SLAC, Menlo Park, California, USA
CERN, Geneva, Switzerland
SLAC, Menlo Park, California, USA
SLAC, Menlo Park, California, USA
Photonic band gap (PBG) fibers with hollow core defects are being designed and fabricated for use as laser driven accelerators because they appear capable of providing gradients of several GeV/m at picosecond pulse lengths. While we expect to have fiber down to 1.5-2.0 micron wavelengths we still lack a viable means for efficient coupling of laser power into these structures. The reasons for this include the very different character of these TM-like modes from those familiar in the telecom field and the fact that the defect must function as both a longitudinal waveguide for the accelerating field and a transport channel for the particles. We discuss the status of our coupling work in terms of what has been done and the options we are pursuing for both end and side coupling. In both basic coupler types, the symmetry of the PBG crystal leads to significant differences between this and the telecom field. We show that side coupling provides more possibilities and is preferred. Our motivation is to test new fiber for gradient, mode content and throughput on the NLCTA at SLAC.
TUODN5
SLAC, Menlo Park, California, USA
The determination of wakefields for short bunches in accelerator structures with complex geometries and large spatial dimensions requires significant computational resources. The time domain code T3P developed at SLAC employs the higher-order finite element method for high fidelity modeling and parallel computation for large-scale simulation on state-of-the-art supercomputers. To facilitate wakefield calculation for short bunches, T3P has been enhanced through the implementation of a moving window technique which reduces computing resource requirements by orders of magnitude. For local refinement in the moving window, both a finer unstructured mesh and higher-order finite element basis functions can be employed. Applications demonstrating the efficacy of the technique include wakefield calculations of shallow tapers in storage rings, complex and long vacuum chamber transitions in energy recovery linacs (ERL) and higher-order-mode (HOM) couplers in superconducting rf cavities.
Muons, Inc, Batavia, USA
CLASSE, Ithaca, New York, USA
SLAC, Menlo Park, California, USA
Superconducting RF (SRF) systems typically contain resonances at unwanted frequencies, or higher order modes (HOM). For storage ring and linac applications, these higher modes must be damped by absorbing them in ferrite and other lossy ceramic materials. Typically, these absorbers are brazed to substrates that are often located in the drift tubes adjacent to the SRF cavity. These HOM absorbers must have broadband microwave loss characteristics and must be thermally and mechanically robust, but the ferrites and their attachments are weak under tensile and thermal stresses and tend to crack. Based on prior work on HOM loads for high current storage rings and for an ERL injector cryomodule, a HOM absorber with improved materials and design is being developed for high-gradient SRF systems. This work will use novel construction techniques (without brazing) to maintain the ferrite in mechanical compression. Attachment techniques to the metal substrates will include process techniques for fully-compressed ferrite rings. Prototype structures will be fabricated and tested for mechanical strength under thermal cycling conditions.
SLAC, Menlo Park, California, USA
Fermilab, Batavia, USA
SLAC, Menlo Park, California, USA
Stanford University, Stanford, California, USA
Optical scale dielectric structures offer a promising medium for high-gradient, compact, low-cost acceleration of charged particles. An experimental program is underway at the SLAC E163 facility to demonstrate acceleration in photonic bandgap structures driven by short laser pulses. We present initial experimental results, discuss structure and experimental design, and present first estimates of achievable gradient.
SLAC, Menlo Park, California, USA
The SLAC Beam Physics group and collaborators continue to study options for implementing a near diffraction-limited ring-based light source in the 2.2-km PEP-II tunnel that will serve the SSRL scientific program in the future. The study team has completed the baseline design for a 4.5-GeV storage ring having 160-pm-rad emittance with stored beam current of 1.5 A, providing >1022 brightness for multi-keV photon beams from 3.5-m undulator sources. The team is now investigating possible 5-GeV ERL configurations which, similar to the Cornell and KEK ERL plans, would have ~30 pm-rad emittance with 100 mA current, and ~10 pm-rad emittance with 25 mA or less. In the next year, a diffraction-limited storage ring using on-axis injection in order to reach 30 pm-rad or less emittance will be investigated. An overview of the PEP-X design study and SSRL’s plans for defining the performance parameters that will guide the choice of implementation options is presented.