BNL, Upton, Long Island, New York
CERN, Geneva
Lancaster University, Lancaster
KEK, Ibaraki
SLAC, Menlo Park, California
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
LBNL, Berkeley, California
Fermilab, Batavia
Funding: This work was partially performed under the auspices of the US DOE and the European Community-Research Infrastructure, FP6 programme (CARE, contract number RII3-CT-2003-506395)}
The LHC crab cavity program is advancing rapidly towards a first prototype which is anticipated to be tested during the early stages of the LHC phase I upgrade and commissioning. Some aspects related to crab optics, collimation, aperture constraints, impedances, noise effects, beam transparency and machine protection critical for a safe and robust operation of LHC beams with crab cavities are addressed here.
SLAC, Menlo Park, California
LBNL, Berkeley, California
BNL, Upton, Long Island, New York
Funding: This work was supported by DOE contract No. DE-AC02-76SF00515 NERSC
The muon cooling cavity for Muon Collider works under strong external magnetic fields. It has been observed that this external magnetic field can enhance the multipacting activities and dark current heating. As part of a broad effort to optimize external magnetic field map and cavity shape for minimal dark current and multipacting, we use SLAC’s 3D parallel code Track3P to analyze the multipacting and dark current issues of the design. Track3P has been successfully used to predict multipacting phenomena in cavity and coupler designs. It provides unprecedented capabilities for simulating large-scale accelerator structure systems, including realistic 3D details and low turn-around times. In this paper, we present the comprehensive multipacting and dark current simulations for Muon Collider cavities.
SLAC, Menlo Park, California
CERN, Geneva
KEK, Ibaraki
Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.
Normal conducting accelerator structures such as the X-Band NLC structures and the CLIC structures have been found to suffer damage due to RF breakdown and/or dark current when processed to high gradients. Improved understanding of these issues is desirable for the development of structure designs and processing techniques that improve the structure high gradient performance. While vigorous experimental efforts have been put forward to explore the gradient parameter space via high power testing, comprehensive numerical multipacting and dark current simulations would complement measurements by providing an effective probe for observing interior quantities. In this paper, we present studies of multipacting, dark current, and the associated surface heating in high gradient accelerator structures using the parallel finite element simulation code Track3P. Comparisons with the high power test of the CLIC accelerator structures will be presented.
SLAC, Menlo Park, California
Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.
Crab cavities are proposed for the LHC upgrade to improve the luminosity. In the local crabbing scheme, the crab cavities are located close to the interaction region and the transverse separation between the two beam lines at the crab cavity location can only accommodate an 800-MHz cavity of the conventional elliptical shape. Thus the baseline crab cavity design for the LHC upgrade is focused on the 800-MHz elliptical cavity shape although a lower frequency cavity is preferable due to the long bunch length. In this paper, we present a compact 400-MHz design as an alternative to the 800-MHz baseline design. The compact design is of a half-wave resonator (HWR) shape that has a small transverse dimension and can fit into the available space in the local crabbing scheme. The optimization of the HWR cavity shape and the couplers for the HOM, LOM, and SOM damping will be presented.
SLAC, Menlo Park, California
Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.
In this paper, we present a 800MHz crab cavity conceptual design for LHC upgrade, including the cell shape optimization, and LOM, SOM, HOM and input coupler design. The compact coax-to-coax coupler scheme is proposed to couple to the LOM and SOM modes which can provide strong coupling to the LOM and SOM modes. HOM coupler design uses a two-stub antenna with a notch filter to couple to the HOM modes in the horizontal plane and reject the operating mode at 800MHz. All the damping results for the LOM/SOM/HOM modes satisfy their damping requirements. The multipacting in cell and couplers is simulated as well. And the issue of the cross-coupling between the input coupler and LOM/SOM couplers due to cavity asymmetry is addressed. The power coming out of the LOM/SOM/HOM couplers are estimated. All the simulations are carried out using SLAC developed parallel EM simulation codes Omega3P, S3P and Track3P.
SLAC, Menlo Park, California
Funding: Work supported by the DOE under contract DE-AC02-76SF00515.
The Multi-TeV colliders should have the capability to accelerate low emittance beam with high rf efficiency, X-band normal conducting high gradient accelerating structure is one of the promising candidate. However, the long range transverse wake field which can cause beam emittance dilution is one of the critical issues. We examined effectiveness of dipole mode damping in three kinds of X-band, π-mode standing wave structures at 11.424GHz with no detuning considered. They represent three damping schemes: damping with cylindrical iris slot, damping with choke cavity and damping with waveguide coupler. We try to reduce external Q factor below 20 in the first two dipole bands, which usually have very high (RT/Q)T. The effect of damping on the acceleration mode is also discussed.
SLAC, Menlo Park, California
CERN, Geneva
Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.
In recent years, SLAC's Advanced Computations Department (ACD) has developed the parallel 3D Finite Element electromagnetic time-domain code T3P. Higher-order Finite Element methods on conformal unstructured meshes and massively parallel processing allow unprecedented simulation accuracy for wakefield computations and simulations of transient effects in realistic accelerator structures. Applications include simulation of wakefield damping in the Compact Linear Collider (CLIC) Power Extraction and Transfer Structure (PETS).
SLAC, Menlo Park, California
BNL, Upton, Long Island, New York
Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.
SLAC's Advanced Computations Department (ACD) has developed the parallel 3D Finite Element electromagnetic Particle-In-Cell code Pic3P. Designed for simulations of beam-cavity interactions dominated by space charge effects, Pic3P solves the complete set of Maxwell-Lorentz equations self-consistently and includes space-charge, retardation and boundary effects from first principles. Higher-order Finite Element methods with adaptive refinement on conformal unstructured meshes lead to highly efficient use of computational resources. Massively parallel processing with dynamic load balancing enables large-scale modeling of photoinjectors with unprecedented accuracy, aiding the design and operation of next-generation accelerator facilities. Applications include the LCLS RF gun and the BNL polarized SRF gun.
SLAC, Menlo Park, California
JLAB, Newport News, Virginia
Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515 and used resources of NERSC supported by DOE Contract No. DE-AC02-05CH11231, and of NCCS supported by DOE Contract No. DE-AC05-00OR22725.
SLAC has developed a multi-physics simulation code TEM3P for simulating integrated effects of electromagnetic, thermal and structural effects. TEM3P shares the same finite element infrastructure with EM finite elements codes developed at SLAC. This enables simulations within a single framework. Parallel implementation allows large scale computation, and high fidelity and high accuracy simulations can be performed in faster time. In this paper, TEM3P is used to analyze thermal loading in the coupler end-groups of the JLAB SCRF cavity. The results are benchmarked against measurements.
SLAC, Menlo Park, California
Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.
An L-band (1.3 GHz) sheet beam klystron that will nominally produce 10 MW, 1.6 ms pulses is being developed at SLAC for the ILC program. In recent particle-in-cell transport simulations of the 115 kV DC beam through the klystron buncher section without rf drive, a hose-type instability has been observed that is the result of beam noise excitation of transverse modes trapped between the rf cells. In this paper we describe analytical calculations and numerical simulations that were done to study the nature of this instability and explore the required mode damping and changes in the beam focusing to suppress it.