IPAC2014 - List of Authors (Xiao, L.)

Paper	Title	Page
WEPRI067	Multi-Physics Analysis of CW Superconducting Cavity for the LCLS-II using ACE3P	2645
	Z. Li, C. Adolphsen, O. Kononenko, T.O. Raubenheimer, C.H. Rivetta, M.C. Ross, L. Xiao SLAC, Menlo Park, California, USA
	Funding: Work was supported by the U.S. DOE contract DE-AC02-76SF00515 and used the resources of NERSC at LBNL under US DOE Contract No. DE-AC03-76SF00098. The LCLS-II linac utilizes superconducting technology operating at continuous wave to accelerate the 1-MHz electron beams to 4 GeV to produce tunable FELs. The TESLA 9-cell superconducting cavity is adopted as the baseline design for the linac. The design gradient is approximately 16 MV/m. The highest operating current is 300 μA. Assuming that the RF power is matched at the highest current, the optimal loaded QL of the cavity is found to be around 4·10⁷. Because of the high QL, the cavity bandwidth approaches the background microphonic detuning, and the performance of the cavity is tightly coupled to the mechanical perturbations of the cavity/cryomodule system. The resulting large phase and amplitude variations in the cavity require active feedback to achieve the 0.01% amplitude and phase stability requirements. To understand the cavity RF response and feedback requirements to the microphonics and Lorentz Force detuning, we have developed a simulation model of the RF-mechanical coupled system using parameters obtained with the multi-physics solver ACE3P. We will present the simulation results of the LCLS-II linac under different power feed scenarios and feedback schemes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI067
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THPRI075	S-Band Structure Study for the MaRIE Project	3940
	Z. Li, C. Adolphsen, M.V. Fazio, S.G. Tantawi, L. Xiao SLAC, Menlo Park, California, USA
	Funding: Work was supported by the US Department of Energy through the LANL/LDRD Program. The Matter-Radiation Interactions in Extremes (MaRIE) facility proposed at LANL utilizes a 20-GeV electron linac to drive a 50-keV XFEL. Experimental requirements drive a need for multiple photon bunches over time durations of about 10 microsecond produced by a bunch train of interleaving 0.1 nC very low-emittance bunches with 2-nC electron bunches. The linac is required not only to provide high gradient and high efficient acceleration, but also a controlled wakefield profile to maintain the beam quality. In this paper, we explore the feasibility of using the S-Band technology to meet such acceleration requirements. We will present the design optimization and comparison of S-Band structures based on different design considerations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI075
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THPRI077	Electric Field Enhancement Study using an L-band Photocathode Gun	3946
	J.H. Shao, W. Gai ANL, Argonne, Illinois, USA H.B. Chen, J. Shi TUB, Beijing, People's Republic of China C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA F.Y. Wang, L. Xiao SLAC, Menlo Park, California, USA
	RF breakdown in high gradient accelerating structures is a fundamental problem that is still needed better understanding. Past studies have indicated that field emission, which is usually represented by electric field enhancement (i.e. β) produced from the Fowler-Nordheim plot, is strongly coupled to the breakdown problem. A controlled surface study using a high gradient L-band RF gun is being carried out. With a flat cathode, the maximum electric field on the surface reached 10³ MV/m. And electric field as high as 565 MV/m on the surface was achieved by a pin-shaped cathode. The field enhancement factor was measured at different surface field during the conditioning process. Initial results of the study are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI077
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THPRI078	Experimental Study of Surface RF Magnetic Field Enhancement Caused by Closely Spaced Protrusions	3949
	F.Y. Wang, C. Adolphsen, J.P. Eichner, C.D. Nantista, L. Xiao SLAC, Menlo Park, California, USA
	The RF magnetic field enhancement between two closely spaced protrusions on a metallic surface has been studied theoretically. It is found that a large enhancement occurs when the field is perpendicular to the gap between the protrusions. This mechanism could help explain the melting that has been observed on cavity surfaces subjected to pulsed heating that would nominally be well below the melting temperature of the surface material. To test this possibility, an experiment was carried out in which a pair of copper “pins” was attached to the base plate of an X-band cavity normally used to study pulsed heating. Melting was observed between the pins when the predicted peak temperature was near or exceeded the copper melting temperature.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI078
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Paper

Title

Page

Multi-Physics Analysis of CW Superconducting Cavity for the LCLS-II using ACE3P

2645

Z. Li, C. Adolphsen, O. Kononenko, T.O. Raubenheimer, C.H. Rivetta, M.C. Ross, L. Xiao
SLAC, Menlo Park, California, USA

Funding: Work was supported by the U.S. DOE contract DE-AC02-76SF00515 and used the resources of NERSC at LBNL under US DOE Contract No. DE-AC03-76SF00098.
The LCLS-II linac utilizes superconducting technology operating at continuous wave to accelerate the 1-MHz electron beams to 4 GeV to produce tunable FELs. The TESLA 9-cell superconducting cavity is adopted as the baseline design for the linac. The design gradient is approximately 16 MV/m. The highest operating current is 300 μA. Assuming that the RF power is matched at the highest current, the optimal loaded QL of the cavity is found to be around 4·10⁷. Because of the high QL, the cavity bandwidth approaches the background microphonic detuning, and the performance of the cavity is tightly coupled to the mechanical perturbations of the cavity/cryomodule system. The resulting large phase and amplitude variations in the cavity require active feedback to achieve the 0.01% amplitude and phase stability requirements. To understand the cavity RF response and feedback requirements to the microphonics and Lorentz Force detuning, we have developed a simulation model of the RF-mechanical coupled system using parameters obtained with the multi-physics solver ACE3P. We will present the simulation results of the LCLS-II linac under different power feed scenarios and feedback schemes.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI067

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THPRI075

S-Band Structure Study for the MaRIE Project

3940

Z. Li, C. Adolphsen, M.V. Fazio, S.G. Tantawi, L. Xiao
SLAC, Menlo Park, California, USA

Funding: Work was supported by the US Department of Energy through the LANL/LDRD Program.
The Matter-Radiation Interactions in Extremes (MaRIE) facility proposed at LANL utilizes a 20-GeV electron linac to drive a 50-keV XFEL. Experimental requirements drive a need for multiple photon bunches over time durations of about 10 microsecond produced by a bunch train of interleaving 0.1 nC very low-emittance bunches with 2-nC electron bunches. The linac is required not only to provide high gradient and high efficient acceleration, but also a controlled wakefield profile to maintain the beam quality. In this paper, we explore the feasibility of using the S-Band technology to meet such acceleration requirements. We will present the design optimization and comparison of S-Band structures based on different design considerations.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI075

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THPRI077

Electric Field Enhancement Study using an L-band Photocathode Gun

3946

J.H. Shao, W. Gai
ANL, Argonne, Illinois, USA
H.B. Chen, J. Shi
TUB, Beijing, People's Republic of China
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA
F.Y. Wang, L. Xiao
SLAC, Menlo Park, California, USA

RF breakdown in high gradient accelerating structures is a fundamental problem that is still needed better understanding. Past studies have indicated that field emission, which is usually represented by electric field enhancement (i.e. β) produced from the Fowler-Nordheim plot, is strongly coupled to the breakdown problem. A controlled surface study using a high gradient L-band RF gun is being carried out. With a flat cathode, the maximum electric field on the surface reached 10³ MV/m. And electric field as high as 565 MV/m on the surface was achieved by a pin-shaped cathode. The field enhancement factor was measured at different surface field during the conditioning process. Initial results of the study are presented in this paper.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI077

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPRI078

Experimental Study of Surface RF Magnetic Field Enhancement Caused by Closely Spaced Protrusions

3949

F.Y. Wang, C. Adolphsen, J.P. Eichner, C.D. Nantista, L. Xiao
SLAC, Menlo Park, California, USA

The RF magnetic field enhancement between two closely spaced protrusions on a metallic surface has been studied theoretically. It is found that a large enhancement occurs when the field is perpendicular to the gap between the protrusions. This mechanism could help explain the melting that has been observed on cavity surfaces subjected to pulsed heating that would nominally be well below the melting temperature of the surface material. To test this possibility, an experiment was carried out in which a pair of copper “pins” was attached to the base plate of an X-band cavity normally used to study pulsed heating. Melting was observed between the pins when the predicted peak temperature was near or exceeded the copper melting temperature.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI078

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