SRF2013 - List of Keywords (coupling)

Paper	Title	Other Keywords	Page
MOIOC01	Heat Transfer at the Interface Between Niobium and Liquid Helium for 6 GHz SRF Cavities	cavity, niobium, interface, operation	57
	V. Palmieri INFN/LNL, Legnaro (PD), Italy
	Cavity Thermal Boundary Resistance is something extremely complex and not completely understood by the theory. Often identified with the Kapitza resistance or with the Khalatnikov acoustic phonon mismatch at the interface metal-liquid Helium, it depends on so many different and uncontrolled parameters, that its interpretation is not covered by a complete treatise of the phenomenon. Therefore, 99% of the literature on superconducting cavities worries about the cavity interior surface state,while almost nothing is reported on treatments applied to the exterior. In the authors opinion, there is a lack in experimental data analysis due to the fact that the cavity is often considered as a whole adiabatic entity interacting only with RF fields. On the contrary, the cavity is immersed in liquid Helium and the cavity behavior cannot prescind from its thermal properties. Indeed in the normal state He-I has poor thermal conductivity and high specific heat. Moreover the heat exchange at HeII obeys to further mechanisms besides the phonon mismatch. Driven by the hypothesis that thermal losses are dominant for ultraclean cavities, we have collected a plethora of surprising experimental results.
	Slides MOIOC01 [15.558 MB]

TUP053	Estimation of Small Geometry Deviation for TESLA-Shape Cavities Due to Inner Surface Polishing	cavity, superconductivity, factory, data-analysis	537
	A.A. Sulimov, G. Kreps, J.K. Sekutowicz DESY, Hamburg, Germany
	Two well know polishing methods are used for the inner surface cleaning of superconducting TESLA-shape cavities: electro-polishing (EP) or buffered chemical polishing (BCP). The amount of removed material is relatively small and varies from 10 till 140 um. The cavity after polishing is closed to prevent the scratches or dust appearing on its inner surface. The estimation of the removed material amount is possible by different criteria, for example by comparison of weight before and after cleaning, or by the time - cleaning procedure duration. Both calculations could give us only approximate average value of the removed material amount. We describe the method for estimation of small geometry deviation basing on RF frequency measurements, which allows calculating the different influence of surface treatment on the iris and equator areas.
	Poster TUP053 [0.785 MB]

TUP055	Electropolishing of the ANL Deflecting Cavity for the APS Upgrade	cavity, niobium, SRF, background	544
	Y. Yang, J.D. Fuerst, J.P. Holzbauer, J.A. Kaluzny, A. Nassiri, G. Wu ANL, Argonne, USA A.C. Crawford Fermilab, Batavia, USA P. Dhakal, J.D. Mammosser, H. Wang JLAB, Newport News, Virginia, USA Y. Yang TUB, Beijing, People's Republic of China
	Studies on the application of electropolishing (EP) of the ANL superconducting deflecting cavity have shown promising results. This cavity geometry is a squashed single-cell cavity with Y-end group waveguide as well as on-cell LOM damper. The cavity works at TM110-like deflecting mode, in which the iris between the cavity cell and the Y-end group is the highest magnetic field region. Before EP, the cavity had been chemically etched (BCP) several times. Forty-um EP processing was performed on one Mark II prototype deflecting cavity at Fermilab. No mild baking was performed before the cavity vertical test. The test showed that the low-field Q had improved from 2·10⁹ to 3·10⁹ and the high-field Q-slope had been successfully removed. The quench limit was slightly improved from 10⁶ mT to 113 mT. Fast T-mapping had detected a significant decrease of local temperature rise in the cavity iris. Optical inspection before EP found a lot of grooves around the iris, which might be related to the gas bubbles generated during BCP. This suggests that horizontal EP is a promising processing technique to remove the high-field Q-slope and improve the deflecting cavity performance.

THIOA01	Infrastructure, Methods and Test Results for the Testing of 800 Series Cavities for the European XFEL	cavity, operation, controls, feedback	812
	D. Reschke DESY, Hamburg, Germany
	Funding: The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no 283745 (CRISP). The main linac of the European XFEL will consist of 100 accelerator modules, i.e. 800 superconducting accelerator cavities operated at a design gradient of 23.6 MV/m. The fabrication and surface preparation of the cavities in industry is in full swing. This talk describes the infrastructure and procedures of the vertical acceptance test in the "Accelerator Module Test Facility AMTF" at DESY. The present status of the test results is given.
	Slides THIOA01 [1.998 MB]

THP003	Cold Measurements on the 325 MHz CH-Cavity	cavity, linac, ion, operation	896
	M. Busch, F.D. Dziuba, H. Podlech, U. Ratzinger IAP, Frankfurt am Main, Germany M. Amberg HIM, Mainz, Germany
	Funding: GSI, BMBF Contr. No. 06FY7102, 06FY9089I At the Institute for Applied Physics (IAP), Frankfurt University, a sc 325 MHz CH-Cavity has been designed and built. This 7-cell cavity has a geometrical beta of 0.16 corresponding to a beam energy of 11.4 AMeV. The design gradient is 5 MV/m. Novel features of this resonator are a compact design, low peak fields, easy surface processing and high power coupling. After successful tests at Research Instruments (RI) and in Frankfurt the cavity was processed and cleaned at RI and power tests at 4K have been performed at the cryo lab in Frankfurt. In this paper these measurements will be presented.

THP027	Multipactor Analysis of the HWR at RISP	cavity, electron, simulation, resonance	955
	G.-T. Park IBS, Daejeon, Republic of Korea
	We report on the progress of the HWR development at RISP. The multipaction of the HWR was studied using CST-PS (PIC) solver and multipacting band is predicted. Additional considerations were given to see the effects of the coupling ports and the coupler on the multipaction. We present the modified cavity design without multipaction at our operation accelerating voltage~1.2MV.

THP050	Development of Power Coupler for Superconducting Spoke Cavities for China ADS Proton Linac	cavity, vacuum, simulation, Windows	1024
	X. Chen, T.M. Huang, H.Y. Lin, Q. Ma, F. Meng, W.M. Pan, Y.H. Peng IHEP, Beijing, People's Republic of China
	Abstract: The China-ADS proton linac adopts β=0.12 superconducting Spoke cavities. Each cavity is powered via a 325MHz coaxial power coupler. The coupler is to feed 6kW maximum power though it is designed to handle at 15kW .Two coupler sets have been made by IHEP so far, and a 10kW RF power in continuous travelling wave mode has passed through the coupler during high power test in late January 2013. An introduction of this coupler design and the room temperature test results are presented in this paper.

THP062	Optimisation of the 3-Stub Tuner for Matching the Diamond SCRF Cavities	cavity, simulation, operation, storage-ring	1061
	S.A. Pande, C. Christou, P. Gu, M. Jensen Diamond, Oxfordshire, United Kingdom
	The Diamond Storage Ring cavities are aperture coupled resulting in a fixed external Q. This results in the cavities being matched under certain conditions depending on the loss per turn, the beam current and the accelerating voltage. Operationally, there are advantages to limiting the accelerating voltage to improve reliability and lifetime, which at high beam current results in a mismatch and high reflected power. To match the cavities under such non-optimum operating conditions we use 3-stub tuners in the waveguide feeds. It has been observed, that certain configurations of the 3-stub tuners can improve the match of the cavity, but this can result in strong heating of the waveguide in the cryostat. Numerical simulations of the cavity along with the coupling waveguide and 3-stub tuners have been carried out using CST Studio for different beam loading conditions to optimise the 3-stub tuners for acceptable match and heating. In this paper we present the results of our simulations and comparisons with measurements for operation with different beam currents and cavity voltages.

THP064	HOM Couplers for CERN SPL Cavities	HOM, cavity, dipole, linac	1066
	K. Papke, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany F. Gerigk CERN, Geneva, Switzerland
	Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF) Higher-Order-Modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the SPL, which is studied at CERN as the driver for future neutrino facilities. In order to limit beam-induced HOM effects CERN considers the use of HOM couplers on the cut-off tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes which are designed to couple to modes of a specific frequency range. In this paper the design process is presented and a comparison is made between various design options for the medium and high-beta SPL cavities, both operating at 704 MHz. The RF characteristics, thermal behaviour and multipacting sensitivity of the various designs are discussed and 2 options are presented, which will be tested as warm prototypes on 5-cell high-beta copper cavity models.

FRIOA03	Fabrication and Testing of Deflecting Cavities for APS	cavity, operation, niobium, SRF	1170
	J.D. Mammosser JLab, Newport News, Virginia, USA P. Dhakal, J. Henry, R.A. Rimmer, H. Wang, K.M. Wilson JLAB, Newport News, Virginia, USA J.F. Fuerst, J.P. Holzbauer, J.S. Kerby, A. Nassiri, G.J. Waldschmidt, G. Wu, Y. Yang ANL, Argonne, USA F. He PKU, Beijing, People's Republic of China Z. Li SLAC, Menlo Park, California, USA
	Abstract Jefferson Lab in Newport News, Virginia, in collaboration with Argonne National Laboratory, Argonne, Il, has fabricated and tested three production, 2.815 GHz crab cavities for Argonne’s Short-Pulse X-ray project. These cavities are unique in that the cavity and waveguides were milled from bulk large grain niobium ingot material directly from 3D CAD files. No forming of sub components was used with the exception of the beam-pipes. The cavity and helium vessel design along with the RF performance requirements makes this project extremely challenging for fabrication. Production challenges and fabrication techniques as well as testing results will be discussed in this paper.
	Slides FRIOA03 [22.677 MB]

Paper

Title

Other Keywords

Page

MOIOC01

Heat Transfer at the Interface Between Niobium and Liquid Helium for 6 GHz SRF Cavities

cavity, niobium, interface, operation

57

V. Palmieri
INFN/LNL, Legnaro (PD), Italy

Cavity Thermal Boundary Resistance is something extremely complex and not completely understood by the theory. Often identified with the Kapitza resistance or with the Khalatnikov acoustic phonon mismatch at the interface metal-liquid Helium, it depends on so many different and uncontrolled parameters, that its interpretation is not covered by a complete treatise of the phenomenon. Therefore, 99% of the literature on superconducting cavities worries about the cavity interior surface state,while almost nothing is reported on treatments applied to the exterior. In the authors opinion, there is a lack in experimental data analysis due to the fact that the cavity is often considered as a whole adiabatic entity interacting only with RF fields. On the contrary, the cavity is immersed in liquid Helium and the cavity behavior cannot prescind from its thermal properties. Indeed in the normal state He-I has poor thermal conductivity and high specific heat. Moreover the heat exchange at HeII obeys to further mechanisms besides the phonon mismatch. Driven by the hypothesis that thermal losses are dominant for ultraclean cavities, we have collected a plethora of surprising experimental results.

Slides MOIOC01 [15.558 MB]

TUP053

Estimation of Small Geometry Deviation for TESLA-Shape Cavities Due to Inner Surface Polishing

cavity, superconductivity, factory, data-analysis

537

A.A. Sulimov, G. Kreps, J.K. Sekutowicz
DESY, Hamburg, Germany

Two well know polishing methods are used for the inner surface cleaning of superconducting TESLA-shape cavities: electro-polishing (EP) or buffered chemical polishing (BCP). The amount of removed material is relatively small and varies from 10 till 140 um. The cavity after polishing is closed to prevent the scratches or dust appearing on its inner surface. The estimation of the removed material amount is possible by different criteria, for example by comparison of weight before and after cleaning, or by the time - cleaning procedure duration. Both calculations could give us only approximate average value of the removed material amount. We describe the method for estimation of small geometry deviation basing on RF frequency measurements, which allows calculating the different influence of surface treatment on the iris and equator areas.

Poster TUP053 [0.785 MB]

TUP055

Electropolishing of the ANL Deflecting Cavity for the APS Upgrade

cavity, niobium, SRF, background

544

Y. Yang, J.D. Fuerst, J.P. Holzbauer, J.A. Kaluzny, A. Nassiri, G. Wu
ANL, Argonne, USA
A.C. Crawford
Fermilab, Batavia, USA
P. Dhakal, J.D. Mammosser, H. Wang
JLAB, Newport News, Virginia, USA
Y. Yang
TUB, Beijing, People's Republic of China

Studies on the application of electropolishing (EP) of the ANL superconducting deflecting cavity have shown promising results. This cavity geometry is a squashed single-cell cavity with Y-end group waveguide as well as on-cell LOM damper. The cavity works at TM110-like deflecting mode, in which the iris between the cavity cell and the Y-end group is the highest magnetic field region. Before EP, the cavity had been chemically etched (BCP) several times. Forty-um EP processing was performed on one Mark II prototype deflecting cavity at Fermilab. No mild baking was performed before the cavity vertical test. The test showed that the low-field Q had improved from 2·10⁹ to 3·10⁹ and the high-field Q-slope had been successfully removed. The quench limit was slightly improved from 10⁶ mT to 113 mT. Fast T-mapping had detected a significant decrease of local temperature rise in the cavity iris. Optical inspection before EP found a lot of grooves around the iris, which might be related to the gas bubbles generated during BCP. This suggests that horizontal EP is a promising processing technique to remove the high-field Q-slope and improve the deflecting cavity performance.

THIOA01

Infrastructure, Methods and Test Results for the Testing of 800 Series Cavities for the European XFEL

cavity, operation, controls, feedback

812

D. Reschke
DESY, Hamburg, Germany

Funding: The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no 283745 (CRISP).
The main linac of the European XFEL will consist of 100 accelerator modules, i.e. 800 superconducting accelerator cavities operated at a design gradient of 23.6 MV/m. The fabrication and surface preparation of the cavities in industry is in full swing. This talk describes the infrastructure and procedures of the vertical acceptance test in the "Accelerator Module Test Facility AMTF" at DESY. The present status of the test results is given.

Slides THIOA01 [1.998 MB]

THP003

Cold Measurements on the 325 MHz CH-Cavity

cavity, linac, ion, operation

896

M. Busch, F.D. Dziuba, H. Podlech, U. Ratzinger
IAP, Frankfurt am Main, Germany
M. Amberg
HIM, Mainz, Germany

Funding: GSI, BMBF Contr. No. 06FY7102, 06FY9089I
At the Institute for Applied Physics (IAP), Frankfurt University, a sc 325 MHz CH-Cavity has been designed and built. This 7-cell cavity has a geometrical beta of 0.16 corresponding to a beam energy of 11.4 AMeV. The design gradient is 5 MV/m. Novel features of this resonator are a compact design, low peak fields, easy surface processing and high power coupling. After successful tests at Research Instruments (RI) and in Frankfurt the cavity was processed and cleaned at RI and power tests at 4K have been performed at the cryo lab in Frankfurt. In this paper these measurements will be presented.

THP027

Multipactor Analysis of the HWR at RISP

cavity, electron, simulation, resonance

955

G.-T. Park
IBS, Daejeon, Republic of Korea

We report on the progress of the HWR development at RISP. The multipaction of the HWR was studied using CST-PS (PIC) solver and multipacting band is predicted. Additional considerations were given to see the effects of the coupling ports and the coupler on the multipaction. We present the modified cavity design without multipaction at our operation accelerating voltage~1.2MV.

THP050

Development of Power Coupler for Superconducting Spoke Cavities for China ADS Proton Linac

cavity, vacuum, simulation, Windows

1024

X. Chen, T.M. Huang, H.Y. Lin, Q. Ma, F. Meng, W.M. Pan, Y.H. Peng
IHEP, Beijing, People's Republic of China

Abstract: The China-ADS proton linac adopts β=0.12 superconducting Spoke cavities. Each cavity is powered via a 325MHz coaxial power coupler. The coupler is to feed 6kW maximum power though it is designed to handle at 15kW .Two coupler sets have been made by IHEP so far, and a 10kW RF power in continuous travelling wave mode has passed through the coupler during high power test in late January 2013. An introduction of this coupler design and the room temperature test results are presented in this paper.

THP062

Optimisation of the 3-Stub Tuner for Matching the Diamond SCRF Cavities

cavity, simulation, operation, storage-ring

1061

S.A. Pande, C. Christou, P. Gu, M. Jensen
Diamond, Oxfordshire, United Kingdom

The Diamond Storage Ring cavities are aperture coupled resulting in a fixed external Q. This results in the cavities being matched under certain conditions depending on the loss per turn, the beam current and the accelerating voltage. Operationally, there are advantages to limiting the accelerating voltage to improve reliability and lifetime, which at high beam current results in a mismatch and high reflected power. To match the cavities under such non-optimum operating conditions we use 3-stub tuners in the waveguide feeds. It has been observed, that certain configurations of the 3-stub tuners can improve the match of the cavity, but this can result in strong heating of the waveguide in the cryostat. Numerical simulations of the cavity along with the coupling waveguide and 3-stub tuners have been carried out using CST Studio for different beam loading conditions to optimise the 3-stub tuners for acceptable match and heating. In this paper we present the results of our simulations and comparisons with measurements for operation with different beam currents and cavity voltages.

THP064

HOM Couplers for CERN SPL Cavities

HOM, cavity, dipole, linac

1066

K. Papke, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
F. Gerigk
CERN, Geneva, Switzerland

Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF)
Higher-Order-Modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the SPL, which is studied at CERN as the driver for future neutrino facilities. In order to limit beam-induced HOM effects CERN considers the use of HOM couplers on the cut-off tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes which are designed to couple to modes of a specific frequency range. In this paper the design process is presented and a comparison is made between various design options for the medium and high-beta SPL cavities, both operating at 704 MHz. The RF characteristics, thermal behaviour and multipacting sensitivity of the various designs are discussed and 2 options are presented, which will be tested as warm prototypes on 5-cell high-beta copper cavity models.

FRIOA03

Fabrication and Testing of Deflecting Cavities for APS

cavity, operation, niobium, SRF

1170

J.D. Mammosser
JLab, Newport News, Virginia, USA
P. Dhakal, J. Henry, R.A. Rimmer, H. Wang, K.M. Wilson
JLAB, Newport News, Virginia, USA
J.F. Fuerst, J.P. Holzbauer, J.S. Kerby, A. Nassiri, G.J. Waldschmidt, G. Wu, Y. Yang
ANL, Argonne, USA
F. He
PKU, Beijing, People's Republic of China
Z. Li
SLAC, Menlo Park, California, USA

Abstract Jefferson Lab in Newport News, Virginia, in collaboration with Argonne National Laboratory, Argonne, Il, has fabricated and tested three production, 2.815 GHz crab cavities for Argonne’s Short-Pulse X-ray project. These cavities are unique in that the cavity and waveguides were milled from bulk large grain niobium ingot material directly from 3D CAD files. No forming of sub components was used with the exception of the beam-pipes. The cavity and helium vessel design along with the RF performance requirements makes this project extremely challenging for fabrication. Production challenges and fabrication techniques as well as testing results will be discussed in this paper.

Slides FRIOA03 [22.677 MB]