WEPEC  —  Poster Session   (26-May-10   16:00—18:00)

Paper Title Page
WEPEC001 Cryogenic Tests of a 704 MHZ 1MW Power Coupler 2884
 
  • G. Devanz, D. Braud, P. Carbonnier, J.-P. Charrier, S. Chel, M. Desmons, A. Hamdi, H. Jenhani, D. Roudier, P. Sahuquet
    CEA, Gif-sur-Yvette
 
 

Coaxial power couplers capable of handling 1MW peak power have been developped for high intensity superconducting proton linacs. They have been conditioned in travelling wave up to the maximum power available on the Saclay test bench, 1.2 MW forward peak power, up to 10% duty cycle. One coupler has been assembled on a 5-cell medium beta cavity in the class 10 area of the clean room, and installed in our horizontal test cryostat CryHoLab. This paper focusses on the RF operation of the coupler in this cryogenic environment and thermal aspects.

 
WEPEC002 Titanium Nitride Coating as a Multipactor Suppressor 2887
 
  • W. Kaabi, A. Variola
    LAL, Orsay
  • A. Brinkmann
    DESY, Hamburg
  • G. Keppel, V. Palmieri
    INFN/LNL, Legnaro (PD)
  • I. Montero
    CSIC, Madrid
 
 

LAL-Orsay is developing an important effort on R&D and technology studies on RF power couplers for superconductive cavities. 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. The most important method to reduce the multipactor is to decrease the secondary emission yield of the ceramic window. Due to its low Secondary electron Emission Yield (SEY), TiN thin film is used as a multipactor suppressor coating on RF ceramic coupler windows. In this frame work, TiN deposition was made by magnetron reactive sputtering. XPS and XRD analysis were performed to control the film composition and stoechiometry. Coating thickness was optimized so that the TiN coating effectively reduces the SEY but does not cause excessive heating, due to ohmic loss. For this purpose, SEY measurements on covered and uncovered TiN Alumina substrates, multipactor level breakdown on TiN coated Cupper substrates and RRR measurements were performed for different deposit thicknesses.

 
WEPEC003 Industrial Production and Delivery of 670 Fundamental Power Couplers for the XFEL Linac 2890
 
  • L. Lukovac, E. Genesseau
    LAL, Orsay
 
 

Within the XFEL project Laboratoire d'Accélérateur Linéaire (LAL) is engaged to deliver 800 fundamental power couplers operating at 1.3 GHz at nominal power of 120 kW for the superconducting linac. This paper presents the strategies chosen for industrial production along with that of conditioning so as to deliver couplers at the rate of 8 per week.

 
WEPEC004 CW Adaptation of TESLA Technology in HoBiCaT 2893
 
  • O. Kugeler, W. Anders, J. Knobloch, A. Neumann
    Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
 
 

The HoBiCaT facility has been has been set-up and operated at the Helmholtz-Zentrum-Berlin and BESSY since 2005. Its purpose is testing superconducting cavities horizontally in CW mode of operation and it was successfully demonstrated, that TESLA pulsed technology can be used for CW mode of operation with only minor changes. A specific topic is addressed in this paper: elevated dynamic thermal losses in the cavity walls due to trapped magnetic flux.

 
WEPEC005 Optical Inspection of SRF Cavities at DESY 2896
 
  • S. Aderhold
    DESY, Hamburg
 
 

The prototype of a camera system developed at KEK/Kyoto University for the optical inspection of the inner surface of cavities is in operation at DESY since September 2008. More than 20 prototype nine-cell cavities for the European XFEL have been inspected. The unique illumination system combined with the optical sensors allows for the in-situ search of surface defects in high resolution. Such defects may limit the gradient when causing a breakdown of the superconducting state (quench). The comparison of features detected in the optical inspection and hotspots from the temperature mapping during RF-measurements give evidence for correlations. Consecutive inspections of cavities in different stages of the surface preparation process monitor the evolution of surface defects. There are examples for defects traced from the untreated surface condition to the RF-test with temperature map, which identify the defect as the quench location.

 
WEPEC006 Towards PLM-based Quality Assurance in the Fabrication of the Superconducting Cavities for the European XFEL 2899
 
  • L. Hagge, J.A. Dammann, J. Iversen, J. Kreutzkamp, W. Singer
    DESY, Hamburg
 
 

For the series production of s.c. cavities for European XFEL, thorough quality assurance procedures are under preparation to ensure that all cavities satisfy their performance requirements. Each cavity needs to pass a number of quality gates at different levels of completion. At each quality gate, the so-far available manufacturing data and documentation is reviewed and approved by the XFEL cavity production team. To ensure reliable and repeatable procedures with timely responses, the QA efforts are supported by the DESY Product Lifecycle Management (PLM) System, aka DESY EDMS. The EDMS manages fabrication data, coordinates acceptance tests, manages signoffs and provides fabrication progress monitoring. In particular, the EDMS tracks the entire history of all individual cavities, their parts and their semi-finished products. The setup benefits from experience which has been gained at DESY in the cavity production for FLASH. The poster explains the planned QA procedures and customization of the EDMS, and reports inital experience.

 
WEPEC007 Surface Investigation on Prototype Cavities for the European XFEL 2902
 
  • X. Singer, S. Aderhold, A. Ermakov, W. Singer, K. Twarowski
    DESY, Hamburg
  • M. Hoss, F. Schoelz, B. Spaniol
    W.C. Heraeus GmbH, Materials Technology Dept., Hanau
 
 

Performance of XFEL prototype cavities fabricated at the industry and treated at DESY demonstrates big scattering from 15 to 41 MV/m. Most cavities satisfy the XFEL specification. Few cavities with low performance (15-17 MV/m) are limited by thermal break down without field emission. The T-map analysis detected the quench areas mainly close to the equator. Optical control by high resolution camera has been applied and allowed to monitor the defects in some cases with good correlation to T-map data. In order to understand the cause of reduced performance and get more detailed information of defects origin some samples have been extracted from two cavities and investigated by light microscope, 3D- microscope, SEM, EDX and Auger spectroscopy. Several surface flaws with sizes from few μm to hundreds of μm were detected by microscopy. The defects can be separated in two categories. The first category of defects indicates foreign elements (often increased content of carbon). Inclusions with increased content of carbon adhered on the surface and presumably have a hydrocarbon nature. Deviation from smooth surface profile characterizes the second type of defects (holes, bumps and pits).

 
WEPEC008 HOM Spectrum and Q-factor Estimations of the High-Beta CERN-SPL-Cavities 2905
 
  • H.-W. Glock, T. Galek, G. Pöplau, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
 
 

Beam energy deposited in Higher-Order-Modes may affect both beam stability and cryo power requirements of the planned CERN Superconducting Proton Linac SPL. We report on numerical studies of the high-beta cavity type, analyzing it's HOM spectrum. The most dangerous modes are identified and different possibilities of appropriate damping are discussed.

 
WEPEC009 Designing of 9 Cell Reduced Beta Elliptical Cavity for High Intensity Proton Linac 2908
 
  • A. Saini
    University of Delhi, Delhi
  • C.S. Mishra, K. Ranjan, N. Solyak, V.P. Yakovlev
    Fermilab, Batavia
 
 

A superconducting rf cavity is designed for acceleration of particles travelling at 81% the speed of light. The cavity will operate at 1.3 GHz & is to be used in SILC section of the proposed high intensity proton linac at Fermilab. At present cavity will serve to accelerate the particles for energy range 466 MeV to 1.2 GeV. The cavity will be shorter than 9 cell beta =1 cavity but nearly same ratio of surface magnetic field to surface electric field. Cell to cell coupling coefficient is also optimized to get the good field flatness. The cavity is studied for monopole modes and higher order modes. The shapes of end cells are optimized to avoid dangerous modes with keeping same field flatness & same operating frequency.

 
WEPEC010 Optimization of End Cells of Low Beta Cavity of Higher Energy Part of Project X 2911
 
  • A. Saini
    University of Delhi, Delhi
  • A. Lunin, C.S. Mishra, K. Ranjan, N. Solyak, V.P. Yakovlev
    Fermilab, Batavia
 
 

Eleven cell elliptical cavity is designed for acceleration of particles traveling at 81 % of the speed of light. It will operate at 1.3 GHz and will be used to accelerate the particles from 0.4 GeV to 1.2 GeV. The cavity is studied for higher order mode (HOM) and trapped modes. The shapes of end cells of cavity is optimized to increase the field amplitude in end cells so that coupling of trapped modes may increase with HOM coupler and they can be extracted easily but keeping the field flatness & operating frequency undisturbed.

 
WEPEC011 Multipacting Analysis of Superconducting RF Cavities using a Finite Element-based Code employing Leap Frog Method 2914
 
  • S. Ghatak, A.S. Dhavale, K.C. Mittal
    BARC, Mumbai
 
 

BARC is involved in the development of superconducting cavities for Accelerator Driven Sub-critical System (ADSS). The performance of superconducting RF structure can be greatly affected due to multipacting. Hence 2D and 3D multipaction simulation studies have been carried out for a medium velocity (β=0.49) elliptical Niobium cavity operating at 1050 MHz. An in-house code has been developed which uses finite element method based software to calculate electromagnetic field of the structure. Leap frog method algorithm has been used to solve Lorenz force equation for trajectory tracking of electrons which are launched inside from different initial positions. Electron trajectories are tracked until they hit the surface. An interpolation function is used to calculate SEY at different impact energies. By repeating the process at different field level for different primary electrons multipacting field levels are identified. The study revealed that the cavity structure is not multipacting prone up to 17 MV/m average accelerating field. Two point first order multipacting is observed at the equatorial region of the cavity when the accelerating field is between 18 MV/m and 28 MV/m.

 
WEPEC012 Study of Multipacting in a Coaxial Coupler 2917
 
  • A.S. Dhavale
    BARC, Mumbai
  • K.C. Mittal
    BARC-EBC, Mumbai
 
 

The performance of superconducting cavity, couplers and ceramic windows is greatly affected due to multipacting. The present paper describes the multipacting simulations carried out on the co-axial coupler. The equation of motion of electron in RF field is calculated numerically. The enhanced counter function (ECF) is calculated to find out whether a particular electron will give rise to the multipacting. The simulation was carried out for a co-axial coupler having the inner conductor diameter of 34.78 mm and outer conductor diameter of 80 mm at a RF frequency of 350MHz, 700MHz and 1050MHz.

 
WEPEC013 Phase Locking of Superconducting Quarter Wave Resonator by Piezoelectric Actuator 2920
 
  • B.K. Sahu, R. Ahuja, G.K. Chowdhury, R.N. Dutt, S. Ghosh, D. Kanjilal, D.S. Mathuria, A. Pandey, P. Patra, A. Rai, A. Roy, K. Singh
    IUAC, New Delhi
 
 

The existing phase locking scheme of the quarter wave resonators(QWR) in the first operational module of the superconducting heavy ion linear accelerator of Inter University Accelerator Centre consists of a fast (electronic) and a slow time scale control. Helium gas operated slow tuner turns out to be a complicated, somewhat unreliable and expensive for long term operation of the linac. In an alternate scheme to handle the slow time part of the phase control, the tuner plate is deflected by using a combination of a stepper motor for course adjustments and a piezoelectric crystal for fine adjustment of the frequency. The piezoelectric actuator is used in closed loop along with dynamic I-Q based electronic tuner to phase lock the superconducting cavities. During a recent cold test of a QWR, the frequency range of the resonator by the piezoelectric tuner was measured to be 1 kHz. In this test, the fundamental frequency of the QWR was first brought to 97.000 MHz by the mechanical course tuner. The resonator was then locked at a field of 3.8 MV/m at 6 W of helium power and 40 W of forward power from the RF amplifier using the resonator controller along with the piezoelectric tuner.

 
WEPEC015 Development of a Prototype Module for the ERL Superconducting Main Linac at KEK 2923
 
  • T. Furuya, K. Hara, K. Hosoyama, Y. Kojima, H. Nakai, K. Nakanishi, H. Sakai, K. Umemori
    KEK, Ibaraki
  • M. Sawamura
    JAEA/ERL, Ibaraki
  • K. Shinoe
    ISSP/SRL, Chiba
 
 

A prototype module including a couple of 1.3 GHz superconducting 9-cell cavities has been designed as the main linac of cERL which is the test facility to establish the basic ERL technology at KEK. The shape of 9-cell Nb structure has been optimized to accelerate a CW beam of 100 mA with sufficiently damped higher order modes (HOM) which is achieved by adopting an eccentric fluted beam pipe and a cylindrical beam pipe of a large diameter of 123 mm. Extracted HOMs are absorbed by the ferrite cylinders bonded on the copper beam pipes by HIP process. A power coupler with double disk-ceramics has been developed to transfer an RF of 20 kW CW to the cavity in full reflection. The test results of fabrication, cooling and RF performance for these components are integrated as the prototype module of the main linac for cERL facility.

 
WEPEC016 Preparation Status of Cryomodule Tests of Tesla-like Cavities in S1-Global Project at KEK 2926
 
  • E. Kako, H. Hayano, S. Noguchi, N. Ohuchi, M. Satoh, T. Shishido, K. Watanabe, Y. Yamamoto
    KEK, Ibaraki
 
 

Cryomodule tests of four Tesla-like cavities is under preparation for S1-global project at KEK. An average maximum accelerating gradient (Eacc,max) of four cavities in the vertical tests at 2 K was reached to approximately 25 MV/m. Conditioning of four STF-2 input couplers was carried out at a high power test stand with a 5MW-pulsed klystron. Two types of frequency tuning system with a slide-jack tuner and a piezo tuner is installed at the center or end position of the He jacket. String asssembly of the four cavities will be started in March, and the first cool-down test of the cryomodule is scheduled in June, 2010.

 
WEPEC018 Application of Electrochemical Buffing onto Niobium SRF Cavity Surface 2929
 
  • S. Kato, M. Nishiwaki
    KEK, Ibaraki
  • S. Azuma, F. Yamamoto
    Ultra Finish Technology Co., Ltd., Yokosuka
  • P.V. Tyagi
    Sokendai, Ibaraki
 
 

Niobium electropolishing for SRF cavities are generally considered to be the best technology today. However, hydrofluoric and sulphuric acid mixture usually used in the EP process is harmful and requires us carefully controlled handling of it and the many additional facilities. In this article, we propose a new application of electrochemical buffing onto niobium SRF cavity. In the method of electrochemical buffing, a rotating disk with abrasive fine particles where electrolyte is supplied is pressed against the workpiece. The disk and the work function as a cathode and an anode, respectively and an aqueous solution of sodium nitrate is used for the electrolyte. This technique brings us a couple of advantages like high etching rate, ultra small surface roughness, cost-effective and environment-compatible polishing.

 
WEPEC020 Realistic Evaluation of Local Field Enhancement based on Precision Profilometry of Surface Defects 2932
 
  • Y. Morozumi
    KEK, Ibaraki
 
 

The limitation of the accelerating gradient is one of the current major issues in the development of 1.3 GHz superconducting RF accelerator structures. While some of single-cell cavities and a few of 9-cell structures have occasionally seen accelerating gradients over 50 MV/m and 40 MV/m respectively, the reproducibility of high gradient performance is still poor. Field emission and thermal breakdown due to surface imperfections are supposed to limit the gradient. Magnetic field enhancement at small surface defects can give rise to thermal breakdown through local heating ending up with low gradients. Simulations with idealized primitive models are totally unrealistic since real existing defects have complicated and irregular shapes. Profilometry-based realistic high-fidelity modelling of field enhancement will be presented.

 
WEPEC021 Measurement of Hydrogen Absorbed in Niobium 2935
 
  • K. Nakanishi, K. Hara, K. Hosoyama, A. Kabe, Y. Kojima
    KEK, Ibaraki
 
 

Hydrogen absorbed in niobium was measured using effect of hydrogen Q-degradation. A niobium cavity was designed and manufactured for this experiment. Hydrogen was introduced from outside of the cavity by electrolysis of diluted sulfuric acid on the outer surface of the cavity with an anode made by stainless steel. The Q-factor is one of the most unstable property of superconducting cavities. Especially, the reproducibility of Q-factor cannot be so expected after disassembled and reassembled it. In this experiment, the Q-factor was measured without disassembling, because hydrogen was introduced from outside of the cavity. The Q-degradation was observed successfully. And the Q-factor becomes worse and worse, when hydrogen was introduced more and more. To estimate the amount of hydrogen which is absorbed in niobium, small and thin niobium samples were prepared. They were warmed by the energizing heating in vacuum after having introduced hydrogen. The out-gas was analyzed by QMS, and the amount of hydrogen was estimated. This method can be applied to measure the absorbed hydrogen during electro or chemical polishing of cavities without some influence of changing the surface morphology.

 
WEPEC022 Beam Behavior due to Crab Cavities Break down 2938
 
  • K. Nakanishi, Y. Funakoshi, M. Tobiyama
    KEK, Ibaraki
 
 

Crab cavities were installed in KEKB in 2007. The function of the cavity is to tilt the bunch of the beam in the longitudinal direction. But if the RF phase gets out of control, the cavity kicks the beam like a steering magnet. To avoid this unwanted kick, the RF phase must be controlled well. In beam operation, some disturbances may occur such as a discharge, a quench, etc. When such disturbances occur, it is very difficult to control the RF phase precisely. We can't trust measured RF phase at that time. In KEKB, beam is aborted quickly when a disturbance is detected. Beam behavior before detect the disturbances has been investigated. We discuss following items. (1)How fast should the beam be aborted after detecting disturbances? (2)How fast should RF be turned off after detecting disturbances? (3)What a kind of disturbance is harmful? (4)Is the beam abort necessary at all? (Is just to turn RF off OK?)

 
WEPEC023 Surface Study on Niobium Stain after Electro-polishing for Super-conducting RF Cavity 2941
 
  • M. Nishiwaki, H. Hayano, S. Kato, T. Saeki, M. Sawabe
    KEK, Ibaraki
  • P.V. Tyagi
    Sokendai, Ibaraki
 
 

In development of superconducting radio-frequency niobium cavities, there are problems in low performances of electro-polished (EP) cavities with a fresh EP solution due to stains on the surfaces with discoloration. Although the stain problems have been known from the past researches, the detailed study with surface analysis has not been carried out. In this study, the stains on the niobium surfaces were observed with x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy and scanning electron microscope. According to results of XPS, there are some differences in atomic components at the stained and non-stained surfaces, ex, a little amount of fluorine and no metal oxide were found only at the stained surface. In this article, we will describe the detail of the XPS results.

 
WEPEC024 Present Status of Superconducting Cavity System for cERL Injector Linac at KEK 2944
 
  • S. Noguchi, E. Kako, M. Satoh, T. Shishido, K. Watanabe, Y. Yamamoto
    KEK, Ibaraki
 
 

A superconducting cavity system has been developing for cERL injector Linac at KEK. Two prototype 2-cell niobium cavities and two prototype input couplers were fabricated. The vertical tests of the cavities at 2 K were carried out to qualify their performance. The rf conditioning of the input couplers were carried out at a high power test stand with a cw-300kW klystron. The results of the cavity performances at high gradients and the conditioning of the input couplers will be presented in this paper.

 
WEPEC027 Long-period Monitoring of Electro-polishing Electrolyte in EP Facility at KEK 2947
 
  • M. Sawabe., H. Hayano, S. Kato, M. Nishiwaki, T. Saeki
    KEK, Ibaraki
  • P.V. Tyagi
    Sokendai, Ibaraki
 
 

We have constructed an Electro-polishing (EP) Facility in the Superconducting RF Test Facility (STF) at KEK in 2008. The EP facility has been used for the EP process of Superconducting RF (SRF) 9-cell cavities for more than one year. In the EP facility, the capacity of the EP-electrolyte reservoir tank is 2,000 L. This size is relatively large if compared with EP facilities in other laboratories. It means that the quality control of EP electrolyte is more difficult because the status of EP-electrolyte changes as the aging of EP-electrolyte proceeds. In the real EP-process operations, we circulated the EP electrolyte of 1,100 L which was firstly delivered into the tank in January 2008 and was disposed in May 2009. During this period, we performed the EP processes 40 times and periodically measured the concentration of Nb ,Al ,HF in the EP electrolyte. In this article, we report the detailed results of the EP-electrolyte monitoring as well as the observation of changing electronic current oscillation in the EP processes during this period in the EP facility at STF/KEK.

 
WEPEC028 Cavity Diagnostics using Rotating Mapping System for 1.3GHz ERL 9-Cell Superconducting Cavity 2950
 
  • H. Sakai, T. Furuya, S. Sakanaka, T. Takahashi, K. Umemori
    KEK, Ibaraki
  • M. Sawamura
    JAEA/ERL, Ibaraki
  • K. Shinoe
    ISSP/SRL, Chiba
 
 

We are developing the superconducting (SC) cavity for Energy Recovery Linac (ERL) in Japan. In order to survey the electron emission and the heating spot of the cavity inner surface in detail, cavity diagnostics with the rotating mapping system was applied. Two types of sensors, one of which is the carbon resistor and the other is the Si PIN photo diode, were set to detect the temperature rise and electron emission. By rotating the sensor arrays around the cavity axis, a lot of information is obtained all over the cavity surface in detail. This paper reports the results of vertical tests by using this rotating mapping system with Nb 9-cell ERL cavity.

 
WEPEC029 Power Coupler Development for ERL Main LINAC in Japan 2953
 
  • H. Sakai, T. Furuya, S. Sakanaka, T. Takahashi, K. Umemori
    KEK, Ibaraki
  • A. Ishii, N. Nakamura, K. Shinoe
    ISSP/SRL, Chiba
  • M. Sawamura
    JAEA/ERL, Ibaraki
 
 

We started to develop an input power coupler for a 1.3GHz ERL superconducting cavity for ERL main linac. Required input power is about 20kW for the cavity acceleration field of 20MV/m and the beam current of 100mA in energy recovery operation. The input coupler is designed based on the STF-BL input coupler, especially choke-mode type ceramic window was applied. After that some modifications are applied for the CW 20kW power operation. We fabricated input coupler components such as ceramic windows and bellows and carried out the high-power test of the components by using a 30kW IOT power source and a test stand constructed.

 
WEPEC030 Results of Vertical Tests for KEK-ERL 9-cell Superconducting Cavity 2956
 
  • K. Umemori, T. Furuya, H. Sakai, T. Takahashi
    KEK, Ibaraki
  • M. Sawamura
    JAEA/ERL, Ibaraki
  • K. Shinoe
    ISSP/SRL, Chiba
 
 

In order to verify the technology needed for ERL main linac cavities, we fabricated a prototype of L-band 9-cell KEK-ERL superconducting cavity. For the ERL, along with high gradient and high Q-value, strong HOM damping is required. Its cell shape is optimized for the HOM damping. The cavity has large irises of 80 mm diameter, large beampipes of 120 mm and 100 mm diameter and the eccentric fluted beampipe. After a series of surface treatment, such as annealing, electro-polishing, high-pressure-rinsing and baking, several vertical tests have been performed. As for cavity diagnostics, a rotating X-ray and temperature mapping system was constructed. The cavity performance was limited to less than 20 MV/m by the field emissions. The X-ray distributions caused by field emission were clearly observed by X-ray mapping system. In this report, we summarize the recent results of the vertical tests.

 
WEPEC031 Observation of Resonance Mode in Coaxial-type Input Coupler 2959
 
  • K. Umemori, T. Furuya, H. Sakai
    KEK, Ibaraki
  • M. Sawamura
    JAEA/ERL, Ibaraki
  • K. Shinoe
    ISSP/SRL, Chiba
 
 

The coaxial-type input couplers are frequently used for accelerators, since it can successfully propagate high power of RF. Thus we have been developing the coaxial-type input coupler for ERL main linac, operated at 1.3 GHz. When performing high power test of its component, however, we suffered from the heat load due to unexpected loss. A resonance just around 1.3 GHz was found from the low-level measurement. In order to investigate the cause of that resonance, precise calculation was done with MW-studio and HFSS codes. Both codes showed one of dipole modes exists at around 1.3 GHz, near coaxial ceramic window. Details of the mode were further investigated. It showed that the resonant frequency of it depends on, for example, the thickness of the ceramic, the permittivity of the ceramic, and the sizes of inner and outer conductors. In this report, we summarize the experimental observations and the some results from the calculations.

 
WEPEC032 Surface Inspection on MHI-01~09 Cavities 2962
 
  • K. Watanabe, H. Hayano, E. Kako, S. Noguchi, T. Shishido, Y. Yamamoto
    KEK, Ibaraki
  • Y. Iwashita
    Kyoto ICR, Uji, Kyoto
  • Y. Kikuchi
    Tohoku Gakuin University, Miyagi
 
 

Nine 1.3 GHz 9-cell superconducting cavities (MHI-01 ~ 09) for International Linear Collider (ILC) project were fabricated from 2005 to 2009 at KEK-STF. The vertical test (with temperature and X-ray mapping) and optical inspection using by high resolution camera system for nine cavities were carried out from 2006 to 2009 for STF Phase-I project and S1-Global project at KEK. The cavities were separated to three series. The first series is MHI-01 ~ 04 (fabricated at 2005). They were made the Centrifugal barrel polishing (CBP) at initial surface treatment. The second series is MHI-05 and 06 (fabricated 2008). The third series is MHI-07 ~ 09 (fabricated at 2009). The surface treatments of second and third series cavity were made only Electro Polishing (EP) process (without CBP), because of the EBW seams of equator and iris were improved by the feedback of optical inspection method. A good correlation has been so far observed between the hot spots localized by thermometry measurements in the vertical test and the positions of surface defects found by this system. The result of optical inspection will be reported in this paper.

 
WEPEC033 Repair Techniques of Superconducting Cavity for Improvement Cavity Performance at KEK-STF 2965
 
  • K. Watanabe, H. Hayano, E. Kako, S. Noguchi, T. Shishido, Y. Yamamoto
    KEK, Ibaraki
  • Y. Iwashita
    Kyoto ICR, Uji, Kyoto
 
 

The repair techniques of superconducting cavity is important to obtain better yield of accelerating gradient of superconducting 1.3 GHz 9-cell cavities. The techniques for repair of the cavity are combination of the optical inspection, make a replica of defect, the local grinding and the result of temperature mapping in vertical test. The pit type defect (size: 0.7 mm x 0.5 mm, depth: about 115 um) was found at the quench location of MHI-08 cavity at 16 MV/m by optical inspection after 1st vertical test at June 2009. The location of defect is boundary between EBW seam and heat affected zone at 172 degree of 2-cell equator. If a cause of field limitation for MHI-08 is really this pit type defect, then the cavity can repair to remove the defect by mechanical grinding method. The defect was removed completely by the special grinding machine. After grinding, Electric polishing process and optical inspection were carried out to check the surface condition at grinding area. The 2nd vertical test of MHI-08 was carried out at October 2009. The accelerating field was improved from 16 MV/m to 27 MV/m. The result of repair of MHI-08 will be reported in this paper.

 
WEPEC034 Various Rinsing Effects to Mitigate Contaminates Brought by BCP on Niobium SRF Cavity Surface 2968
 
  • P.V. Tyagi
    Sokendai, Ibaraki
  • H. Hayano, S. Kato, M. Nishiwaki, T. Saeki, M. Sawabe
    KEK, Ibaraki
 
 

Buffered chemical polishing (BCP) has been widely used as a final recipe of the surface treatment for niobium cavities and there is still much room to improve this technology since it is environment friendly, cheaper and simpler than electro-polishing. To examine BCPed surface in detail, we carried out BCP experiment followed by various rinsing methods on a series of niobium samples at KEK. As a result of the BCP process some contaminants like fluorine, carbon, etc. have been detected at the surfaces which may be the prominent cause of limiting the performance of SRF cavities. To remove these contaminants, various rinsing processes such as ultra pure water rinse, ultrasonic pure water rinse, alcoholic rinse, detergent rinse, high pressure water rinse (HPR) had been tested after the BCP. The preliminary results show that, only HPR had potential to mitigate these contaminants. In this article, we describe the surface analysis results using X-ray photo electron spectroscopy etc and a comparative study of niobium BCPed samples followed by above mentioned rinsing processes.

 
WEPEC035 Multipoint T-map System for Vertical Test of the Superconducting Accelerator Cavities 2971
 
  • H. Tongu, H. Fujisawa, Y. Iwashita
    Kyoto ICR, Uji, Kyoto
  • H. Hayano, K. Watanabe, Y. Yamamoto
    KEK, Ibaraki
 
 

The vertical test is a performance trial done by cooling the superconducting cavity, and injecting the high-frequency electricity. The temperature mapping (T-map) system is developed for the vertical test. T-map system can find heat sources that may be caused by defects on inner surfaces of superconducting cavities. The purpose of our studies on T-map is to realize a high spacial resolution and easy installation of the sensors. CMOS analog multiplexers in the cryogenic temperature can manage about thousand sensors per 9 cells to send their signals with fewer lines. Inspection efficiencies to raise the production yield of the cavities would be improved by using such a high resolution T-map system. The preliminary test of the cryogenic temperature by the T-map system is reported.

 
WEPEC039 IHEP Low-loss Large Grain 9-cell Cavity Fabrication and Processing 2974
 
  • J.Y. Zhai, J.P. Dai, L. Dong, J. Gao, Z.D. Guo, Z.Q. Li, L.L. Men, Q.Y. Wang
    IHEP Beijing, Beijing
  • J.Z. Chen, J.Q. Qiao
    HJL, Beijing
  • J.X. Wang, H. Yu, H. Yuan
    BIAM, Beijing
  • W.P. Xie
    Ningxia Orient Tantalum Industry Co., Ltd., Dawukou District, Shizuishan city
  • T.X. Zhao
    IHEP Beiing, Beijing
 
 

The combination of the low-loss shape and large grain niobium material is expected to be the possible way to achieve higher gradient and lower cost for ILC 9-cell cavities. As the key component of the 'IHEP 1.3 GHz SRF Accelerating Unit and Horizontal Test Stand Project', a low-loss shape 9-cell cavity using Ningxia large grain niobium has been fabricated and surface treated at IHEP and will be tested at KEK. The fabrication procedure, surface treatment recipes as well as the SRF facilities are presented in this paper.

 
WEPEC041 Manufacturing of the Main Accelerator with TESLA-like 9-cell SRF Cavities at Peking University 2977
 
  • F.S. He, J. Dai, J.K. Hao, S. Jin, Y.M. Li, L. Lin, K.X. Liu, X.Y. Lu, S.W. Quan, W. Xu, B.C. Zhang, K. Zhao, F. Zhu
    PKU/IHIP, Beijing
 
 

Peking University is striving for constructing a superconducting radio-frequency accelerator test facility (PKU-SETF) to provide coherent radiations [1]. A cryomodule consisting of a China made 9-cell TESLA type cavity was designed and constructed for this purpose, which is expected to provide 15-20 MeV energy gain at an operating temperature of 2K. Some technical issues in the manufacturing progress are reported, including the tungsten inert gas (TIG) welding of the LHe vessel and the superconducting cavity, the demagnetization of the vacuum vessel made of pure iron, and the manufacturing of the main power coupler.

 
WEPEC042 A Possible Concept to Improve the Efficiency of the Very Low Beta SC Accelerating Structure 2980
 
  • L. Yang
    Peking University, School of Physics, Beijing
  • X.Y. Lu
    PKU/IHIP, Beijing
 
 

This paper introduce a possible solution to improve the efficiency of the very low beta SC accelerating structure, via extending the gaps number of 4-gap interdigital QWR by doubling its stems number. The new cavity is a 8-gap QWR, which is comprised of two parallel TEM resonant lines operating in opposing phase from each other. It maintains the 4-gap QWR's good EM parameters and enables the use of demountable flange. The more important advantage is the potential improvement of efficiency. According to a preliminary estimation of longitudinal dynamics, the 8-gap QWR could stably accelerate heavy ion at the velocities 0.01<v/c<0.05.

 
WEPEC043 R&D of PKU Single Spoke Cavity 2983
 
  • Z.Y. Yao, C. Chang, J.K. Hao, F.S. He, Y.M. Li, L. Lin, K.X. Liu, X.Y. Lu, S.W. Quan, B.C. Zhang, K. Zhao, F. Zhu
    PKU/IHIP, Beijing
  • L. Yang
    Peking University, School of Physics, Beijing
 
 

Spoke cavities have been developed and have apparent advantages for high current proton accelerator based on superconductivity at low and medium energy region. As the research and the technical reserve, Peking University has started the R&D program of single spoke cavity (SSC). The work is proposed to do beam load experiment on the HI-13 Tandem at CIAE. The maximum kinetic energy of proton beam is 26MeV, and the frequency of the chopper for superconducting is 150MHz. It leads us to the choice of a 450MHz and β=0.2 single spoke cavity. In this paper, the RF design, mechanical study, fabrication arts, tolerance analysis, and room temperature RF test is presented.

 
WEPEC044 RF Test of Two-cell Prototype for the PEFP Proton Linac Extension 2986
 
  • H.S. Kim, Y.-S. Cho, H.-J. Kwon
    KAERI, Daejon
  • S. An
    PAL, Pohang, Kyungbuk
 
 

A superconducting RF cavity with a geometrical beta of 0.42 and a resonant frequency of 700 MHz has been under investigation for an extension program of Proton Engineering Frontier Project (PEFP) to accelerate the proton beam above 100 MeV. We developed and tested a two-cell prototype in order to confirm the fabrication procedure and check the RF and mechanical properties of such a low-beta elliptical cavity. The prototype has been fabricated with high RRR niobium sheets (RRR > 250). Double-ring structure was adopted to reduce the Lorentz force detuning effect. For the vertical test of the prototype cavity, a cryostat was designed and fabricated. Operating temperature is 4.2 K, therefore, pumping to reduce the pressure is not required. We applied 40 layers of superinsulation around the helium vessel in addition to the vacuum insulation between the helium vessel and outer chamber. The status of the prototype development and RF test results will be presented in this paper.

 
WEPEC045 Taper Shape Effects on the HOM Damping of the PLS-II SRF Cavities 2989
 
  • S. An, Y.D. Joo, H.-S. Kang, C.D. Park, I.S. Park, Y.U. Sohn
    PAL, Pohang, Kyungbuk
 
 

In the PLS-II storage ring, the available length of a long straight section for RF system is 6.28 m, which is from quadrupole magnet to quadrupole magnet beam-pipe valves with an elliptical transverse cross section. In this room, two beam-pipe transitions from elliptical to circle cross section, two commercial cryomodules with a circle transverse cross section, three bellows for adjusting cryomodule length and four vacuum valves could need to be installed. Two commercial cryomodules are too long to be installed into this section. In order to install two cryomodules into this section, we need to modify the tapers for reducing the total length of these parts. In this paper, the HOM damping effects for different taper shapes has been studied. The beam loss factor influence and broad-band impedance change due to taper shape changes have been estimated.

 
WEPEC046 Design of Superconducting RF System for PLS-II Upgrade 2992
 
  • Y.U. Sohn, S. An, M.-H. Chun, Y.D. Joo, H.-S. Kang, H.-G. Kim, K.R. Kim, C.D. Park, H.J. Park, I.S. Park, I.H. Yu
    PAL, Pohang, Kyungbuk
 
 

The RF system for PLS-II upgrade, of which beam current and emittance are 400 mA and 5.6 nmrad at 3 GeV, becomes much more important compared to PLS. To reduce the HOM intensity in RF cavities for stable beam, a superconducting RF cavity is selected for the PLS-II. The RF system has to compensate beam loss power of 663 kW from 24 bending magnets, 20 insertion devices and other losses by RF HOM and broadband losses along vacuum chambers. For sufficient energy acceptance and lifetime the design RF voltage is 4.5 MV. Three 500 MHz superconducting cavities will be operated from October 2012, following successful commissioning with PLS NC cavities from July 2011. For the 3 SRF cryomodules, a 700 W class He cryogenic system will be prepared in 2011. The design of PLS-II SRF system including cryogenic system will be reported in the paper.

 
WEPEC047 New Methods for Thin Film Deposition and First Investigations of the use of High Temperature Superconductors for Thin Film Cavities 2995
 
  • A.E. Gustafsson, S. Calatroni, W. Vollenberg
    CERN, Geneva
  • R. Seviour
    Cockcroft Institute, Lancaster University, Lancaster
 
 

Niobium thin film cavities have shown good and reliable performance for LEP and LHC, although there are limitations to overcome if this technique should be used for new accelerators such as the ILC. New coating techniques like High Power Impulse Magnetron Sputtering (HiPIMS) has shown very promising results and we will report on its possible improvements for Nb thin film cavity performance. Current materials used in accelerator SRF technologies operate at temperatures below 4 K, which require complex cryogenic systems. Researchers have investigated the use of High Temperature Superconductors (HTS) to form RF cavities, with limited success*. We propose a new approach to achieve a high-temperature SRF cavity based on the superconducting 'proximity effect'**. The superconducting proximity effect is the effect through which a superconducting material in close proximity to a non-superconducting material induces a superconducting condensate in the latter. Using this effect we hope to overcome the problems that have prevented the use of HTS for accelerating structures so far. We will report the preliminary studies of magnetron sputtered thin films of Cu on Nb.


* E. J. Minehara et al, Superconductivity 3, p277 (1990)
** R. Seviour et al, Superlattices and Microstructures, 25, p647 (1999)

 
WEPEC048 Daresbury International Cryomodule Coupler Progress 2998
 
  • A.E. Wheelhouse, C.D. Beard, P. Davies, J.-L. Fernandez-Hernando, E. Frangleton, P.A. McIntosh, A.J. Moss, J.F. Orrett
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • S.A. Belomestnykh, P. Quigley, V. Veshcherevich
    CLASSE, Ithaca, New York
  • M.A. Cordwell, J. Strachan
    STFC/DL, Daresbury, Warrington, Cheshire
 
 

The Daresbury international Cryomodule Collaboration requires a suitable RF coupler that will fit into the footprint of the ALICE cryomodule, with the ability of transfering potentially up to 30 kW CW of RF power into the cavity whilst maximising the capability for adjusting the coupling. For this a modified Cornell Injector coupler has been used. Modifications to the cold section was carried out. These couplers have now been assembled into a test cavity and conditioned to 30 kW pulsed, 10 kW CW. This paper describes the modifications required to fit inside the cryomodule and details of the tests that were carried out.

 
WEPEC049 Novel Geometries for the LHC Crab Cavity 3001
 
  • B.D.S. Hall, G. Burt, C. Lingwood
    Cockcroft Institute, Lancaster University, Lancaster
  • R.A. Rimmer, H. Wang
    JLAB, Newport News, Virginia
 
 

The planned luminosity upgrade to LHC is likely to necessitate a large crossing angle and a local crab crossing scheme. For this scheme crab cavities align bunches prior to collision. The scheme requires at least four such cavities, a pair on each beam line either side of the interaction point (IP). Upstream cavities initiate rotation and downstream cavities cancel rotation. Cancellation is usually done at a location where the optics has re-aligned the bunch. The beam line separation near the IP necessitates a more compact design than is possible with elliptical cavities such as those used at KEK. The reduction in size must be achieved without an increase in the operational frequency to maintain compatibility with the long bunch length of the LHC. This paper proposes a suitable superconducting variant of a four rod coaxial deflecting cavity (to be phased as a crab cavity), and presents analytical models and simulations of suitable designs.

 
WEPEC051 3D Simulation of the Effects of Surface Defects on Field Emitted Electrons 3004
 
  • A. Zarrebini, M. Ristic
    Imperial College of Science and Technology, London
  • K.R. Long
    Imperial College of Science and Technology, Department of Physics, London
  • R. Seviour
    Cockcroft Institute, Lancaster University, Lancaster
 
 

The ever-growing demand for higher beam energies has dramatically increased the risk of RF breakdown, limiting the maximum achievable accelerating gradient. Field emission is the most frequently encountered RF breakdown where it occurs at regions of locally enhanced electric field. Electrons accelerated across the cavity as they tunnel through the surface in the presence of microscopic defects. Upon Impact, most of the kinetic energy is converted into heat and stress. This can inflict irreversible damage to the surface, creating additional field emission sites. This work aims to investigate, through simulation, the physics involved during both emission and impact of electrons. A newly developed 3D field model of an 805 MHz cavity is generated by COMSOL Multiphysics. Electron tracking is performed using a Matlab based code, calculating the relevant parameters needed by employing fourth Order Runge Kutta integration. By studying such behaviours in 3D, it is possible to identify how the cavity surface can alter the local RF field and lead to breakdown and subsequent damages. The ultimate aim is to introduce new surface standards to ensure better cavity performance.

 
WEPEC052 Higher Order Modes in Third Harmonic Cavities for XFEL/FLASH 3007
 
  • I.R.R. Shinton, R.M. Jones, N. Juntong
    UMAN, Manchester
  • N. Baboi
    DESY, Hamburg
  • N. Eddy, T.N. Khabiboulline
    Fermilab, Batavia
  • T. Flisgen, H.-W. Glock, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
 
 

We analyse the higher order modes in the 3.9GHz bunch shaping cavities recently installed in the XFEL/FLASH facility at DESY. We report on recent experimental results on the frequency spectrum, both beam and probe based. These are compared to those predicted by finite element computer codes, globalised scattering matrix calculations and a two-band circuit model. This study is focused on the dipole component of the multiband expansion of the wakefield.

 
WEPEC053 High Gradient Superconducting Cavity with Low Surface EM Fields and Well-suppressed HOMs for The ILC 3010
 
  • N. Juntong, R.M. Jones
    UMAN, Manchester
 
 

We present an optimized geometry for a 1.3 GHz superconducting cavity in which the surface electromagnetic fields have been minimized and the bandwidth of the fundamental mode has been maximized. We refer to this design as the New Low Surface Field (NLSF) cavity*. Earlier work* focused the fundamental mode properties. Here we study higher order modes (HOMs), means of damping them, and short range wakefields. A two-band circuit model is employed in order to facilitate rapid characteristic of the HOMs in the cavity.


* N. Juntong and R.M. Jones, High-Gradient SRF Cavity with Minimized Surface E.M. Fields and Superior Bandwidth for The ILC, SRF2009, THPPO024, 2009.

 
WEPEC054 Status of the CLIC RTML Studies 3013
 
  • F. Stulle, D. Schulte, J. Snuverink
    CERN, Geneva
  • A. Latina
    Fermilab, Batavia
  • S. Molloy
    Royal Holloway, University of London, Surrey
 
 

Over the last months the general layout of the CLIC main beam RTML has stabilized and most important lattices are existing. This allowed us to perform detailed studies of tolerances on magnetic stray fields and on magnet misalignment. Additionally, beam lines could be improved in terms of performance and flexibility. We discuss the overall layout as will be described in the CLIC conceptual design report, highlight the improvements which have been made and show results of tolerance studies.

 
WEPEC055 Simulations of Proposed Accelerating Cavities for the CERN SPL 3016
 
  • S. Molloy
    Royal Holloway, University of London, Surrey
  • R. Calaga
    BNL, Upton, Long Island, New York
 
 

The Superconducting Proton Linac (SPL) is part of the proposed upgrade of the LHC injection chain, intended to significantly improve the characteristics of the beam circulating in the collider. SPL will rely on two classes of superconducting cavities; beta=0.65 and beta=1; each containing 5-cells resonant at 704 MHz. Presented here are the results of some initial simulations of the beta=1 design, performed at the NERSC supercomputing facility with the highly-parallelised ACE3P codes released by the Advanced Computations Department at SLAC National Accelerator Laboratory. The HOM spectrum in the baseline design has been calculated, and dangerous modes identified by their high R/Q value. In addition, perturbations due to the location of the various couplers, and the structure of the beampipes have been investigated, and are presented here.

 
WEPEC056 Optimization Studies for Radiation Shielding of a Superconducting RF Cavity Test Facility 3019
 
  • C.M. Ginsburg, I.L. Rakhno
    Fermilab, Batavia
 
 

Test facilities for high-gradient superconducting RF cavities must be shielded for particle radiation, which is generated by field emitted electrons in the cavities. A major challenge for the shielding design is associated with uncertainty in modeling the field emission. In this work, a semi-empirical method that allows us to predict the intensity of the generated field emission is described. Spatial, angular and energy distributions of the generated radiation are calculated with the Fishpact code*. The Monte Carlo code MARS** is used for modeling the radiation transport in matter. The detailed distributions of the generated field emission were used for studies with ILC-type superconducting RF cavities with accelerating gradients up to 35 MV/m in the Fermilab Vertical Cavity Test Facility. This approach allows us to minimize the amount of shielding inside cryostat which is an essential operational feature.


* E. Donoghue et al., Proc. SRF-2005, Ithaca NY, June 2005, TuP67.
** N. V. Mokhov and S. I. Striganov, Proc. Hadronic Shower Simulation Workshop, Batavia, Illinois, USA, 6-8 September, 2006.

 
WEPEC057 Single Spoke Cavities for Low-energy Part of CW Linac of Project X. 3022
 
  • I.G. Gonin, M.S. Champion, T.N. Khabiboulline, A. Lunin, N. Perunov, N. Solyak, V.P. Yakovlev
    Fermilab, Batavia
 
 

In the low-energy part of the Project X H-linac there families of 325 MHz SC single spoke cavities will be used, having beta = 0.11, 0.22 and 0.4. Two versions of the beta = 0.11 cavity were considered: low-beta single-spoke cavity and half-wave cavity. Results of detailed optimization of both versions are presented. Single spoke cavity was selected for the linac because of higher r/Q. Results of the beam dynamics optimization for initial stage of the linac with beta=0.11 single spoke cavity are presented as well.

 
WEPEC059 The Beam Splitter for the Project X 3025
 
  • N. Solyak, I.G. Gonin, D.E. Johnson, S. Nagaitsev, V.P. Yakovlev
    Fermilab, Batavia
 
 

In the Project X facility a 2.6 GeV, H- CW beam is delivered to three users simultaneously by way of selectively filling appropriate RF buckets at the front end of the linac and then RF splitting them to three different target halls. With the desire to split the H- beam three ways, an RF separator directs two quarters of the beam to one user (Mu2e), one quarter to another user (Kaon), and one quarter to the third (unidentified) user. The natural way is to use a SC structure with the deflecting TM110 mode. Basic requirements to the deflecting RF structure are formulated and design of the deflecting SC cavities is presented.

 
WEPEC060 Beam Pipe HOM Absorber for 750 MHz RF Cavities 3028
 
  • M.L. Neubauer, A. Dudas, R. Sah
    Muons, Inc, Batavia
  • G.H. Hoffstaetter, M. Liepe, H. Padamsee, V. Shemeli
    CLASSE, Ithaca, New York
 
 

Superconducting RF (SRF) systems typically contain unwanted frequencies or higher order modes (HOM). For storage ring and linac applications, these higher modes must be damped by absorbing them in ferrite and other lossy ceramic materials. Typically, these absorbers are brazed to substrates that are strategically located, often in the drift tubes adjacent to the SRF cavity. These HOM loads must have broadband microwave loss characteristics and be robust both thermally and mechanically, but the ferrites and their attachments are weak under tensile and thermal stresses and tend to crack. Based on existing work on HOM loads for high current storage rings and for an ERL injector cryomodule, a HOM absorber with improved materials and design will be developed for high-gradient 750 MHz superconducting cavity systems for storage ring and linac radiation sources. This work will build on novel construction techniques to maintain the ferrite in mechanical compression without brazing. 750 MHz RF system designs will be numerically modeled to determine the optimum ferrite load required to meet broadband loss specifications.

 
WEPEC061 Novel Crab Cavity RF Design 3031
 
  • M.L. Neubauer, A. Dudas, R. Sah
    Muons, Inc, Batavia
  • G.A. Krafft, R.A. Rimmer
    JLAB, Newport News, Virginia
 
 

The design and construction of electron-ion colliders will be facilitated by the development of an SRF "crab crossing" cavity with 0.5 to 1.5 GHz frequency and 20 to 50 MV integrated voltage. These RF cavities provide a transverse kick to the particle beam. Current state of the art crab cavities provide 2-5 MV of integrated voltage, and most of the existing designs require complex schemes to damp unwanted RF modes. We propose a novel system for implementing TEM-like two-bar structures. Two phase-locked sources 180° out of phase each drive a half-wavelength coax antenna inside of a cavity designed for the fewest possible unwanted modes. The cavity design will required a high-Q system composed of coax windows designed for maximizing the shunt impedance of the structure. A series of cavities could be installed in a beam line, and individual phase adjustment for each module will accommodate their longitudinal spacing and will provide the required integrated voltage.

 
WEPEC062 High Power Coax Window 3034
 
  • M.L. Neubauer, A. Dudas, R. Sah
    Muons, Inc, Batavia
  • T.S. Elliott, R.A. Rimmer, M. Stirbet
    JLAB, Newport News, Virginia
 
 

A superconducting RF (SRF) power coupler capable of handling 500 kW CW RF power is required for present and future storage rings and linacs. There are over 35 coupler designs for SRF cavities ranging in frequency from 325 to 1500 MHz. Coupler windows vary from cylinders to cones to disks, and RF power couplers are limited by the ability of ceramic windows to withstand the stresses due to heating and mechanical flexure. We propose 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. Using compressed window techniques on disk co-axial windows will make significant improvements in the power handling of SRF couplers. We present the bench test results of two window assemblies back to back, as well as individual window VSWR in EIA3.125 coax. A vacuum test assembly was made and the windows baked out at 155C. The processes used to build windows is scalable to larger diameter coax and to higher power levels.

 
WEPEC063 Using a Resistive Material for HOM Damping 3037
 
  • V.D. Shemelin
    Private Address, Freeville
  • S.A. Belomestnykh
    CLASSE, Ithaca, New York
 
 

Ferrites and lossy ceramics used in HOM (higher order mode) load for superconducting accelerators, have shortcomings such as poor batch-to-batch reproducibility of electromagnetic properties, extremely low electric conductivity at cryogenic temperatures leading to accumulation of charge on the material surface, brittleness, which may cause contamination of the nearby SRF cavities by lossy dust, etc. A proposal to use a resistive material free of these shortcomings is presented.

 
WEPEC065 Coupled Electromagnetic-Thermal-Mechanical Simulations of Superconducting RF Cavities 3040
 
  • S.E. Posen, M. Liepe, N.R.A. Valles
    CLASSE, Ithaca, New York
 
 

The high magnetic and electric radio-frequency fields in superconducting microwave cavities cause heating of the inner cavity surface and generate Lorentz-forces, which deform the shape of the cavity and thereby result in a shift of the fundamental mode frequency. 3-dimensional numerical codes can create complex coupled simulations of the electromagnetic fields excited in a cavity, of heat dissipation and heat transfer, as well as of mechanical effects. In this paper we summarize our simulation results using the engineering simulation package ANSYS.

 
WEPEC066 Latest Results and Test Plans from the 100 mA Cornell ERL Injector SCRF Cryomodule 3043
 
  • M. Liepe, S.A. Belomestnykh, E.P. Chojnacki, Z.A. Conway, G.H. Hoffstaetter, R.P.K. Kaplan, S.E. Posen, P. Quigley, J. Sears, V.D. Shemelin, V. Veshcherevich
    CLASSE, Ithaca, New York
 
 

Cornell University has developed and fabricated a SCRF injector cryomodule for the acceleration of a high current, low emittance beam in the Cornell ERL injector prototype. This cryomodule is based on superconducting rf technology with five 2-cell rf cavities operated in the cw mode, supporting beam currents of up to 100 mA. After a rework of this cryomodule in 2009 to implement several improvements, it is now in beam operation again. In this paper we report on latest results and discuss future test plans.

 
WEPEC068 Cavity Design for Cornell's Energy Recovery Linac 3046
 
  • N.R.A. Valles, M. Liepe
    CLASSE, Ithaca, New York
 
 

This paper discusses the optimization of superconducting RF cavities to be used in Cornell's Energy Recovery Linac, a next generation light source. We discuss the determination of a parameter corresponding to beam break-up current and the results of introducing a realistic higher-order-mode absorber constructed of carbon nanotubes rather than a ferrite based absorber. We conclude by comparing the threshold current of the new design and show differences are due to the new absorber material.

 
WEPEC073 A Cryogenic RF Material Testing Facility at SLAC 3049
 
  • J. Guo, D.W. Martin, S.G. Tantawi, C. Yoneda
    SLAC, Menlo Park, California
 
 

Superconducting RF is increasingly important for particle accelerators. A lot of effort has been made in the SRF material research recently, aiming to find the superconducting materials with better performance. We developed a testing system using a resonant cavity with high quality factor and an interchangeable wall for the testing of different materials. The system is capable for high power RF cryogenic test to find the critical magnetic field at different temperature. The facility can be also used on testing the low temperature properties of the normal conducting material. Different Cu, Nb and MgB2 samples have been tested. In this paper, we will present the most recent development of the system, along with a discussion on the recent testing results.

 
WEPEC076 Recent Progress on High-Current SRF Cavities at JLab 3052
 
  • R.A. Rimmer, W.A. Clemens, J. Henry, P. Kneisel, K. Macha, F. Marhauser, L. Turlington, H. Wang
    JLAB, Newport News, Virginia
 
 

JLab has designed and fabricated several prototype SRF cavities with cell shapes optimized for high current beams and with strong damping of unwanted higher order modes. We report on the latest test results of these cavities and on developments of concepts for new variants optimized for particular applications such as light sources and high-power proton accelerators, including betas less than one. We also report on progress towards a first beam test of this design in the recirculation loop of the JLab ERL based FEL. With growing interest worldwide in applications of SRF for high-average power electron and hadron machines, a practical test of these concepts is highly desirable. We plan to package two prototype cavities in a de-mountable cryomodule for temporary installation into the JLab FEL for testing with RF and beam. This will allow verification of all critical design and operational parameters paving the way to a full-scale prototype cryomodule.

 
WEPEC077 RF and Structural Characterization of SRF Thin Films 3055
 
  • A-M. Valente-Feliciano, H.L. Phillips, C.E. Reece, J.K. Spradlin, B. Xiao, X. Zhao
    JLAB, Newport News, Virginia
  • D.B. Beringer, R.A. Lukaszew
    The College of William and Mary, Williamsburg
  • D. Gu
    ODU, Norfolk, Virginia
  • K.I. Seo
    NSU, Newport News
 
 

In the past years, energetic vacuum deposition methods have been developed in different laboratories to improve Nb/Cu technology for superconducting cavities. Jefferson Lab and collaborators are pursuing energetic condensation deposition via Electron Cyclotron Resonance. As part of this study, the influence of the deposition energy, the coating temperature and the substrate's nature on the material and RF properties of the Nb thin film is investigated. The film surface and structure analyzes are conducted with various techniques like X-ray diffraction, Transmission Electron Microscopy, Auger Electron Spectroscopy and RHEED. The microwave properties of the films are characterized on 50 mm disk samples with a 7.5 GHz surface impedance characterization system. This paper presents surface impedance measurements in correlation with surface and material characterization for Nb films produced on various substrates with different bias voltages. Emerging opportunities for developing multi-layer superconducting rf films are also highlighted with the commissioning results of a new deposition system.

 
WEPEC078 Plasma Treatment of Niobium SRF Cavity Surfaces 3058
 
  • S. Popović, M. Rašković, J. Upadhyay, L. Vušković
    ODU, Norfolk, Virginia
  • H.L. Phillips, A-M. Valente-Feliciano
    JLAB, Newport News, Virginia
 
 

Plasma based surface modification provides an excellent opportunity to eliminate non-superconductive pollutants in the penetration depth region of the SRF cavity surface and to remove mechanically damaged surface layer improving surface roughness. We have demonstrated on flat samples that plasma etching in Ar/Cl2 of bulk Nb is a viable alternative surface preparation technique to BCP and EP methods, with comparable etching rates. The geometry of SRF cavities made of bulk Nb defines the use of asymmetric RF discharge configuration for plasma etching. In a specially designed single cell cavity with sample holders, discharge parameters are combined with etched surface diagnostics to obtain optimum combination of etching rates, roughness and homogeneity in a variety of discharge types, conditions, and sequences. The optimized experimental conditions will ultimately be applied to single cell SRF cavities.

 
WEPEC079 Design and Prototype Progress toward a Superconducting Crab Cavity Cryomodule for the APS 3061
 
  • H. Wang, G. Cheng, G. Ciovati, J. Henry, P. Kneisel, R.A. Rimmer, G. Slack, L. Turlington
    JLAB, Newport News, Virginia
  • R. Nassiri, G.J. Waldschmidt
    ANL, Argonne
 
 

A squashed, elliptical supercondconducting (SC) cavity with waveguide dampers on the beam pipes has currently been chosen as the baseline design [1] for the Short Pulse X-ray (SPX) project at the Advanced Photon Source (APS). An alternate cavity design, with a waveguide damper located directly on the cavity cell for improved damping characteristics, has also been designed and cold-tested with promising results. In either case, eight cavities would be operated CW in a single cryomodule at 2K to produce an electron bunch chirp of 4MV at a frequency of 2.815 GHz. Detailed analysis of multipactoring (MP), lorentz force detuning (LFD), and the thermal properties of the baseline design has led to an engineering specification of the basic parameters of the cryomodule.

 
WEPEC080 Progress of Bep Treatments on Nb at JLAB* 3064
 
  • A.T. Wu, S. Jin, R.A. Rimmer
    JLAB, Newport News, Virginia
  • X.Y. Lu, K. Zhao
    PKU/IHIP, Beijing
 
 

Recent experimental results have indicated that Buffered Electropolishing (BEP) is a promising candidate for the next generation of surface treatment technique for Nb superconducting radio frequency (SRF) cavities to be used in particle accelerators. In order to lay the foundation for using BEP as the next generation surface treatment technique for Nb SRF cavities, some fundamental aspects of BEP treatments for Nb have to be investigated. In this report, recent progress on BEP study at JLab is shown. Improvements on the existing vertical BEP are made to allow water cooling from outside of a Nb single cell cavity in addition to cooling provided by acid circulation so that the temperature of the cavity can be stable during processing. Some investigation on the electrolyte mixture was performed to check the aging effect of the electrolyte. It is shown that good polishing results can still be obtained on Nb at a current density of 171 mA/cm when the BEP electrolyte was at the stationary condition and was more than 1.5 years old.


* A.T. Wu et al, Proc. of 14th Conference on SRF, Germany, 2009, THPPO064. ** S. Jin et al, the same as 1, THPPO097.
*** F. Eozenou et al, the same as 1 THPPO068.

 
WEPEC081 Study of Low Temperature Baking Effect on Field Emission on Nb Samples Treated by BEP, EP, and BCP 3067
 
  • A.T. Wu, R.C. Ike, S. Jin, R.A. Rimmer
    JLAB, Newport News, Virginia
  • X.Y. Lu, K. Zhao
    PKU/IHIP, Beijing
  • L.C. Macintyre
    NSU, Newport News, Virginia
 
 

Field emission is still one of the major obstacles facing Nb superconducting radio frequency (SRF) community for allowing Nb SRF cavities to reach routinely accelerating gradient of 35 MV/m that is required for the international linear collider. Nowadays, the well know low temperature backing at 120 oC for 48 hours is a common procedure used in the SRF community to improve the high field Q slope. However, some cavity production data have showed that the low temperature baking may induce field emission for cavities treated by EP. On the other hand, an earlier study of field emission on Nb flat samples treated by BCP showed an opposite conclusion. In this presentation, the preliminary measurements of Nb flat samples treated by BEP, EP, and BCP via our unique home-made scanning field emission microscope before and after the low temperature baking are reported. Some correlations between surface smoothness and the number of the observed field emitters were found. The observed experimental results can be understood, at least partially, by a simple model that involves the change of the thickness of the pent-oxide layer on Nb surfaces.


* L.C. MacIntyre, R. Ike, and A.T. Wu, 2005, unpublished

 
WEPEC082 Computational Modeling of Muons passing through Gas Pressured RF Cavities 3070
 
  • A. Samolov, A.L. Godunov
    ODU, Norfolk, Virginia
 
 

Using high-pressure RF cavities for muon colliders would provide higher accelerating gradients, that is crucial for fast acceleration of short-living muons .This approach requires a good evaluation for mechanisms of muon - low-Z gas interaction, including such effects as multiple scattering and space charge effects. Most present simulation tools (GEANT4, G4MICE) for muon beams are based on single particle tracking, where collective effects are not taken into account. We use a modified molecular dynamic simulation technique to study effects of both multiple scattering and space charge screening by the gas on scattering, energy loss, and propagation of muons during both ionization cooling and acceleration.

 
WEPEC083 Tomographic Analysis of SRF Cavities as Asymmetric Plasma Reactors 3072
 
  • M. Nikolić, A.L. Godunov, S. Popović, A. Samolov, J. Upadhyay, L. Vušković
    ODU, Norfolk, Virginia
  • H.L. Phillips, A-M. Valente-Feliciano
    JLAB, Newport News, Virginia
 
 

The tomographic reconstruction of local plasma parameters for nonequilibrium plasma sources is a developing approach, which has a great potential in understanding the fundamental processes and phenomena during plasma processing of SRF cavity walls. Any type of SRF cavity presents a plasma rector with limited or distorted symmetry and possible presence of high gradients. Development of the tomographic method for SRF plasma analysis consists of several steps. First, we define the method based on the inversion of the Abel integral equation for a hollow spherical reactor. Second step is application of the method for the actual elliptical cavity shape. Third step consists of study of the effects of various shapes of the driven electrode. Final step consists of testing the observed line-integrated optical emission data. We will show the typical results in each step and the final result will be presented in the form of correlation between local plasma parameter distributions and local etching characteristics.

 
WEPEC084 Higher Order Mode Properties of Superconducting Parallel-Bar Cavities 3075
 
  • S.U. De Silva, J.R. Delayen
    ODU, Norfolk, Virginia
  • S.U. De Silva
    JLAB, Newport News, Virginia
 
 

The superconducting parallel-bar cavity* has properties that makes it attractive as a deflecting or crabbing rf structure. For example it is under consideration as an rf separator for the Jefferson Lab 12 GeV upgrade and as a crabbing structure for a possible LHC luminosity upgrade. Initial cavity shape optimization has been performed to obtain a high transverse deflecting voltage with low surface fields. We present here a study of the Higher Order Mode (HOM) properties of this structure. Frequencies, R/Q and field profiles of HOMs have been evaluated and are reported.


* J.R. Delayen and H. Wang, Phys. Rev. ST Accel. Beams 12, 062002 (2009).

 
WEPEC085 Simulation of the High-Pass Filter for 56 MHz Cavity for RHIC 3078
 
  • Q. Wu, I. Ben-Zvi
    BNL, Upton, Long Island, New York
 
 

The damper of 56 MHz cavity is designed to extract all modes to the resistance load outside, including the fundamental mode. Therefore a high-pass filter is required to reflect the fundamental mode back into the cavity. A preliminary design of the filter was previously done. In this paper, we optimize all elements to eliminate the poor filter performance above 1 GHz. The circuit diagram is extracted from microwave lumped elements that reproduce the frequency spectrum of the finalized filter. We also show mode damping results with dampers and filters in the desired configuration, determining the final performance of the cavity.

 
WEPEC086 Optimization of Higher Order Mode Dampers in the 56 MHz SRF Cavity for RHIC 3081
 
  • Q. Wu, I. Ben-Zvi
    BNL, Upton, Long Island, New York
 
 

A 56 MHz cavity was designed for a luminosity upgrade of the Relativistic Heavy Ion Collider (RHIC), including requirements for Higher Order Mode (HOM) damping. A preliminary design of the HOM damper was previously done without optimization. In this paper, we describe our optimization of the damper's performance, and modifications made to its original design. We also show the cavity damper efects with different geometries. Magnetic field enhancement at the ports is reduced to a value less than the highest field in the cavity to eliminate electrical breakdown. All HOMs up to 1 GHz are simulated with their frequencies, mode configurations, R/Qs and shunt impedances, and all modes are well-damped with the optimized design and configuration.