SRF2013 - List of Keywords (interface)

Paper	Title	Other Keywords	Page
MOIOC01	Heat Transfer at the Interface Between Niobium and Liquid Helium for 6 GHz SRF Cavities	cavity, niobium, coupling, 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]

TUP010	Simulation of Non-linear RF Losses Derived from Characteristic Nb Topography	cavity, simulation, niobium, SRF	441
	C. Xu, M.J. Kelley JLAB, Newport News, Virginia, USA M.J. Kelley, C. Xu The College of William and Mary, Williamsburg, USA C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A simplified model has been developed to simulate non-linear rf losses on Nb surfaces due exclusively to topographical enhancement of surface magnetic fields. If local sharp edges are small enough, where local surface fields exceed Hc, small volumes of material may become normal conducting without thermal runaway leading to quench. These small volumes of normal material yield increases in the effective surface resistance of the Nb. Using topographic data from typical BCP’d and EP’d fine grain niobium, we have simulated field-dependent losses and find that when extrapolated to resulting cavity performance correspond well to characteristic BCP/EP high field Q0 performance differences for fine grain Nb. We will describe the structure of the model, its limitations, and the effects of this type of non-linear loss contribution to SRF cavities.

TUP079	ECR Nb Films Grown on Amorphous and Crystalline Cu Substrates: Influence of Ion Energy	ion, ECR, SRF, electron	631
	A-M. Valente-Feliciano, G.V. Eremeev, H.L. Phillips, C.E. Reece JLAB, Newport News, Virginia, USA C. Cao Illinois Institute of Technology, Chicago, IL, USA Th. Proslier ANL, Argonne, USA J.K. Spradlin JLab, Newport News, Virginia, USA T. Tao UIC, Chicago, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. Using energetic condensation of ions extracted from plasma generated by Electron Cyclotron Resonance, it has been demonstrated that Nb films with good structural properties and RRR comparable to bulk values can be produced on metallic substrates. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. Particular attention is given to the nucleation conditions to create a favorable template for growing the final surface exposed to SRF fields. The influence of the deposition energy for both hetero-epitaxial and fiber growth modes on copper substrates is investigated with the characterization of the film surface, structure, superconducting properties and RF performance.

THP041	Optimization of the Double Quarter Wave Crab Cavity Prototype for Testing at SPS	cavity, HOM, acceleration, luminosity	995
	S. Verdú-Andrés, S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA R. Calaga CERN, Geneva, Switzerland Z. Li SLAC, Menlo Park, California, USA
	Funding: Research supported by EU FP7 HiLumi LHC – No. 284404, and by US DOE through Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 and the US LHC Accelerator Research Program (LARP). The crab cavity program for LHC luminosity upgrade envisages the testing of at least one of the three competing crab cavities in the Super Proton Synchrotron (SPS) of CERN by 2016. This paper presents the design optimization of a Double Quarter Wave Crab Cavity (DQWCC) prototype suited for testing in SPS.

THP098	LLRF and Data Acquisition Systems for Spoke012 Cavity Vertical Test at IHEP	cavity, LLRF, LabView, data-acquisition	1158
	J.P. Dai, H. Huang, H. Li, H.Y. Lin, P. Sha, Y. Sun, Q.Y. Wang, J. Zhang IHEP, Beijing, People's Republic of China
	Development of two Spoke 012 cavities and their vertical tests have been completed successfully at IHEP with a LLRF system and DAQ (data acquisition) system specially designed. The LLRF system is developed on the basis of the proven analog system used for the test of the BEPCII 500 MHz spare cavity. The Labview 2009-based DAQ system is in charge of the communications of the measuring instruments, the local machine and the remote machine. It also completes drawing the test curve online and obtaining the test result in real time. The data connection between Labview and EPICS is implemented. The vertical test result shows that the LLRF system and the DAQ system in operation perform stably and reliably as expected. This paper introduces the two systems and the general situation for Spoke 012 cavity vertical test.

Paper

Title

Other Keywords

Page

MOIOC01

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

cavity, niobium, coupling, 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]

TUP010

Simulation of Non-linear RF Losses Derived from Characteristic Nb Topography

cavity, simulation, niobium, SRF

441

C. Xu, M.J. Kelley
JLAB, Newport News, Virginia, USA
M.J. Kelley, C. Xu
The College of William and Mary, Williamsburg, USA
C.E. Reece
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A simplified model has been developed to simulate non-linear rf losses on Nb surfaces due exclusively to topographical enhancement of surface magnetic fields. If local sharp edges are small enough, where local surface fields exceed Hc, small volumes of material may become normal conducting without thermal runaway leading to quench. These small volumes of normal material yield increases in the effective surface resistance of the Nb. Using topographic data from typical BCP’d and EP’d fine grain niobium, we have simulated field-dependent losses and find that when extrapolated to resulting cavity performance correspond well to characteristic BCP/EP high field Q0 performance differences for fine grain Nb. We will describe the structure of the model, its limitations, and the effects of this type of non-linear loss contribution to SRF cavities.

TUP079

ECR Nb Films Grown on Amorphous and Crystalline Cu Substrates: Influence of Ion Energy

ion, ECR, SRF, electron

631

A-M. Valente-Feliciano, G.V. Eremeev, H.L. Phillips, C.E. Reece
JLAB, Newport News, Virginia, USA
C. Cao
Illinois Institute of Technology, Chicago, IL, USA
Th. Proslier
ANL, Argonne, USA
J.K. Spradlin
JLab, Newport News, Virginia, USA
T. Tao
UIC, Chicago, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. Using energetic condensation of ions extracted from plasma generated by Electron Cyclotron Resonance, it has been demonstrated that Nb films with good structural properties and RRR comparable to bulk values can be produced on metallic substrates. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. Particular attention is given to the nucleation conditions to create a favorable template for growing the final surface exposed to SRF fields. The influence of the deposition energy for both hetero-epitaxial and fiber growth modes on copper substrates is investigated with the characterization of the film surface, structure, superconducting properties and RF performance.

THP041

Optimization of the Double Quarter Wave Crab Cavity Prototype for Testing at SPS

cavity, HOM, acceleration, luminosity

995

S. Verdú-Andrés, S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA
R. Calaga
CERN, Geneva, Switzerland
Z. Li
SLAC, Menlo Park, California, USA

Funding: Research supported by EU FP7 HiLumi LHC – No. 284404, and by US DOE through Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 and the US LHC Accelerator Research Program (LARP).
The crab cavity program for LHC luminosity upgrade envisages the testing of at least one of the three competing crab cavities in the Super Proton Synchrotron (SPS) of CERN by 2016. This paper presents the design optimization of a Double Quarter Wave Crab Cavity (DQWCC) prototype suited for testing in SPS.

THP098

LLRF and Data Acquisition Systems for Spoke012 Cavity Vertical Test at IHEP

cavity, LLRF, LabView, data-acquisition

1158

J.P. Dai, H. Huang, H. Li, H.Y. Lin, P. Sha, Y. Sun, Q.Y. Wang, J. Zhang
IHEP, Beijing, People's Republic of China

Development of two Spoke 012 cavities and their vertical tests have been completed successfully at IHEP with a LLRF system and DAQ (data acquisition) system specially designed. The LLRF system is developed on the basis of the proven analog system used for the test of the BEPCII 500 MHz spare cavity. The Labview 2009-based DAQ system is in charge of the communications of the measuring instruments, the local machine and the remote machine. It also completes drawing the test curve online and obtaining the test result in real time. The data connection between Labview and EPICS is implemented. The vertical test result shows that the LLRF system and the DAQ system in operation perform stably and reliably as expected. This paper introduces the two systems and the general situation for Spoke 012 cavity vertical test.