IPAC2011 - List of Authors (Lu, X.Y.)

Paper	Title	Page
MOPC117	Advance in Vertical Buffered Electropolishing on Niobium for Particle Accelerators*	352
	A.T. Wu, S. Jin, J.D. Mammosser, C.E. Reece, R.A. Rimmer JLAB, Newport News, Virginia, USA L. Lin, X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China
	Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes. Niobium (Nb) is the most popular material that has been employed for making superconducting radio frequency (SRF) cavities to be used in various particle accelerators over the last couple of decades. One of the most important steps in fabricating Nb SRF cavities is the final chemical removal of 150 μm of Nb from the inner surfaces of the SRF cavities. This is usually done by either buffered chemical polishing (BCP) or electropolishing (EP). Recently a new Nb surface treatment technique called buffered electropolishing (BEP) has been developed at Jefferson Lab. It has been demonstrated that BEP can produce the smoothest surface finish on Nb ever reported in the literature while realizing a Nb removal rate as high as 10 μm/min that is more than 25 and 5 times quicker than those of EP and BCP(112) respectively. In this contribution, recent advance in optimizing and understanding BEP treatment technique is reviewed. Latest results from RF measurements on BEP treated Nb single cell cavities by our unique vertical polishing system will be reported. Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.

MOPC118	Effects of the Thickness of Niobium Surface Oxide Layers on Field Emission*	355
	A.T. Wu, S. Jin, J.D. Mammosser, R.A. Rimmer JLAB, Newport News, Virginia, USA X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China
	Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes. Field emission on the inner surfaces of niobium superconducting radio frequency cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results* seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3 nm up to 460 nm. A home-made scanning field emission microscope was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The SFEM experimental results were analyzed in terms of surface morphology and oxide thickness of Nb samples and chemical composition and geographic shape of the emitters. A model based on the classic electromagnetic theory was developed trying to understand the experimental results. Possibly implications for Nb SRF cavity applications from this study will be discussed. * A.T. Wu et al., Proc. of IPAC 2010, Kyoto, Japan, WEPEC081, p. 3067 (2010). Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.

MOPC119	Fastest Electropolishing Technique on Niobium for Particle Accelerators*	358
	A.T. Wu, S. Jin, R.A. Rimmer JLAB, Newport News, Virginia, USA X.Y. Lu, K. Zhao PKU/IHIP, Beijing, People's Republic of China
	Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes. Field emission on the inner surfaces of niobium (Nb) superconducting radio frequency (SRF) cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results [1] seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3nm up to 460nm. A home-made scanning field emission microscope (SFEM) was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The experimental results could be understood by a simple model calculation based on classic electromagnetic theory as shown in Ref.1. Possibly implications for Nb SRF cavity applications from this study will be discussed. Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.

TUPC108	Beam Diagnostics Based on Higher Order Mode for High Repetition Beam	1269
	X. Luo, X.Y. Lu, F. Wang PKU/IHIP, Beijing, People's Republic of China F.S. He JLAB, Newport News, Virginia, USA
	The signals from the HOM ports on superconducting cavities can be used as beam position monitors. The HOM amplitude of dipole mode is proportional to the beam offset. For high repetition bunches operation, the spectrum is consist of the HOMs peaks and the peaks which is integer times of the bunch repetition. The HOMs amplitudes should be separated from the two kinds of peaks. Based on the simulation from a TESLA 2-cell cavity, the transform matrix between the HOMs amplitudes and beam offsets has been found, as well as the cavity axis. The simulation results have demonstrated that beam diagnostics based on HOMs is feasible while high repetition bunches operation.

Paper

Title

Page

Advance in Vertical Buffered Electropolishing on Niobium for Particle Accelerators*

352

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

Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
Niobium (Nb) is the most popular material that has been employed for making superconducting radio frequency (SRF) cavities to be used in various particle accelerators over the last couple of decades. One of the most important steps in fabricating Nb SRF cavities is the final chemical removal of 150 μm of Nb from the inner surfaces of the SRF cavities. This is usually done by either buffered chemical polishing (BCP) or electropolishing (EP). Recently a new Nb surface treatment technique called buffered electropolishing (BEP) has been developed at Jefferson Lab. It has been demonstrated that BEP can produce the smoothest surface finish on Nb ever reported in the literature while realizing a Nb removal rate as high as 10 μm/min that is more than 25 and 5 times quicker than those of EP and BCP(112) respectively. In this contribution, recent advance in optimizing and understanding BEP treatment technique is reviewed. Latest results from RF measurements on BEP treated Nb single cell cavities by our unique vertical polishing system will be reported.
Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.

MOPC118

Effects of the Thickness of Niobium Surface Oxide Layers on Field Emission*

355

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

Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
Field emission on the inner surfaces of niobium superconducting radio frequency cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results* seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3 nm up to 460 nm. A home-made scanning field emission microscope was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The SFEM experimental results were analyzed in terms of surface morphology and oxide thickness of Nb samples and chemical composition and geographic shape of the emitters. A model based on the classic electromagnetic theory was developed trying to understand the experimental results. Possibly implications for Nb SRF cavity applications from this study will be discussed.
* A.T. Wu et al., Proc. of IPAC 2010, Kyoto, Japan, WEPEC081, p. 3067 (2010).
Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.

MOPC119

Fastest Electropolishing Technique on Niobium for Particle Accelerators*

358

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

Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
Field emission on the inner surfaces of niobium (Nb) superconducting radio frequency (SRF) cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results [1] seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3nm up to 460nm. A home-made scanning field emission microscope (SFEM) was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The experimental results could be understood by a simple model calculation based on classic electromagnetic theory as shown in Ref.1. Possibly implications for Nb SRF cavity applications from this study will be discussed.
Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.

TUPC108

Beam Diagnostics Based on Higher Order Mode for High Repetition Beam

1269

X. Luo, X.Y. Lu, F. Wang
PKU/IHIP, Beijing, People's Republic of China
F.S. He
JLAB, Newport News, Virginia, USA

The signals from the HOM ports on superconducting cavities can be used as beam position monitors. The HOM amplitude of dipole mode is proportional to the beam offset. For high repetition bunches operation, the spectrum is consist of the HOMs peaks and the peaks which is integer times of the bunch repetition. The HOMs amplitudes should be separated from the two kinds of peaks. Based on the simulation from a TESLA 2-cell cavity, the transform matrix between the HOMs amplitudes and beam offsets has been found, as well as the cavity axis. The simulation results have demonstrated that beam diagnostics based on HOMs is feasible while high repetition bunches operation.