SRF2015 - List of Keywords (plasma)

Paper	Title	Other Keywords	Page
MOPB003	Superconducting Cavity for the Measurements of Frequency, Temperature, RF Field Dependence of the Surface Resistance	cavity, coupling, cryogenics, experiment	70
	H. Park, S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA H. Park JLab, Newport News, Virginia, USA
	In order to better understand the contributions of the various physical processes to the surface resistance of superconductors the ODU Center for Accelerator Science is developing a half-wave resonator capable of operating between 325 MHz and 1.3 GHz. This will allow the measurement of the temperature and rf field dependence of the surface resistance on the same surface over the range of frequency of interest for particle accelerators and identify the various sources of power dissipation.
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MOPB085	Efforts of the Improvement of Cavity Q-Value by Plasma Cleaning Technology: Plan and Results From Cornell University	cavity, experiment, SRF, ECR	333
	G.M. Ge, F. Furuta, G.H. Hoffstaetter, M. Liepe, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	We reported the plasma works at Cornell University. The plasma has been generated for 1) surface cleaning to reduce field emission; 2) the cavity quality factor improvement. The experiment design, including RF design, the gas type and pressure selection, the external DC magnetic field calculation, had been discussed. The plasma experiment set-up by using a 1.3GHz single-cell cavity is shown. Argon and helium plasma was successfully ignited in the cavity; the results of the plasma processing will be displayed.
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MOPB115	Surface Studies of Plasma Processed Nb Samples	cavity, vacuum, SRF, ion	438
	P.V. Tyagi, R. Afanador, B. DeGraff, M. Doleans, B.S. Hannah, M.P. Howell, S.-H. Kim, J.D. Mammosser, C.J. McMahan, J. Saunders, S.E. Stewart ORNL, Oak Ridge, Tennessee, USA
	Funding: This work is supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. Contaminants present at top surface of superconducting radio frequency (SRF) cavities can act as field emitters and restrict the cavity accelerating gradient. A room temperature in-situ plasma processing technology for SRF cavities aiming to clean hydrocarbons from inner surface of cavities has been recently developed at the Spallation Neutron Source (SNS). Surface studies of the plasma processed Nb samples by Secondary ion mass spectrometry (SIMS) and Scanning Kelvin Probe (SKP) showed that the NeO2 plasma processing is very effective to remove carbonaceous contaminants from top surface and improves the surface work function by 0.5 to 1.0 eV. M. Doleans et al., Proc. 2013 SRF, Paris, France. P. V. Tyagi, et al., Proc. Linac14, Geneva, Switzerland. **M. Doleans et al., These proceedings.
	Poster MOPB115 [0.524 MB]
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TUPB027	Developments on SRF Coatings at CERN	cavity, SRF, simulation, cathode	617
	A. Sublet, S. Aull, B. Bártová, S. Calatroni, T. Richard, G.J. Rosaz, M. Taborelli, M. Therasse, W. Venturini Delsolaro, P. Zhang CERN, Geneva, Switzerland
	The thin films techniques applied to Superconducting RF (SRF) has a long history at CERN. A large panel of cavities have been coated from LEP, to LHC. For the current and future projects (HIE-ISOLDE, HL-LHC, FCC) there is a need for further higher RF-performances with focus on minimizing residual resistance Rres and maximizing quality factor Q0 of the cavities. This paper will present CERN’s developments on thin films to achieve these goals through the following main axes of research: The first one concerns the application of different coating techniques for Nb (DC-bias diode sputtering, magnetron sputtering and HiPIMS). Another approach is the investigation of alternative materials like Nb3Sn. These lines of development will be supported by a material science approach to characterize and evaluate the layer properties by means of FIB-SEM, TEM, XPS, XRD, etc. In addition a numerical tool for plasma simulation will be exploited to develop adapted coating systems and optimize the coating process, from plasma generation to thin film growth.
	Poster TUPB027 [1.070 MB]
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TUPB029	Material Quality & SRF Performance of Nb Films Grown on Cu via ECR Plasma Energetic Condensation	ECR, SRF, ion, interface	622
	A-M. Valente-Feliciano, G.V. Eremeev, C.E. Reece, J.K. Spradlin JLab, Newport News, Virginia, USA S. Aull CERN, Geneva, Switzerland Th. Proslier ANL, Argonne, Illinois, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The RF performance of bulk Nb cavities has continuously improved over the years and is approaching the intrinsic limit of the material. Although some margin seems still available with processes such as N surface doping, long term solutions for SRF surfaces efficiency enhancement need to be pursued. Over the years, Nb/Cu technology, despite its shortcomings, has positioned itself as an alternative route for the future of superconducting structures used in accelerators. Significant progress has been made in recent years in the development of energetic deposition techniques such as Electron Cyclotron Resonance (ECR) plasma deposition. Nb films with very high material quality have then been produced by varying the deposition energy alluding to the promise of performing SRF films. This paper presents RF measurements, correlated with surface and material properties, for Nb films showing how, by varying the film growth conditions, the Nb film quality and surface resistance can be altered and how the Q-slope can be eventually overcome.
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TUPB032	Energetic Condensation Growth of Nb on Cu SRF Cavities	cavity, cathode, niobium, SRF	629
	K.M. Velas, S.F. Chapman, I. Irfan, M. Krishnan AASC, San Leandro, California, USA
	Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0011371 Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma from the cathode consists exclusively of 60-120eV Nb ions (Nb+ and Nb2+) that penetrate a few monolayers into the substrate and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film. AASC is coating 1.3 GHz SRF cavities using a graded anode to ensure uniform film thickness in the beam tube and elliptical regions. Copper cavities are centrifugal barrel polished and electropolished (done for us by the Fermilab Technical Division, Superconducting RF Development Department and by Thomas Jefferson National Accelerator Facility (JLAB)) before coating, to ensure good adhesion and improved film quality. The Nb coated copper cavities will undergo RF tests at JLAB and at Fermilab to measure Qo vs. E.
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TUPB034	Bulk Niobium Polishing and Electropolishing Steps for Thinfilm Coated Copper SRF Cavities	cavity, SRF, ion, cathode	633
	M. Krishnan, S.F. Chapman, I. Irfan, K.M. Velas AASC, San Leandro, California, USA J.K. Spradlin, H. Tian JLab, Newport News, Virginia, USA
	Funding: Research supported at AASC by the US DOE via SBIR grant: DE-SC0011371. The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma consists of 60-120eV Nb ions (Nb+ and Nb++) [1] that penetrate a few monolayers into the substrate [2] and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film [3]. One limitation of CED thinfilms is the presence of Nb macroparticles (~0.1-10 microns) that could be deleterious to high field performance of the SRF cavity. One way to remove such macroparticles [4] is to grow a thick film (~3-5 microns), followed by mechanical polishing (MP) using the finest media as might be applied in Centrifugal Barrel Polishing (CBP) to achieve a 0.4 micron surface figure, and an electropolishing (EP) step to remove ~1 micron of Nb that also removes all traces of embedded media in the film. The residual 2-4 micron Nb film should more nearly resemble the surface of a bulk Nb cavity that has been subjected to the same steps. This paper describes experiments conducted on Cu coupons as a prelude to an SRF Cu cavity coating.
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TUPB038	Superconducting Coatings Synthetized by CVD/PECVD for SRF Cavities	niobium, SRF, superconductivity, accelerating-gradient	643
	P. Pizzol, P. Chalker, T. Heil The University of Liverpool, Liverpool, United Kingdom A.N. Hannah, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G.B.G. Stenning STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	Finding a way to overcome the acceleration gradient limits that bulk niobium cavities can provide is a major challenge, fundamental to allow the accelerator science field to progress. In order to overcome the accelerating gradient limits of bulk niobium and reduce manufacturing and operation costs, the idea of using thin layers of niobium deposited on a copper cavity is being explored. This approach has lower material cost with higher availability and more importantly higher thermal conductivity. Physical vapour deposition (PVD) method is currently the preferred method to coat superconducting cavities, but its lack of conformity renders complicated shapes such as crab cavities very difficult to coat. By using chemical vapour deposition (CVD) and plasma enhanced chemical vapour deposition (PECVD) it is possible to deposit thin Nb layers uniformly with density very close to bulk material. This project explores the use of PECVD / CVD techniques to deposit metallic niobium on copper using NbCl5 as precursor and hydrogen as a coreagent. The samples obtained were then characterized via SEM, XRD, and EDX as well as assessing their superconductivity characteristics (RRR and Tc)
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THPB083	Energetic Copper Coating on Stainless Steel Power Couplers for SRF Application	SRF, cathode, laser, ion	1330
	I. Irfan, S.F. Chapman, M. Krishnan, K.M. Velas AASC, San Leandro, California, USA W. Kaabi LAL, Orsay, France
	Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0009581 Delivering RF power from the outside (at room temperature) to the inside of SRF cavities (at ~4 K temperature), requires a power coupler to be thermally isolating, while still electrically conducting on the inside. Stainless steel parts that are coated on the insides with a few skin depths of copper can meet these conflicting requirements. The challenge has been the adhesion strength of copper coating on stainless steel coupler parts when using electroplating methods. These methods also require a nickel flash layer that is magnetic and can therefore pose problems. Alameda Applied Sciences Corporation (AASC) uses Coaxial Energetic Deposition (CED) from a cathodic arc plasma to grow copper films directly on stainless steel coupler parts with no Ni layer and no electrochemistry. The vacuum arc plasma consists of ~100 eV Cu ions that penetrate a few monolayers into the stainless steel substrate to promote growth of highly adhesive films with crystalline structure. Adhesion strength and coating quality of copper coatings on complex stainless steel tubes, bellows, mock coupler parts and an actual Tesla Test Facility (TTF) type coupler part, are discussed. * Adhesion and Cu quality testing were done for us by the Fermilab Technical Division, Superconducting RF Development Department
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THPB100	Nb Coatings on Bellows Used in SRF Accelerators	SRF, cavity, ion, impedance	1379
	S.F. Chapman, I. Irfan, M. Krishnan, K.M. Velas AASC, San Leandro, California, USA
	Funding: This research is supported by the US DOE via SBIR grant: DE-SC0007678 Alameda Applied Sciences Corporation (AASC) is developing bellows with the strength and flexibility of stainless steel and the low surface impedance of a superconductor. Such unique bellows would enable alignment of SRF cavity sections with greatly reduced RF losses. To that end, we grow Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. Films of Nb were grown on stainless steel bellows, with and without an intermediate layer of Cu deposited via the same technique, to produce a working bellows with a well adhered superconducting inner layer. The Nb coated bellows have undergone tests conducted by our collaborators to evaluate their RF performance.
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Paper

Title

Other Keywords

Page

MOPB003

Superconducting Cavity for the Measurements of Frequency, Temperature, RF Field Dependence of the Surface Resistance

cavity, coupling, cryogenics, experiment

70

H. Park, S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA
H. Park
JLab, Newport News, Virginia, USA

In order to better understand the contributions of the various physical processes to the surface resistance of superconductors the ODU Center for Accelerator Science is developing a half-wave resonator capable of operating between 325 MHz and 1.3 GHz. This will allow the measurement of the temperature and rf field dependence of the surface resistance on the same surface over the range of frequency of interest for particle accelerators and identify the various sources of power dissipation.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB085

Efforts of the Improvement of Cavity Q-Value by Plasma Cleaning Technology: Plan and Results From Cornell University

cavity, experiment, SRF, ECR

333

G.M. Ge, F. Furuta, G.H. Hoffstaetter, M. Liepe, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

We reported the plasma works at Cornell University. The plasma has been generated for 1) surface cleaning to reduce field emission; 2) the cavity quality factor improvement. The experiment design, including RF design, the gas type and pressure selection, the external DC magnetic field calculation, had been discussed. The plasma experiment set-up by using a 1.3GHz single-cell cavity is shown. Argon and helium plasma was successfully ignited in the cavity; the results of the plasma processing will be displayed.

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MOPB115

Surface Studies of Plasma Processed Nb Samples

cavity, vacuum, SRF, ion

438

P.V. Tyagi, R. Afanador, B. DeGraff, M. Doleans, B.S. Hannah, M.P. Howell, S.-H. Kim, J.D. Mammosser, C.J. McMahan, J. Saunders, S.E. Stewart
ORNL, Oak Ridge, Tennessee, USA

Funding: This work is supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
Contaminants present at top surface of superconducting radio frequency (SRF) cavities can act as field emitters and restrict the cavity accelerating gradient. A room temperature in-situ plasma processing technology for SRF cavities aiming to clean hydrocarbons from inner surface of cavities has been recently developed at the Spallation Neutron Source (SNS). Surface studies of the plasma processed Nb samples by Secondary ion mass spectrometry (SIMS) and Scanning Kelvin Probe (SKP) showed that the NeO2 plasma processing is very effective to remove carbonaceous contaminants from top surface and improves the surface work function by 0.5 to 1.0 eV.
*M. Doleans et al., Proc. 2013 SRF, Paris, France.
**P. V. Tyagi, et al., Proc. Linac14, Geneva, Switzerland.
***M. Doleans et al., These proceedings.

Poster MOPB115 [0.524 MB]

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TUPB027

Developments on SRF Coatings at CERN

cavity, SRF, simulation, cathode

617

A. Sublet, S. Aull, B. Bártová, S. Calatroni, T. Richard, G.J. Rosaz, M. Taborelli, M. Therasse, W. Venturini Delsolaro, P. Zhang
CERN, Geneva, Switzerland

The thin films techniques applied to Superconducting RF (SRF) has a long history at CERN. A large panel of cavities have been coated from LEP, to LHC. For the current and future projects (HIE-ISOLDE, HL-LHC, FCC) there is a need for further higher RF-performances with focus on minimizing residual resistance Rres and maximizing quality factor Q0 of the cavities. This paper will present CERN’s developments on thin films to achieve these goals through the following main axes of research: The first one concerns the application of different coating techniques for Nb (DC-bias diode sputtering, magnetron sputtering and HiPIMS). Another approach is the investigation of alternative materials like Nb3Sn. These lines of development will be supported by a material science approach to characterize and evaluate the layer properties by means of FIB-SEM, TEM, XPS, XRD, etc. In addition a numerical tool for plasma simulation will be exploited to develop adapted coating systems and optimize the coating process, from plasma generation to thin film growth.

Poster TUPB027 [1.070 MB]

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TUPB029

Material Quality & SRF Performance of Nb Films Grown on Cu via ECR Plasma Energetic Condensation

ECR, SRF, ion, interface

622

A-M. Valente-Feliciano, G.V. Eremeev, C.E. Reece, J.K. Spradlin
JLab, Newport News, Virginia, USA
S. Aull
CERN, Geneva, Switzerland
Th. Proslier
ANL, Argonne, Illinois, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The RF performance of bulk Nb cavities has continuously improved over the years and is approaching the intrinsic limit of the material. Although some margin seems still available with processes such as N surface doping, long term solutions for SRF surfaces efficiency enhancement need to be pursued. Over the years, Nb/Cu technology, despite its shortcomings, has positioned itself as an alternative route for the future of superconducting structures used in accelerators. Significant progress has been made in recent years in the development of energetic deposition techniques such as Electron Cyclotron Resonance (ECR) plasma deposition. Nb films with very high material quality have then been produced by varying the deposition energy alluding to the promise of performing SRF films. This paper presents RF measurements, correlated with surface and material properties, for Nb films showing how, by varying the film growth conditions, the Nb film quality and surface resistance can be altered and how the Q-slope can be eventually overcome.

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TUPB032

Energetic Condensation Growth of Nb on Cu SRF Cavities

cavity, cathode, niobium, SRF

629

K.M. Velas, S.F. Chapman, I. Irfan, M. Krishnan
AASC, San Leandro, California, USA

Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0011371
Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma from the cathode consists exclusively of 60-120eV Nb ions (Nb+ and Nb2+) that penetrate a few monolayers into the substrate and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film. AASC is coating 1.3 GHz SRF cavities using a graded anode to ensure uniform film thickness in the beam tube and elliptical regions. Copper cavities are centrifugal barrel polished and electropolished (done for us by the Fermilab Technical Division, Superconducting RF Development Department and by Thomas Jefferson National Accelerator Facility (JLAB)) before coating, to ensure good adhesion and improved film quality. The Nb coated copper cavities will undergo RF tests at JLAB and at Fermilab to measure Qo vs. E.

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TUPB034

Bulk Niobium Polishing and Electropolishing Steps for Thinfilm Coated Copper SRF Cavities

cavity, SRF, ion, cathode

633

M. Krishnan, S.F. Chapman, I. Irfan, K.M. Velas
AASC, San Leandro, California, USA
J.K. Spradlin, H. Tian
JLab, Newport News, Virginia, USA

Funding: Research supported at AASC by the US DOE via SBIR grant: DE-SC0011371. The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma consists of 60-120eV Nb ions (Nb+ and Nb++) [1] that penetrate a few monolayers into the substrate [2] and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film [3]. One limitation of CED thinfilms is the presence of Nb macroparticles (~0.1-10 microns) that could be deleterious to high field performance of the SRF cavity. One way to remove such macroparticles [4] is to grow a thick film (~3-5 microns), followed by mechanical polishing (MP) using the finest media as might be applied in Centrifugal Barrel Polishing (CBP) to achieve a 0.4 micron surface figure, and an electropolishing (EP) step to remove ~1 micron of Nb that also removes all traces of embedded media in the film. The residual 2-4 micron Nb film should more nearly resemble the surface of a bulk Nb cavity that has been subjected to the same steps. This paper describes experiments conducted on Cu coupons as a prelude to an SRF Cu cavity coating.

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TUPB038

Superconducting Coatings Synthetized by CVD/PECVD for SRF Cavities

niobium, SRF, superconductivity, accelerating-gradient

643

P. Pizzol, P. Chalker, T. Heil
The University of Liverpool, Liverpool, United Kingdom
A.N. Hannah, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G.B.G. Stenning
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

Finding a way to overcome the acceleration gradient limits that bulk niobium cavities can provide is a major challenge, fundamental to allow the accelerator science field to progress. In order to overcome the accelerating gradient limits of bulk niobium and reduce manufacturing and operation costs, the idea of using thin layers of niobium deposited on a copper cavity is being explored. This approach has lower material cost with higher availability and more importantly higher thermal conductivity. Physical vapour deposition (PVD) method is currently the preferred method to coat superconducting cavities, but its lack of conformity renders complicated shapes such as crab cavities very difficult to coat. By using chemical vapour deposition (CVD) and plasma enhanced chemical vapour deposition (PECVD) it is possible to deposit thin Nb layers uniformly with density very close to bulk material. This project explores the use of PECVD / CVD techniques to deposit metallic niobium on copper using NbCl5 as precursor and hydrogen as a coreagent. The samples obtained were then characterized via SEM, XRD, and EDX as well as assessing their superconductivity characteristics (RRR and Tc)

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THPB083

Energetic Copper Coating on Stainless Steel Power Couplers for SRF Application

SRF, cathode, laser, ion

1330

I. Irfan, S.F. Chapman, M. Krishnan, K.M. Velas
AASC, San Leandro, California, USA
W. Kaabi
LAL, Orsay, France

Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0009581
Delivering RF power from the outside (at room temperature) to the inside of SRF cavities (at ~4 K temperature), requires a power coupler to be thermally isolating, while still electrically conducting on the inside. Stainless steel parts that are coated on the insides with a few skin depths of copper can meet these conflicting requirements. The challenge has been the adhesion strength of copper coating on stainless steel coupler parts when using electroplating methods. These methods also require a nickel flash layer that is magnetic and can therefore pose problems. Alameda Applied Sciences Corporation (AASC) uses Coaxial Energetic Deposition (CED) from a cathodic arc plasma to grow copper films directly on stainless steel coupler parts with no Ni layer and no electrochemistry. The vacuum arc plasma consists of ~100 eV Cu ions that penetrate a few monolayers into the stainless steel substrate to promote growth of highly adhesive films with crystalline structure. Adhesion strength and coating quality of copper coatings on complex stainless steel tubes, bellows, mock coupler parts and an actual Tesla Test Facility (TTF) type coupler part, are discussed.
* Adhesion and Cu quality testing were done for us by the Fermilab Technical Division, Superconducting RF Development Department

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THPB100

Nb Coatings on Bellows Used in SRF Accelerators

SRF, cavity, ion, impedance

1379

S.F. Chapman, I. Irfan, M. Krishnan, K.M. Velas
AASC, San Leandro, California, USA

Funding: This research is supported by the US DOE via SBIR grant: DE-SC0007678
Alameda Applied Sciences Corporation (AASC) is developing bellows with the strength and flexibility of stainless steel and the low surface impedance of a superconductor. Such unique bellows would enable alignment of SRF cavity sections with greatly reduced RF losses. To that end, we grow Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. Films of Nb were grown on stainless steel bellows, with and without an intermediate layer of Cu deposited via the same technique, to produce a working bellows with a well adhered superconducting inner layer. The Nb coated bellows have undergone tests conducted by our collaborators to evaluate their RF performance.

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