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Single bunch instabilities in an SSC

Description: In this note coherent instability thresholds are estimated for the SSC and discuss some of the subsequent design restrictions. The various instabilities are set out in a block diagram with the essential features of each. The assumption is made that long wavelength coupled bunch effects can be cured effectively by a feedback system (both longitudinal and transverse) and that the impedance of the feedback system is such as to cancel that of the environment (at low frequency). Alternatively, the long wake field is assumed to be exactly canceled, on the average, by a feedback wake field. This leaves only single bunch effects. Thresholds for fast-blowup are discussed both in the longitudinal and transverse and the transverse mode coupling instability more familiar in electron/positron storage rings is covered. The impedances considered are a broadband impedance and the resistive wall impedance.
Date: January 1, 1984
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Vertical coherent instabilities in bunched particle-beams

Description: The purpose of this paper is to study the vertical coherent instabilities which occur in bunched particle beams. The problem is complicated by the fact that the velocity of a single particle in a bunch is not constant, but rather consists of an equilibrium velocity and an oscillation about that. This synchrotron oscillation occurs at a frequency which is in general much less than the other characteristic frequencies of the system: the revolution frequency and the transverse betatron frequencies. The approach used here to study coherent instabilities illuminates the effect of the synchrotron frequency in setting the time scale for an instability, without making restrictive assumptions on the relative size of the synchrotron frequency and the coherent frequency shift (or growth rate).
Date: July 1, 1981
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Report of the working group for polarization in the SSC main ring

Description: The task of the main ring working group was to study polarized beams in the SSC main ring. Many problems were studied; however, the primary emphasis was in the determination of the acceptable resonance strengths and the number of Siberian Snakes which would be necessary given those resonance strengths. During the workshop all of the members of the working group realized that there was much more work to be done, and consequently there have been some changes in the general conclusions during the following months. The present conclusion really reflects a balance between pessimism and optimism. At present we feel that if the resonance strengths in the SSC main ring are kept below about 5, then about 78 Siberian Snakes would be sufficient to maintain polarization. However, since the calculations here indicate a quadratic dependence on the resonance strength, if resonance strengths could be kept below 3, then only about 26 snakes would be needed. These numbers are estimates, and with further calculation we may find a solution which lowers the number of Siberian Snakes. This paper should be viewed as a brief introduction to the problem and as a 'road map' to the many excellent contributions to these proceedings by the members of the working group.
Date: January 1, 1986
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Report on the international workshop on next generation linear colliders

Description: Many laboratories around the world have begun vigorous research programs on a next generation linear collider (NLC). However, it has been recognized that the research towards NLC is beyond the capabilities of any one laboratory presently. This workshop was organized to begin a series of workshops that address this problem. Specifically, the main goals of the workshop were to discuss research programs of the various laboratories around the world, to identify common areas of interest in the various NLC designs, and finally to advance these programs by collaboration. The particular topics discussed briefly in this paper are: parameters, rf power, structures, final focus, beam dynamics, damping rings, and instrumentation. 2 refs., 3 figs., 6 tabs.
Date: May 1, 1989
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

The status of the SLC

Description: On October 10,1987, the SLC ceased commissioning activities to move the Mark II detector into the beam line for the spring physics run. The planned shutdown is for a period of 13 weeks. In this paper, the various subsystems and their status as of October 10, 1987 are briefly discussed. 3 refs., 4 figs., 1 tab.
Date: November 1, 1987
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Summary of the Linear Collider Working Group

Description: The focus of the Linear Collider Working Group was on a next generation linear collider. Topics discussed are: parameters; damping rings; bunch compression and pre-acceleration; linac; final focus; and multibunch effects. 8 refs., 3 figs., 7 tabs.
Date: January 1, 1989
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Beam dynamics issues for linear colliders

Description: In this paper we discuss various beam dynamics issues for linear colliders. The emphasis is to explore beam dynamics effects which lead to an effective dilution of the emittance of the beam and thus to a loss of luminosity. These considerations lead to various tolerances which are evaluated for a particular parameter set.
Date: September 1, 1987
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Multi-bunch energy compensation

Description: To obtain a luminosity of 10{sup 34} cm{sup {minus}2} sec{sup {minus}1} in a TeV Linear Collider (TLC), it will probably be necessary to accelerate many bunches in one filling of the rf structure. This has the effect of extracting more energy from the structure and thus enhances the overall efficiency of the accelerator. However, this leads to many problems. First, the train bunches is subject to cummulative beam breakup transversely. This can be controlled by damping the transverse modes with slots in the irises coupled to waveguides. In addition, the energy of the bunches must be kept the same to high precision. For the fundamental mode, this entails adjusting the timing of the rf fill and also the bunch spacing. The higher longitudinal modes, although they do not induce instability, also may lead to bunch-to-bunch variations in energy. However, it also seems possible to damp these modes to cure this problem. Of course, there are also problems associated with damping a train of bunches in a damping ring. In this paper we discuss some of the issues of multi-bunch energy compensation. In the first two sections, we review some basics about energy extraction by a single bunch, and then, multi-bunch energy compensation is treated. We discuss various tolerance issues associated with deviations of amplitude and phase of the rf away from the ideal.
Date: February 1, 1988
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Plasma accelerators

Description: In this paper we discuss plasma accelerators which might provide high gradient accelerating fields suitable for TeV linear colliders. In particular we discuss two types of plasma accelerators which have been proposed, the Plasma Beat Wave Accelerator and the Plasma Wake Field Accelerator. We show that the electric fields in the plasma for both schemes are very similar, and thus the dynamics of the driven beams are very similar. The differences appear in the parameters associated with the driving beams. In particular to obtain a given accelerating gradient, the Plasma Wake Field Accelerator has a higher efficiency and a lower total energy for the driving beam. Finally, we show for the Plasma Wake Field Accelerator that one can accelerate high quality low emittance beams and, in principle, obtain efficiencies and energy spreads comparable to those obtained with conventional techniques.
Date: March 1, 1986
Creator: Ruth, R.D. & Chen, P.
Partner: UNT Libraries Government Documents Department

Comparison of the plasma beat wave accelerator and the plasma wake field accelerator

Description: In this paper we compare the Plasma Beat Wave Accelerator and Plasma Wake Field Accelerator. We show that the electric fields in the plasma for both schemes are very similar, and thus the dynamics of the driven beams are very similar. The differences appear in the parameters associated with the driving beams. In particular to obtain a given accelerating gradient, the Plasma Wake Field Accelerator has a higher efficiency and a lower total energy for the driving beam. 7 refs., 2 tabs.
Date: March 1, 1985
Creator: Chen, P. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Test facilities for future linear colliders

Description: During the past several years there has been a tremendous amount of progress on Linear Collider technology world wide. This research has led to the construction of the test facilities described in this report. Some of the facilities will be complete as early as the end of 1996, while others will be finishing up around the end 1997. Even now there are extensive tests ongoing for the enabling technologies for all of the test facilities. At the same time the Linear Collider designs are quite mature now and the SLC is providing the key experience base that can only come from a working collider. All this taken together indicates that the technology and accelerator physics will be ready for a future Linear Collider project to begin in the last half of the 1990s.
Date: December 1, 1995
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Study of invariant surfaces and their break-up by the Hamilton-Jacobi method

Description: A method is described to compute invariant tori in phase space for calssical non-integrable Hamiltonian systems. Our procedure is to solve the Hamilton-Jacobi equation stated as a system of equations for Fourier coefficients of the generating function. The system is truncated to a finite number of Fourier modes and solved numerically by Newton's method. The resulting canonical transformation serves to reduce greatly the non-integrable part of the Hamiltonian. In examples studied to date the convergence properties of the method are excellent, even near chaotic regions and on the separatrices of isolated broad resonances. We propose a criterion for breakup of invariant surfaces, namely the vanishing of the Jacobian of the canonical transformation to new angle variables. By comparison with results from tracking, we find in an example with two nearly overlapping resonances that this criterion can be implemented with sufficient accuracy to determine critical parameters for the breakup ('transition to chaos') to an accuracy of 5 to 10%.
Date: August 1, 1986
Creator: Warnock, R.L. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Plasma laser accelerator: longitudinal dynamics, the plasma/laser interaction, and a qualitative design

Description: In this paper we present our studies on a plasma laser accelerator. First we look at the longitudinal dynamics and the trapping of particles in the potential well due to the longitudinal electric field in a plasma density wave. Next we study the plasma/laser interaction to obtain power requirements. Lastly, we qualitatively design a plasma/laser accelerator with parameters somewhat more modest than existing suggestions.
Date: April 1, 1982
Creator: Ruth, R.D. & Chao, A.W.
Partner: UNT Libraries Government Documents Department

Transverse and longitudinal coupled bunch instabilities in trains of closely spaced bunches

Description: Damping rings for the next generation of linear collider may need to contain several bunch trains within which the bunches are quire closely spaced (1 or 2 RF wavelengths). Methods are presented for studying the transverse and longitudinal coupled bunch instabilities, applicable to this problem and to other cases in which the placement of the bunches is not necessarily symmetric. 5 refs., 1 fig.
Date: March 1, 1989
Creator: Thompson, K.A. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Analytic estimates of coupling in damping rings

Description: In this paper we present analytic formulas to estimate the vertical emittance in weakly coupled electron/positron storage rings. We consider contributions from both the vertical dispersion and linear coupling of the betatron motions. In addition to simple expressions for random misalignments and rotations of the magnets, formulas are presented to calculate the vertical emittance blowup due to orbit distortions. The orbit distortions are assumed to be caused by random misalignments, but because the closed orbit is correlated from point to point, the effects must be treated differently. We consider only corrected orbits. Finally, the analytic expressions are compared with computer simulations of storage rings with random misalignments. 6 refs., 3 figs.
Date: March 1, 1989
Creator: Raubenheimer, T.O. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Bounds on nonlinear motion for a finite time

Description: Recent improvements in numerical methods to compute canonical transformations make it feasible to set interesting bounds on the motion of nonlinear Hamiltonian systems over a finite interval of time. 7 refs.
Date: June 1, 1989
Creator: Warnock, R.L. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Bunch lengthening calculations for the SLC (Stanford Linear Collider) damping rings

Description: The problem of bunch lengthening in electron storage rings has been treated by many people, and there have been many experiments. In the typical experiment, the theory is used to determine the impedance of the ring. What has been lacking thus far, however, is a calculation of bunch lengthening that uses a carefully calculated ring impedance (or wakefield). In this paper we begin by finding the potential well distortion due to some very simple impedance models, in order to illustrate different types of bunch lengthening behavior. We then give a prescription for extending potential well calculations into the turbulent regime once the threshold is known. Then finally, using the wakefield calculated for the SLC damping rings, combined with the measured value of the threshold, we calculate bunch lengthening for the damping rings, and compare the results with the measurements. 9 refs., 6 figs.
Date: March 1, 1989
Creator: Bane, K.L.F. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Multibunch beam breakup in high energy linear colliders

Description: The SLAC design for a next-generation linear collider with center-of-mass energy of 0.5 to 1.0 TeV requires that multiple bunches (/approximately/10) be accelerated on each rf fill. At the beam intensity (/approximately/10/sup 10/ particles per bunch) and rf frequency (11--17 GHz) required, the beam would be highly unstable transversely. Using computer simulation and analytic models, we have studied several possible methods of controlling the transverse instability: using damped cavities to damp the transverse dipole modes; adjusting the frequency of the dominant transverse mode relative to the rf frequency, so that bunches are placed near zero crossings of the wake; introducing a cell-to-cell spread in the transverse dipole mode frequencies; and introducing a bunch-to-bunch variation in the transverse focusing. The best cure(s) to use depend on the bunch spacing, intensity, and other features of the final design. 8 refs., 3 figs.
Date: March 1, 1989
Creator: Thompson, K.A. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Emittance control in linear colliders

Description: In this paper, we discuss the generation and control of the emittance in a next-generation linear collider. The beams are extracted from a damping ring and compressed in length by the first bunch compressor. They are then accelerated in a preaccelerator linac up to an energy appropriate for injection into a high gradient linac. In many designs this pre-acceleration is followed by another bunch compression to reach a short bunch. After acceleration in the linac, the bunches are finally focused transversely to a small spot. The proposed vertical beam sizes at the interaction point are the order of a few nanometers while the horizontal sizes are about a factor of 100 larger. This cross-sectional area is about a factor of 10{sup 4} smaller than the SLC. However, the main question is: what are the tolerances to achieve such a small size, and how do they compare to present techniques for alignment and stability These tolerances are very design dependent. Alignment tolerances in the linac can vary from 1 {mu}m to 100 {mu}m depending upon the basic approach. In this paper we discuss techniques of emittance generation and control which move alignment tolerances to the 100 {mu}m range.
Date: May 1, 1991
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

The development of the Next Linear Collider at SLAC

Description: At SLAC, we are pursuing the design of a Next Linear Collider (NLC) which would begin with a center-of-mass energy of 0.5 TeV and be upgradable to at least 1.0 TeV, and possibly 1.5 TeV. The luminosity is designed to be 10{sup 33} cm{sup {minus}2}s{sup {minus}1} at the lower energy and 10{sup 34} cm{sup {minus}2}s{sup {minus}1} at the top energy. In this paper, we discuss the accelerator physics issues which are important in our approach, and also the present state of the technology development. We also review the impact that the SLC has had in the evolution of our basic approach.
Date: February 1, 1992
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Transverse multibunch modes for non-rigid bunches, including mode coupling

Description: A method for computing transverse multibunch growth rates and frequency shifts in rings, which has been described previously, is applied to the PEP-II B factory. The method allows multibunch modes with different internal-bunch oscillation modes to couple to one another, similar to single-bunch mode coupling. Including coupling between the multibunch modes gives effects similar to those seen in single-bunch mode coupling. These effects occur at currents that are lower than the single-bunch mode coupling threshold.
Date: August 1, 1995
Creator: Bert, J.S. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Transverse multibunch instabilities for non-rigid bunches

Description: In this paper, the authors present a method for computing growth rates and frequency shifts of a beam containing multiple non-rigid bunches. With this approach, they calculate non-rigid multibunch effects which can impact phenomena which are traditionally treated as single-bunch effects, such as the transverse mode-coupling instability. This approach is important for high current storage rings such as PEP-II at SLAC (the B-Factory) which have very strong interbunch forces. Typical calculations treat multibunch and single bunch effects separately, and thus eliminate important interactions between the two. To illustrate the technique, the authors calculate growth rates and frequency shifts using PEP-II as an example.
Date: May 1, 1995
Creator: Berg, J.S. & Ruth, R.D.
Partner: UNT Libraries Government Documents Department

The Next Linear Collider test accelerator: Status and results

Description: At SLAC, the authors are pursuing the design of a Next Linear Collider (NLC) which would begin with a center-of-mass energy of 0.5 TeV, and would be upgradable to 1.0 TeV and beyond. To achieve this high energy, for the past several years they have been working on the development of a high-gradient 11.4-GHz (X-band) linear accelerator for the main linac of the collider. In this paper, they present the status and initial results from the ``Next Linear Collider Test Accelerator`` (NLCTA). The goal of the NLCTA is to model the high gradient linac of the NLC. It incorporates the new technologies of X-band accelerator structures, rf pulse compression systems and high-power klystrons into a 0.5 to 1.0 GeV linac which is a test bed for beam dynamics issues related to high-gradient acceleration.
Date: June 1, 1996
Creator: Ruth, R.D.
Partner: UNT Libraries Government Documents Department

Superconvergent tracking and invariant surfaces in phase space

Description: The question of long term beam stability in very large storage rings presents an extraordinary challenge in nonlinear dynamics. Since current computational methods seem less than adequate on the long time scales involved, we have undertaken a program of evaluating several methods that either are new or have not been tried in accelerator problems heretofore. The methods we investigate fall into two categories: (1) iteration of maps describing concatenated machine elements, for tracking of single particles, and (2) infinite-time methods for direct computation of invariant surfaces in phase space.
Date: April 1, 1985
Creator: Ruth, R.D.; Raubenheimer, T. & Warnock, R.L.
Partner: UNT Libraries Government Documents Department