CAEP/IFP, Mainyang, Sichuan
TUB, Beijing
CAEP/IAE, Mianyang, Sichuan
It has been three decades since the research and development of key technologies and components started at the Institute of Fluid Physics, CAEP, for the linear induction accelerator (LIA). The first LIA was built in 1989 with beam parameters of 1.5 MeV, 3 kA and pulse width of 90 ns. Later the SG-I LIA (3.3 MeV, 2 kA, 90 ns) was developed for FEL in 1991. The first Linear Induction Accelerator X-Ray Facility (LIAXF, 10 MeV, 2 kA, 90 ns, spot size about 6 mm in diameter) was built in 1993 and upgraded to 12 MeV with higher performance (LIAXFU, 12 MeV, 2.5 kA, 90 ns, spot size about 4 mm in diameter) in 1995. The Dragon-I LIA with the best quality (20 MeV, 2.5 kA, 80 ns, spot size about 1 mm in diameter) in the world was finished in 2003. The smallest LIA with double pulses separated by 300 ns (MiniLIA, 200 keV, 1 A, 80 ns) was developed in 2007 for beam physics studies.
Cockcroft Institute, Lancaster University, Lancaster
BNL, Upton, Long Island, New York
JLAB, Newport News, Virginia
Lancaster University, Lancaster
In 2017 the LHC is envisioned to increase is luminosity via an upgrade. This upgrade is likely to require a large crossing angle hence a crab cavity is required to align the bunches prior to collision. There are two possible schemes for crab cavity implementation, global and local. In a global crab cavity the crab cavity is far from the IP and the bunch rotates back and forward as it traverses around the accelerator in a closed orbit. For this scheme a two cell elliptical squashed cavity at 800 MHz is preferred. To avoid any potential beam instabilities all the modes of the cavities must be damped strongly, however crab cavities have lower order and same order modes in addition to the usual higher order modes and hence a novel damping scheme must be used to provide sufficient damping of these modes. In the local scheme two crab cavities are placed at each side of the IP two start and stop rotation of the bunches. This would require crab cavities much smaller transversely than in the global scheme but the frequency cannot be increased any higher due to the long bunch length of the LHC beam. This will require a novel compact crab cavity design.
ANL, Argonne
JLAB, Newport News, Virginia
Funding: * Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
A superconducting multi-cell cavity for the production of short x-ray pulses at the Advanced Photon Source (APS) has been explored as an alternative to a single-cell cavity design in order to improve the packing factor and potentially reduce the number of high-power RF systems and low-level RF controls required. The cavity will operate at 2815 MHz in the APS storage ring and will require heavy damping of parasitic modes to maintain stable beam operation. Novel on-cell dampers, attached directly to the cavity body, have been utilized by taking advantage of the magnetic field null on the equatorial plane in order to enhance damping. Design issues and simulation results will be discussed.
JLAB, Newport News, Virginia
ODU, Norfolk, Virginia
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
The CEBAF accelerator at Jefferson Lab has had, since first demonstration in 1996, the ability to deliver a 5-pass electron beam to experimental halls (A, B, and C) simultaneously. This capability was provided by a set of three, room temperature 499 MHz rf separators in the 5th pass beamline. The separator was two-rod, TEM mode type resonator, which has a high shunt impedance. The maximum rf power to deflect the 6 GeV beams was about 3.4kW. The 12 GeV baseline design does not preserve the capability of separating the 5th pass, 11 GeV beam for the 3 existing halls. Several options for restoring this capability, including extension of the present room temperature system or a new superconducting design in combination with magnetic systems, are under investigation and are presented.
JLAB, Newport News, Virginia
ODU, Norfolk, Virginia
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
A new concept for a deflecting and crabbing rf structure based on half-wave resonant lines was introduced recently*. It offers significant advantages to existing designs and, because of it compactness, allows low frequency operation. This concept has been further refined and optimized for superconducting implementation. Results of this optimization and application to a 400 MHz crabbing cavity and a 499 MHz deflecting cavity are presented.
*A New TEM-Type Deflecting and Crabbing RF Structure, J. R. Delayen and H. Wang, Proc. LINAC08
JLAB, Newport News, Virginia
ANL, Argonne
Funding: This manuscript has been authored by Jefferson Science Associates, LLC and by UChicago Argonne, LLC under U.S. DOE Contract numbers DE-AC05-06OR23177 and DE-AC02-06CH11357.
After design optimization of a squashed elliptical single-cell crab cavity at 2.8 GHz, a copper prototype has been bench measured in order to determine its rf properties and the effectiveness of waveguide damping of parasitic modes, especially the low-order mode (LOM)*. We also present detailed results of the RF cold test at 2K on niobium single-cell and two-cell prototype cavities operating either in the zero or pi mode. Further progress will be discussed on the design of high-order mode (HOM) waveguide damping, the analysis of the Lorenz force detuning simulations by ANSYS, and the prototype of on-cell damping in which a waveguide port is attached directly on the cavity’s long equator. Details of LOM/HOM impedance calculations and experimental bench measurements will be reported and compared to strict requirements for satisfying the APS impedance budget.
*J. Shi et. al., “Superconducting RF Deflecting Cavity Design and Prototype for Short X-ray Pulse Generation”, EPAC 2008, paper MOPP155.
JLAB, Newport News, Virginia
The College of William and Mary, Williamsburg
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Much remains to be learned regarding the details of SRF performance effects with material variation, including niobium treated in different ways, and different bulk/thin film materials that are fabricated under different conditions. A facility that can measure small samples’ RF properties in a range of 0~180mT magnetic field and 2~20k temperature is necessary in order to answer this question. The Jefferson Lab surface impedance characterization (SIC) system has been designed to attempt to meet this requirement. The SIC system uses a sapphire-loaded cylindrical Nb cavity at 7.5GHz with 50mm diameter flat sample placed on a non-contacting end plate and a calorimetric technique to directly measure the rf dissipation in the sample in response to known rf fields over ~1 cm2. We report on the commissioning of this system and its first uses for characterizing materials. Preliminary tests with Nb thin film sample sputtered on Cu substrate, and bulk Nb sample have been done at low field. The presently available hardware is expected to enable tests up to 20 mT peak magnetic field on the sample CW. Paths to higher field tests have been identified.
JLAB, Newport News, Virginia
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
For the planned CEBAF upgrade ten new cryomodules are required to increase the beam energy to the envisaged 12 GeV. Extensive cavity and cryomodule R&D has been done previously, including the installation of a new cryomodule dubbed “Renascence” in CEBAFs north linac in 2007. It houses both seven-cell low loss and high gradient type of cavities thereby serving as a testbed to address and cope with crucial technological challenges. Based on this experience a final iteration on the upgrade cavity has been performed to improve various aspects of HOM-damping and thermal stability. Two such cavities have been produced and qualified. A thorough cavity HOM-survey has been performed to verify the integrity of the cavities and to guarantee the impedance requirements of each crucial HOM. This paper details the results of HOM-surveys performed for the first two upgrade style low loss cavities tested both individually in a vertical Dewar and horizontally in a dedicated cavity pair cryomodule. The safety margin to the worst beam break-up scenario at 12 GeV has been concluded.
JLAB, Newport News, Virginia
Tech-X, Boulder, Colorado
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
In this paper, we present benchmarking results for high-class 3D electromagnetic (EM) codes in designing RF cavities today. These codes include Omega3P [1], VORPAL [2], CST Microwave Studio [3], Ansoft HFSS [4], and ANSYS [5]. Two spherical cavities are selected as the benchmark models. We have compared not only the accuracy of resonant frequencies, but also that of surface EM fields, which are critical for superconducting RF cavities. By removing degenerated modes, we calculate all the resonant modes up to 10 GHz with similar mesh densities, so that the geometry approximation and field interpolation error related to the wavelength can be observed.
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.
JLAB, Newport News, Virginia
Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
With the proposal of medium to high average current accelerator facilities the demand for cavities with extremely low HOM impedances is increasing. Modern numerical tools are still under development to more thoroughly predict impedances that need to take into account complex absorbing boundaries and lossy materials. With the usually large problem size it is preferable to utilize massive parallel computing when applicable and available. Apart from such computational issues, we have developed methods using available computer resources to enhance the information that can be extracted from a cavities’ wake potential computed in time domain. In particular this is helpful for a careful assessment of the extracted RF power and the mitigation of potential beam breakup or emittance diluting effects, a figure of merit for the cavity performance. The methods are described as well as examples of their implementation.