Muons, Inc, Batavia, USA
JLAB, Newport News, Virginia, USA
A 20-50 MV integrated transverse voltage is required for the Electron-Ion Collider. The most promising of the crab cavity designs that have been proposed in the last five years are the TEM type crab cavities because of the higher transverse impedance. The TEM design approach is extended here to a hybrid crab cavity that includes the input power coupler as an integral part of the design. A prototype was built with Phase I monies and tested at JLAB. The results reported on, and a system for achieving 20-50 MV is proposed.
JLAB, Newport News, Virginia, USA
Tech-X, Boulder, Colorado, USA
To benchmark a multi-physics code VORPAL developed by Tech-X, the High Order Mode (HOM) coaxial coupler design implemented in Jefferson Lab’s 12GeV upgrade cryomodules is analyzed by use of commercial codes, such as ANSYS, HFSS and Microwave Studio. Testing data from a Horizontal Test Bed (HTB) experiment on a dual-cavity prototype are also utilized in the verification of simulation results. The work includes two stages: first, the HOM feedthrough that has a high RRR niobium probe and sapphire insulator is analyzed for the RF-thermal response when there is traveling wave passing through; second, the HTB testing condition is simulated and results from simulation are compared to thermal measurements from HTB tests. The analyses are of coupled-field nature and involve highly nonlinear temperature dependent thermal conductivities and electric resistivities for the eight types of materials used in the design. Accuracy and efficiency are the main factors in evaluation of the performance of the codes.
JLAB, Newport News, Virginia, USA
SLAC, Menlo Park, California, USA
A superconducting cavity of the same shape as used for the development of superconducting photo injectors has been built for the studies of high magnetic field induced Q slope due to the local heating. The multipactoring problem has been observed on the TE011 mode, 3.3GHz with magnetic field barriers. To understand and overcome this problem, 3D multipactoring simulations by Omega3P and Track3P have been done and found these to be one-point multipactors pulled out from the flat bottom surface by finite normal component of electric field. Asymmetric coupling ports on the side of the beam tube could have caused the distortion of the TE011 mode. The thermometry measurement later confirmed the predicted impact locations. A structure modification has been adopted based on the simulation prediction. More experimental results with the new geometry will allow further comparison with the 3D multipactoring simulations.
Tech-X, Boulder, Colorado, USA
JLAB, Newport News, Virginia, USA
Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference time-domain simulation tool. We highlight thermal benchmarking work with a complex HOM feed-through geometry, done in collaboration with researchers at the Thomas Jefferson National Accelerator Laboratory, and discuss upcoming design studies with this emerging tool. This work is part of an effort to generalize the VORPAL framework to include generalized PDE capabilities, for wider multi-physics capabilities in the accelerator, vacuum electronics, plasma processing and fusion R&D fields, and we will also discuss user interface and algorithmic upgrades which facilitate this emerging multiphysics capability.
JLAB, Newport News, Virginia, USA
ANL, Argonne, USA
Two single-cell, superconducting, squashed elliptical crab cavities with waveguides to damp Higher Order Modes (HOM) and Lower Order Mode (LOM) have been designed and prototyped for the Short Pulse X-ray (SPX) project at the Advanced Photon Source (APS). The Baseline cavity with LOM damper on the beam pipe has been vertically tested and exceeded its performance specification with over 0.5MV deflecting voltage. The Alternate cavity design which uses an “on-cell” waveguide damper is preferred due to its larger LOM impedance safety margin. Its prototype cavity has been fabricated by a Computer Numerical Controlled (CNC) machine and is subject to further testing. The conceptual design, layout and analysis for various cryomodule components are presented.
ANL, Argonne, USA
JLAB, Newport News, Virginia, USA
Superconducting cavities have been analyzed for the short-pulse x-ray (SPX) project at the Advanced Photon Source (APS). Due to the strong damping requirements in the APS storage ring, single-cell superconducting cavities have been designed. The geometry has been optimized for lower-order and higher-order mode damping, reduced peak surface magnetic fields, and compact size. The integration of the cavity assembly, with dampers and waveguide input coupler, into a cryomodule will be discussed.
JLAB, Newport News, Virginia, USA
ITER Organization, St. Paul lez Durance, France
The Thomas Jefferson National Accelerator Facility has recently completed the C50 cryomodule refurbishment project. The goal of this project was to enable robust 6 GeV, 5 pass operation of the Continuous Electron Beam Accelerator Facility (CEBAF). The scope of the project included removal, refurbishment and reinstallation of ten CEBAF cryomodules at a rate of three per year. The refurbishment process included reprocessing of SRF cavities to eliminate field emission and to increase the nominal gradient from the original 5 MV/m to 12.5 MV/m. New “dogleg“ couplers were installed between the cavity and helium vessel flanges to intercept secondary electrons that produce arcing in the fundamental Power Coupler (FPC). Other changes included new ceramic RF windows for the air to vacuum interface of the FPC and improvements to the mechanical tuner. Damaged or worn components were replaced as well. All ten of the refurbished cryomodules are now installed in CEBAF and are currently operational. This paper will summarize the performance of the cryomodules. This paper will also look at problems that must be addressed by future refurbishment projects.
The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
ANL, Argonne, USA
LBNL, Berkeley, California, USA
JLAB, Newport News, Virginia, USA
The Advanced Photon Source Upgrade project (APS-U) at Argonne includes implementation of Zholents’* deflecting cavity scheme for production of short x-ray pulses. This is a joint project between Argonne National Laboratory, Thomas Jefferson National Laboratory, and Lawrence Berkeley National Laboratory. This paper describes performance characteristics of the proposed source and technical issues related to its realization. Ensuring stable APS storage ring operation requires reducing quality factors of these modes by many orders of magnitude. These challenges reduce to those of the design of a single-cell SC cavity that can achieve the desired operating deflecting fields while providing needed damping of all these modes. The project team is currently prototyping and testing several promising designs for single-cell cavities with the goal of deciding on a winning design in the near future.
*A. Zholents et al., NIM A 425, 385 (1999).
JLAB, Newport News, Virginia, USA
Northern Illinois University, DeKalb, Illinois, USA
Cockcroft Institute, Warrington, Cheshire, United Kingdom
GOO Zaryad, Novosibirsk, Russia
ANL, Argonne, USA
ODU, Norfolk, Virginia, USA
SLAC, Menlo Park, California, USA
An electron-ion collider (MEIC) is envisioned as the primary future of the JLab nuclear science program beyond the 12 GeV upgraded CEBAF. The present MEIC design selects a ring-ring collider option and covers a CM energy range up to 51 GeV for both polarized light ions and un-polarized heavy ions, while higher CM energies could be reached by a future upgrade. The MEIC stored colliding ion beams, which will be generated, accumulated and accelerated in a green field ion complex, are designed to match the stored electron beam injected at full energy from the CEBAF in terms of emittance, bunch length, charge and repetition frequency. This design strategy ensures a high luminosity above 1034 s−1cm-2. A unique figure-8 shape collider ring is adopted for advantages of preserving ion polarization during acceleration and accommodation of a polarized deuteron beam for collisions. Our recent effort has been focused on completing this conceptual design as well as design optimization of major components. Significant progress has also been made in accelerator R&D including chromatic correction and dynamical aperture, beam-beam, high energy electron cooling and polarization tracking.
PPPL, Princeton, New Jersey, USA
LLNL, Livermore, California, USA
A variety of masks were installed on the Paul Trap Simulator Experiment (PTSX) cesium ion source in order to perform experiments with modified transverse distribution functions. Masks were used to block injection of ions into the PTSX chamber, thereby creating injected transverse beam distributions that were either hollow, apertured and centered, apertured and off-center, or comprising five beamlets. Experiments were performed using either trapped plasmas or the single-pass, streaming, mode of PTSX. The transverse streaming current profiles clearly demonstrated centroid oscillations. Further analysis of these profiles also shows the presence of certain collective beam modes, such as azimuthally symmetric radial modes. When these plasmas are trapped for thousands of lattice periods, the plasma quickly relaxes to a state with an elevated effective transverse temperature and is subsequently stable. Both sinusoidal and periodic step function waveforms were used and the resulting difference in the measured transverse profiles will be discussed.
PPPL, Princeton, New Jersey, USA