^- collider in the tunnel of a 50 + 50 TeV superferric hadron collider. This machine would be an extrapolation of LEP technology. Assuming a diameter of 170 km, a maximum radiated power of 100 MW, this collider should have a maximum energy of 500 - 600 GeV (c.m.) and should be able to produce a luminosity L = 0.9 \cdot 10^33 cm^-2sec^-1 at a center of mass energy of 360 GeV, (somewhat less at higher or lower energies) which would make it useful for producing top quarks or light Higgs bosons. Design problems include the very low field magnets, synchrotron radiation power, beam stability, and vacuum systems. Preliminary magnet, vacuum chamber and cooling designs will be presented along with possible construction techniques, and some costing algorithms.

[8W.02] Transverse Polarization beyond the Z Energy at LEP

Experimental results on transverse polarization obtained at LEP at a beam energy of 50 GeV are reported. The application of the refined orbit correction procedure known as Harmonic Spin Matching, implemented to compensate for depolarizing effects originating from orbit errors and misalignments of the machine elements, is described. Prospects and plans to improve the transverse polarization level at higher energies to extend the range of application of the direct and precise calibration with resonant depolarization are reported.

[8W.03] Determination of the Centre-of-Mass Energy for the LEP Experiments

The knowledge of the Center-of-Mass Energy at the LEP Interaction Points, where four Experimental Collaborations have their detectors installed since the beginning of the LEP operation for Physics in 1989, is important to reduce the systematic errors in the determination of the mass and width of the Z resonance and for the experimental activity at the W-pair energies which started with the 1996 physics run. The present understanding of the behaviour of the LEP energy is reported together with progress in the evolution of the time-dependent energy model based on effects identified as major sources of beam energy shifts and variations. Prospectives for the determination of the CM Energy in the W-pair region are accounted for.

[8W.04] Trapped Modes in CESR Sliding Joints

Trapped modes in the sliding joints in CESR may eventually set a limit on the currents in the machine. To detect these modes, experiments were performed where pairs of bunches of positrons were run through at various spacings. It was hoped that constructive and destructive interference of wake fields would produce varying amounts of heating. Data taking was time consuming, and insufficient numbers of data points could be taken to fit to the wake fields. To help solve this, the frequency of the mode was measured on the bench. A single trapped mode and its profile were observed. The trapped mode has a frequency of 3.59 GHz, just below the TM cutoff. The mode was used to predict a shunt impedance of 4.9 ohms. The corresponding loss factor is slightly higher than the total loss factor found in previous time domain measurements /footnoteBilling, Mike. Higher power Mode Loss Limitations for Beam Currents in CESR. CBN 84-15 (1984). The program ZAP/footnoteZisman, Michael, Swapan Chattopadhyay, and Joseph Bisognano. was used to predict an instability threshold of about 2.1 A.

[8W.05] CESR Status

The Cornell Electron Storage Ring has been reconfigured to operate with trains of bunches. In the interaction region the closely spaced bunches in one beam are separated from the bunches in the opposing beam by a horizontal crossing angle (\theta\sim \pm2.3mrad). In the machine arcs the beams are separated by a differential closed orbit distortion that is supported by electrostatic deflectors. CESR has achieved a peak luminosity of 4.0\times 10^32 cm^-2s^-1 with a total current of 320mA and nine two-bunch trains in each beam. The temporal spacing of the bunches in the trains is 42ns. For the 1996 calender year a total of 2.69fb^-1 was delivered to the CLEO experiment at energies on or near the \Upsilon_4s resonance, 5.3GeV/beam. We report details of the machine performance and work underway to increase single beam current limits related to longitudinal instabilities, separator photocurrent, and heating due to synchrotron radiation. We also describe efforts to reduce guide field nonlinearities and to increase the beam-beam tune shift parameter.

[8W.06] Beam-beam simulation of Möbius-modified CESR

Colliding beam experiments at CESR with beams made round by running on the coupling resonance have been performed,(E. Young et al.), abstract, this conference and runs are planned with the beams made round by Möbius modification.(R. Talman, Phys. Rev. Lett. 74), 1590, (1995) Performance in these configurations has been simulated using TEAPOT++ tracking, map generation, stochastic, and beam-beam modules within the Unified Accelerator Libraries(N. Malitsky et al.), abstract, this conference The true CESR lattice including sextupoles and element apertures is used. Outputs from the calculation include beam profile modification, tune optimization, maximum luminosity, and (with extrapolation) beam lifetimes.

[8W.07] Status of BEPC upgrade project

This paper describes the studies and progresses of the Beijing Electron Positron Collider (BEPC) upgrade in recent years. To upgrade the peak and the integrated luminosity, we mainly adopt the following ways: 1. the low-beta scheme 2. increasing the emittance 3. single interaction point (IP) scheme 4. full energy injection. The corresponding hardwares have been installed. The control system and the beam diagnostic system have been considerably improved. We already used several ways above and increased the luminosity by a factor of 1.5, and the full energy (E=1.548 GeV) injection was realized in the first half of the last year. We shall try to control the emittance and use single IP scheme to increase the luminosity in the future. Of course, a lot of hardware must be improved in order to keep the machine run stable. All of these studies and efforts have made the contributions not only for the upgrade of BEPC luminosity and the operation quality, but also for the research of the Beijing Tau-Charm Factory (BTCF).

[8W.08] Status of the KEKB Project

KEKB, an asymmetric, two-ring, electron-positron collider for B-physics, is under construction at KEK. 8-GeV electrons and 3.5-GeV positrons collide at one interaction point (IP) at a finite angle of \pm11 mrad. The BELLE detector surrounds the IP. The luminosity of the machine, 10^34cm^-2s^-1, requires large stored currents (1.1 A for electrons and 2.6 A for positrons) distributed into 5000 bunches and a small beta-value at the interaction point in the vertical direction (1 cm). Machine study done at the accumulation ring, AR, of TRISTAN, in July, October and November of 1996 showed that HOM-free normal-conducting cavities, called ARES, and superconducting, single-cell, single-mode cavities being developed could be used for KEKB. Fast beam-ion instability was also studied experimentally. Coupled-bunch instability due to photo-electrons in the positron ring is being studied at BEPC in Beijing jointly by KEK and IHEP. Installation of equipment in the 3000-m long tunnel starts from January 1997. Commissioning of the machine will take place whole 1998 starting from the upgraded injector linac early 1998 to the beam collision towards the end of the year, which will be followed by the start of physics experiment early 1999.

[8W.09] Simulation of Tail Distributions due to Random Processes and Beam-Beam Interaction in KEKB

A simulation that uses a new technique to obtain tail distributions in electron-positron storage rings is applied to KEKB. This program makes it possible to investigate tail distribution in simple and fast simulation technique. The simulation now includes beam-beam interaction for six dimensional phase space and various rare random processes, including bremsstrahlungs and scatterings from a beam-beam interaction and beam-residual gas in the ring. An estimate of the lifetimes for KEKB is also presented.

[8W.10] HOM Heating at the PEP-II IR Beryllium Vacuum Pipe.

The PEP-II IR geometry consists of a central beryllium vacuum pipe connected to each incoming beam line through a series of synchrotron masks which are not collinear and vary in dimensions along the beam axis. HOM fields generated by the colliding beams is a concern if the masks trap much of the HOM power inside the beryllium pipe, and if the HOM frequency coincides with a beam harmonic (multibunch effect). The worst case estimate indicates that this resonant heating can indeed lead to thermal loading beyond cooling design limits. This is based on simulations of the wall dissipation generated by a transit bunch charge and on the estimate of the HOM decay time (Q_e). The major heat contribution is from TE modes which are excited at a set of non-collinear masks at one end of the beryllium pipe via mode conversion. By shaping the masks such that the HOM fields are evanescent in this region the TE HOM power generated becomes much less. In addition, the masks at the other end can also be modified to detrap the HOM's more effectively so that their Q_e's are now substantially lower. Simulation shows that these two modifications are adequate in reducing the heating to a level that satisfies existing cooling requirements.

[8W.11] The PEPII Injection Kicker System

PEPII or the B factory consists of two asymmetric storage rings. The injection energy for electrons is 9~GeV, while that for positrons is 3.1~GeV. The bend angle into the high energy ring (HER) is 0.35~m-rad, and the angle into the low energy ring (LER) is 0.575~m-rad. The magnetic length for the HER kicker is 0.85~m, and 0.55~m for the LER kicker. The field produced by the magnet is therefore 123.5~G for the HER, and 132~G for the LER. Each ring has a kicker magnet upstream of the injection line which is used to distort the orbit of the stored beam. An identical magnet downstream of the injection line is used to restore the orbit of the stored beam and inject the incoming beam. The two magnets are driven in parallel by the modulator. The aperature of the magnets is 3.86 x 3.46~cm (HxV). Therefore the current required to drive the HER is 863~A, while for the LER it is 756~A. The inductance of the magnet is approximately 1.4~\muH/m. The current pulse is a critically damped sinusoid with a rise time of less than 300~ns. A kicker system has been designed which can be used for injection of both beams by varying the charge voltage. The modulator uses a conjugate circuit to match the impedance of the magnet, and coupling to the beam chamber.

[8W.12] Status of the PEP-II B-Factory

The PEP-II B-Factory project was given DOE authorization in 1994 to construct an e^+e^- colliding beam storage ring complex on the SLAC site. PEP-II is designed to produce a luminosity of 3 \times 10^33 \rmcm^-2s^-1 at a center-of-mass energy of 10.6 GeV with unequal energy beams of 3.1 and 9.0 GeV. The particle physics goal is to study CP violation in the B meson system. The project is being built by a collaboration of the Stanford Linear Accelerator Center, Lawrence Berkeley National Laboratory, and Lawrence Livermore National Laboratory. The asymmetric beam energies require two storage rings with the low energy ring supported above the high energy ring. The rings are filled using on-energy injection. There will be one interaction point with head-on collisions requiring, magnetic separation of the beams, low beta function values, and magnetic elements inside the solenoid of the BaBar physics detector. The high luminosity necessitates the use of a large number of beam bunches which require advances in the vacuum design, damped RF cavities, and bunch-by-bunch feedback systems. Status of this project is given including recent commissioning results and projections for beam-beam collisions in summer of 1998.

[8W.13] Wakefield Dynamics in Quasi Periodical Structures

The behavior of longitudinal wake fields of very short bunches, excited in in multicell accelerating structures, that are proposed for projects of Linear Colliders (TESLA, SBLC and NLC) has been studied. Computations were performed for bunch lengths down to 50 micrometers. The loss factor, which gives the global energy loss of the bunch and the profile of the wake function, which is of major interest for bunch energy spread calculations, has been carefully studied.

A strong modification of wake fields along the finite train of multicell cavities was clearly found for short bunchlengths. In particular, the wakes induced by the bunch, as it proceeds down the successive cavities, decrease in amplitude and become more linear around the bunch center, with a profile very close to the integral of charge density. The loss factor, decreasing also with the number of cavities, becomes independent of bunchlength for very short bunches and tends asymptotically to a finite value.

However, any periodicity (or multi-periodicity) break will spoil the wake distribution and increase the wakefield amplitude.

[8W.14] A Statistical Approach to Analyse Effect of Misalignments and Correction Algorithms in High-Energy Linacs

This paper presents a new and general tracking method capable of analysing, in a statistical way, the dipole wakefield effects on a high--energy charged--particle beam. More precisely, starting from a given probability law for the misalignments of the beam line components, a given trajectory correction scheme, and a given focusing lattice, the method computes the statistical distribution laws of certain quantities relative to the beam itself; for instance, this method can estimate the ``beam--emittance--distribution'' \(\rho_\epsilon(\epsilon)\), i.e the ``density of probability'' to obtain a beam with a final emittance between \(\epsilon\) and \(\epsilon+d\epsilon\). Therefore, the power of this new approach lies in the fact that it can generate, in one single passage, some statistical results which could be reproduced by a classical tracking program, but in a much more tedious way (several runs on seeveral machines with randomly generated misalignments). Moreover, it permits the study of the so--called ``long--range correlation effects'', that a classical tracking method cannot do properly.

[8W.15] Emittance Dilution in the Linacs of Linear Colliders with Energies of 1 and 5 TeV.

In this paper, we describe the single and multibunch sources of emittance dilution in the linacs of both 1 and 5 TeV center-of-mass energy linear colliders. The linacs operate at high rf accelerating gradients with a frequency around 30 GHz. At this high accelerating frequency, the wakefields are very strong and we discuss the BNS damping and correction procedures as well as the alignment and construction tolerances that are required to preserve the transverse emittance. Finally, because the collider must operate with long bunch trains, we consider the multibunch emittance dilution for two cases: that where the long-range transverse wakefield is purely damped and that where the wakefield is decreased by a combination of weak damping and detuning.

[8W.16] A Low Equilibrium Emittance Lattice for the CLIC Damping Ring

Damping rings with very small normalized equilibrium emittance and short damping times are required to deliver trains of bunches with high repetition rate for the high luminosity linear colliders. Using analytic expressions for the equilibrium emittance as a function of deflection angle per dipole, as well as the expression for the Twiss parameters providing the minimum emittance, a strategy to stay close to this minimum is described. In order to get as close as possible to the optimum Twiss parameters values, a quadruplet lattice with high horizontal phase advance is introduced. Finally, this approach is applied to the particular case of the CLIC rings and the resulting performance is described.

[8W.17] Nulling Emittance Measurement Technique for CLIC Test Facility

In order to test the principle of Two-Beam Acceleration (TBA), the CLIC Test Facility utilizes a high-intensity drive beam of 640 to 1000 nC to generate 30 GHz accelerating fields. To ensure that the beam is transported efficiently, a robust measurement of beam emittance and Twiss parameters is required. This is accomplished by measuring the beam size on a profile monitor, while scanning five or more upstream quadrupoles in such a fashion that the Twiss parameters at the profile monitor remain constant while the phase advance through the beam line changes. In this way the beam size can be sampled at different phases while a near-constant size is maintained at the profile monitor. This eases many of the difficulties of such measurement devices, especially those associated with limited dynamic range. In addition, the beam size is explicitly constant for a matched beam, which provides a ``nulling'' measurement of the match. Details of the technique, simulations, and results of the measurements are discussed.

[8W.18] A 30 GHz 5-TeV Linear Collider

As a CERN/SLAC collaboration, we present parameters for a linear collider with a 5 TeV center-of-mass energy that utilizes conventional rf technology operating at a frequency around 30 GHz. We discuss the scaling laws and assumed limitations that lead to the parameters described and we compare the merits and liabilities of different technological options including rf power source, accelerator structure, and final focus system design. Finally, we outline the components of the collider while specifying the required alignment and construction tolerances.

[8W.19] Simulation of Ground Motion Induced Beam Jitter in the SBLC Main Linac

To keep the two beams of linear colliders in collision, the beam offset with respect to each other should be significantly below the beam size. To investigate the effect of ground motion on the beam trajectory, a ground motion simulation algorithm has been developed. This code models measurements taken at various laboratory sites and pays special attention to coherence properties of ground motion. Additionally, possible stabilization feedback algorithms are included. The code can be adapted to a broad range of vibration spectra and coherence properties. As a specific application, beam jitter in the main linac of the S-band Linear Collider SBLC has been investigated. The resulting rms beam jitter of \sigma_y\approx 1.3\,\mum corresponds to a luminosity degradation of only 1\,%. The jitter can be reduced to about 0.45\,\mum using active stabilization of quadrupole vibrations. This indicates that, with respect to ground vibration, there is significant luminosity upgrade potential for SBLC.

[8W.20] Theoretical study of power relativistic amplifiers for electron beam bunching

The modern approach to an injector of the Two Beam Accelerator driver is based on bunched beam using. The bunching process in the Free Electron Lasers (FEL) was proposed for generating of drive beam in (W.B. Colson and A.M. Sessler, Annu. Rev. Nucl. Part. Sci., v. 35, 1985, p.25.) The first direct observation of the bunching of a relativistic electron beam, produced by a high power FEL interaction, was performed in (J. Gardelle, J. Labrouche, and J.L. Rullier, Preprint CESTA/4, 1996.) The simulation results and comparison of the bunching of a relativistic electron beam produced by a FEL and a TWT at the low energy region of electron beams are under discussion here. With the help of a rather simple model it is shown that the electron beam bunching in the TWT occurs at a shorter length as compared with FEL according to the well known fact that the space gain in the TWT is higher than in the FEL at low electron energies. The comparison of the simulation and experimental results on the FEL bunching are presented too.

[8W.21] Emittance Dilution and Magnet Design for the TTF FEL Second Bunch Compressor

This paper presents results of investigation of the transverse emittance dilution in the TTF FEL bunch compression system. The requirements for the bending magnet field of the dipole magnets of the second bunch compressor are determined. The dipole magnet design for the bunch compression system is performed. The dipole magnets are optimized to obtain minimum transverse emittance dilution.

[8W.22] A Linear Collider with Smaller Vertical Emittance

Luminosities in current designs of JLC/NLC-type linear colliders are basically limited by their vertical emittances, \gamma\varepsilon_y \sim 30~nm. On the other hand, the designs of damping rings in those machines assume quite loose machine-tolerances compared to their main linacs. If a design of a damping ring with same level of tolerances as the linacs is allowed, the vertical emittance can be reduced to several nanometers, and the luminosity of the collider will be drastically boosted. It is also possible to maintain the tolerances of the linac for such a small emittance by revising machine parameters.

[8W.23] Possibility of precise wake field measurement at ATF Extraction Line

The measurement of wake field is planed at the Extraction Line from the Damping Ring of ATF, Accelerator Test Facility which is constructed for Linear Collider Ramp;D at KEK. An accelerating structure will be installed in the Extraction Line, and beam positions will be measured at down stream. In this experiment, residual long range transverse wake field of the structure and wake field which is proportional to beam offset will be measured. Because that the beam from the Damping Ring is stable and have low emittance, we can measure a small transverse kick of 1.0x10^-8rad by using 500nm resolution BPMs and optimized optics of the beam line.

[8W.24] Beam-based Monitoring of the SLC Linac Optics with a Diagnostic Pulse

The optics of a linear accelerator may be changed significantly by variations in the energy profile along the linac. In particular, diurnal temperature swings in the SLC klystron gallery perturb the phase and amplitude of the accelerating Rf fields. If such changes are not correctly characterized, the resulting errors in the beam energy profile will cause phase advance differences in the beam optics. In addition Rf phase errors also affect the amplitude growth of betatron oscillations. We present an automated, simple procedure to monitor the lattice in the SLC linac routinely and non-invasively. The measured phase advance and oscillation amplitude is shown as a function of time and is compared to the nominal optics.

[8W.25] Observation of Dark-Current Signals from the S-Band Structures of the SLAC linac

Due to the high electromagnetic fields in accelerating RF structures electrons can be set free by field emission. If those electrons are captured and accelerated the RF structure produces a so-called dark-current. We show from measurements with photo-multipliers that dark-current is observed from the SLC S-band structures with nominal gradients of 17~MV/m. It is shown that the dark-current signals at nominal gradients can be strong enough to significantly reduce the signal-to-noise ratio at the SLC beam wire scanners. Results from RF measurements in the dipole band allow us to impose an upper bound on possible dark-current induced beam deflections in SLC.

[8W.26] Observation and Analysis of Static Deflections from Transverse Long-Range Wakefields in the SLC

In the SLC linac a train of three bunches is accelerated with the leading positron bunch followed by two bunches of electrons. When the positron bunch passes off-axis through the RF structures, it excites dipole modes in the structures, such as long-range transverse wakefields, which deflect the subsequent electron bunches. Although the magnitude of the deflections is small, one can infer the deflections by measuring the trajectory difference while changing the spacing between the positron and electron bunches. Knowing the positron trajectory, the misalignments of the accelerating RF structures with respect to the BPM's can be calculated. We present measurements from the SLC linac and discuss the data analysis and errors.

[8W.27] Beam-Based Analysis of Day-Night Performance Variations at the SLC Linac.

Diurnal temperature variations in the SLC linac gallery can affect the amplitude and phase of the rf used to accelerate the beam. The SLC employs many techniques for stabilization and compensation of these effects but residual uncorrected changes still affect the quality of the delivered beam. This paper presents methods developed to monitor and investigate these errors through the beam response. Variations resulting from errors in the rf amplitude or phase can be distinguished by studying six different beam observables: betatron phase advance, oscillation amplitude growth, rms jitter along the linac, measurements of the beam phase with respect to the rf, changes in the required injection phase, and overall energy correction. By quantifying the beam response, a daily uncorrected variation of 14^\circ (S-band) was found in the main rf drive line system between the front and end of the linac.

[8W.28] Longitudinal Phase Space Setup for the SLC Beams.

The longitudinal phase space distribution of the SLC beams is affected by many different machine parameters and constraints. By using a technique of over-compression in the ring to linac transfer line, a small energy spread of 0.12\,% can be achieved at the end of the linac for a bunch length of 1.2 mm (\sigma). In the final focus a small energy spread is desirable to reduce emittance dilution due to chromatic effects. Optimization of the bunch length is also important as a longer bunch of 1.2\,mm can contribute up to 40\,% luminosity enhancement due to disruption. If there is a correlated energy variation along the bunch, for example due to mistuning of the optimal rf phase with respect to the beam, the bunch will be further compressed as it passes through the SLC Arcs. The resulting bunch can be too short to produce the desired disruption enhancement, but will radiate more beamstrahlung during collisions giving a false indication of higher luminosity. This paper discusses the interplay of these issues from the damping ring to the interaction point.

[8W.29] Dynamic Focusing Schemes for Linear Colliders

By using the intense fields of a demagnified bunch as a final lens, one can greatly simplify and shorten the conventional final focus and collimation systems of linear colliders. In the dynamic focusing schemes described here, the lens bunches enter the interaction region through separate beamlines. Design details and constraint equations for such focusing schemes are developed and applied to the Next Linear Collider interaction point beam parameters.

[8W.30] The Short--Range Wakefields in the SBLC Linac

The short--range longitudinal and transverse wakefields of a point charge in the SBLC linac are obtained using a modal summation technique. Simple functional fits to these wakes are given, which can be used as Green functions in beam dynamics simulations of bunches. These results, however, are valid only after the beam has traversed a critical number of cells N_crit. Using time domain computations with Gaussian bunches we have obtained results that are consistent with N_crit varying as \alpha a^2/(L\sigma_z), with a the iris radius and L the period length of the structure, \sigma_z the bunch length and \alpha a constant near 1.

[8W.31] An Asymmetric Muon-Proton Collider

An asymmetric muon-proton collider is proposed as an instrument for possible quark structure search. Energy of proton beam is supposed to be some 5-6 times of muon energy. Estimated luminosity of the collider with two rings - the Tevatron accelerator and muon-ring - is found to be of the order 10^33 s^-1 cm^-2.

[8W.32] Interaction Region Design for Beijing \tau-Charm Factory

In high luminosity colliders with large number of bunches, the design of interaction region (IR) is very complicated since it must satisfy many requirements. The quadrupoles have to be placed close to the interaction point to focus the beam to the smallest possible spot size, the beams must also be separated as close to the IP as possible to avoid unwanted crossings of the two beams. The main design issues and criteria of the IR of the Beijing \tau-Charm Factory (BTCF) are described in this paper. The IR configuration, the compensation scheme of the detector solenoid field and the supporting system are also discussed.

[8W.33] An Asymmetric Linac-Ring Collider for Barion Timelike Form Factor and Total Hadronic Cross Section Measurements exploiting existing high energy storage rings

\quad Nucleon timelike form factors have been found quite unexpected. However at present there are quite a few data, for instance in the case of the neutron only one experiment has been done. In fact, besides the low cross sections, an additional difficulty in these measurements is due to the low kinetic energy of the emerging particles. The boost achieved in an asymmetric collider should help quite a lot in detecting these events. We studied the possibility of using an existing positron storage ring (PETRA or CESR) and a low emittance, high duty cycle linac of 100- 200 MeV to realize an asymmetric collider providing a luminosity \cal L=10^30\, cm^-2s^-1 . The peculiar features of such a machine are discussed. A suitable linac can be the superconducting linac of the TESLA Test Facility (TTF) in construction at DESY, or a smaller dedicated machine exploiting the Ramp;D from the TTF program to optimize performance/cost ratio. The requirements for luminosity upgrade and c.m. energy increase up to the J/\psi are also considered.

[8W.34] Bremsstrahlung intensity and average energy increase, it's divergence reduction in the target of new type

Target fabricated on foil basis and installed in the transverse magnetic field was developed and researched. Electron beam recirculation permits practically completely to utilize electron energy similarly complete absorption targets. At the same time bremsstrahlung quantum decelerating and scattering is essentially less, than in the target with optimum thickness, determined by means of the compromise between electron and bremsstrahlung quantum decelerating and scattering. It permits to receive a small diver ence of the radiation and to increase its average energy. Test results received on the electron accelerator confirmed theoretical estimations.

[8W.35] Linear Optics Correction in the CEBAF Accelerator

During the commissioning of the CEBAF accelerator, correction of dispersion, momentum compaction and transverse transfer matrices was essential for robust operation. With changing machine conditions, repeated correction was found necessary. To speed the diagnostic process we developed a method which allows one to rapidly track the machine optics. The method is based on measuring the propagation of 30 Hz modulated betatron oscillations downstream of a point of perturbation. Compared to the usual methods of dispersion or difference orbit measurement, synchronous detection of the beam displacement, as measured by beam position monitors, offers significantly improved speed and accuracy. The beam optics of the accelerator was also altered to decrease lattice sensitivity at critical points and to simplify control of the betatron function match. The calculation of the Courant-Snyder invariant from signals of each pair of nearby beam position monitors has allowed on-line measurement and correction of the lattice properties. The experience of optics correction and its long and short term reproducibility obtained during 1996 and early 1997 are also discussed.

[8W.36] Spotsize Stabilization Studies for the TESLA Beam Delivery System

Studies of the ground motion induced spotsize growth in the interaction region of the TESLA linear collider and some tools to recover are presented here. Analytical results are given and compared with simulations by particle tracking. Performance of different procedures, such as orbit correction, adaptive alignment and knob scan, studied by tracking simulations, is reported.

Part 8 of program listing