IPAC2012 - List of Keywords (superconductivity)

Paper	Title	Other Keywords	Page
TUOAC02	Development of HTS Magnets	dipole, resonance, synchrotron, neutron	1095
	K. Hatanaka, M. Fukuda, N. Hamatani, N. Izumi, K. Kamakura, T. Saito, H. Ueda, Y. Yasuda, T. Yorita RCNP, Osaka, Japan T. Kawaguchi KT Science Ltd., Akashi, Japan
	A quarter of a century has passed since the discovery of high-temperature superconductor (HTS) materials in 1986. Although many prototype devices using HTS wires have been developed, these applications are presently rather limited in accelerator and beam line facilities. We have investigated the performance of HTS wires applied for magnets excited by alternating current (AC) as well as direct current (DC) for a decade. In order to check feasibilities of pulse magnets using HTS wire, we have fabricated a super-ferric dipole magnet to be operated by lumping currents. Upper and lower coil consists of 3 double pancakes of 200 turns. Critical currents were measured of wire measured at 77K. Self-field Ic of wire was higher than 160A. Ic values of double pancakes were 60-70A. After stacking, they were 47A and 51A for the upper and lower coil, respectively. Cooling tests were successfully done and the Ic values were measured to be 280A at 20K. Performance tests are ongoing in the pulse mode operation.
	Slides TUOAC02 [5.252 MB]

WEEPPB011	Analysis of High Field Non-Linear Losses on SRF Surfaces Due to Specific Topographic Roughness	simulation, niobium, SRF, feedback	2188
	C. Xu The College of William and Mary, Williamsburg, USA M.J. Kelley, C.E. Reece, C. Xu JLAB, Newport News, Virginia, USA
	Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The high-field performance of SRF cavities will eventually be limited by the realization of fundamental material limits, whether it be Hc1 or Hsh, or some derivative thereof, at which the superconductivity is lost. Before reaching this fundamental field limit at the macro level, it must be encountered at localized, perhaps microscopic, sites of field enhancement due to local topography. If such sites are small enough, they may produce thermally stabilized normal-conducting regions which contribute non-linear losses when viewed from the macro resonant field perspective, and thus produce degradation in Q0. We have undertaken a calculation of local surface magnetic field enhancement from specific fine topographic structure by conformal mapping method and numerically. A solution of the resulting normal conducting volume has been derived and the corresponding RF ohmic loss simulated.

WEEPPB015	Temperature Dependence of the Superheating Field: DC and RF Critical Fields	cavity, niobium, electron, SRF	2197
	N.R.A. Valles, M. Liepe CLASSE, Ithaca, New York, USA
	The superheating field is a metastable state at which the Meissner state persists at fields higher than would be predicted from steady-state energy considerations. Previous work demonstrated that a phenomenological approach based on the RF superheating field scaling near the critical temperature is also consistent with low temperature results. This work expands upon the RF results by measuring the DC superheating field, and comparing it to RF results and theoretical predictions.

WEPPC007	Image Processing for Characterization of Surfaces of Superconducting RF Cavities	cavity, LabView, linear-collider, collider	2218
	M. Wenskat, S. Aderhold, E. Elsen, S. Karstensen, F. Schlander, L. Steder DESY, Hamburg, Germany
	Funding: ILC HiGrade Optical inspection of finished Nb superconducting RF cavities has worldwide been established as an important tool for identification of field limiting surface features. Single defects in a single cell of a 9-cell cavity may severely constrain the maximum gradient while the micro-structure in the vicinity of a welding seam could affect the quench behavior. DESY has automated the imaging of critical cavity surface areas, in particular those of high magnetic field. With resolution of ~10 μm2 the information volume is large and the systematic examination becomes a necessity. The development of image processing algorithms has been started with two goals: automatic characterization of cavity surface properties and defect detection. The former results aid the quality assessment of cavities after manufacture; the latter serves to push the gradient performance. The status and prospects of the image processing for the European XFEL and ILC will be presented.

WEPPC065	Cleanroom Techniques to Improve Surface Cleanliness and Repeatability for SRF Coldmass Production	SRF, cavity, vacuum, controls	2357
	L. Popielarski, L.J. Dubbs, K. Elliott, I.M. Malloch, R. Oweiss, J. Popielarski FRIB, East Lansing, Michigan, USA
	Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University. The Facility for Rare Isotope Beams (FRIB) and ReA linear accelerator projects at Michigan State University (MSU) utilize Superconducting Radio-Frequency (SRF) cavities for their accelerating structures. The structures are cleaned and assembled in a cleanroom to reduce particle contamination. The project requires more than 350 SRF cavities. In preparation for production we want to maximize repeatable processes and reduce work time. The cleanroom assembly group at MSU investigates process techniques performed in the cleanroom. Various diagnostic tools; such as liquid particle counter, surface particle counter and airborne particle counter are used to quantify environments and optimize processes. We desire to define procedure specifications for cleaner processes and repeatability. We investigate effective part cleaning and storage, high pressure rinse and ultra pure water quality, and critical component rinsing. We study vacuum assembly, pump down and purge effects. The experiments are independent of cavity results with a focus to create cleanest surface and environment in the most effective manner. In this paper, we describe experiments, summarize the results and conclusions.

WEPPC069	Construction, Evaluation, and Application of a Temperature Map for Multi-cell SRF Cavities	cavity, SRF, controls, vacuum	2369
	G.M. Ge, F. Furuta, D.L. Hartill, K.M.V. Ho, G.H. Hoffstaetter, E.N. Smith CLASSE, Ithaca, New York, USA
	Temperature mapping (T-mapping) system is able to locate hot-spot of SRF cavity, thus it is a very powerful tool for cavity’s Q-value research. Recently Cornell University is developing a T-mapping system for multi-cell SRF cavities. The system includes more than two thousands Allen-Bradley resistors. Electronic of the system uses multiplexing of sensors which is able to dramatically reduce wire numbers, and allow the whole system is feasible for multi-cell cavity application. A new cavity testing insert which is for T-mapping system has been constructed.

WEPPC071	Quench Studies of a Superconducting RF Cavity	cavity, superconducting-RF, resonance, superconducting-cavity	2375
	D. Gonnella, M. Liepe, S. Posen CLASSE, Ithaca, New York, USA
	In tests of superconducting RF cavities, it is important to understand the cause of high field quenches. Quenches at high field above 25 MV/m are a limiting factor in the performance of high accelerating field cavities but their causes are currently not well understood. An ILC shaped single cell cavity with quench field near 40 MV/m was tested with temperature mapping to determine the cause of its hard quench. Prior to quench, heating on the order of 25 mK was concentrated in two hot spots. After a quench, these two hot spots remain and a new one appears with much higher heating (about 40 mK). The quench location was found by the temperature mapping system to be centered at the new hot spot, not at the two hot spot locations before that dominated quench. By studying the quench location and heating on the surface of the cavity, some hints were gained as to the cause of this quench.

WEPPC094	Optimizing Centrifugal Barrel Polishing for Mirror Finish SRFCavity and Rf Tests at Jefferson Lab	cavity, SRF, radio-frequency, controls	2435
	A.D. Palczewski, R.L. Geng, H. Tian JLAB, Newport News, Virginia, USA
	Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We performed Centrifugal Barrel Polishing (CBP) on a 1.3GHz fine grain ILC SRF cavity following a modified version of the recipe* originally developed at Fermilab (FNAL)*. We were able to obtain a mirror like surface similar to that obtained at FNAL, while reducing the number of CBP steps. This paper will discuss the change in surface and subsequent cavity performance before CBP on a raw cavity and post CBP, after a 800C bake (no pre-bake chemistry) and minimal controlled electro-polishing (below 10 micron). In addition to Q vs. Eacc thermometry maps with preheating characteristics and optical inspection of the cavity before and after CBP will also be shown. A. D. Palczewski et al., Proc. of SRF2011, THPO071 (2011). ** C.A. Cooper et al., FERMILAB-PUB-11-032-TD, (May 31, 2011).

WEPPR037	First-Principle Approach for Optimization of Cavity Shape for High Gradient and Low Loss	cavity, wakefield, multipactoring, superconducting-cavity	3015
	V.D. Shemelin, G.H. Hoffstaetter CLASSE, Ithaca, New York, USA
	Funding: Supported by NSF award DMR-0807731. Minimization of surface fields for a given accelerating rate is the subject of cavity optimization because high electric and magnetic fields lead to field emission or thermal breakdown, respectively. The ratio between peak electric and magnetic fields is a function of geometry and the desired ratio depends on application. For each application the optimal geometry may be different. The elliptic shape of the cavity have been found evolutionarily: starting from a pill-box with beam-pipes having rounded corners. No attempts up to now are known for a search of non-elliptical optimal shapes. Here we describe the search for a cavity shape that has the lowest surface fields, not restricting to the conventional elliptical cavity shapes.

THPPC093	SRF Cavity Surface Topography Characterization Using Replica Techniques	cavity, SRF, niobium, radio-frequency	3497
	C. Xu, M.J. Kelley The College of William and Mary, Williamsburg, USA C.E. Reece JLAB, Newport News, Virginia, USA
	Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. To better understand the roll of topography on SRF cavity performance, we seek to obtain detailed topographic information from the curved practical cavity surfaces. Replicas taken from a cavity interior surface provide internal surface molds for fine Atomic Force Microscopy (AFM) and stylus profilometry. In this study, we confirm the replica resolution both on surface local defects such as grain boundary and etching pits and compare the surface uniform roughness with the aid of Power Spectral Density (PSD) where we can statistically obtain roughness parameters at different scales. A series of sampling locations are at the same magnetic field chosen at the same latitude on a single cell cavity to confirm the uniformity. Another series of sampling locations at different magnetic field amplitudes are chosen for this replica on the same cavity for later power loss calculation. We also show that application of the replica followed by rinsing does not adversely affect the cavity performance.

THPPD051	New Power Supply of the Injection Bump Magnet for Upgrading the Injection Energy in the J-PARC 3-GeV RCS	power-supply, injection, linac, proton	3626
	T. Takayanagi, N. Hayashi, M. Kinsho, N. Tani, T. Togashi, T. Ueno JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
	With the energy upgrading of LINAC (Linear accelerator) to 400 MeV in the J-PARC (Japan Proton Accelerator Research Complex), a new power supply of the injection bump magnet has been designed for the 3-GeV RCS (Rapid Cycling Synchrotron). The new power supply is composed with the capacitor bank which has function to form the output current pattern. This power supply is a commutation strategy using the electrical charge and discharge of the capacitor, and the frequency of the switch that becomes the source of the noise is a little. Comparing to the conventional switching-type power supply, this power supply is switched only twice for the pattern formation. Thus, the ripple due to the switching can be expected to be much lower. The 1/16 scale model was manufactured and the characteristics was evaluated. This paper summarizes the design parameter and the experimental result of the new power supply.

Paper

Title

Other Keywords

Page

TUOAC02

Development of HTS Magnets

dipole, resonance, synchrotron, neutron

1095

K. Hatanaka, M. Fukuda, N. Hamatani, N. Izumi, K. Kamakura, T. Saito, H. Ueda, Y. Yasuda, T. Yorita
RCNP, Osaka, Japan
T. Kawaguchi
KT Science Ltd., Akashi, Japan

A quarter of a century has passed since the discovery of high-temperature superconductor (HTS) materials in 1986. Although many prototype devices using HTS wires have been developed, these applications are presently rather limited in accelerator and beam line facilities. We have investigated the performance of HTS wires applied for magnets excited by alternating current (AC) as well as direct current (DC) for a decade. In order to check feasibilities of pulse magnets using HTS wire, we have fabricated a super-ferric dipole magnet to be operated by lumping currents. Upper and lower coil consists of 3 double pancakes of 200 turns. Critical currents were measured of wire measured at 77K. Self-field Ic of wire was higher than 160A. Ic values of double pancakes were 60-70A. After stacking, they were 47A and 51A for the upper and lower coil, respectively. Cooling tests were successfully done and the Ic values were measured to be 280A at 20K. Performance tests are ongoing in the pulse mode operation.

Slides TUOAC02 [5.252 MB]

WEEPPB011

Analysis of High Field Non-Linear Losses on SRF Surfaces Due to Specific Topographic Roughness

simulation, niobium, SRF, feedback

2188

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

Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The high-field performance of SRF cavities will eventually be limited by the realization of fundamental material limits, whether it be Hc1 or Hsh, or some derivative thereof, at which the superconductivity is lost. Before reaching this fundamental field limit at the macro level, it must be encountered at localized, perhaps microscopic, sites of field enhancement due to local topography. If such sites are small enough, they may produce thermally stabilized normal-conducting regions which contribute non-linear losses when viewed from the macro resonant field perspective, and thus produce degradation in Q0. We have undertaken a calculation of local surface magnetic field enhancement from specific fine topographic structure by conformal mapping method and numerically. A solution of the resulting normal conducting volume has been derived and the corresponding RF ohmic loss simulated.

WEEPPB015

Temperature Dependence of the Superheating Field: DC and RF Critical Fields

cavity, niobium, electron, SRF

2197

N.R.A. Valles, M. Liepe
CLASSE, Ithaca, New York, USA

The superheating field is a metastable state at which the Meissner state persists at fields higher than would be predicted from steady-state energy considerations. Previous work demonstrated that a phenomenological approach based on the RF superheating field scaling near the critical temperature is also consistent with low temperature results. This work expands upon the RF results by measuring the DC superheating field, and comparing it to RF results and theoretical predictions.

WEPPC007

Image Processing for Characterization of Surfaces of Superconducting RF Cavities

cavity, LabView, linear-collider, collider

2218

M. Wenskat, S. Aderhold, E. Elsen, S. Karstensen, F. Schlander, L. Steder
DESY, Hamburg, Germany

Funding: ILC HiGrade
Optical inspection of finished Nb superconducting RF cavities has worldwide been established as an important tool for identification of field limiting surface features. Single defects in a single cell of a 9-cell cavity may severely constrain the maximum gradient while the micro-structure in the vicinity of a welding seam could affect the quench behavior. DESY has automated the imaging of critical cavity surface areas, in particular those of high magnetic field. With resolution of ~10 μm2 the information volume is large and the systematic examination becomes a necessity. The development of image processing algorithms has been started with two goals: automatic characterization of cavity surface properties and defect detection. The former results aid the quality assessment of cavities after manufacture; the latter serves to push the gradient performance. The status and prospects of the image processing for the European XFEL and ILC will be presented.

WEPPC065

Cleanroom Techniques to Improve Surface Cleanliness and Repeatability for SRF Coldmass Production

SRF, cavity, vacuum, controls

2357

L. Popielarski, L.J. Dubbs, K. Elliott, I.M. Malloch, R. Oweiss, J. Popielarski
FRIB, East Lansing, Michigan, USA

Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University.
The Facility for Rare Isotope Beams (FRIB) and ReA linear accelerator projects at Michigan State University (MSU) utilize Superconducting Radio-Frequency (SRF) cavities for their accelerating structures. The structures are cleaned and assembled in a cleanroom to reduce particle contamination. The project requires more than 350 SRF cavities. In preparation for production we want to maximize repeatable processes and reduce work time. The cleanroom assembly group at MSU investigates process techniques performed in the cleanroom. Various diagnostic tools; such as liquid particle counter, surface particle counter and airborne particle counter are used to quantify environments and optimize processes. We desire to define procedure specifications for cleaner processes and repeatability. We investigate effective part cleaning and storage, high pressure rinse and ultra pure water quality, and critical component rinsing. We study vacuum assembly, pump down and purge effects. The experiments are independent of cavity results with a focus to create cleanest surface and environment in the most effective manner. In this paper, we describe experiments, summarize the results and conclusions.

WEPPC069

Construction, Evaluation, and Application of a Temperature Map for Multi-cell SRF Cavities

cavity, SRF, controls, vacuum

2369

G.M. Ge, F. Furuta, D.L. Hartill, K.M.V. Ho, G.H. Hoffstaetter, E.N. Smith
CLASSE, Ithaca, New York, USA

Temperature mapping (T-mapping) system is able to locate hot-spot of SRF cavity, thus it is a very powerful tool for cavity’s Q-value research. Recently Cornell University is developing a T-mapping system for multi-cell SRF cavities. The system includes more than two thousands Allen-Bradley resistors. Electronic of the system uses multiplexing of sensors which is able to dramatically reduce wire numbers, and allow the whole system is feasible for multi-cell cavity application. A new cavity testing insert which is for T-mapping system has been constructed.

WEPPC071

Quench Studies of a Superconducting RF Cavity

cavity, superconducting-RF, resonance, superconducting-cavity

2375

D. Gonnella, M. Liepe, S. Posen
CLASSE, Ithaca, New York, USA

In tests of superconducting RF cavities, it is important to understand the cause of high field quenches. Quenches at high field above 25 MV/m are a limiting factor in the performance of high accelerating field cavities but their causes are currently not well understood. An ILC shaped single cell cavity with quench field near 40 MV/m was tested with temperature mapping to determine the cause of its hard quench. Prior to quench, heating on the order of 25 mK was concentrated in two hot spots. After a quench, these two hot spots remain and a new one appears with much higher heating (about 40 mK). The quench location was found by the temperature mapping system to be centered at the new hot spot, not at the two hot spot locations before that dominated quench. By studying the quench location and heating on the surface of the cavity, some hints were gained as to the cause of this quench.

WEPPC094

Optimizing Centrifugal Barrel Polishing for Mirror Finish SRFCavity and Rf Tests at Jefferson Lab

cavity, SRF, radio-frequency, controls

2435

A.D. Palczewski, R.L. Geng, H. Tian
JLAB, Newport News, Virginia, USA

Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We performed Centrifugal Barrel Polishing (CBP) on a 1.3GHz fine grain ILC SRF cavity following a modified version of the recipe* originally developed at Fermilab (FNAL)**. We were able to obtain a mirror like surface similar to that obtained at FNAL, while reducing the number of CBP steps. This paper will discuss the change in surface and subsequent cavity performance before CBP on a raw cavity and post CBP, after a 800C bake (no pre-bake chemistry) and minimal controlled electro-polishing (below 10 micron). In addition to Q vs. Eacc thermometry maps with preheating characteristics and optical inspection of the cavity before and after CBP will also be shown.
* A. D. Palczewski et al., Proc. of SRF2011, THPO071 (2011).
** C.A. Cooper et al., FERMILAB-PUB-11-032-TD, (May 31, 2011).

WEPPR037

First-Principle Approach for Optimization of Cavity Shape for High Gradient and Low Loss

cavity, wakefield, multipactoring, superconducting-cavity

3015

V.D. Shemelin, G.H. Hoffstaetter
CLASSE, Ithaca, New York, USA

Funding: Supported by NSF award DMR-0807731.
Minimization of surface fields for a given accelerating rate is the subject of cavity optimization because high electric and magnetic fields lead to field emission or thermal breakdown, respectively. The ratio between peak electric and magnetic fields is a function of geometry and the desired ratio depends on application. For each application the optimal geometry may be different. The elliptic shape of the cavity have been found evolutionarily: starting from a pill-box with beam-pipes having rounded corners. No attempts up to now are known for a search of non-elliptical optimal shapes. Here we describe the search for a cavity shape that has the lowest surface fields, not restricting to the conventional elliptical cavity shapes.

THPPC093

SRF Cavity Surface Topography Characterization Using Replica Techniques

cavity, SRF, niobium, radio-frequency

3497

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

Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
To better understand the roll of topography on SRF cavity performance, we seek to obtain detailed topographic information from the curved practical cavity surfaces. Replicas taken from a cavity interior surface provide internal surface molds for fine Atomic Force Microscopy (AFM) and stylus profilometry. In this study, we confirm the replica resolution both on surface local defects such as grain boundary and etching pits and compare the surface uniform roughness with the aid of Power Spectral Density (PSD) where we can statistically obtain roughness parameters at different scales. A series of sampling locations are at the same magnetic field chosen at the same latitude on a single cell cavity to confirm the uniformity. Another series of sampling locations at different magnetic field amplitudes are chosen for this replica on the same cavity for later power loss calculation. We also show that application of the replica followed by rinsing does not adversely affect the cavity performance.

THPPD051

New Power Supply of the Injection Bump Magnet for Upgrading the Injection Energy in the J-PARC 3-GeV RCS

power-supply, injection, linac, proton

3626

T. Takayanagi, N. Hayashi, M. Kinsho, N. Tani, T. Togashi, T. Ueno
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan

With the energy upgrading of LINAC (Linear accelerator) to 400 MeV in the J-PARC (Japan Proton Accelerator Research Complex), a new power supply of the injection bump magnet has been designed for the 3-GeV RCS (Rapid Cycling Synchrotron). The new power supply is composed with the capacitor bank which has function to form the output current pattern. This power supply is a commutation strategy using the electrical charge and discharge of the capacitor, and the frequency of the switch that becomes the source of the noise is a little. Comparing to the conventional switching-type power supply, this power supply is switched only twice for the pattern formation. Thus, the ripple due to the switching can be expected to be much lower. The 1/16 scale model was manufactured and the characteristics was evaluated. This paper summarizes the design parameter and the experimental result of the new power supply.