SRF2011 - List of Authors (Rimmer, R.A.)

Paper

Title

Page

Some Design Analysis on the Low-Beta Multi-Spoke Cavities

141

F.S. He, K. Zhao
PKU/IHIP, Beijing, People's Republic of China
R.A. Rimmer, H. Wang
JLAB, Newport News, Virginia, USA

The spoke cavities have achieved promising gradients worldwide, which make them good candidates for accelerating low beta proton and ions. Although, there is still a space to further optimize them, especially for multi-spoke cavities. The design and optimization are re-considered based on the total capital and operational efficiencies over a given beta range. An initial result of the 3D EM design optimization by the CST MWS code for a double-spoke, β ~ 0.5 cavity is reported. An equivalent circuit for the double-spoke cavity is also developed.

Poster MOPO029 [0.577 MB]

MOPO070

Preliminary Test Results from 650 MHz Single Cell Medium Beta Cavities for Project X

271

P. Kneisel, A. Burrill, P. Kushnick, F. Marhauser, R.A. Rimmer
JLAB, Newport News, Virginia, USA

Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We have fabricated two single cell 650 MHz cavities of a JLab design [1], for possible project X application. Both cavities were manufactured at Jlab from RRR>250 niobium sheet of 4 mm thickness using standard techniques such as deep drawing, EBW, BCP , hydrogen degassing heat treatment, high pressure ultrapure water rinsing and clean room assembly. A detailed description of the design and fabrication procedures is forthcoming [2]. Initially cavity #1 was – after final surface treatment by bcp – measured without any provisions for stiffening . As expected, the pressure sensitivity and the Lorentz Force detuning coefficients were quite high; however, the RF performance was very encouraging: the cavity exhibited a Q-value > 10¹¹ at 1.6K, corresponding to a residual resistance of < 1.5 nOhm The initial gradient was limited to Eacc ~ 18 MV/m, limited by field emission. In a subsequent test, we are re-rinsing the cavity and are making provisions for stiffening up the cavity. By the time of this writing, this test is in progress; the results will be reported at this conference as well as results from the second cavity.
[1] F. Marhauser, JLab-TN-10-043
[2] F. Marhauser et al; IPAC 2011 to be published

TUPO022

Effects of Cathode Shapes on BEP and EP During Vertical Surface Treatments on Niobium

411

S. Jin, X.Y. Lu, K. Zhao
PKU/IHIP, Beijing, People's Republic of China
R.A. Rimmer, A.T. Wu
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
This paper reports the research results of effects of cathode shapes during buffered and conventional vertical electropolishing treatments for single cell superconducting radio frequency (SRF) niobium cavities. Several different cathodes shapes such as, for instance, bar, ball, ellipsoid, wheel, etc. were employed. Detailed electropolishing parameters at different locations inside a single cell SRF cavity were measured using a unique JLab home-made demountable cavity, including I-V characteristic, removal rate, surface roughness, polishing uniformity and so on. It was demonstrated that optimal polishing results could be achieved by changing the cathode shape for both BEP and EP. Implications on the electropolishing mechanism of Nb cavities for both BEP and EP based on the obtained experimental results are discussed.

TUPO031

Update on the R&D of Vertical Buffered Electropolishing on Nb Samples and SRF Single Cell Cavities

442

A.T. Wu, J.D. Mammosser, R.A. Rimmer
JLAB, Newport News, Virginia, USA
S. Jin, L. Lin, X.Y. Lu, K. Zhao
PKU/IHIP, Beijing, People's Republic of China

Electropolishing (EP) has become a popular choice as the final step of the surface removal process during the fabrication of Nb superconducting radio frequency (SRF) cavities. One of the major reasons for the choice is that Nb SRF cavities treated by EP tend to have a better chance to reach an accelerating gradient of 30MV/m or higher. This advantage of EP over BCP can at least be partially attributed to the smoother Nb surfaces that EP can produce. Recently a Nb surface removal technique called buffered electropolishing (BEP) was developed at JLab, which could produce the smoothest surface finish. In this contribution, R&D efforts of vertical BEP on Nb small samples and SRF single cell cavities since the last SRF conference in 2009 will be updated. It is shown that under a suitable condition, BEP can have a Nb removal rate as high as 10 μm/mim that is more than 25 and 5 times quicker than those of EP and BCP(112) respectively. Possible mechanisms responsible for the high Nb removal rate are proposed. Clues on the optimization of vertical BEP and EP treatments on Nb SRF cavities from recent experimental results obtained on a Nb single cell demountable cavity will be discussed.
Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

TUPO033

Study of I-V Characteristics at Different Locations Inside a Demountable Nb SRF Cavity During Vertical BEP and EP Treatments

450

S. Jin, X.Y. Lu, K. Zhao
PKU/IHIP, Beijing, People's Republic of China
R.A. Rimmer, A.T. Wu
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
For a normal superconducting radio frequency (SRF) cavity, it is hard to obtain detailed information of an electropolishing process. So, a demountable cavity was firstly made by JLab to resolve this problem. This paper reports the measurements of I-V characteristics at three different locations inside the demountable cavity during buffered electropolishing (BEP) and electropolishing (EP) treatments. The polishing plateau appeared earlier on the surface areas close to iris and later on those near equator. To find the reason for this phenomenon, the electric field distribution in the cavity was considered and simulated by means of Poisson Superfish. Correlations were found between the measured I-V characteristics and the simulated results. This implies that electric field distribution inside a SRF cavity had an important effect on the polishing processes during vertical BEP and EP.

TUPO038

Superconducting RF Cavity Development With UK Industry

464

A.E. Wheelhouse, R. Bate, R.K. Buckley, P. Goudket, A.R. Goulden, P.A. McIntosh, J.F. Orrett
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.R. Everard, N. Shakespeare
Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom
P. Kneisel, S. Manning, R.A. Rimmer
JLAB, Newport News, Virginia, USA

As part of a STFC Industrial Programme Support Scheme (PIPSS) grant Daresbury Laboratory and Shakespeare Engineering Ltd have fabricated, processed and tested a single cell 1.3 GHz superconducting RF cavity, in collaboration with Jefferson Laboratory. The overall aim of the project through a knowledge exchange programme was to develop the capability of UK industry to fabricate and process a single cell niobium superconducting cavity, as part of a long term strategy to enable UK industry to address the large potential market for superconducting RF structures. As a means of measuring the performance of the fabrication and processing an objective of the programme of work was to achieve an accelerating gradient of greater than 15 MV/m at an unloaded quality factor of 1.0 x 10¹⁰ or better. Three cavities were fabricated by Shakespeare Engineering, and electron beam welded at Jefferson Laboratory in the USA. Processing and testing of the cavities was then performed both at Jefferson Laboratory and at Daresbury Laboratory. The fabrication and process methods are discussed in this paper along with the results obtained from the testing performed in the vertical test facilities.

Poster TUPO038 [0.196 MB]

Paper	Title	Page
MOPO029	Some Design Analysis on the Low-Beta Multi-Spoke Cavities	141
	F.S. He, K. Zhao PKU/IHIP, Beijing, People's Republic of China R.A. Rimmer, H. Wang JLAB, Newport News, Virginia, USA
	The spoke cavities have achieved promising gradients worldwide, which make them good candidates for accelerating low beta proton and ions. Although, there is still a space to further optimize them, especially for multi-spoke cavities. The design and optimization are re-considered based on the total capital and operational efficiencies over a given beta range. An initial result of the 3D EM design optimization by the CST MWS code for a double-spoke, β ~ 0.5 cavity is reported. An equivalent circuit for the double-spoke cavity is also developed.
	Poster MOPO029 [0.577 MB]

MOPO070	Preliminary Test Results from 650 MHz Single Cell Medium Beta Cavities for Project X	271
	P. Kneisel, A. Burrill, P. Kushnick, F. Marhauser, R.A. Rimmer JLAB, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We have fabricated two single cell 650 MHz cavities of a JLab design [1], for possible project X application. Both cavities were manufactured at Jlab from RRR>250 niobium sheet of 4 mm thickness using standard techniques such as deep drawing, EBW, BCP , hydrogen degassing heat treatment, high pressure ultrapure water rinsing and clean room assembly. A detailed description of the design and fabrication procedures is forthcoming [2]. Initially cavity #1 was – after final surface treatment by bcp – measured without any provisions for stiffening . As expected, the pressure sensitivity and the Lorentz Force detuning coefficients were quite high; however, the RF performance was very encouraging: the cavity exhibited a Q-value > 10¹¹ at 1.6K, corresponding to a residual resistance of < 1.5 nOhm The initial gradient was limited to Eacc ~ 18 MV/m, limited by field emission. In a subsequent test, we are re-rinsing the cavity and are making provisions for stiffening up the cavity. By the time of this writing, this test is in progress; the results will be reported at this conference as well as results from the second cavity. [1] F. Marhauser, JLab-TN-10-043 [2] F. Marhauser et al; IPAC 2011 to be published

TUPO022	Effects of Cathode Shapes on BEP and EP During Vertical Surface Treatments on Niobium	411
	S. Jin, X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China R.A. Rimmer, A.T. Wu JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. This paper reports the research results of effects of cathode shapes during buffered and conventional vertical electropolishing treatments for single cell superconducting radio frequency (SRF) niobium cavities. Several different cathodes shapes such as, for instance, bar, ball, ellipsoid, wheel, etc. were employed. Detailed electropolishing parameters at different locations inside a single cell SRF cavity were measured using a unique JLab home-made demountable cavity, including I-V characteristic, removal rate, surface roughness, polishing uniformity and so on. It was demonstrated that optimal polishing results could be achieved by changing the cathode shape for both BEP and EP. Implications on the electropolishing mechanism of Nb cavities for both BEP and EP based on the obtained experimental results are discussed.

TUPO031	Update on the R&D of Vertical Buffered Electropolishing on Nb Samples and SRF Single Cell Cavities	442
	A.T. Wu, J.D. Mammosser, R.A. Rimmer JLAB, Newport News, Virginia, USA S. Jin, L. Lin, X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China
	Electropolishing (EP) has become a popular choice as the final step of the surface removal process during the fabrication of Nb superconducting radio frequency (SRF) cavities. One of the major reasons for the choice is that Nb SRF cavities treated by EP tend to have a better chance to reach an accelerating gradient of 30MV/m or higher. This advantage of EP over BCP can at least be partially attributed to the smoother Nb surfaces that EP can produce. Recently a Nb surface removal technique called buffered electropolishing (BEP) was developed at JLab, which could produce the smoothest surface finish. In this contribution, R&D efforts of vertical BEP on Nb small samples and SRF single cell cavities since the last SRF conference in 2009 will be updated. It is shown that under a suitable condition, BEP can have a Nb removal rate as high as 10 μm/mim that is more than 25 and 5 times quicker than those of EP and BCP(112) respectively. Possible mechanisms responsible for the high Nb removal rate are proposed. Clues on the optimization of vertical BEP and EP treatments on Nb SRF cavities from recent experimental results obtained on a Nb single cell demountable cavity will be discussed. Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

TUPO033	Study of I-V Characteristics at Different Locations Inside a Demountable Nb SRF Cavity During Vertical BEP and EP Treatments	450
	S. Jin, X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China R.A. Rimmer, A.T. Wu JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. For a normal superconducting radio frequency (SRF) cavity, it is hard to obtain detailed information of an electropolishing process. So, a demountable cavity was firstly made by JLab to resolve this problem. This paper reports the measurements of I-V characteristics at three different locations inside the demountable cavity during buffered electropolishing (BEP) and electropolishing (EP) treatments. The polishing plateau appeared earlier on the surface areas close to iris and later on those near equator. To find the reason for this phenomenon, the electric field distribution in the cavity was considered and simulated by means of Poisson Superfish. Correlations were found between the measured I-V characteristics and the simulated results. This implies that electric field distribution inside a SRF cavity had an important effect on the polishing processes during vertical BEP and EP.

TUPO038	Superconducting RF Cavity Development With UK Industry	464
	A.E. Wheelhouse, R. Bate, R.K. Buckley, P. Goudket, A.R. Goulden, P.A. McIntosh, J.F. Orrett STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J.R. Everard, N. Shakespeare Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom P. Kneisel, S. Manning, R.A. Rimmer JLAB, Newport News, Virginia, USA
	As part of a STFC Industrial Programme Support Scheme (PIPSS) grant Daresbury Laboratory and Shakespeare Engineering Ltd have fabricated, processed and tested a single cell 1.3 GHz superconducting RF cavity, in collaboration with Jefferson Laboratory. The overall aim of the project through a knowledge exchange programme was to develop the capability of UK industry to fabricate and process a single cell niobium superconducting cavity, as part of a long term strategy to enable UK industry to address the large potential market for superconducting RF structures. As a means of measuring the performance of the fabrication and processing an objective of the programme of work was to achieve an accelerating gradient of greater than 15 MV/m at an unloaded quality factor of 1.0 x 10¹⁰ or better. Three cavities were fabricated by Shakespeare Engineering, and electron beam welded at Jefferson Laboratory in the USA. Processing and testing of the cavities was then performed both at Jefferson Laboratory and at Daresbury Laboratory. The fabrication and process methods are discussed in this paper along with the results obtained from the testing performed in the vertical test facilities.
	Poster TUPO038 [0.196 MB]