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radio-frequency

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MOPAS075 RF-Thermal-Structural Analysis of a Waveguide Higher Order Mode Absorber simulation, vacuum, higher-order-mode, storage-ring 605
 
  • G. Cheng
  • E. Daly, R. A. Rimmer, M. Stirbet, L. Vogel, H. Wang, K. Wilson
    Jefferson Lab, Newport News, Virginia
  Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177, and by The Office of Naval Research under contract to the Dept. of Energy.

For an ongoing high current cryomodule project, a total of 5 higher order mode (HOM) absorbers are required per cavity. The load is designed to absorb RF heat induced by HOMs in a 748.5MHz cavity. Each load is targeted at a 4 kW dissipation capability. Embedded cooling channels are employed to remove the heat generated in ceramic tiles and by surface losses on the waveguide walls. A sequentially coupled RF-thermal-structural analysis was developed in ANSYS to optimize the HOM load design. Frequency dependent dielectric material properties measured from samples and RF power spectrum calculated by the beam-cavity interaction codes were considered. The coupled field analysis capability of ANSYS avoided mapping of results between separate RF and thermal/structural simulation codes. For verification purposes, RF results obtained from ANSYS were compared to those from MAFIA, HFSS, and Microwave Studio. Good agreement was reached and this confirms that multiple-field coupled analysis is a desirable choice in analysis of HOM loads. Similar analysis could be performed on other particle accelerator components where distributed RF heating and surface current induced losses are inevitable.

 
 
TUOAAB01 Self-Consistent Simulations of Multipacting in Superconducting Radio Frequencies electron, simulation, vacuum, plasma 769
 
  • C. Nieter
  • P. J. Mullowney, S. Ovtchinnikov, D. S. Smithe, P. Stoltz
    Tech-X, Boulder, Colorado
  Multipacting continues to be an important issue in Superconducting Radio Frequency (SRF) cavities, particularly near waveguide couplers. Most modern simulations of multipacting are not self-consistent, using the fields from a purely electromagnetic simulation to drive the motion of multipacting electrons. This approach works well for the onset on multipacting but as the electron density increases in the cavity it can have an effect on the cavity mode. Recently VORPAL* has demonstrated its ability to mode the electrodynamics of SRF cavities using finite difference time domain (FDTD) algorithms coupled with the Dey-Mittra** method for modeling conformal boundaries. The FDTD approach allows us to easily incorporate multipacting electrons as PIC particles in the simulations. To allow multipacting simulations to be done with EM-PIC we have been developing particle boundaries for the cut-cells. Recently we have added particle removal boundaries at the particle sinks which will correct the unphysical build up of image charge at the boundaries. Work has begun on incorporating secondary electron emission into these boundaries so VORPAL can model multipacting trajectories self-consistently.

* C. Nieter, J. R. Cary, J. Comp. Phys. 196 (2004) 448.** S. Dey, R. Mittra, IEEE Microwave and Guided Wave Letters 7 (1997) 273.

 
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TUPAN055 Present Status of J-PARC Ring RF Ring RF Systems power-supply, synchrotron, acceleration, controls 1511
 
  • M. Yoshii
  • S. Anami, E. Ezura, K. Hara, Y. Hashimoto, C. Ohmori, A. Takagi, M. Toda
    KEK, Ibaraki
  • K. Haga, K. Hasegawa, M. Nomura, A. Schnase, F. Tamura, M. Yamamoto
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
  The RCS high frequency accelerating systems are prepared for beam commissioning in September 2007. Installations of cavities, power supplies and amplifiers have been carried out. The systems have been checked for operation and interoperability. For the MR high frequency accelerating system, the examination of the whole system and its final adjustment are done aiming at installation in October 2007. Here, we report on various issues which had been found and solved during the examination and installation period.

masahito.yoshii@kek.jp

 
 
WEPMN010 Linearization of Downconversion for IQ Detection Purposes controls, linac, simulation 2068
 
  • M. K. Grecki
  • W. Koprek, S. Simrock
    DESY, Hamburg
  Funding: We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 ''Structuring the European Research Area'' program (CARE, contract number RII3-CT-2003-506395).

Measurements of effective Radio Frequency (RF) field parameters (amplitude and phase) are tasks of great importance in high-energy accelerators*. The RF signal is downconverted in frequency to intermediate frequency (IF) but keeping the information about amplitude and phase. The IF signal is then sampled in ADC and processed in digital IQ detector computing the I and Q components**. The downconverter is a nonlinear device thus not only the fundamental frequency but also its harmonics are present and sampled by ADC. For a typical downconverter (used in FLASH LLRF system) the higher order harmonics levels depend on RF signal level and are about 40dBm lower than the fundamental frequency component. These harmonics can produce errors in IQ detector of up to few percent in amplitude and few degree in phase. These errors depends not only on nonlinearity of downconverter but also on the IQ detection scheme*** (IF and sampling rate SR). The paper presents the optimization of the IQ detection scheme (choosing the IF and SR) taking into account the nonlinear characteristics of the downconverter.

*Grelick A. et all:A High-Resolution…, Proc. LINAC 2004,715-718**Grecki M. et all:Estimation of IQ…, Proc. MIXDES 2005,783-788***Simrock S. et all:Considerations…, Proc. EPAC 2006,1462-1464

 
 
WEPMN052 FPGA - based Control System for Piezoelectric Stacks used for SC Cavity's Fast Tuner controls, resonance, simulation, feedback 2155
 
  • P. M. Sekalski
  • J. W. Jalmuzna, A. Napieralski
    TUL-DMCS, Lodz
  • L. Lilje, K. P. Przygoda, S. Simrock
    DESY, Hamburg
  • R. P. Paparella
    INFN/LASA, Segrate (MI)
  Funding: We acknowledge the support of the ECRIA under the FP6 program (CARE, contract number RII3-CT-2003-506395), and Polish National Science Council Grant "138/E-370/SPB/6. PR UE/DIE 354/2004-2007"

The SC cavities need a fast tuning system, which is able to adjust the shape during the pulse operation. The first attempts were focused on the compensation of the repetitive and periodic distortion. The algorithms were implemented in Matlab and allow compensating only the Lorentz force detuning. However, the previous solution was too slow to be able to compensate the microphonics. The paper presents recent development in the field. The previously worked out algorithms are implemented in the FPGA-based control system. The SIMCON board is used, which allows to perform parallel, deeply pipelined calculation. The new approach allows integrating the algorithm dedicated for cavity shape control with the LLRF system used for vector sum control. Moreover, the new algorithm for on-line detuning calculation which base on the electromechanical model of the cavity is presented. The system is tested with Module Test Stand (MTS) at DESY with the high gradient cavities (37 MV/m). The active elements are the NOLIAC's and PI's multilayer, low voltage piezostacks. The paper will present the first results from these measurements.

 
 
WEPMN083 Design of A Direct Power Converter for High Power RF Applications controls, power-supply, booster, target 2221
 
  • D. Cook
  • J. Clare, P. W. Wheeler
    University of Nottingham, Nottingham
  • J. S. Przybyla
    e2v, Essex
  This paper presents practical results from a new type of power supply for high power RF applications for CW operation. The converter is a direct topology, utilising a high frequency resonant link and a high frequency transformer. High operating frequency reduces the transformer and filter size. Soft switching is employed to reduce losses. Two variants of this topology are presented. The first incorporates the high frequency transformer into the resonant circuit. The principle feature of this topology is that parasitic elements associated with all transformers are employed in operation of the converter. However, this requires that the circulating current in the resonant tank flows in the transformer windings. The second topology does not incorporate the transformer into the resonant circuit, therefore requires a smaller transformer. However, the topology will be affected by the parasitic elements of the transformer. Advantages of both these topologies over conventional approaches are discussed. The RF power generated by both topologies is stable and predictable, whilst reduced energy storage in filter components removes the need for crowbar circuits.  
 
WEPMN093 Multipactor Simulations in Superconducting Cavities simulation, RF-structure, electron, linac 2248
 
  • I. G. Gonin
  • J. F. DeFord, B. Held
    STAR, Inc., Mequon, Wisconsin
  • N. Solyak
    Fermilab, Batavia, Illinois
  The multipactor (MP) is a well-known phenomenon. The existence of resonant trajectories can lead to electron avalanche under certain field level and surface conditions. In this paper we describe features of the extension of Analyst software - PT3P code developed for MP simulations in a real 3D RF structures, such as cavities, couplers, RF windows etc. Also we present the results of MP simulations in HOM couplers of TESLA, SNS β=0.61 and β=0.81 and FNAL 3-rd harmonic cavities. We discuss the comparison of simulations with experimental results.  
 
WEPMN105 Fast Thermometry for Superconducting RF Cavity Testing superconducting-RF, kaon, higher-order-mode, instrumentation 2280
 
  • D. F. Orris
  • L. Bellantoni, R. H. Carcagno, H. Edwards, E. R. Harms, T. N. Khabiboulline, S. Kotelnikov, A. Makulski, R. Nehring, Y. M. Pischalnikov
    Fermilab, Batavia, Illinois
  Funding: Work supported by Universities Research Association Inc. under Contract No. DE-AC02-76CH03000 with the United States Department of Energy.

Fast readout of strategically placed low heat capacity thermometry can provide valuable information of Superconducting RF (SRF) cavity performance. Such a system has proven very effective for the development and testing of new cavity designs. Recently, several RTDs were installed in key regions of interest on a new 9 cell 3.9 GHz SRF cavity with integrated HOM design at FNAL. A data acquisition system was developed to read out these sensors with enough time and temperature resolution to measure temperature changes on the cavity due to heat generated from multipacting or quenching within power pulses. The design and performance of this fast thermometry system will be discussed along with results from tests of the 9 cell 3.9GHz SRF cavity.

 
 
WEPMN110 Fabrication and Test of the First Normal-Conducting Crossbar H-type Accelerating Cavity at Fermilab for HINS focusing, linac, vacuum, lattice 2292
 
  • L. Ristori
  • G. Apollinari, I. G. Gonin, T. N. Khabiboulline, G. Romanov
    Fermilab, Batavia, Illinois
  Funding: This work was supported by the U. S. Department of Energy under contract number DE-AC02-76CH03000

The proposed High Intensity Neutrino Source at Fermilab is based on an 8 GeV linear proton accelerator which consists of a normal-conducting and a superconducting section. The normal-conducting (warm) section is composed of an ion source, a radio frequency quadrupole, a medium energy beam transport and 16 normal-conducting crossbar H-type cavities that accelerate the beam from 2.5 MeV to 10 MeV (from β=0.0744 to β=0.1422). These warm cavities are separated by superconducting solenoids enclosed in individual cryostats. Beyond 10 MeV, the design uses superconducting spoke resonators to accelerate the beam up to 8 GeV. In this paper, we illustrate the completion of the first normal-conducting crossbar h-type cavity (β=0.0744) explaining in detail the mechanical engineering aspects related to the machining and brazing processes. The radio-frequency measurements and tuning performed at Fermilab on the resonator and the comparisons with the former simulations are also discussed.

 
 
WEPMS005 Temperature Mapping Results on the High-Field Q-Slope of 1500 MHz Single Cell Superconducting Radiofrequency Cavities Baked In-situ at 400 C. superconductivity, vacuum 2334
 
  • G. V. Eremeev
  • H. Padamsee
    CLASSE, Ithaca
  Funding: NSF

The heat treatment of a niobium cavity between 100 C - 120 C for 48 hours substantially improves cavity performance, presumably by healing the nature of the oxide-metal interface, although the nature of the healing is not yet understood. The heat treatment at higher temperatures is found to deteriorate the performance. Our tests on 1500 MHz single cell cavities are always equipped with a temperature mapping system consisting of 700 thermometers. The effect of heat treatment at various temperatures has been studied in detail using the temperature mapping system. In this contribution we report on several interesting findings from studies of a 400 C heat treatment.

 
 
WEPMS031 Development of a Temperature Mapping System for 1.3-GHz 9-Cell SRF Cavities superconductivity, diagnostics, linear-collider, collider 2406
 
  • A. Canabal
  • J. D. Bowyer
    NMSU, Las Cruces, New Mexico
  • P. Chacon, N. A. Gillespie, M. A. Madrid, T. Tajima
    LANL, Los Alamos, New Mexico
  The mapping of outer wall temperature during the vertical test of a superconducting radio-frequency (SRF) cavity has been one of the most useful tools to detect bad spots of the cavity. However, few systems except a rotating-arm type one have been developed so far for 9-cell cavities. Since it will be an essential tool to identify the failure of the cavities, we started to develop a fix-type temperature mapping system that will enable us to map the temperature of 9-cell cavities in a much shorter time than rotating-arm type. This paper describes the design, status of the development and hopefully some results of the mapping of actual cavities.  
 
WEPMS032 Pre-conceptual Design of Automated Systems for SRF Cavity Assembly and Optical Inspection linear-collider, superconductivity, feedback, vacuum 2409
 
  • T. Tajima
  • M. J. Borden, A. Canabal, T. A. Harden, P. C. Pittman
    LANL, Los Alamos, New Mexico
  The International Linear Collider (ILC) will require ~20,000 Superconducting Radio- Frequency (SRF) cavities. Improving the yield of high-gradient (>35 MV/m) cavities is currently one of the most critical issues for the ILC. The LANL has been tasked to analyze the failure and feedback the results to the industry and academia. We have started an effort to develop a pre-conceptual design of an automated system to optically inspect the inner surface that showed heating with a thermometry system. We have also started a pre-conceptual design of an automated system for assembling and sealing the flanges after high-pressure rinsing in the clean room. This could reduce the chance of particle contamination due to touch labor, leading to a field emission free cavities and higher yield of high-gradient cavities.  
 
THPAS105 Stern-Gerlach Force on a Precessing Magnetic Moment dipole, storage-ring 3729
 
  • M. Conte
  • A. U. Luccio, W. W. MacKay
    BNL, Upton, Long Island, New York
  • M. Pusterla
    Univ. degli Studi di Padova, Padova
  The use of the Stern-Gerlach interaction for attaining the spin-states separation of an (anti)proton beam circulating in a ring is reconsidered in a new method where the particle magnetic moments are made to precess while they are undergoing energy exchanges, either positive or negative, with the e.m. fields of an array of radio frequency resonators tuned in the Transverse Electric mode. This proposal represents an improvement with respect to cases considered in the past when the magnetic moments were conserving their directions in space.