| Paper | Title | Page |
|---|
| WEP01 | Studies of alternative techniques for niobium cavity fabrication | 429 |
| | - C. Compton, D. Baars, T. Bieler, J. Bierwagen, S. Bricker, W. Hartung, D. Pendell, R. York
Michigan State University - L. Cooley, H. Jiang, B. Kephart
Fermilab
| |
| | Alternative fabrication techniques for superconducting
radio frequency (SRF) cavities are being investigated.
The main goals are to reduce cavity fabrication costs and
expand possibilities for advanced cavity designs. At
present, SRF cavities are fabricated via deep drawing of
parts from sheet material and electron beam welding
(EBW) to join the parts together. EBW produces welds of
high quality, but the procedures are costly and timeconsuming.
Alternative technologies being explored
include tungsten inert gas (TIG) welding of Nb,
hydroforming of Nb, and electron-beam free form
fabrication (EBFFF) of Nb. If techniques can be
developed which do not degrade the Nb purity, TIG
welding could reduce or eliminate the need for EBW.
Hydroforming could also be an alternative to deep
drawing and EBW. As has been demonstrated by several
other groups, complete cavities can be hydroformed from
Nb tubes in one step using internal pressure and outer
dies. Hydroforming of cavities in an industrial setting is
presently being explored. EBFFF is a new technique for
forming parts from wire stock with an electron beam.
Though it may not be suitable for fabrication of a
complete cavity, EBFFF could be used to produce tubes
for hydroforming or parts for drift tube cavities.
Additionally, the possibility of producing single crystal
tubes using EBFFF is being explored. | |
| WEP02 | Superconducting RF Photocathode Gun for Low Emittance Polarized Electron Beams | 434 |
| | - D. Holmes, H. Bluem, B. Abel, A. Favale, E. Peterson, J. Rathke, T. Schultheiss, A. Todd
Advanced Energy Systems, Inc. - J. Kewisch, I. Ben-Zvi, A. Burrill, R. Grover, D. Pate, T. Rao, R. Todd
Brookhaven National Laboratory
| |
| | The use of an RF electron gun with a magnetized
cathode in place of a DC gun for ILC may eliminate the
need for emittance damping rings. So far only DC guns
have been used to provide polarized electron beams
because of the very high vacuum level needed for
survival of the Gallium Arsenide (GaAs) cathode
material used to generate polarized electrons.
Maintaining adequate lifetime of GaAs cathode material
requires vacuum levels in the 10-11 torr range. While
vacuum levels around the 10-9 torr range are common in a
normal conducting RF gun, the cryogenic pumping of the
cavity walls of a superconducting RF (SRF) gun may
maintain vacuum in the range needed for GaAs cathode
longevity.
Advanced Energy Systems, Inc. is collaborating with
Brookhaven National Laboratory to investigate the
generation of polarized electron beams using a SRF
photocathode gun. The team is developing an
experiment to study the quantum lifetime of a GaAs
cathode in a SRF cavity and investigate long term cavity
performance while integrated with a cesiated GaAs
cathode [1]. This paper reviews the design and analysis
performed to develop a method to prepare and install
GaAs cathodes into a SRF cavity in support of this
experiment. | |
| WEP04 | Surface roughness characterization of niobium subjected to incremental BCP and EP processing steps | 438 |
| | - H. Tian, M. J. Kelley
TJNAF/College of William and Mary - G. Ribeill
North Carolina State University - C. E. Reece
TJNAF
| |
| | The surface of niobium samples polished under
incremental Buffered Chemical Polish (BCP) and Electro-
Polishing (EP) have been characterized through Atomic
Force Microscopy (AFM) and stylus profilometry across a
range of length of scales. The results were analyzed using
Power Density Spectral (PSD) technique to determine
roughness and characteristic dimensions. This study has
shown that the PSD method is a valuable tool that
provides quantitative information about surface roughness at different length scales. | |
| WEP05 | Testing the FLASH superconducting accelerating modules | 442 |
| | - D. Kostin, W. -D. Moeller, A. Goessel, R. Lange
DESY Hamburg
| |
| | The Free-electron LASer in Hamburg (FLASH),
operating in the VUV wavelengths range, is not only the
outstanding research facility in Europe, but also the test
bench for the ILC superconducting linac technology.
Started XFEL, as well as planned ILC, both depend on the
progress made here. [1], [2], [3]. New module test stand
was recently put into operation at DESY. The FLASH
linac has been upgraded to 6 superconducting modules.
The accelerating modules testing experience and the
results of the tests are put in the base of this paper,
describing the recent developments of the XFEL / ILC
technology. | |
| WEP06 | SPIRAL 2 coupler preparation and RF conditioning | 446 |
| | - T. Cabanel, Y. GomezMartinez, D. Marchand, R. Micoud, F. Pancher, D. Tourres, F. Vezzu
LPSC
| |
| | Five radiofrequency coupler prototypes have been
manufactured. Three of them will be mounted in the
cryomodules of the SPIRAL 2 superconducting LINAC
(LINear ACcelerator). This paper describes the coupler
preparation and the first results of their conditioning. | |
| WEP08 | Upgrade of the low-beta section of the PIAVE-ALPI linac at LNL | 450 |
| | - D. Zenere, A. Facco, F. Scarpa
INFN-LNL
| |
| | The superconducting linac PIAVE-ALPI includes a low-beta
section made of 20 bulk niobium quarter wave resonators,
working at 80 MHz, with beta=0.047 and 0.055. Originally
designed for operation at 3 MV/m with 7 W RF power,
their high Q allows significantly higher gradient, limited
at present by the existing RF system capabilities. An
upgrade program has started at LNL that includes the
construction of 4 additional cavities, the adoption of 1
kW RF power amplifiers and modifications of the
cryostats that will allow for cooling of the RF couplers.
The final goal is to increase the voltage gain in the low-beta
section from the present value of ~10 to above 20
MeV/q, allowing efficient acceleration of heavy ions with
mass number around 200. | |
| WEP10 | Vertical test results on the STF baseline 9-cell cavities at KEK | 453 |
| | - E. Kako, H. Hayano, S. Noguchi, T. Shishido, K. Umemori, K. Watanabe, Y. Yamamoto
KEK - H. Sakai, K. Shinoe
ISSP, Univ. of Tokyo - S. I. Moon
POSTECH - Q. J. Xu
IHEP, CAS
| |
| | The STF-Baseline superconducting cavity system,
which includes four TESLA-type 9-cell cavities, input
couplers and frequency tuners, has been developed for the
future ILC project. A main improvement in the cavity
system is a very stiff design in a He vessel and a cavity
tuning system, which can relax a cavity deformation due
to Lorentz force. Making clear the performance level of
four 9-cell cavities, which were fabricated by a Japanese
company and were prepared by existent infrastructures at
KEK, is the most important purpose in the whole vertical
test. Total 14 vertical tests on four 9-cell cavities were
carried out repeatedly. The obtained Eacc,max in the final
performance was 29.4 MV/m in the #2 cavity, and the
others are 20.8, 20.5 and 20.2 MV/m, where the Qo
values higher than 1x1010 was achieved in all cavities.
Peculiar phenomena, like increasing of Qo values with
higher Eacc or very slow degradation of Qo values, were
observed in the vertical tests. Summary of the vertical test
results on four 9-cell cavities is described in this paper. | |
| WEP11 | Parameter measurement of 2-cell superconducting cavity | 458 |
| | - X. M. Shen, W. Bai
Institute of Applied electronics, CAEP - H. Sun, M. Q. Ge
Superconducting test Lab. IHEP
| |
| | The main parameters of a 1.3GHz, 2cell TESLA type
superconducting niobium cavity, designed and developed
by Peking University, are simulated using MAFIA in
institue of applied electronics, CAEP. The curves of Eacc
to Q0 and Rs to 1/T relations are measured at 2K
temperature, after this cavity treated by CP, rinsed by high
pressure de-ionized water and vacuum pumped. Results
show that Eacc and Q0 of this cavity. | |
| WEP12 | Design of the compact high average current DC-SC photoinjector at Peking University | 461 |
| | - F. Zhu, S. W. Quan, W. C. Xu, J. K. Hao, Z. C. Liu, K. Zhao, B. C. Zhang
IHIP, Peking University
| |
| | A new compact high average current DC-SC photoinjector
has been designed at Peking University. The main
Part of the injector consists of a DC pierce gun and a
3+1/2cell superconducting cavity. The optimization of the
DC gun and superconducting cavity are presented in this
paper. The simulation results show that the new injector
can provide high average current electron beams with
bunch charge of 100pc, cw (or high repetition rate mode)
operation, transversal emittance lower than 2 mm-mrad
and bunch length of 4 ps. | |
| WEP13 | Cavity diagnostic system for the vertical test of the baseline SC cavity in KEK-STF | 464 |
| | - Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, T. Shishido, K. Umemori, K. Watanabe
KEK - H. Sakai, K. Shinoe
ISSP, Univ. of Tokyo - S. I. Moon
POSTECH - Q. J. Xu
IHEP, CAS
| |
| | Four STF-Baseline superconducting cavities were
fabricated from 2005 to 2006. They were named BL1, 2,
3 and 4. The feature is that these cavities have the stiffer
structure than TESLA cavity. From Feb/2006 to Feb/2007,
the vertical tests were done totally 14 times at KEK.
These cavities were re-processed and measured
repeatedly. The surface treatment processes are composed
of Centrifugal Barrel Polish (CBP), Electro-Polish (EP)
and High Pressure Rinsing (HPR). And, HF or H2O2
rinsing were added as the additional process later.
In the vertical tests, a monitoring system was
introduced to search the heating spot on the equator and
to check the radiation level around the cavity. It is
composed of the carbon resistors and the PIN photo
diodes. They were attached on the equator of each cell
every 90 degree, a few resistors around the HOM couplers and a
few diodes on the top and bottom flanges of the cavity.
MX-100 (YOKOGAWA) for the carbon resistors and
NR-1000 (KEYENCE) for the PIN photo diodes are used
as the data logger. The sampling time is 100 or 200msec.
The heating spot was successfully observed during the
test. The appearance of that on the equator was coincident
with the quench of the cavity. On the other hand, the
diodes were useful for checking the presence or absence
of the field emission and they also were useful for
monitoring the radiation level during the RF processing.
The mapping display was introduced to identify the
location. Consequently, it is conceivable that the quality
of the electron beam welding was somewhat poor, when
the dumbbells were connected. | |
| WEP14 | Commissioning and early operating experience with the Fermilab horizontal test facility | 469 |
| | - R. Carcagno, B. Chase, E. Harms, A. Hocker, P. Prieto, J. Reid, A. Rowe, J. Theilacker, M. Votava
Fermilab
| |
| | Fermilab has constructed a facility for testing dressed
superconducting radiofrequency (RF) cavities at 1.8 K
with high-power pulsed RF. This test stand was designed
to test both 9-cell 1.3 GHz TESLA-style cavities and 9-
cell 3.9 GHz cavities being built by Fermilab for DESY's
TTF-FLASH facility. An overview of the test stand and a
description of its initial commissioning is described here. | |
| WEP15 | Initial results from Fermilab's vertical test stand for SRF cavities | 472 |
| | - J. P. Ozelis, R. Carcagno, C. M. Ginsburg, Y. Huang, R. Nehring, B. Norris, V. Poloubotko, R. Rabehl, I. Rakhno, C. Reid, T. Peterson, D. A. Sergatskov, C. Sylvester, M. Wong, C. Worel, A. Yuan
Fermilab - C. Grenoble, T. J. Powers
TJNAF
| |
| | Fermilab has constructed a facility for vertical testing
of SRF cavities, operating at a nominal temperature of
2K, to be used as part of the global International Linear
Collider (ILC) effort to improve cavity processing and
performance reproducibility. Following successful
cryogenic commissioning, the first tests of single cell and
9-cell ILC-style cavities were performed. These first test
results are presented in detail, along with a brief
discussion of present measurement accuracy. | |
| WEP16 | Commissioning of BEPCII superconducting RF system | 477 |
| | - Y. Sun, G. W. Wang, W. M. Pan, Z. Q. Li, Q. Ma, H. Y. Lin, S. P. Li, K. He, Y. P. Liu, H. Huang, B. Xu, Q. Y. Wang, T. M. Huang
IHEP, CAS
| |
| | BEPC single-ring machine had been upgraded to
BEPCII double-ring machine in the past four years, four
199.6MHz RT cavities were replaced by two 499.8MHz
superconducting cavities.
Two SRF stations of BEPCII had passed the first beam
commissioning, physical problems such as changing
frequency from 200MHz to 500MHz and compressing
the bunch length in colliding mode, have been solved
step by step. The engineering problems such as feeding
100KW beam power had also been solved. The SRF
system of BEPCII project had finished on schedule. This
paper gives a brief introduction to the commissioning of
the SRF system of BEPCII. | |
| WEP17 | Considerations on the third harmonic RF of the European XFEL | 481 |
| | - E. Vogel, M. Dohlus, M. Huening, K. Jensch, A. Matheisen, W. -D. Moeller, A. Schmidt, W. Singer
DESY Hamburg - H. Edwards, E. Harms, T. Khabiboulline
Fermilab
| |
| | Ultra short bunches with high peak current are required for the creation of high brilliance coherent light in the x-ray range in undulators. At the European x-ray free electron laser (XFEL) they will be obtained by a two stage bunch compression scheme based on off the rf field crest acceleration and transverse magnetic chicanes. The deviation of the rf field's sine shape from a straight line leads to long bunch tails and reduce peak current. This effect will be eliminated by adding a third harmonic rf system. The paper surveys the basic principle for the third harmonic rf, the most relevant design parameters, the actual status of beam physical examinations and potential concepts for the technical realization. | |
| WEP19 | Cryogenic system for BEPCII superconducting cavities | 486 |
| | - Y. P. Liu, S. P. Li, K. He, M. J. Sang, R. Ge, C. W. Lv, L. Bian, Z. Zhang
IHEP, CAS
| |
| | In order to improve the luminosity of the Beijing
electron positron collider, two KEKB type 500MHz
superconducting cavities are adopted in the upgrade
project which is named as BEPCII. These two cavities are
installed in e+ and e- ring, respectively. They are cooled
in liquid helium bath contained in a vacuum insulated
vessel. Cryogenic system is designed and constructed to
provide the superconducting operating circumstance for
the cavities. This paper is dedicated to briefly introduce
the BEPCII rf side cryogenic system. | |
| WEP20 | 325 MHz power couplers of spokes cavities for modular, multiple power levels | 489 |
| | - Q. S. Shu, J. Susta, G. F. Chen, I. Phipps, F. H. Lu
AMAC Inc - T. Khabiboulline, N. Solyak
Fermilab
| |
| | In order to increase the protons energy up to 8 GeV
in a driver Linac, the particles must be accelerated
through various stages and three different power levels
(25kW, 100kW and 210kW) are required for the 325
MHz Fermilab Proton Driver couplers. The problem
identified by the project is that no High RF power coupler
for these cavities has ever been designed and produced
using US industrial capabilities. AMAC proposed a novel
resolution by development of innovative modular,
multiple power levels, 325 MHz spoke cavities power
couplers, which to meet three type cavities with one
coupler design. The simulation and concept design are
presented. The results of HFSS, MAFIA, ANSYS, and
Multipacting are also discussed. | |
| WEP21 | Electrical axes of TESLA cavities | 493 |
| | | |
| | Precise alignment of cavities to the beam is one of
strong requirements in order to obtain high quality beam.
A missalignment could cause unwanted interaction
between the beam and electromagnetic fields in the
cavity, both accelerating field and wakefields. Up to now
the eccentricity of cells is measured mechanically on the
outer side of cell equators. In this way measured
eccentricity could be not precise in case of not uniform
cavity wall thickness or in case of cavity wall deformation
on other place than measured equator. Therefore an
alternative method based on small perturbation field
mapping was developed and applied on some cavities. | |
| WEP22 | Electron activity interlock for XFEL input couplers | 498 |
| | | |
| | One of dangers for TESLA-based linacs is uncontrolled
discharge in vacuum parts of the input power couplers -
discharge in residual gasses, field emission and
multipacting. These may be destructive if the RF power is
not reduced or switched off at the right time. The recent
TTF3 input couplers have three electron pickups to detect
the electron activity. But these vacuum feed-throughs and
the electronic front-end are complicated and expensive.
The goal of this work is to replace them by simpler and
cheaper solution - by use of the inner conductor of the
coupler as electron pickup. | |
| WEP23 | Fabrication and test of the 500 MHz SC modules for the BEPCII | 503 |
| | - Z. Q. Li, G. W. Wang, W. M. Pan, Y. Sun, S. P. Li, Q. Ma
IHEP, CAS - T. Furuya, S. Mitsunobu, K. Akai, Y. Yamamoto
KEK - Y. Kijima, M. Arakawa, Y. Okada
MELCO, Mitsubishi Electric Co.
| |
| | Two KEKB type HOM damped SC cavities were
constructed during past three years. These SC modules
were re-designed to meet the RF frequency of 500 MHz
of the BEPCII, the upgrade project of the Beijing Electron
and Positron Collider, and have already been operated
smoothly. It is a product of the successful collaboration
among Mitsubishi Electric Co. (MELCO), KEK and
IHEP of China. The cavity modules were fabricated and
surface-treated by MELCO with the help and support of
KEK. The vertical test of niobium cell, and the high
power test of couplers and dampers were carried out in
KEK, and the final acceptance tests were done in IHEP. | |
| WEP24 | Field emission from single crystal and large grain niobium cathodes | 506 |
| | - A. Dangwal, G. Mueller
Berg. Universitat Wuppertal - D. Reschke, X. Singer
DESY
| |
| | Appreciable suppression of field emission from
metallic surfaces has been achieved by the use of
improved surface cleaning techniques, and dry ice
cleaning has emerged recently as a very effective tool in
this respect. In order to understand the effects of surface
preparation on field emission, systematic measurements
were performed on five single crystal and three large
grain samples of high purity (RRR > 300) Nb by means of
AFM, XRD, SEM and dc field emission scanning
microscope. The samples were treated with buffered
chemical polishing (BCP), half of those for 30 um and
others for 100 um removal of surface damage layer,
followed by a final high pressure water rinsing. The
samples with longer BCP treatment showed the onset of
field emission at slightly higher fields. A low temperature
(~ 150 degree C) heat treatment in high vacuum (10-6 mbar)
chamber for 14 hours, on a selected large grain Nb
sample, gives the evidence for the grain boundary assisted
FE at very high fields of 250 and 300 MV/m. Finally, an
interesting correlation between sizes of all investigated
emitters derived from SEM images with respect to their
respective onset fields has been found, which might
facilitate the quality control of superconducting radiofrequency
cavities for linear accelerators. | |
| WEP25 | Final tests and commissioning of the 400MHz LHC superconducting cavities | 512 |
| | - P. Maesen, E. Ciapala, G. Pechaud
CERN
| |
| | The four LHC RF modules, each containing four 400
MHz single cell cavities, were successfully completed
and installed in the LHC tunnel in 2006. A number of
minor modifications were made to the original
construction to improve reliability in operation and to
obtain tighter control on the otherwise large spread in the
tuning ranges of individual cavities. After fitting of the
variable power couplers, careful power processing was
applied to bring all cavities to 8 MV/m, i.e. 1.5 times the
nominal, and to the maximum 300 kW forward power.
Reaching the goal of full performance without major
incident has been the result of careful clean room
assembly, careful vacuum operation and ensuring proper
operation of all protection systems during RF operation.
Preparation for operation in the LHC is now ongoing,
where the modules will operate from same cryogenics
distribution line as the LHC's superconducting magnets. | |
| WEP26 | High power tests of input couplers for Cornell ERL injector | 517 |
| | - V. Veshcherevich, S. Belomestnykh, P. Quigley, J. Reilly, J. Sears
Cornell University
| |
| | RF power couplers for the ERL injector, currently
under construction at Cornell University, have been
fabricated. The couplers were assembled in pairs in the
liquid nitrogen cryostat, built for their tests. First two
prototype couplers were tested using an IOT transmitter
and a resonant ring for additional power amplification.
They were tested up to the goal power level of 50 kW CW
and used later for tests of the first injector cavity.
However, the first pair of couplers showed excessive
temperature rise in some points. Therefore, minor
changes in the design have been done to improve cooling.
The couplers of updated design were successfully tested
from a klystron up to the power level of 60 kW CW. In
situ baking was implemented for coupler installed in the
cryostat. | |
| WEP27 | Horizontal tests for crab cavities in KEKB | 520 |
| | - Y. Yamamoto, K. Akai, K. Ebihara, T. Furuya, K. Hara, T. Honma, K. Hosoyama, A. Kabe, Y. Kojima, S. Mitsunobu, Y. Morita, H. Nakai, K. Nakanishi, M. Ono
KEK - H. Hara, K. Sennyu, T. Yanagisawa
MHI Kobe - T. Kanekiyo
HITACHI - T. Nakazato
JASRI
| |
| | Two Crab cavities were fabricated at KEK in 2006.
After the completion of the assembly, a horizontal test is
normally carried out for a superconducting cavity in KEK.
The horizontal test is an overall test for the cavity without
a beam. Both cavities achieved above an operational kick
voltage of 1.4MV. Although the HER (High Energy Ring
for electron) Crab cavity had no trouble, the LER (Low
Energy Ring for positron) had a trouble of tuner operation.
Due to the limited time, both cavities were installed into
the tunnel at the beginning of Jan. in 2007. After the beam
commissioning, it was found that this problem was not so
much significant for the operation. The LER Crab cavity
is being operated above 1A at present. | |
| WEP28 | Latest Results of ILC High-Gradient R&D 9-cell Cavities at JLAB | 525 |
| | - R. L. Geng, R. Afanador, A. C. Crawford, G. K. Davis, D. Forehand, C. Dreyfus, C. Grenoble, B. Golden, R. Johnson, P. Kushnick, K. Macha, J. Mammosser, J. Saunders, A. Wu
JLab - D. Bice, D. A. Sergatskov
Fermilab
| |
| | It has been over a year since JLAB started processing
and testing ILC 9-cell cavities in the frame work of
ILC high-gradient cavity R&D, aiming at the goal of a
35 MV/m gradient at a Q0 of 1E10 with a yield of 90%.
The necessary cavity processing steps include field flatness
tuning, electropolishing (EP), hydrogen out-gassing under
vacuum, high-pressure water rinsing, clean room assembly,
and low temperature bake. These are followed by RF
test at 2 Kelvin. Ultrasonic cleaning with Micro-90, an effective
post-EP rinsing recipe discovered at JLAB, is routinely
used. Seven industry manufactured 9-cell TESLAshape
cavities are processed and tested repeatedly. So far,
33 EP cycles are accumulated, corresponding to more than
65 hours of active EP time. An emphasis put on RF testing
is to discern cavity quench characteristics, including its nature
and its location. Often times, the cavity performance is
limited by thermal-magnetic quench instead of field emission.
The quench field in some cavities is lower than 20
MV/m and remains unchanged despite repeated EP, implying
material and/or fabrication defects. The quench field
in some other cavities is high but changes unpredictably
after repeated EP, suggesting processing induced defects.
Based on our experience and results, several areas are identified
where improvement is needed to improve cavity performance
as well as yield. | |
| WEP30 | New HOM coupler design for ERL injector at KEK | 530 |
| | - K. Watanabe, H. Hayano, S. Noguchi, E. Kako, T. Shishido
KEK
| |
| | The development of superconducting cavities and
cavity package for ILC and ERL project is under way at
STF (Superconducting RF Test Facility) in KEK. The
TESLA-style coaxial HOM couplers have a problem at
CW operation, which it is pick-up probe and inner
conductor heating of HOM coupler.
The pick-up probe heating was observed at vertical tests.
The probe heating study for CW operation (changing
pick-up probe geometry and probe gap) tried at vertical
tests by using the KEK STF Baseline 1.3 GHz 9-cell
superconducting cavity, and simulated by using HFSS
code ver9.1 for estimate the relation of the limit E-field of
probe heating and the probe surface current.
The design of proto-type coaxial HOM couplers of CW
operation for ERL-injector at KEK was tried based on this
information. The probe heating is generated due to the
probe surface current by the RF load of accelerating mode.
Therefore, as one method, it can be controlled if the RF
load of accelerating mode is reduced by putting the high
pass filter between the coupling loop and the notch filter.
In addition, the target beam current of ERL is about
100mA, therefore, we were considered that the cooling of
inner conductor of HOM coupler by liquid He. It is
necessary to be expected the heating of inner conductor
by RF load of accelerating mode and HOM power of
excited in the beam. The design was held based on these.
In this report, a design of HOM coupler for ERLinjector
at KEK is presented. | |
| WEP31 | Optimization of the SRF Cavity Design for the CEBAF 12 GeV Upgrade | 536 |
| | - C. E. Reece, E. F. Daly, J. Henry, W. R. Hicks, J. Preble, H. Wang, G. Wu
JLab
| |
| | Based on initial testing of the "HG" and "LL" 7-cell
cavities in the prototype cryomodule Renascence, several
opportunities for improved optimization were identified.
The HOM damping configuration was refined so as to
meet the requirements for damping key dipole modes
while simultaneously dramatically reducing risk of HOM
pickup probe heating and also creating beamline clearance
for mounting the tuner to stainless steel helium vessel
endplates (rather than NbTi/Ti transitions to a titanium
helium vessel). Code modeling and bench measurements
were performed. The new design maintains the 7-cell LL
cells and incorporates a brazed transition between Nb and
the SS helium vessel. The resulting configuration is now
called the "C100" design. Cavity design details as well as
vertical dewar and horizontal test bed performance are presented. | |
| WEP32 | Performance of the CEBAF prototype cryomodule renascence | 540 |
| | - C. E. Reece, E. F. Daly, G. K. Davis, M. Drury, W. R. Hicks, J. Preble, H. Wang
JLab
| |
| | The prototype cryomodule Renascence was constructed as
an energy building block for securing 6 GeV operation of
CEBAF and to validate design elements for future
CEBAF upgrade modules. These elements include the
new "HG" and "LL" 7-cell cavity designs and a new tuner
design.[1,2] Issues were identified during initial testing in
2005. The module has been reworked to address the issues
with thermal stability, component breakage, and tuner
motion. In addition, opportunity was taken to employ
upgraded cleaning and assembly techniques for the cavity
string. The HOM coupler heating issue was resolved, and
seven of the eight cavities in the cryomodule have run
stably at an average of 20 MV/m CW. The cryogenic, rf,
and mechanical performance of the cryomodule are presented. Commissioning in CEBAF has just been completed in October 2007. | |
| WEP33 | Realisation of a prototype superconducting CW cavity and cryomodule for energy recovery | 545 |
| | - P. A. McIntosh, R. Bate, C. D. Beard, M. Cordwell, D. M. Dykes, S. Pattalwar, J. Strachan, E. Wooldridge
STFC Daresbury Laboratory - S. Belomestnykh, M. Liepe, H. Padamsee
Cornell University - A. Buechner, F. Gabriel, P. Michel
FZR Rossendorf - T. Kimura, T. I. Smith
Stanford University - J. Byrd, J. N. Corlett, D. Li, S. Lidia
LBNL
| |
| | For Energy Recovery applications, the requirement for
high-Q accelerating structures, operating in CW mode, at
large beam currents, with precise phase & amplitude
stability and modest accelerating gradients are all
fundamental in achieving intense photon fluxes from the
synchronised FEL insertion devices. Both Daresbury
Laboratory and Cornell University are developing designs
for advanced Energy Recovery Linac (ERL) facilities
which require accelerating Linacs which meet such
demanding criteria. The specification for the main ERL
accelerator for both facilities dictates a modest
accelerating gradient of 20 MV/m, at a Qo of better than
10^10, with a Qext of up to 10^8. A collaborative R&D
program has been set-up to design and fabricate a 'proof-of-
principle' cryomodule (which is well underway) that
can be tested on ERLP at Daresbury and also on the
Cornell ERL injector. This paper details the new
cryomodule design, provides an insight to the design
solutions employed and reports on the present status of
the project. | |
| WEP34 | Research and development of 1.3 GHz low loss cavities made of China large grain at IHEP | 549 |
| | - Z. G. Zong, J. Gao, H. Sun, F. C. Zhao, M. Q. Ge, J. Gu, Q. J. Xu, J. Z. Zhai
IHEP, CAS - L. Zhang, L. Q. Liu
TIPC, CAS
| |
| | Institute of High Energy Physics, IHEP, has studied
superconducting RF cavities since Oct. 2000. To
contribute to International Linear Collider (ILC) for
which superconducting RF cavity was chosen, research
and development of 1.3 GHz low loss cavities using
China large grain niobium was carried out recently at
IHEP. The study is based on the latest research direction
in the material and the shape of the cavity and involves
the design of low loss shape for higher gradient and
fabrication using large grain niobium material. The shape
and some parameters of the cavity will be presented in
this paper and be compared with alternative structure (low
loss cavity) design data. In the manufacture the cavity
was formed by standard procedures, such as deep drawing,
trimming and welding by electron beam. To prepare the
RF surface for vertically cryogenic test, centrifugal barrel
polishing, barrel chemical polishing, annealing, high
pressure rinsing and baking were employed. This paper
introduces the features of the fabrication and surface
treatments on the large grain cavity and presents the
preliminary results of the research. | |
| WEP35 | RF superconductivity activities of PEFP | 553 |
| | - A. Sun, C. Y. Gao, L. P. Zhang, Y. Z. Tang, Y. M. Li, H. S. Kim, Y. -S. Cho, B. -H. Choi
PEFP, Korea Atomic Energy Research Institute
| |
| | Radio Frequency (RF) superconductivity activities of
the Proton Engineering Frontier Project (PEFP) aim to
develop a superconducting RF linac to accelerate a proton
beam above 80 MeV at 700 MHz. In the past two years,
the preliminary design of a low-beta cryomodule has been
completed. A low-beta (beta=0.42) cavity, a higher-mode
coupler and a fundamental power coupler for the PEFP
cavities have also been designed. The dies, fixtures and
coining rings, as well as the dumbbell tuning sets of the
low-beta cavity have been designed and fabricated. Also a
warm tuner for PEFP cavities has been designed and
fabricated for tuning the PEFP cavity field flatness. Two
prototype copper cavities are under production and
testing. An overview of the RF superconductivity
activities of PEFP in the coming two years is presented. | |
| WEP36 | High current, large aperture, low HOM, single crystal Nb 2.85GHz superconducting cavity | 558 |
| | - Q. S. Shu, J. Susta, F. H. Lu, I. Phipps, J. L. Shi
AMAC Inc - R. P. Redwine, F. H. Wang, D. Wang
MIT
| |
| | There is an increasing demand for High beam Current,
high Radio-Frequency (RF) power S-band cavities in
existing and new accelerator projects, such as for a study
of future electron-ion collider (eRHIC) and a very
brilliant, broadband, teraherz coherent synchrotron
radiation source (CRS). To achieve this goal, the RF
cavities must be upgraded to a gap voltage of 1.5 MV in a
limited space available in the machine with a high
gradient superconducting cavity. At the present time
there are no cavities and accessories designed to support
the high beam currents of up to 10-100 mA and at the
same time provide a high gap voltage at such a high Sband
frequency. AMAC proposed a High Current, Large
Aperture, Low HOM, Single Crystal Nb 2.85GHz
Superconducting Cavity with high RF Power Coupler and
HOM absorber device. | |
| WEP37 | Nondistructive testing instrument of dished Nb sheets for SRF cavities based on squid technology | 562 |
| | - Q. S. Shu, J. Susta, G. F. Cheng, I. Phipps
AMAC Inc - R. Selim, J. Mast
Christopher Newport University - P. Kneisel, G. Myneni
JLab - I. Ben-Zvi
Brookhaven National Lab
| |
| | The performance of superconducting RF cavities used in
accelerators can be enhanced by detecting micro particles
and inclusions which are the most serious source of
performance degradation. These defects prevent the
cavities from reaching the highest possible accelerating
fields. We have developed a SQUID scanning system
based on eddy current technique that allows the scanning
of curved Nb samples. This SQUID scanning system
successfully located Tantalum defects about 100 um
diameter in a flat Nb sample and was able to also locate
the defects in a cylindrical surface sample. Most
importantly, however, the system successfully located the
defects on the backside of the flat sample and curved
sample, both 3-mm thick. This system can be used for the
inspection and detection of such defects during SRF
cavity manufacturing. | |
| WEP39 | Status of ILC cavity processing and testing at Cornell | 567 |
| | - W. J. Ashmanskas
Fermilab - H. Padamsee
Cornell University
| |
| | As part of the coordinated U.S. effort to build up SRF infrastructure
for the ILC, the Cornell SRF lab has developed
tools and procedures for 9-cell 1.3 GHz cavity processing
and vertical testing. Steps performed with 9-cell cavities
at Cornell include tuning for field flatness, vertical electropolishing
(or BCP if desired), high-pressure rinsing in
ultra-pure water, baking at 110C, and RF testing at 2K in a
vertical cryostat. Since spring 2006, Cornell has performed
ILC cavity processing/testing cycles at a rate of about one
per month. We summarize methods, results, and possible
next steps. | |
| WEP40 | Results of beta=0.12 quarter wave resonator for radioactive beams production at SPIRAL2 Facility | 570 |
| | - G. Martinet, D. Longuevergne, S. Blivet, S. Bousson, F. Chatelet, N. Hammoudi, C. Joly, T. Junquera, J. Lesrel, G. Olry, H. Saugnac, P. Szott
IPN Orsay
| |
| | Spiral2 is a French facility which aims at the
construction of superconducting linac to deliver proton,
deuteron (5 mA, 40 MeV) and Q/A=1/3 (1 mA, 14.5
MeV/u) beams. In this framework, IPN is in charge of the
high beta part (beta=0.12). Dedicated Quarter Wave
Resonators working at 88MHz require accelerating field
of 6.5 MV/m. First prototype has been built and we
present here the status of the work performed on it
including Q-disease effect, microphonics and cold tuning
system. | |
| WEP41 | Status of 3.9 GHz superconducting RF cavity technology at Fermilab | 575 |
| | - E. Harms, T. Arkan, L. Bellantoni, H. Carter, H. Edwards, M. Foley, I. Gonin, T. Khabiboulline, D. Mitchell, D. Olis, A. Rowe, N. Solyak
Fermilab
| |
| | Fermilab is involved in an effort to assemble 3.9 GHz
superconducting RF cavities into a four cavity
cryomodule for use at the DESY TTF/FLASH facility as a
third harmonic structure. The design gradient of the
cavities is 14 MV/m. This effort involves design,
fabrication, intermediate testing, assembly, and eventual
delivery of the cryomodule. We report on all facets of this
enterprise from design through future plans. Included will
be test results of single 9-cell cavities, lessons learned,
and current status. | |
| WEP42 | Status of the ILC crab cavity development | 579 |
| | - G. Burt, A. Dexter
Cockcroft Institute, Lancaster University - C. Beard, P. Goudket, P. McIntosh
STFC Daresbury Laboratory - L. Bellantoni
Fermilab - T. Grimm
Niowave, Inc - Z. Li, L. Xiao
SLAC
| |
| | The International Linear Collider (ILC) will require two
dipole cavities to "crab" the electron and positron bunches
prior to their collision. It is proposed to use two 9 cell
SCRF dipole cavities operating at a frequency of 3.9 GHz,
with a transverse gradient of 3.8MV/m in order to provide
the required transverse kick. Extensive numerical
modelling of this cavity and its couplers has been
performed. Aluminium prototypes have been
manufactured and tested to measure the RF properties of
the cavity and couplers. In addition single cell niobium
prototypes have been manufactured and tested in a
vertical cryostat. | |
| WEP44 | The construction of the RF system of BEPC II | 584 |
| | - G. W. Wang, W. M. Pan, Y. Sun, Z. Q. Li, G. Y. Zhao, H. Y. Lin, Y. F. Xu, H. Huang, Q. Ma, B. Xu, Q. Y. Wang, Y. P. Liu, P. Sha, T. M. Huang, R. Liu, R. H. Zeng
IHEP, CAS - T. Furuya, S. Mitsunobu, K. Akai
KEK
| |
| | In this article, we'll introduce the RF system of
BEPCII to readers. It consists of 4 subsystems:
superconducting cavity, high power klystron, cryogenic
system and LLRF. The construction of the RF system had
been finished in late 2006. During the last year of running
till now, it has performed very well. | |
| WEP45 | The first processing of capacitive-coupling coupler at room temperature in a cryomodule at STF | 587 |
| | - T. Saeki, H. Matsumoto, S. Kazakov, F. Furuta, K. Saito, Y. Higashi, T. Higo, H. Inoue, Y. Morozumi, M. Sato, H. Yamaoka
KEK - J. Hong
PAL - J. Zhai
IHEP, CAS
| |
| | We are constructing Superconducting RF Test Facility
(STF) at KEK for the R&D of ILC accelerator. In the
beginning of year 2007, we installed one TESLA-like 9-
cell cavity and one high-gradient Low-Loss (LL) type 9-
cell cavity into cryomodules at STF. For the LL 9-cell
cavity, an Capacitive-Coupling (CC) input-coupler, a ballscrew
tuner and other peripherals were assembled with
the cavity. The assembled cavity package was installed
with thermal shields and so on into a cryomodule. After
the installation, we performed the first processing of
Capacitive-Coupling (CC) input-coupler in a cryomodule
at the room-temperature. We achieved the power of 250
kW with the pulse-width of 1.5 msec at the repetition rate
of 5 pps. This presentation describes about the assembly
of a CC coupler and a high-gradient LL 9-cell cavity in a
clean room and the processing of the CC coupler at the
room temperature in a cryomodule. | |
| WEP47 | BCP system for the ANL-FNAL SCPF | 592 |
| | - A. Rowe, D. Assell, L. Elementi, T. Hamerla, S. Reeves, T. Thode
Fermilab
| |
| | FNAL has undertaken an effort to design, develop,
commission and operate a system that efficiently polishes
the interior and exterior surfaces of superconducting
radiofrequency (SRF) cavities using buffered chemical
polish. This system was designed for the Joint
Superconducting Cavity Processing Facility (SCPF) at
ANL for use during the GDE S0/S1 ILC cavity testing
programs. The demands of the S0/S1 programs required
the development of a pre-industrial type polishing system
that ensures operator safety as well as procedure
reliability and repeatability. The BCP System design
methodology and technical details are presented,
including a discussion on the control system design and
philosophy. The BCP System's safety features, ancillary
hardware, and operational scope are also described. | |
| WEP48 | Design and fabrication of superconducting cavities for industrialization | 597 |
| | - K. Sennyu, H. Hara
MHI Kobe - M. Matsuoka
MHI Hyogo
| |
| | MHI has supplied various types of superconducting
cavities mainly to KEK in Japan since TRISTAN project
started at 1977. We have a lot of experience in the
development of superconducting cavities for Japanese
projects. And we have the technology to design and
fabricate the superconducting cavities. We can present
some ideas to improve the quality, cost, and delivery time
of the superconducting cavities based on our experience.
We designed and fabricated four STF-Baseline
superconducting cavities with frequency tuners, helium
jackets, according to KEK specifications. To decrease a
cavity deformation occurring due to Lorenz force, rigid
jacket systems including tuner were designed. By
fabricating four cavities, some problems and
improvements in the next step are cleared. Some ideas to
reduce the fabrication cost are proposed in this paper. | |
| WEP49 | Flexible application of the JLab pansophy information system for project reports, process monitoring, and R&D sample tracking | 601 |
| | - V. Bookwalter, B. Madre, C. E. Reece
JLab
| |
| | The use and features of the JLab SRF Institute IT
system Pansophy1,2 continue to expand. In support of the
cryomodule rework project for CEBAF, a full set of webbased
travelers has been implemented and an integrated
set of live summary reports has been created. A graphical
user interface within the reports enables navigation to
either higher-level summaries or drill-down to the original
source data. In addition to collection of episodic data,
Pansophy is now used to capture, coordinate, and display
continuously logged process parameter that relate to
technical water systems and clean room environmental
conditions. In a new expansion, Pansophy is being used to
collect and track process and analytical data sets
associated with SRF material samples that are part of the surface creation, processing, and characterization R&D. | |
| WEP50 | Input Couplers for KEKB Crab Cavities | 606 |
| | - K. Nakanishi, K. Hara, K. Hosoyama, Y. Kojima, S. Mitsunobu, Y. Yamamoto
KEK - K. Okihira, K. Sennyu
MHI Kobe - T. Tanaka
Broad Wireless Corporation
| |
| | The RF input couplers for KEKB crab cavities were designed,
fabricated and installed. The input coupler is shown
in figure 1. The RF input coupler has a ceramic RF window
and a T-stub structure. The shape of T-stub structure
and length of the probe were decided using RF simulation
program. The RF window and the doorknob translator may
cause some reflection. The RF windows for superconducting
accelerator cavities for KEKB (KEKB-SCC) and the
doorknob translators for TRISTAN were used. According
to the procedure of assembling the RF input coupler
for KEKB-SCC, they were rinsed and assembled. Aging
was done individually. After that, they were installed into
cryostats for crab cavities. These cryostats were installed
to KEKB and have been working. Three input couplers,
which are included for prototype cryostat, were prepared. | |
| WEP51 | Some fabrication issues on the spare high power input coupler for BEPCII superconductor cavities | 609 |
| | - T. M. Huang, Q. Ma, W. M. Pan, G. W. Wang
IHEP, CAS
| |
| | The BEPCII storage ring adopted two 500MHz
superconducting cavities (SCC). The input coupler for the
SCC is required to feed high RF power up to 150kW
under continuous wave mode (CW). Considering the high
power feeding and the compact structure of the coupler,
the input coupler fabrication is challenged. Up to now,
two units including windows and inner conductor
(antennas) have been made by IHEP for the spare parts of
BEPCII SCC input couplers. Some fabrication issues will
be presented in this paper. | |
| WEP52 | SRF activities at ACCEL instruments | 612 |
| | - M. Pekeler, S. Bauer, M. Peiniger, P. vomStein, H. Vogel
ACCEL
| |
| | We report on the current activities and achievements in
the field of SRF technology at ACCEL Instruments.
During the last two years a wide range of projects
covering cavity and component production, cavity surface
preparation, SRF module development and construction
has been carried out. Details of the results will be
presented in the related papers. | |
| WEP53 | Operation of the SOLEIL RF system | 615 |
| | - P. Marchand, H. Dias, M. Diop, M. ElAjjouri, J. Labelle, R. Lopes, M. Louvet, C. Monnot, F. Ribeiro, T. Ruan, R. Sreedharan, K. Tavakoli
SOLEIL, Gif-sur-Yvette - P. Bosland, P. Bredy, C. Madec
CEA/DSM/DAPNIA, Gif-sur-Yvette
| |
| | The 352 MHz RF accelerating systems for the SOLEIL
Booster (BO) and Storage Ring (SR) are in operation
since mid 2006. In the BO, a 5-cell copper cavity of the
CERN-LEP type is powered with a 35 kW solid state
amplifier. In the SR, the required RF accelerating voltage
(up to 4.4 MV) and power (560 kW at full beam current
of 500 mA) will be provided by two cryomodules, each
containing a pair of superconducting cavities, specifically
designed for SOLEIL. The first cryomodule is operational,
while the second one, which is being constructed by
ACCEL (Germany), will be implemented in May 2008.
Both cryomodules are cooled down to 4.2 K with liquid
helium from a single 350 W liquefier and each cavity is
powered by a 180 kW solid state amplifier. Using a single
cryomodule and two amplifiers, the first objective of
storing 300 mA stable beam was successfully achieved in
2006. The RF system commissioning and operation
results are reported. | |
| WEP54 | A tuner for a superconducting CH-prototype cavity | 618 |
| | - A. Bechtold, M. Busch, H. Liebermann, H. Podlech, U. Ratzinger
IAP, J. W. Goethe-Universitaet
| |
| | The superconducting CH multi-cell prototype cavity
will be equipped with a frequency tuning system. The rftuning
during operation bases on the principle of a slight
elastic deformation at both ends of the tank. This is
causing a change in the gap width of the first and last
accelerating cell and the accompanying variation of
capacity finally results in a frequency shift. The effects on
rf-frequency and field distribution have been measured
and were compared with previous calculations. The tuning
system implies two stages, a slow mechanical device and
a fast piezo system, all parts were manufactured already.
Additionally, the mechanical resonances of the cavity
have been investigated experimentally in the environment
of an acoustical laboratory at room temperature and
recently within the vertical cryostat at 4 K. Moreover, an
active periodic cavity detuning provided by the piezo
tuners was implied, while stable superconducting cavity
operation was kept by a frequency control loop acting on
the rf-frequency oscillator. | |
| WEP55 | Beam-induced RF modes and RF power in the crab cavity for KEKB | 623 |
| | - Y. Morita, K. Akai, T. Furuya, T. Honma, K. Hosoyama, S. Mitsunobu, Y. Yamamoto
KEK
| |
| | Two superconducting crab cavities were installed in the
KEKB rings and the crab crossing operation started early
in 2007. Each crab cavity has two ferrite RF absorbers
(HOM dampers), which were developed for the
superconducting accelerating cavities of KEKB. One is
attached in a beam pipe and the other is attached in a
coaxial coupler. The dampers have to damp not only the
higher order modes but the lower order modes, since the
crabbing mode is not the lowest mode. These parasitic
modes should be sufficiently damped for the high current
operation. Several antennas were set on the beam pipe to
monitor beam-induced RF modes. The most dangerous
mode, TM010-like mode, was detected in the RF
spectrum. However, its Q-factor was below the instability
criterion and consistent with the measured value at the
horizontal test before installation. No dangerous modes
with high Q-factor were observed in the beam-induced
RF spectrum. KEKB stored the beam currents of 1.7A and
1.35 A in the low energy positron ring and the high energy
electron ring, respectively. No serious beam instabilities
caused by the parasitic modes were observed and the
HOM dampers successfully absorbed the beam-induced
RF power up to 12 kW. We will present HOM dampers
used for the KEKB crab cavities, and measurement results
of the beam-induced RF modes and RF power. Simulation
results for the beam-induced RF power will be also
discussed. | |
| WEP56 | Cavity and linac RF and detuning control simulations | 627 |
| | - A. Neumann, J. Knobloch
BESSY
| |
| | Single pass free electron lasers, such as the planned
BESSY-FEL, require a very stable beam with a bunch-tobunch
time jitter of less than 50 fs and a relative energy jitter
below 1e-3. Regarding the low beamloading the 144
cavities of the superconducting linac will be operated in
CW at a high loaded quality factor of 3e^7. To understand
the achievable stability of the beam and the budget of the
individual error sources for the cavity field stability a single
cavity simulation tool has been developed. It includes
the cavity field envelope model, an LLRF feedback system
model and further on mechanical transfer functions, tuner
characteristics, the fast piezo control system, microphonics
and other noise sources measured or developed at HoBi-
CaT. Incorporating realistic beam parameters due the acceleration
process in the photoinjector and the first booster
cavity allows to model the resultant energy and time jitter
of the beam at the end of the linac entering the undulator
section of the FEL. Furthermore the model has been used
to find optimum operation parameters for the cavity and
controller. | |
| WEP57 | Commissioning and Beam Operation of KEKB Crab RF System | 632 |
| | - K. Akai, K. Ebihara, T. Furuya, K. Hara, T. Honma, K. Hosoyama, A. Kabe, Y. Kojima, S. Mitsunobu, Y. Morita, H. Nakai, K. Nakanishi, M. Ono, Y. Yamamoto
KEK
| |
| | Two heavily damped superconducting crab cavities were
installed in KEKB, one for the low-energy positron ring
(LER) and the other for the high-energy electron ring
(HER). After adjusting the RF system and conditioning the
cavities, beam operation started in February 2007. During
the four-and-a-half-month operation until summer shut
down, the crab cavities have been operating very stably
to conduct crab crossing experiment. They have shown
excellent performance with high stored beam currents up
to 1.7 A in the LER and 1.35 A in the HER. It was also
demonstrated that the crab crossing works at a high luminosity
over 10^34/cm2s that exceeds the KEKB design luminosity.
Machine tuning with crab crossing will continue
for achieving a big boost in luminosity, as expected from
beam-beam simulations. In this paper, we present an RF
system for the crab cavities, commissioning process, performance
of the crab cavities with high-current beams, and
beam-loading-related issues on the crabbing mode. | |
| WEP58 | Investigation of passive stabilization- and different tuning systems for TESLA cavities with respect to CW operation | 637 |
| | - O. Kugeler, A. Neumann, J. Knobloch, W. Anders
Bessy
| |
| | BESSY has planned a free-electron-laser that will be
operated with TESLA type cavities at high Q-values in
CW mode. These operating parameters imply a low cavity
bandwidth and thus a high sensitivity towards ponderomotive
oscillations, in particular microphonics. In the Ho-
BiCaT facility, located at BESSY, we have tested various
tuning systems (Saclay I, Saclay II) and compared their
usability for CW operation. Furthermore, the impact of
"Rossendorf"-type stabilization fixtures on the mechanical
properties was investigated. | |
| WEP59 | Conceptual design considerations of a 5-cell dual-axis SRF cavity for ERLs | 641 |
| | | |
| | Recently a dual-axis energy recovery linac has been proposed
for ERL applications, in which accelerating and decelerating
beams can go through separate axes but still recover
energy in novel dual-axis cavities. Here we discuss a
conceptual design of a 5-cell dual-axis cavity evolved from
side-by-side jointed TESLA-type cavities. Instead of an
engineering design, we aim to explore the feasibility of
such a new cavity, giving particular attention to its nonstandard
features that might cause concern to the beam.
This is a preliminary work-in-progress report. | |
| WEP60 | Construction and processing of the variable RF power couplers for the LHC superconducting cavities | 646 |
| | | |
| | The Large Hadron Collider (LHC) will accelerate
beams of protons with a main RF system of sixteen
400 MHz superconducting cavities. The different
requirements at injection and collision together with the
heavy beam loading have imposed the use of a variable
power coupler with a coupling value varying by a factor
20. The power requirements are high; 250 kW cw forward
for several hours and pulses of 1.85 MW local peak
power. In order to withstand these levels, copper sealing
rings are used on the main ceramic. To avoid multipactor
occurring at high powers and beam intensities, a second
ceramic is used to provide a second DC polarization of
the antenna. Twenty-five couplers have already been fully
conditioned using a special dedicated FM+AM
conditioning process, with 16 installed in the cavities in
the LHC tunnel for first powering tests. | |
| WEP61 | Design of the magnetic shield for TRASCO low beta elliptical cavities | 651 |
| | - P. Pierini, S. Barbanotti, L. Monaco, N. Panzeri
INFN Milano-LASA
| |
| | The TRASCO elliptical cavities (beta=0.47) for
intermediate velocity protons will be tested in horizontal
test modules, equipped with a coaxial cold tuner of the
blade type. A magnetic shield which is internal to the
helium vessel has been designed, using CRYOPERM 10
material. The magnetic shield is capable to meet the
performance goals of the 700 MHz cavities and simplifies
the mechanical interface to the cavity/tuner assembly. The
present paper illustrates the technical design of such a
shielding system. | |
| WEP62 | Diagnosis, analysis, and resolution of thermal stability issues with HOM couplers on prototype CEBAF SRF cavities | 656 |
| | - C. E. Reece, E. F. Daly, G. K. Davis, W. R. Hicks, T. Rothgeb, H. L. Phillips, J. Preble, H. Wang, G. Wu
TJNAF
| |
| | During initial testing of the prototype cavities
incorporated into the developmental cryomodule
Renascence severe thermal stability issues were
encountered during CW operation. Additional diagnostic
instrumentation was added. This enabled identification of
an unanticipated thermal impedance between the HOM
coupler probe feedthrough assembly and the cavity
beamtube. Subsequent detailed FE analysis successfully
modeled the situation and indicated the need for alternate
cooling path for the couplers on those cavities. HOM
damping was measured to be adequate employing only
two of the four HOM couplers. The two pickup probes on
the couplers at the input power coupler side of each cavity
were removed, the remaining HOM probe feedthroughs
were heat stationed to two-phase helium supply piping,
and a novel heat sink was added to station both the inner
and outer conductors of the remaining HOM rf cables.
The characterization measurements, analysis,
modifications, and resulting performance are presented. | |
| WEP65 | Study on the buffered electropolishing Jacquet layers on niobium cavity | 660 |
| | - E. D. Wang, T. M. Xin, X. Y. Lu, L. M. Yang, L. Lin, S. Jin, K. Zhao
IHIP, Peking University
| |
| | Buffered electropolishing on niobium cavities has been
developed at Peking University. Some small niobium
samples have been polished very smoothly. An
experiment has demonstrated that both of the liquid and
solid Jacquet layers exist on the surface of anode
simultaneously. The results of experiment, that more than
70% voltage is taken by the Jacquet layers, show us that
the cathode shape is not a necessary condition for
polishing the dumbbell. Flat cathode is available to polish
the dumbbell. We have observed though the experiment
that the different fluid liquid Jacquet layer movements
could cause the different results on the dumbbell surface.
These studies show that BEP can offer a smooth surface
on niobium cavities. | |
| WEP66 | High pressure rinsing system studies | 664 |
| | - D. Sertore, M. Fusetti, P. Michelato, C. Pagani
INFN Milano-LASA - T. Higo, J. Hong, K. Saito
KEK - G. Ciovati, T. Rothgeb
JLab - A. Matheisen, N. Krupka
DESY
| |
| | High pressure rinsing (HPR) is a key process for the
surface preparation of high field superconducting cavities.
HPR water jets used in different laboratories have been
characterized measuring the transferred momentum
between the water jet and a target connected to a load cell.
The information taken during these measurements,
combined with HPR process parameters, allow
calculating new significant measurable variables such as
the jet power, the deposited energy on the cavity surfaces
and the pressure. | |
| WEP67 | Low-level RF control of microphonics in superconducting spoke-loaded cavities | 669 |
| | - Z. A. Conway, M. P. Kelly, S. I. Sharamentov, K. W. Shepard
ANL - G. K. Davis, J. Delayen
TJNAF - L. R. Doolittle
LBNL
| |
| | This paper presents the results of cw RF frequency
control and RF phase-stabilization experiments performed
with a piezoelectric fast tuner mechanically coupled to a
superconducting, 345 MHz, beta = 0.5 triple-spoke-loaded
cavity operating at 4.2K. The piezoelectric fast tuner
damped low-frequency microphonic-noise by an order of
magnitude. Two methods of RF phase-stabilization were
characterized: overcoupling with negative phase feedback,
and also fast mechanical tuner feedback. The beta = 0.5
triple-spoke-loaded cavity RF field amplitude and phase
errors were controlled to +(-)0.5% and +(-)30 respectively. | |
| WEP69 | MgB2 thin films on Nb cavity by pulse laser deposition | 672 |
| | - S. Mitsunobu, S. Inagaki, H. Nakanishi, K. Saito, M. Wake, M. Yoshida
KEK - M. Fukutomi
NIMS
| |
| | The large efforts have been concentrated on Nb
cavities for International Linear Collider (ILC). The
maximum accelerating field gradient of Nb cavities is
limited about 50 MV/m due to Hcsh. MgB2 (MgB2) have
higher Tc than Nb and expected to have higher Hcsh. Thin
films of MgB2 on Nb is useful to increase future ILC
energy upgrading.
At KEK, the preliminary test of thin films on Nb by
Pulse Laser Deposition(PLD) method have been started
and initially the direct deposition of MgB2 film on Nb
discs and single cell cavity was studied. | |
| WEP70 | Nb coating of copper cavities by UHV cathodic arc | 675 |
| | - L. Catani, A. Cianchi, D. DiGiovenale, J. Lorkiewicz, S. Tazzari
INFN Roma - R. Nietubyc, M. J. Sadowski
The Andrzej Soltan Institute for Nuclear Studies - M. Bruchon, B. Visentin
CEA-Saclay - B. Ruggiero, R. Russo
Istituto di Cibernetica del CNR and INFN-Na
| |
| | Niobium thin film coated copper RF cavities are an
interesting alternative to niobium bulk cavities mainly
because copper is cheaper, has higher thermal
conductivity and better mechanical workability and
stability than niobium. Unfortunately the observed
degradation of the sputter-coated cavities quality factor
with increasing accelerating voltage prevents their use
in future accelerators specified to work at field values
higher than 15MV/m. To try and overcome this
limitation we have developed an alternative coating
technique based on a cathodic arc system working
under UHV conditions. Main advantages of this
technique compared to standard sputtering are the
ionized state of the evaporated material, absence of
gases to sustain the discharge, high energy of atoms
reaching the substrate surface and possibility to have
high deposition rates. Recent results on the
characterization of niobium film samples produced by
UHV cathodic arc are presented, showing that the
technique can produce high quality films under
different angle of deposition. The system to
demonstrate the deposition of a single cell cavity have
been commissioned and first tests will be presented and
discussed. | |
| WEP74 | Particle free pump down and venting of UHV vacuum systems | 681 |
| | - K. Zapfe, J. Wojtkiewicz
DESY
| |
| | Vacuum systems containing superconducting cavities
which have to be operated at high gradients need to
preserve the cleanliness of the superconducting cavity
surfaces. In addition to an adequate preparation of the
cavities and the neighbouring vacuum components special
care needs to be taken during pump down and venting.
Neither should be particles introduced into the vacuum
system, nor should particles already present within the
system be moved towards critical areas.
For the superconducting linear accelerators of FLASH
and the European XFEL at DESY a series of
measurements have been performed to study the
movement of particles in long tubes during pump down
and venting. For this purpose an in-situ vacuum particle
counter has been used. By reducing and varying the gas
flow during these processes, it is possible to perform
these actions without moving particles present inside such
systems. Based on these measurements a set-up using
various filters, flow controllers and a pressure gauge has
been developed to avoid introducing particles into the
vacuum system as well as moving existing particles. This
set-up allows automated pump-down and venting of
critical vacuum systems in a reliable and reproducible
way, being much faster than the procedures used so far. | |
| WEP76 | Performance of RF amplifiers for ISAC-II medium beta linac operation | 685 |
| | - A. K. Mitra, K. Fong, R. E. Laxdal, J. Lu, R. Shanks
TRIUMF
| |
| | A heavy ion superconducting linac at TRIUMF to
increase the final energy of radioactive beams from the
existing room temperature ISAC accelerator is now
operational. The linac consists of twenty quarter wave
cavities operating at 106 MHz to produce an accelerating
voltage gain of 20 MV. This paper describes the
operational experience of the 106 MHz rf tube amplifiers
which were installed and commissioned for the medium
beta linac in October 2005. Total rf power installed is 16
kW where one quarter power is used for regular linac
operation. During the initial commissioning of the
amplifiers, only one power tube was found to be noisy
and was replaced. The first major tube failure occurred in
April 2007 after 9000 operating filament hours. Soon
thereafter five more tubes showed signs of loss of gain. It
was evident that most of the tubes reached their tube life
by this time and all were replaced with new tubes. The
extension of tube life, and prediction of tube failure are
the main concerns of these tube amplifiers. Efforts are
being made to incorporate reduced filament power
operation in order to get longer tube life. Systematic
check of the amplifier performance during scheduled
maintenance and shutdown period is undertaken.
Reduction of tube emission and hence gain degradation
from their nominal value causes excessive drive power
from the rf control system to keep the cavity voltage
constant under closed loop. Hence monitoring the drive
power is useful to predict early tube failure. Input drive
power and gain of all the 20 amplifiers are available at the
EPICS data archive which can be monitored and plotted.
This will allow early warning of tube failure so that tubes
can be replaced before they actually fail. The failure
modes of the tubes and diagnostics to predict tube failure
will be described. | |
| WEP77 | Field reconstruction by passband frequency measurement at the Rossendorf SRF-gun cavity | 689 |
| | - A. Arnold, H. Buettig, D. Janssen, G. Staats, J. Teichert
FZD
| |
| | In this paper a method is presented that provides the
field profile of a closed superconducting cavity only by
measuring its passband frequencies with the applied RF
coupling probes. This opens the possibility to estimate
field deformations that are caused by the preload of the
cavity tuner and its tuning during operation.
The method was tested at the 3.5 cell Rossendorf SRF
gun cavity [1] and a comparison between the measured
and predicted field distribution demonstrates the accuracy
within a range of 2%. | |
| WEP78 | Design of a 9-cell cavity ILC test cryomodule in CHINA | 692 |
| | - Q. J. Xu, J. Y. Zhai, C. H. Li, Y. Sun, Z. L. Hou, J. Gao
IHEP, CAS - T. X. Zhao, L. Y. Xiong, W. H. Lu, Z. G. Zong, L. Q. Liu, L. Zhang
TIPC, CAS
| |
| | Technical design of a 9-cell cavity cryomodule has
been finished by a collaboration group between IHEP
(Institute of High Energy Physics) and TIPC (Technical
Institute of Physics and Chemistry), which was set up in
last October for the ILC cryomodule related R&D work in
China. The designed Cryomodule is a "test model" for the
ILC cryomodule, and as a component of a
superconducting accelerator test unit which will be built
in the near future. It also can be used for the horizontal
test of a 9-cell cavity. This paper presents the detail
structure, cryogenic flow diagram, thermal and
mechanical simulation of the cryomodule. | |
| WEP79 | Scattering matrix calculation of higher order modes and sensitivity to cavity fabrication errors for the ILC superconducting cavities | 695 |
| | - I. Shinton, R. M. Jones
University of Manchester/Cockcroft Institute
| |
| | A cascaded scattering matrix approach is used to
determine the eigenmodes and driven modes in the main
linac cavities of the ILC. This approach is used to
compute higher order e.m. modes in the baseline
configuration, and high gradient alternative
configurations. We present results on three cavity
designs: TESLA, Cornell University's re-entrant and,
KEK's "Ichiro". This approach allows realistic
experimental errors to be incorporated in the studies in an
efficient manner and allows several cavities to be
modelled. Implications of indentations in the cavity on the
modal properties of the structure are presented. | |
| WEP80 | Simulations of transverse higher order deflecting modes in the main linacs of ILC | 700 |
| | - C. J. Glasman, R. M. Jones, I. Shinton
The University of Manchester/Cockcroft Institute of Science and Technology - G. Burt
Lancaster University/Cockcroft Institute of Science and Technology
| |
| | We investigate the electromagnetic field excited by a
train of multiple bunches in the main superconducting
linacs of the International Linear Collider (ILC). These
e.m. fields are represented as a wake-field. Detailed
simulations are made for modes constituting the longrange
wake-field in new high gradient cavities. In
particular, we focus our study on the transverse deflecting
modes in high gradient cavity designs known as "Ichiro",
in which the central cells have iris radius of 30 mm.
These cavities have a reduced iris compare to the TESLA
design and will have more intense wake-fields. Several
software packages solving the electromagnetic field,
employing different algorithms have been used to model
the cavity. The performance of these codes is compared. | |
| WEP81 | Tests of air cooled 1.3 GHz waveguide windows using a RF coupler test bench based on a resonant ring | 705 |
| | - H. Buettig, A. Arnold, A. Buechner, F. Gabriel, P. Michel, R. Schurig, G. Staats, J. Teichert, J. Voigtlander, A. Winter
Reserch Center Dresden-Rossendorf
| |
| | A new coupler test bench based on a resonant ring has
been built at ELBE in Dresden-Rossendorf to run window
as well as coupler tests with RF power up to 100 kW. The
ring is driven by a 10 kW klystron. This test bench
includes also liquid nitrogen cooling of the ceramic cold
window of the RF-coupler which allows testing under
almost real conditions. A special waveguide was designed
to match couplers with different antenna tips. In a first
step the waveguide window has been equipped with
additional air-cooling and tested.
The design of the test bench and the gained experience
with warm window tests at the resonant ring as far as it
could be collected within a short time of operation will be
reported. | |
| WEP82 | The measurements of static heat loss and unloaded Q0 on the BEPCII SRF cavities | 708 |
| | - L. Bian, S. P. Li, Y. P. Liu
IHEP, CAS
| |
| | The static heat loss and unloaded Q0 are most
important values for both cryogenic system and RF
system. The BEPCII SRF cavity operates in a liquid
helium bath contained in a vacuum insulated, liquid
nitrogen cooled radiation shielded vessel. During
horizontal test at the test station, thermodynamic method
is used to measure and calculate the static loss and Q0 of
SRF cavity. This paper has briefly introduced the method
and process to measure the static loss and Q0 of the SRF
cavity. Results under different experimental conditions
are also given. These results are also used as important
data for acceptance test of the SRF cavities. | |
| WEP83 | The prototype cryomodule for the EUROTRANS program | 712 |
| | - S. Barbanotti, N. Panzeri, P. Pierini
INFN Milano-LASA - J. L. Biarrotte, S. Bousson, C. Commeaux, E. Rampnoux, M. Souli
IPN Orsay
| |
| | EUROTRANS is a research program funded by the
EURATOM (EC) in the 6th Framework Programme for
the assessment of a nuclear waste transmutation system
driven by a high intensity superconducting linac.
The design of the high energy end of the linac (above
100 MeV) is based on low beta multicell elliptical cavities.
A prototype cryomodule containing a single 5 cell cavity
(built and tested successfully at INFN) is being developed
jointly by INFN and IPN-Orsay. This paper describes the
module layout and its implementation plan at Orsay. | |
| WEP84 | The test bench for the power amplifiers of the SPIRAL-2 SC linac | 717 |
| | - M. DiGiacomo, B. Ducoudret, P. Baret, J-C. Deroy
GANIL
| |
| | The high current driver accelerator of the SPIRAL 2
project uses independently phased SC resonators working
at 88 MHz. Solid state power amplifiers equipped with
circulators are foreseen to drive the cavities with widely
ranging conditions of beam loading. These power devices
are developed by industrial companies and a test bench
has been studied and manufactured to test the prototypes,
to commission all the units before their installation on the
accelerator and to be used to test repaired modules. Even
if designed to be used at 88 MHz, the test bench can be
used at higher frequencies too. The poster describes the
test bench as well as the results on the first amplifiers
bought for the cryomodule power tests. | |
| WEP85 | Waveguide coupler kick to beam bunch and current dependency on SRF cavities | 721 |
| | - G. Wu
Fermilab - H. Wang, C. E. Reece, R. A. Rimmer
JLab
| |
| | JLAB SRF cavities employ waveguide type
fundamental power couplers (FPC). The FPC design for
the 7-cell upgrade cavities was optimized to minimize the
dipole field kick. For continuous wave (CW) operation,
the forwarding RF power will be at different magnitude to
drive the different beam current and cavity gradient. This
introduces some deviation from optimized FPC field for
varying beam loading. This article analyzes the beam
behavior both in centroid kick and head-tail kick under
different beam loading conditions. | |
| WEP86 | Niobium sample surface treatment by buffered electropolishing | 724 |
| | - S. Jin, L. Lin, L. M. Yang, E. D. Wang, T. M. Xin, X. Y. Lu, K. Zhao
IHIP, Peking University
| |
| | The electrolyte of buffered electropolishing (BEP) is
consisted of hydrofluoric, sulfuric and lactic acids. In the
present work, the process of BEP has been familiarized
and the main parameters were investigated. It was
demonstrated that the polishing rate of BEP had a linear
relationship with current density; therefore the polishing
rate can be controlled via current density, which make the
control of BEP easier. Through inspection using a
metallographic optical microscope (MOM) and an Atomic
Force Microscope (AFM), it is proved that Nb surfaces
treated by BEP were much smoother than those treated by
the electropolishing (EP) process widely used in the
superconducting radio frequency community. | |