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THE USE OF RF-KNOCKOUT FOR DETERMINATION OF THE CHARACTERISTICS OF THE TRANSVERSE COHERENT INSTABILITY OF AN INTENSE BEAM

Description: The response of an intense beam of interacting particles to a deflecting rf-signal is computed theoretically and shown to be closely related to transverse coherent beam stability. It is shown that the beam response to sinusoidal excitation provides a direct measure of the stability of beam modes for given machine conditions (beam intensity, octupole current, sextupole current, momentum spread, etc.). This measurement includes the properties of the beam surroundings as well as the frequency spread effective for Landau damping. Since it is generally difficult to evaluate theoretically the wall and beam properties that enter into stability calculations, the information which can be obtained from rf excitation experiments should be very valuable; especially in devising practical procedures for reducing the severity of coherent transverse instabilities.
Date: August 1, 1971
Creator: Muhl, Dieter & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Transverse Resistive Wall Instability in the Two-Beam Accelerator

Description: The transverse resistive wall instability in the Two-Beam Accelerator (TBA) is investigated analytically and numerically. Without any damping mechanism, we find one to four e-folds in 100 m, depending on the design. It is found that Landau damping, due to energy spread within a beam slice, is not effective, due to rapid synchrotron oscillations in the FEL ponderomotive well. Damping due to an energy sweep along the beam is also considered and it is found that a small variation in energy along the beam, decreasing from head to tail, can significantly reduce growth. We conclude that the resistive wall instability is not a severe design constraint on a TBA.
Date: June 1, 1990
Creator: Whittum, D.H.; Sessler, Andrew M. & Neil, V.K.
Partner: UNT Libraries Government Documents Department

Landau damping with high frequency impedance

Description: Coupled bunch longitudinal stability in the presence of high frequency impedances is considered. A frequency domain technique is developed and compared with simulations. The frequency domain technique allows for absolute stability tests and is applied to the problem of longitudinal stability in RHIC with the new 56 MHz RF system.
Date: May 4, 2009
Creator: Blaskiewicz,M.
Partner: UNT Libraries Government Documents Department

Decoherence and Landau-Damping

Description: The terminologies, decoherence and Landau damping, are often used concerning the damping of a collective instability. This article revisits the difference and relation between decoherence and Landau damping. A model is given to demonstrate how Landau damping affects the rate of damping coming from decoherence.
Date: December 1, 2005
Creator: Ng, K.Y.
Partner: UNT Libraries Government Documents Department

Transverse instability digital damper for the Recycler

Description: Transverse beam instability of a coasting beam with a digital damper is examined. Threshold of instability is calculated in specific cases with Landau damping taken into account. The results are applied to the Fermilab Recycler Ring. Some improvement of existing RR damper is proposed.
Date: February 1, 2006
Creator: Balbekov, V.
Partner: UNT Libraries Government Documents Department

Transverse instability of the antiproton beam in the Recycler Ring

Description: The brightness of the antiproton beam in Fermilab's 8 GeV Recycler ring is limited by a transverse instability. This instability has occurred during the extraction process to the Tevatron for large stacks of antiprotons even with dampers in operation. This paper describes observed features of the instability, introduces the threshold phase density to characterize the beam stability, and finds the results to be in agreement with a resistive wall instability model. Effective exclusion of the longitudinal tails from Landau damping by decreasing the depth of the RF potential well is observed to lower the threshold density by up to a factor of two.
Date: March 1, 2011
Creator: Prost, L.R.; Bhat, C.M.; Burov, A.; Crisp, J.; Eddy, N.; Hu, M. et al.
Partner: UNT Libraries Government Documents Department

TRANSVERSE COHERENT RESISTIVE INSTABILITIES OF AZIMUTHALLY BUNCHED BEAMS IN PARTICLE ACCELERATORS

Description: The transverse electromagnetic coupling of bunches of particles with each other is investigated theoretically, and shown to incorporate the possibility (due to the effect of nonperfectly conducting vacuum chamber walls) of coherent instability even when the longitudinal distance between bunches is much larger than the transverse dimensions of the vacuum tank. The modes of oscillation in which the bunches move rigidly are investigated; criteria for stability, and expressions for the small amplitude growth rates under unstable conditions are presented. The case of a single bunch is considered in detail and demonstrated to be stable (even in the absence of landau damping) provided {nu} lies between an integer and the next higher half-integer, where {nu} is the number of transverse free betatron oscillations occurring in one revolution; for many bunches which are sensibly different in intensity (a criterion for this is presented), all modes are stable provided {nu} satisfies the same restriction. For equally spaced bunches of equal numbers of particles, approximately half the modes are unstable without Landau damping. Numerical examples are presented covering some intermediate situations.
Date: April 1, 1966
Creator: Courant, Ernest D. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Head-Tail Modes for Strong Space Charge

Description: Head-tail modes are described here for the space charge tune shift significantly exceeding the synchrotron tune. General equation for the modes is derived. Spatial shapes of the modes, their frequencies, and coherent growth rates are explored. The Landau damping rates are also found. Suppression of the transverse mode coupling instability by the space charge is explained.
Date: December 1, 2008
Creator: Burov, Alexey
Partner: UNT Libraries Government Documents Department

Trapped Ions and Beam Coherent Instability

Description: In accelerators with negatively charged beams, ions generated from the residual gas molecules may be trapped by the beam. Trapped ions may interact resonantly with the beam and cause a beam-ion coherent instability. This coherent instability bears many similarities to the resistive wall instability and can present important limitations to those machines operation. A description of this effect requires a treatment of the beam coherent instability including both the normal machine wake field and the interaction with ions. They present a linear approach incorporating contributions from the machine impedance as well as ion forces. it also includes spreads in beam and ion frequencies and thus Landau damping. The analysis results in a modified stability diagram which will be used together with physical arguments to explain experimental observations in the Fermilab antiproton accumulator.
Date: January 1, 1992
Creator: Zhou, P.; Colestock, P.L.; Werkema, S.J. & /Fermilab
Partner: UNT Libraries Government Documents Department

Landau Damping Revisited

Description: Landau damping, as the term is used in accelerator science, is a physical process in which an ensemble of harmonic oscillators--an accelerator beam, for example--that would otherwise be unstable is stabilized by a spread in the natural frequencies of the oscillators. This is a study of the most basic aspects of that process. It has two main goals: to gain a deeper insight into the mechanism of Landau damping and to find the coherent motion of the ensemble and thus the dependence of the total damping rate on the frequency spread.
Date: December 1, 2008
Creator: Rees, John & Chao, Alexander
Partner: UNT Libraries Government Documents Department

Landau damping of space-charge dominated Fermilab Booster beam

Description: The stable region of the Fermilab Booster beam in the complex coherent-tune-shift plane appears to have been shifted far away from the origin by its intense space-charge making Landau damping impossible. However, it is shown that the bunching structure of the beam reduces the mean space-charge tune shift. As a result, the beam can be stabilized by suitable octupole-driven tune spread.
Date: September 1, 2008
Creator: Ng, K.Y.
Partner: UNT Libraries Government Documents Department

Head-tail instability at Tevatron

Description: Tevatron performance suffers from a coherent transverse instability. Experimental studies and theoretical examination allow identifying the instability as a weak head-tail, driven by the short-range wake fields in presence of the space charge. Growth rates and coherent tune shifts are measured at injection of single high-intensity proton bunches using a fast strip-line pickup. Landau damping through the octupole-generated betatron tune spread for all of unstable head-tail modes has been demonstrated.
Date: May 27, 2003
Creator: al., Petr M Ivanov et
Partner: UNT Libraries Government Documents Department

Toroidal gyrofluid equations for simulations of tokamak turbulence

Description: A set of nonlinear gyrofluid equations for simulations of tokamak turbulence are derived by taking moments of the nonlinear toroidal gyrokinetic equation. The moment hierarchy is closed with approximations that model the kinetic effects of parallel Landau damping, toroidal drift resonances, and finite Larmor radius effects. These equations generalize the work of Dorland and Hammett [Phys. Fluids B 5, 812 (1993)] to toroidal geometry by including essential toroidal effects. The closures for phase mixing from toroidal rB and curvature drifts take the basic form presented in Waltz, et al. [Phys. Fluids B 4, 3138 (1992)], but here a more rigorous procedure is used, including an extension to higher moments, which provides significantly improved accuracy. In addition, trapped ion effects and collisions are incorporated. This reduced set of nonlinear equations accurately models most of the physics considered important for ion dynamics in core tokamak turbulence and is simple enough to be used in high resolution direct numerical simulations.
Date: April 1, 1996
Creator: Beer, M.A. & Hammett, G.W.
Partner: UNT Libraries Government Documents Department

Damping of the Transverse Head-Tail Instability by Periodic Modulation of the Chromaticity

Description: An analytical and numerical study of the suppression of the transverse head-tail instability by modulating the chromaticity over a synchrotron period is presented. We find that a threshold can be developed, and it can be increased to a value larger than the strong head-tail instability threshold. The stability criterion derived agrees very well with the simulations. The underlying physical mechanisms of the damping scheme are rotation of the head-tail phase such that the instability does not occur, and Landau damping due to the incoherent betatron tune spread generated by the varying chromaticity. {copyright} {ital 1997} {ital The American Physical Society}
Date: June 1, 1997
Creator: Cheng, W.; Wurtele, J.S.; Sessler, A.M. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Renormalized dissipation in plasmas with finite collisionality

Description: A nonlinear truncation procedure for Fourier-Hermite expansion of Boltzmann-type plasma equations is presented which eliminates fine velocity scale, taking into account its effect on coarser scales. The truncated system is then transformed back to (x, v) space which results in a renormalized Boltzmann equation. The resulting equation may allow for coarser velocity space resolution in kinetic simulations while reducing to the original Boltzmann equation when fine velocity scales are resolved. To illustrate the procedure, renormalized equations are derived for one dimensional electrostatic plasmas in which collisions are modeled by the Lenard-Bernstein operator.
Date: May 1, 1995
Creator: Parker, S.E. & Carati, D.
Partner: UNT Libraries Government Documents Department

Varying chromaticity: A damping mechanism for the transverse head-tail instability

Description: A detailed analytical and numerical study of the suppression of the transverse head-tail instability by modulating the chromaticity over a synchrotron period is presented. We find that a threshold can be developed, and it can be increased to a value larger than the strong head-tail instability threshold. The stability criterion derived agrees very well with the simulations. The underlying physical mechanisms of the damping scheme are rotation of the head-tail phase such that the instability does not occur, and Landau damping due to the incoherent betatron tune spread generated by the varying chromaticity. {copyright} {ital 1997} {ital The American Physical Society}
Date: October 1, 1997
Creator: Cheng, W.; Wurtele, J.S.; Sessler, A.M. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

ELECTRON CLOUD EFFECTS IN HIGH INTENSITY PROTON ACCELERATORS.

Description: One of the primary concerns in the design and operation of high-intensity proton synchrotrons and accumulators is the electron cloud and associated beam loss and instabilities. Electron-cloud effects are observed at high-intensity proton machines like the Los Alamos National Laboratory's PSR and CERN's SPS, and investigated experimentally and theoretically. In the design of next-generation high-intensity proton accelerators like the Spallation Neutron Source ring, emphasis is made in minimizing electron production and in enhancing Landau damping. This paper reviews the present understanding of the electron-cloud effects and presents mitigation measures.
Date: April 14, 2002
Creator: WEI,J. & MACEK,R.J.
Partner: UNT Libraries Government Documents Department

COLLECTIVE EFFECTS AND THEIR CONTROL AT THE SPALLATION NEUTRON SOURCE RING.

Description: One of the primary tasks in the design of the Spallation Neutron Source (SNS) ring is to control collective effects including space charge, transverse and longitudinal instabilities, and electron cloud. Transverse painting is used to alleviate space charge force; longitudinal painting along with chromatic sextupoles are used to enhance Landau damping; injection kicker vacuum pipes are carefully shielded, and extraction kicker impedances are measured in detail and optimized; beam halo, beam loss and electron production are minimized; finally, damping systems at various frequencies are planned. This paper summarizes these design implementations.
Date: June 3, 2002
Creator: WEI,J.; BLASKIEWICZ,M.; BRODOWSKI,J.; CAMERON,P.; DAVINO,D.; FEDOTOV,A. et al.
Partner: UNT Libraries Government Documents Department

Design consideration of relativistic klystron two-beam accelerator for suppression of beam-break-up

Description: It is demonstrated in this simulation study that by using the scheme of operating rf extraction structures on the betatron nodes of electron drive beam in conjunction with adequate de-Q-ing, appropriate choice of geometries for the rf structures (reducing transverse impedence) and/or staggered tuning we can suppress the overall growth of transverse instabilities to 4 e-folds in a relativistic klystron two-beam accelerator with 200 extraction cavities.
Date: March 1, 1994
Creator: Li, H.; Houck, T. L.; Yu, S. & Goffeney, N.
Partner: UNT Libraries Government Documents Department

Loss of Landau Damping for Bunch Oscillations

Description: Conditions for the existence, uniqueness and stability of self-consistent bunch steady states are considered. For the existence and uniqueness problems, simple algebraic criteria are derived for both the action and Hamiltonian domain distributions. For the stability problem, van Kampen theory is used. The onset of a discrete van Kampen mode means the emergence of a coherent mode without any Landau damping; thus, even a tiny couple-bunch or multi-turn wake is sufficient to drive the instability. The method presented here assumes an arbitrary impedance, RF shape, and beam distribution function. Available areas on the intensity-emittance plane are shown for resistive wall wake and single harmonic, bunch shortening and bunch lengthening RF configurations. Thresholds calculated for the Tevatron parameters and impedance model are in agreement with the observations. These thresholds are found to be extremely sensitive to the small-argument behaviour of the bunch distribution function. Accordingly, a method to increase the LLD threshold is suggested. This article summarizes and extends recent author's publications.
Date: April 11, 2011
Creator: Burov, A.
Partner: UNT Libraries Government Documents Department

Design and Simulation of IOTA - a Novel Concept of Integrable Optics Test Accelerator

Description: The use of nonlinear lattices with large betatron tune spreads can increase instability and space charge thresholds due to improved Landau damping. Unfortunately, the majority of nonlinear accelerator lattices turn out to be nonintegrable, producing chaotic motion and a complex network of stable and unstable resonances. Recent advances in finding the integrable nonlinear accelerator lattices have led to a proposal to construct at Fermilab a test accelerator with strong nonlinear focusing which avoids resonances and chaotic particle motion. This presentation will outline the main challenges, theoretical design solutions and construction status of the Integrable Optics Test Accelerator (IOTA) underway at Fermilab.
Date: May 1, 2012
Creator: Nagaitsev, S.; Valishev, A.; /Fermilab; Danilov, V.V.; Ridge, /Oak; Shatilov, D.N. et al.
Partner: UNT Libraries Government Documents Department

Ring for test of nonlinear integrable optics

Description: Nonlinear optics is a promising idea potentially opening the path towards achieving super high beam intensities in circular accelerators. Creation of a tune spread reaching 50% of the betatron tune would provide strong Landau damping and make the beam immune to instabilities. Recent theoretical work has identified a possible way to implement stable nonlinear optics by incorporating nonlinear focusing elements into a specially designed machine lattice. In this report we propose the design of a test accelerator for a proof-of-principle experiment. We discuss possible studies at the machine, requirements on the optics stability and sensitivity to imperfections.
Date: March 1, 2011
Creator: Valishev, A.; Nagaitsev, S.; Kashikhin, V.; /Fermilab; Danilov, V. & /SNS Project, Oak Ridge
Partner: UNT Libraries Government Documents Department