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Open Access Publications from the University of California

Scholarly Works (35 results)

  • Article
  • Peer Reviewed
LBL Publications (2018)
The effect of rf harmonic cavities on the transverse mode-coupling instability (TMCI) is still not very well understood. We offer a fresh perspective on the problem by proposing a new numerical method for mode analysis and investigating a regime of potential interest to the new generation of light sources where resistive wall is the dominant source of transverse impedance. When the harmonic cavities are tuned for maximum flattening of the bunch profile we demonstrate that at vanishing chromaticities the transverse single-bunch motion is unstable at any current, with growth rate that in the relevant range scales as the 6th power of the current. With these assumptions and radiation damping included, we find that for machine parameters typical of 4th-generation light sources the presence of harmonic cavities could reduce the instability current threshold by more than a factor two.
    • Article
    Lawrence Berkeley National Laboratory (2010)
      Cover page: Dynamics of Longitudinal Phase-Space Modulations in an rf Compressor for Electron Beams
      • Article
      • Peer Reviewed
      LBL Publications (2016)
      Using a 1D steady-state free-space coherent synchrotron radiation (CSR) model, we identify a special design setting for a triple-bend isochronous achromat that yields vanishing emittance growth from CSR. When a more refined CSR model with transient effects is included in the analysis, numerical simulations show that the main effect of the transients is to shift the emittance growth minimum slightly, with the minimum changing only modestly.
        Cover page: Design of a triple-bend isochronous achromat with minimum coherent-synchrotron-radiation-induced emittance growth
        • Article
        • Peer Reviewed
        LBL Publications (2009)
          Cover page: Linear Gain for the Microbunching Instability in an RF Compressor
          • Article
          Lawrence Berkeley National Laboratory (2010)

          Velocity bunching (or RF compression) represents a promising technique complementary to magnetic compression to achieve the high peak current required in the linac drivers for FELs. Here we report on recent progress aimed at characterizing the RF compression from the point of view of the microbunching instability. We emphasize the development of a linear theory for the gain function of the instability and its validation against macroparticle simulations that represents a useful tool in the evaluation of the compression schemes for FEL sources.

            Cover page: Microbunching and RF Compression
            • Article
            LBL Publications (2011)
            We report on on-going studies of a superconducting CW linac driver intended to support a high repetition rate FEL operating in the soft x-rays spectrum. We present a pointdesign for a 1.8 GeV machine tuned for 300 pC bunches and delivering low-emittance, low-energy spread beams as needed for the SASE and seeded beamlines.
              Cover page: Studies of a Linac Driver for a High Repetition Rate X-Ray FEL
              • Article
              Lawrence Berkeley National Laboratory (2010)

              One of the proposals under consideration for future upgrades of the LHC injector complex entails the replacement of the PS with the PS2, a longer circumference and higher energy synchrotron, with electron cloud effects representing a potentially serious limitation to the achievement of the upgrade goals. We report on ongoing numerical studies aiming at estimating the e-cloud density threshold for the occurrence of single bunch instabilities.

                Cover page: E-Cloud Drivent Single-Bunch Instabilities in PS2
                • Article
                • Peer Reviewed
                LBL Publications (2022)
                We examine the effect of higher-harmonic passive cavities (HHCs) on the beam response to rf noise. Upon invoking certain assumptions to make the problem tractable, we employ Vlasov methods to show that when the dipole approximation applies the HHCs have a generally limited impact. Beam loading in the main cavity is included in the analysis. We illustrate our results and the limitations of our model in application to the Lawrence Berkeley National Laboratory ALS (Advanced Light Source) and the future ALS Upgrade (ALS-U) offering validation against macroparticle simulations.
                  Cover page: Beam response to rf-generator noise in the presence of higher-harmonic passive cavitiesCreative Commons 'BY-NC' version 4.0 license
                  • Article
                  Lawrence Berkeley National Laboratory (2011)
                  One of the options considered for future upgrades of the LHC injector complex entails the replacement of the PS with the PS2, a longer circumference and higher energy synchrotron. Electron cloud effects represent an important potential limitation to the achievement of the upgrade goals. We report the results of numerical studies aiming at estimating the e-cloud density thresholds for the occurrence of single bunch instabilities.
                    Cover page: E-Cloud Effects on Singe-Bunch Dynamics in the Proposed PS2
                    • Article
                    LBL Publications (2004)
                    The need to accommodate the long bunch trains suitable for a cold linear collider and limitations to the kicker technology will cause the International Linear Collider (ILC) damping rings to be fairly large. A several Km long circumference and small emittance at extraction will combine to produce a sizeable and potentially harmful vertical space-charge tuneshift - an unusual feature for high-energy electron storage rings. We report on our study of space-charge effects for the lattice designs presently under consideration including the coupling bumps that have been proposed to tame the magnitude of those effects. We employ the code MaryLie/Impact and explore several models of beam dynamics with varying degree of accuracy and self-consistency in the treatment of space-charge.
                      Cover page: Space-charge effects in the ILC damping rings
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