ANL, Lemont, Illinois, USA
RadiaSoft LLC, Boulder, Colorado, USA
UCSC, Santa Cruz, California, USA
The Advanced Photon Source Upgrade will use a multi-bend achromatic lattice to reduce vertical and horizontal beam emittances by one- and two-orders of magnitude respectively; in addition operating current will double. The resulting electron beam will be capable of depositing more than 150 MGy on machine protection collimators creating high-energy-density conditions. Work is underway to couple the beam dynamics code Elegant with the particle-matter interaction program MARS and the magnetohydrodynamics code FLASH to model the effects of whole beam dumps on the collimators. Loss distributions from Elegant are input to MARS which provide dose maps to FLASH. We also examine the propagation of downstream shower components after the beam interacts with the collimator. Electrons and positrons are tracked to determine locations of beam loss. Beam dump experiments conducted in the APS storage-ring, generated dose levels as high as 30 MGy resulting in severe damage to the collimator surfaces with melting in the bulk. The deformed collimator surface may lead to beam deposition in unexpected locations. A fan-out kicker is planned to mitigate the effects of whole beam dumps on the collimators.
ANL, Lemont, Illinois, USA
Fringe fields effects in dipoles can give rise to important linear and nonlinear contributions. This paper describes how to extend the classic results of Brown [1] and the more recent calculations of Hwang and Lee [2] to Cartesian dipoles with transverse and/or longitudinal gradients. We do this by 1) introducing a more general definition of the fringe field that can be applied to longitudinal gradient dipoles, 2) allowing for quadrupole and/or sextupole content in the magnet body, and 3) showing how to employ the resulting fringe field maps as a symplectic transformation of the coordinates. We compare our calculation results with tracking for longitudinal and transverse gradient dipoles planned for the APS-U.
[1] K.L. Brown, Report SLAC-75, 1982.
[2] K. Hwang and S.Y. Lee, Phys. Rev. Accel. Beams, vol. 18, p. 122401 2015.
ANL, Lemont, Illinois, USA
We analyze the dynamics of multibunch longitudinal instabilities including bunch-by-bunch feedback under the assumption that the synchrotron tune is small. We find that increasing the feedback response does not always guarantee stability, even in the ideal case with no noise. As an example, we show that if the growth rate of a cavity-driven mode is of the order of the synchrotron frequency, then there are parameter regions for which the instability cannot be controlled by feedback irrespective of its gain. We verify these calculations with tracking simulations relevant to the APS-U, and find that the dynamics do not depend upon whether the longitudinal feedback relies on phase-sensing or energy-sensing technology. Hence, this choice should be dictated by measurement accuracy and noise considerations.
ANL, Lemont, Illinois, USA
We have developed a set of tools to simulate particle dynamics in the full magnetic field using the generalized gradients representation. Generalized gradients provide accurate and analytic representations of the magnetic field that allow for symplectic tracking [1]. We describe the tools that convert magnetic field data into generalized gradients representations suitable for tracking in Elegant, and discuss recent results based upon tracking with the full field representations for all magnets in the APS-U storage ring.
[1] A. Dragt. Lie Methods for Nonlinear Dynamics with Applications to Accelerator Physics. University of Maryland (2019).
BNL, Upton, New York, USA
ANL, Lemont, Illinois, USA
University of Chicago, Chicago, Illinois, USA
We report on the effects of electron beam arrival time and energy jitter on the power level and the fluctuations of the output of an X-ray FEL oscillator (XFELO). For this study, we apply the FEL driven paraxial resonator model of XFELO along with an analytical reflectivity profile to mimic the phase shift and spectral filtering effects of Bragg-crystals. The thresholds for acceptable timing jitters and energy jitters are determined in terms of the fluctuations of the steady-state power output. We explore potential ways to mitigate the power output fluctuations in the presence of unavoidable electron beam jitters.