TRIUMF, Vancouver
PAVAC, Richmond, B.C.
The ISAC-II heavy ion linear accelerator has been in operation at TRIUMF since 2006. The high beta section of the accelerator, consisting of twenty cavities with optimum beta=0.11, is currently under production and is scheduled for completion in 2009. The cavities are superconducting bulk Niobium two-gap quarter-wave resonators with a frequency of 141 MHz, providing, as a design goal, a voltage gain of Veff=1.08 MV at 7 W power dissipation. Production of the cavities is with a Canadian company, PAVAC Industries of Richmond, B.C. after two prototype cavities were developed, produced and successfully tested. Cavity production details and test results will be presented and discussed.
Euclid TechLabs, LLC, Solon, Ohio
ANL, Argonne
UMD, College Park, Maryland
Funding: Work supported by the US Department of Energy.
The development of high gradient rf driven dielectric accelerating structures is in part limited by the problem of multipactor. The first high power experiments with an 11.424-GHz rf driven alumina accelerating structure exhibited single surface multipactor. Unlike the well understood multipactor problem for dielectric rf windows, where the rf electric field is tangential and the rf power flow is normal to the dielectric surface, strong normal and tangential rf electric fields are present from the TM01 accelerating mode in the DLA and the power flow is parallel to the surface at the dielectric-beam channel boundary. While a number of approaches have been developed, no one technology for MP mitigation is able to completely solve the problem. In this paper we report on numerical calculations of the evolution of the MP discharge, and give particular attention to MP dependence on the rf power ramp profile and the use of engineered surface features on the beam channel wall to interrupt the evolution of the multipactor discharge.
CERN, Geneva
aurorasat, Paterna
DCOM-iTEAM-UPV, Valencia
WBFB, Berlin
Universidad Politecnica de Madrid, ETSI Aeronauticos, Madrid
UAM, Madrid
UVEG, Burjasot (Valencia)
ESA-ESTEC, Noordwijk
CSIC, Madrid
Multipactor phenomena which are closely linked to the SEY (secondary electron yield) can be mitigated by many different methods including groves in the metal surface as well as using electric or magnetic bias fields. However frequently the application of global magnetic or electric bias field is not practicable considering the weight and power limitations on-board satellites. Additionally, surface grooves may degrade the RF performance. Here we present a novel technique which is based on a magnetostatic field pattern on the metallic surface with fast spatial modulation in the order of 30 micron. This field pattern is produced by proper magnetization of an underlying ferromagnetic layer such as nickel. Simulations and preliminary experimental results will be shown and a number of applications, both for particle accelerators and satellite microwave payloads are discussed.
FZJ, Jülich
CEA, Gif-sur-Yvette
The driver of the International Fusion Material Irradiation Facility (IFMIF) consists of two 125 mA, 40 MeV cw deutron accelerators. A superconducting option for the 5 to 40 MeV linac is based on Half-Wave Resonators (HWR) has been choosen. The first cryomudule should contain 8 HWR's with resonant frequency of 175 MHz and beta=v/c=0.094. The paper describes RF design of half-wave length resonator. The requirents on high power coupler define its installation in the cavity central region. Few options of cavity tune were investigated, the capacitive tuner installed opposite to the coupler port have been accepted. The cavity structural analyses have been conducted and cavity stiffening has been worked out.
ANL, Argonne
Funding: U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
Work is underway to improve the reilability and power handling capability of input couplers used in the Advanced Photon Source single-cell and five-cell cavities. Coupler performance during conditioning in a test cavity suggests that ceramic material defects and field enhancement caused by a mechanical gap in the coupler design may be responsible for past coupler failures at high power. Simulation results and high-power test data will be discussed.
INFN/LNF, Frascati (Roma)
STAAR/AWR Corporation, Mequon
SLAC, Menlo Park, California
CERN, Geneva
To suppress the vertical beam instability in the CTF3 Combiner Ring caused by vertical trapped modes in the rf deflectors, two new devices have been constructed. In the new structures special antennas absorb the power released by the beam to the modes. They have been realized in aluminium to reduce the costs and delivery time and have been successfully installed in the ring. In the paper we illustrate the electromagnetic design, the realization procedures, the rf measurement and high power test results.
LAL, Orsay
INFN/LNL, Legnaro (PD)
LAL-Orsay is developing an important effort on R&D studies on RF power couplers. One of the most critical components of those devices is the ceramic RF window that allows the power flux to be injected in the coaxial line. The presence of a dielectric window on a high power RF line has a strong influence on the multipactor phenomena. To reduce this effect, the decrease the secondary emission yield (SEY)of the ceramic window is needed. Due to its low SEY coefficient, TiN coating is used for this goal. In this framework, a TiN sputtering bench has been developed in LAL. The reactive sputtering of TiN needs the optimisation of gas flow parameters and electrical one, to obtain stoechiometric deposit. XRD analysis was performed to control the film composition and stoechiometry. Measurements point out how the Nitrogen vacancy on the film can be controlled acting on the N2 flow. In addition, the coating thickness must be optimized so that the TiN coating effectively reduces the SEY coefficient but does not cause excessive heating, due to ohmic loss. For this purposes, multipactor level breakdown and resistance measurements were done for different deposit thickness.
Muons, Inc, Batavia
JLAB, Newport News, Virginia
Funding: Supported in part by DOE SBIR grant DE-FG02-08ER85171 Supported in part by USDOE Contract DE-AC05-84-ER-40150
There are over 35 coupler designs for SRF cavities ranging in frequency from 325 to 1500 MHz. Two-thirds of these designs are coaxial couplers using disk or cylindrical ceramics in various combinations and configurations. While it is well known that dielectric losses go down by several orders of magnitude at cryogenic temperatures, it not well known that the thermal conductivity also goes down, and it is the ratio of thermal conductivity to loss tangent (SRF ceramic Quality Factor) and ceramic volume which will determine the heat load of any given design. We describe a novel robust co-axial SRF coupler design which uses compressed window technology. This technology will allow the use of highly thermally conductive materials for cryogenic windows. The mechanical designs will fit into standard-sized ConFlat® flanges for ease of assembly. Two windows will be used in a coaxial line. The distance between the windows is adjusted to cancel their reflections so that the same window can be used in many different applications at various frequencies.
NRL, Washington, DC
ANL, Argonne
Euclid TechLabs, LLC, Solon, Ohio
Icarus Research, Inc., Bethesda, Maryland
Funding: Department of Energy, Office of Naval Research, and DoE SBIR Phase II grant DE-FG02-06ER84463
Dielectric-loaded accelerating (DLA) structures, in which a dielectric liner is placed inside a cylindrical metal tube, offer the potential of a simple, inexpensive alternative to copper disk-loaded structures for use in high-gradient rf linear accelerators. A joint Naval Research Laboratory/Euclid Techlabs/Argonne National Laboratory study is under way to investigate the performance of X-band DLA structures using high-power 11.43-GHz radiation from the NRL Magnicon Facility*. The initial goal of the program has been to develop structures capable of sustaining high accelerating gradients. The two significant limitations that have been discovered relate to multipactor loading of the structures and rf breakdown at joints between ceramic sections. We will report the results of several recent structure tests that have demonstrated significant progress in addressing both of these issues. The longer-range goal of the program is to study electron acceleration in DLA structures. For this purpose, we are developing an X-band DLA test accelerator. We will also report the results of initial operation of a 5-MeV injector for the new accelerator.
*C. Jing, W. Gai, J. Power, R. Konecny, S. Gold, W. Liu and A. Kinkead, IEEE Trans. Plasma Sci., vol. 33, pp.1155-1160, August 2005.
MEPhI, Moscow
TRIUMF, Vancouver
The results of 3D multipacting simulation in coaxial superconducting quarter wave cavities of the linear accelerator of heavy ions ISAC-II are presented. The multipacting simulation was done using MultP-M code. Dangerous areas of structure and levels of an accelerating field are revealed. Examples of electrons resonant trajectories are presented. Simulation results are compared with experimental results obtained during several superconducting cavities processing.
UMD, College Park, Maryland
Funding: Office of High Energy Physics, US Department of Energy (DoE).
Multipactor (MP) may occur in many situations: one- and two-surface MP, resonant and poly-phase-MP, on the surface of metals and dielectrics etc. We consider this phenomenon in dielectric loaded accelerator (DLA) structures. The starting point for our work is experimental and theoretical studies of such structures jointly done by Argonne National Lab and Naval Research Lab*. In the theoretical model developed during those studies, the space charge field due to the accumulated charged particles is taken into account as a parameter. We offer a non-stationary 2D cylindrical model where the DC field is taken into account self-consistently. We have improved our previous model** and demonstrated that its predictions are in good agreement with the results of other studies***. We also demonstrate some recent results where the effects of axial particle motion are taken into account.
*J.G. Power et al., PRL, 92, 164801, 2004
**O.V. Sinitsyn et. al., AIP Proc. 13th Advanced Accelerator Concepts, 2008
***J.G. Power, S.H. Gold, AIP Proc.12th Advanced Accelerator Concepts, 2006
TUB, Beijing
The Multipactor Electron Gun (MEG) can produce high current self-bunching electron beams. In this paper, the primary experimental results of an S-band MEG based accelerator are presented. The accelerator was modified from a 6MeV standing wave accelerator to integrate the MEG, which has an adjusting structure to control both the cathode-grid distance and frequency tuner. The designed output energy is 5MeV and average current is 100mA. The experiment included low power microwave parameter measurement and high power beam test. In the microwave parameter measurement, the relationship between tuner position and E-field distribution was investigated. Platinum was used as the secondary electron emitters of the MEG. The multipacting process was observed and an average current of 40mA was collected by an aluminum target.