LINAC2012 - List of Keywords (superconductivity)

Paper	Title	Other Keywords	Page
SUPB001	Analyzing Surface Roughness Dependence of Linear RF Losses	SRF, scattering, niobium, radio-frequency	1
	C. Xu, M.J. Kelley 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. Topographic structure on Superconductivity Radio Frequency (SRF) surfaces can contribute additional cavity RF losses describable in terms of surface RF reflectivity and absorption indices of wave scattering theory. At isotropic homogeneous extent, Power Spectrum Density (PSD) of roughness is introduced and quantifies the random surface topographic structure. PSD obtained from different surface treatments of niobium, such as Buffered Chemical Polishing (BCP), Electropolishing (EP), Nano-Mechanical Polishing (NMP) and Barrel Centrifugal Polishing (CBP) are compared. A perturbation model is utilized to calculate the additional rough surface RF losses based on PSD statistical analysis. This model will not consider that superconductor becomes normal conducting at fields higher than transition field. One can calculate the RF power dissipation ratio between rough surface and ideal smooth surface within this field range from linear loss mechanisms.

SUPB026	Multipacting Analysis of High-velocity Superconducting Spoke Resonators	electron, cavity, site, simulation	68
	C.S. Hopper, J.R. Delayen ODU, Norfolk, Virginia, USA
	Some of the advantages of superconducting spoke cavities are currently being investigated for the high-velocity regime. When determining a final, optimized geometry, one must consider the possible limiting effects multipacting could have on the cavity. We report on the results of analytical calculations and numerical simulations of multipacting electrons in superconducting spoke cavities and methods for reducing their impact.

SUPB029	Impact of Trapped Flux and Systematic Flux Expulsion in Superconducting Niobium	niobium, cavity, SRF, controls	77
	J.M. Vogt, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	The intrinsic quality factor Q₀ of superconducting cavities is known to depend on various factors like niobium material properties, treatment history and magnetic shielding. We already reported an additional impact of temperature gradients during the cool-down on the obtained Q₀. We believe cooling conditions can influence the level of flux trapping and hence the residual resistance. For further studies we have constructed a test stand using niobium rods to study flux trapping. Here we can precisely control the temperature and approach T_c in the superconducting state. Although the sample remains in the superconducting state a change in the amount of trapped flux is visible. The procedure can be applied repeatedly resulting in a significantly lowered level of trapped flux in the sample. Applying a similar procedure to a superconducting cavity could allow for reduction of the magnetic contribution to the surface resistance and result in a significant improvement of Q₀.

SUPB038	Multipole Field Effects for the Superconducting Parallel-Bar Deflecting/Crabbing Cavities	dipole, multipole, cavity, luminosity	92
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA S.U. De Silva JLAB, Newport News, Virginia, USA
	The superconducting parallel-bar deflecting/crabbing cavity is currently being considered as one of the design options in rf separation for the Jefferson Lab 12 GeV upgrade and for the crabbing cavity for the proposed LHC luminosity upgrade. Knowledge of multipole field effects is important for accurate beam dynamics study of rf structures. The multipole components can be accurately determined numerically using the electromagnetic surface field data in the rf structure. This paper discusses the detailed analysis of those components for the fundamental deflecting/crabbing mode and higher order modes in the parallel-bar deflecting/crabbing cavity.

MOPB018	Analyzing Surface Roughness Dependence of Linear RF Losses	SRF, scattering, niobium, radio-frequency	210
	C. Xu The College of William and Mary, Williamsburg, USA M.J. Kelley, C.E. Reece JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Topographic structure on Superconductivity Radio Frequency (SRF) surfaces can contribute additional cavity RF losses describable in terms of surface RF reflectivity and absorption indices of wave scattering theory. At isotropic homogeneous extent, Power Spectrum Density (PSD) of roughness is introduced and quantifies the random surface topographic structure. PSD obtained from different surface treatments of niobium, such as Buffered Chemical Polishing (BCP), Electropolishing (EP), Nano-Mechanical Polishing (NMP) and Barrel Centrifugal Polishing (CBP) are compared. A perturbation model is utilized to calculate the additional rough surface RF losses based on PSD statistical analysis. This model will not consider that superconductor becomes normal conducting at fields higher than transition field. One can calculate the RF power dissipation ratio between rough surface and ideal smooth surface within this field range from linear loss mechanisms.

MOPB056	Multipacting Analysis of High-Velocity Superconducting Spoke Resonators	electron, cavity, site, simulation	303
	C.S. Hopper, J.R. Delayen ODU, Norfolk, Virginia, USA
	Some of the advantages of superconducting spoke cavities are currently being investigated for the high-velocity regime. When determining a final, optimized geometry, one must consider the possible limiting effects multipacting could have on the cavity. We report on the results of analytical calculations and numerical simulations of multipacting electrons in superconducting spoke cavities and methods for reducing their impact.

MOPB060	RF Surface Impedance Characterization of Potential New Materials for SRF-based Accelerators	niobium, SRF, cavity, impedance	312
	B. P. Xiao, G.V. Eremeev, H.L. Phillips, C.E. Reece JLAB, Newport News, Virginia, USA M.J. Kelley, B. P. Xiao The College of William and Mary, Williamsburg, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. In the development of new superconducting materials for possible use in SRF-based accelerators, it is useful to work with small candidate samples rather than complete resonant cavities. The recently commissioned Jefferson Lab rf Surface Impedance Characterization (SIC) system* can presently characterize the central region of 50 mm diameter disk samples of various materials from 2 to 40 K exposed to RF magnetic fields up to 14 mT at 7.4 GHz. We report the measurement results from bulk Nb, thin film Nb on Cu and sapphire substrates, and thin film MgB₂ on sapphire substrate provided by colleagues at JLab and Temple University. We also report on efforts to extend the operating range to higher fields. * B.P. Xiao, et al., RSI, 2011. 82: p. 056104

MOPB065	Impact of Trapped Magnetic Flux and Systematic Flux Expulsion in Superconducting Niobium	niobium, cavity, SRF, controls	327
	J.M. Vogt, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	The intrinsic quality factor Q₀ of superconducting cavities is known to depend on various factors like niobium material properties, treatment history and magnetic shielding. We already reported an additional impact of temperature gradients during the cool-down on the obtained Q₀. We believe cooling conditions can influence the level of flux trapping and hence the residual resistance. For further studies we have constructed a test stand using niobium rods to study flux trapping. Here we can precisely control the temperature and approach T_c in the superconducting state. Although the sample remains in the superconducting state a change in the amount of trapped flux is visible. The procedure can be applied repeatedly resulting in a significantly lowered level of trapped flux in the sample. Applying a similar procedure to a superconducting cavity could allow for reduction of the magnetic contribution to the surface resistance and result in a significant improvement of Q₀.

THPB062	Multipole Field Effects for the Superconducting Parallel-Bar/RF-Dipole Deflecting/Crabbing Cavities	dipole, multipole, cavity, luminosity	981
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA S.U. De Silva JLAB, Newport News, Virginia, USA
	The superconducting parallel-bar deflecting/crabbing cavity is currently being considered as one of the design options in rf separation for the Jefferson Lab 12 GeV upgrade and for the crabbing cavity for the proposed LHC luminosity upgrade. Knowledge of multipole field effects is important for accurate beam dynamics study of rf structures. The multipole components can be accurately determined numerically using the electromagnetic surface field data in the rf structure. This paper discusses the detailed analysis of those components for the fundamental deflecting/crabbing mode and higher order modes in the parallel-bar deflecting/crabbing cavity.

Paper

Title

Other Keywords

Page

SUPB001

Analyzing Surface Roughness Dependence of Linear RF Losses

SRF, scattering, niobium, radio-frequency

1

C. Xu, M.J. Kelley
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.
Topographic structure on Superconductivity Radio Frequency (SRF) surfaces can contribute additional cavity RF losses describable in terms of surface RF reflectivity and absorption indices of wave scattering theory. At isotropic homogeneous extent, Power Spectrum Density (PSD) of roughness is introduced and quantifies the random surface topographic structure. PSD obtained from different surface treatments of niobium, such as Buffered Chemical Polishing (BCP), Electropolishing (EP), Nano-Mechanical Polishing (NMP) and Barrel Centrifugal Polishing (CBP) are compared. A perturbation model is utilized to calculate the additional rough surface RF losses based on PSD statistical analysis. This model will not consider that superconductor becomes normal conducting at fields higher than transition field. One can calculate the RF power dissipation ratio between rough surface and ideal smooth surface within this field range from linear loss mechanisms.

SUPB026

Multipacting Analysis of High-velocity Superconducting Spoke Resonators

electron, cavity, site, simulation

68

C.S. Hopper, J.R. Delayen
ODU, Norfolk, Virginia, USA

Some of the advantages of superconducting spoke cavities are currently being investigated for the high-velocity regime. When determining a final, optimized geometry, one must consider the possible limiting effects multipacting could have on the cavity. We report on the results of analytical calculations and numerical simulations of multipacting electrons in superconducting spoke cavities and methods for reducing their impact.

SUPB029

Impact of Trapped Flux and Systematic Flux Expulsion in Superconducting Niobium

niobium, cavity, SRF, controls

77

J.M. Vogt, J. Knobloch, O. Kugeler
HZB, Berlin, Germany

The intrinsic quality factor Q₀ of superconducting cavities is known to depend on various factors like niobium material properties, treatment history and magnetic shielding. We already reported an additional impact of temperature gradients during the cool-down on the obtained Q₀. We believe cooling conditions can influence the level of flux trapping and hence the residual resistance. For further studies we have constructed a test stand using niobium rods to study flux trapping. Here we can precisely control the temperature and approach T_c in the superconducting state. Although the sample remains in the superconducting state a change in the amount of trapped flux is visible. The procedure can be applied repeatedly resulting in a significantly lowered level of trapped flux in the sample. Applying a similar procedure to a superconducting cavity could allow for reduction of the magnetic contribution to the surface resistance and result in a significant improvement of Q₀.

SUPB038

Multipole Field Effects for the Superconducting Parallel-Bar Deflecting/Crabbing Cavities

dipole, multipole, cavity, luminosity

92

S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA
S.U. De Silva
JLAB, Newport News, Virginia, USA

The superconducting parallel-bar deflecting/crabbing cavity is currently being considered as one of the design options in rf separation for the Jefferson Lab 12 GeV upgrade and for the crabbing cavity for the proposed LHC luminosity upgrade. Knowledge of multipole field effects is important for accurate beam dynamics study of rf structures. The multipole components can be accurately determined numerically using the electromagnetic surface field data in the rf structure. This paper discusses the detailed analysis of those components for the fundamental deflecting/crabbing mode and higher order modes in the parallel-bar deflecting/crabbing cavity.

MOPB018

Analyzing Surface Roughness Dependence of Linear RF Losses

SRF, scattering, niobium, radio-frequency

210

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

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Topographic structure on Superconductivity Radio Frequency (SRF) surfaces can contribute additional cavity RF losses describable in terms of surface RF reflectivity and absorption indices of wave scattering theory. At isotropic homogeneous extent, Power Spectrum Density (PSD) of roughness is introduced and quantifies the random surface topographic structure. PSD obtained from different surface treatments of niobium, such as Buffered Chemical Polishing (BCP), Electropolishing (EP), Nano-Mechanical Polishing (NMP) and Barrel Centrifugal Polishing (CBP) are compared. A perturbation model is utilized to calculate the additional rough surface RF losses based on PSD statistical analysis. This model will not consider that superconductor becomes normal conducting at fields higher than transition field. One can calculate the RF power dissipation ratio between rough surface and ideal smooth surface within this field range from linear loss mechanisms.

MOPB056

Multipacting Analysis of High-Velocity Superconducting Spoke Resonators

electron, cavity, site, simulation

303

C.S. Hopper, J.R. Delayen
ODU, Norfolk, Virginia, USA

Some of the advantages of superconducting spoke cavities are currently being investigated for the high-velocity regime. When determining a final, optimized geometry, one must consider the possible limiting effects multipacting could have on the cavity. We report on the results of analytical calculations and numerical simulations of multipacting electrons in superconducting spoke cavities and methods for reducing their impact.

MOPB060

RF Surface Impedance Characterization of Potential New Materials for SRF-based Accelerators

niobium, SRF, cavity, impedance

312

B. P. Xiao, G.V. Eremeev, H.L. Phillips, C.E. Reece
JLAB, Newport News, Virginia, USA
M.J. Kelley, B. P. Xiao
The College of William and Mary, Williamsburg, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
In the development of new superconducting materials for possible use in SRF-based accelerators, it is useful to work with small candidate samples rather than complete resonant cavities. The recently commissioned Jefferson Lab rf Surface Impedance Characterization (SIC) system* can presently characterize the central region of 50 mm diameter disk samples of various materials from 2 to 40 K exposed to RF magnetic fields up to 14 mT at 7.4 GHz. We report the measurement results from bulk Nb, thin film Nb on Cu and sapphire substrates, and thin film MgB₂ on sapphire substrate provided by colleagues at JLab and Temple University. We also report on efforts to extend the operating range to higher fields.
* B.P. Xiao, et al., RSI, 2011. 82: p. 056104

MOPB065

Impact of Trapped Magnetic Flux and Systematic Flux Expulsion in Superconducting Niobium

niobium, cavity, SRF, controls

327

J.M. Vogt, J. Knobloch, O. Kugeler
HZB, Berlin, Germany

The intrinsic quality factor Q₀ of superconducting cavities is known to depend on various factors like niobium material properties, treatment history and magnetic shielding. We already reported an additional impact of temperature gradients during the cool-down on the obtained Q₀. We believe cooling conditions can influence the level of flux trapping and hence the residual resistance. For further studies we have constructed a test stand using niobium rods to study flux trapping. Here we can precisely control the temperature and approach T_c in the superconducting state. Although the sample remains in the superconducting state a change in the amount of trapped flux is visible. The procedure can be applied repeatedly resulting in a significantly lowered level of trapped flux in the sample. Applying a similar procedure to a superconducting cavity could allow for reduction of the magnetic contribution to the surface resistance and result in a significant improvement of Q₀.

THPB062

Multipole Field Effects for the Superconducting Parallel-Bar/RF-Dipole Deflecting/Crabbing Cavities

dipole, multipole, cavity, luminosity

981

S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA
S.U. De Silva
JLAB, Newport News, Virginia, USA

The superconducting parallel-bar deflecting/crabbing cavity is currently being considered as one of the design options in rf separation for the Jefferson Lab 12 GeV upgrade and for the crabbing cavity for the proposed LHC luminosity upgrade. Knowledge of multipole field effects is important for accurate beam dynamics study of rf structures. The multipole components can be accurately determined numerically using the electromagnetic surface field data in the rf structure. This paper discusses the detailed analysis of those components for the fundamental deflecting/crabbing mode and higher order modes in the parallel-bar deflecting/crabbing cavity.