IPAC2016 - List of Authors (Guo, J.)

Paper	Title	Page
MOPMW038	Measurements of Copper RF Surface Resistance at Cryogenic Temperatures for Applications to X-Band and S-Band Accelerators	487
	A.D. Cahill, A. Fukasawa, J.B. Rosenzweig UCLA, Los Angeles, California, USA G.B. Bowden, V.A. Dolgashev, M.A. Franzi, S.G. Tantawi, P.B. Welander, C. Yoneda SLAC, Menlo Park, California, USA J. Guo JLab, Newport News, Virginia, USA Y. Higashi OIST, Onna-son, Okinawa, Japan
	Funding: Funding from DOE SCGSR and DOE/SU Contract DE-AC02-76-SF00515 Recent SLAC experiments with cryogenically cooled X-Band standing wave copper accelerating cavities have shown that these structures can operate with accelerating gradients of ~250 MV/m and low breakdown rates. These results prompted us to perform systematic studies of copper rf properties at cryogenic temperatures and low rf power. We placed copper cavities into a cryostat cooled by a pulse tube cryocooler, so cavities could be cooled to 4K. We used different shapes of cavities for the X-Band and S-Band measurements. Properties of the cavities were measured using a network analyzer. We calculated rf surface resistance from measured Q0 and Q external of the cavity at temperatures from 4 K to room temperature. The results were then compared to the theory proposed by Reuter and Sondheimer. These measurements are a part of studies with the goal of reaching very high operational accelerating gradients in normal conducting rf structures.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMW038
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MOPMY003	Transient Beam Loading Effects in RF Systems in JLEIC	518
	H. Wang, J. Guo, R.A. Rimmer, S. Wang JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The pulsed electron bunch trains generated from the Continuous Electron Beam Accelerator Facility (CEBAF) linac to inject into the proposed Jefferson Lab Electron Ion Collider (JLEIC) e-ring will produce transient beam loading effects in the Superconducting Radio Frequency (SRF) systems that, if not mitigated, could cause unacceptably large beam energy deviation in the injection capture, exceed the energy acceptance of CEBAF's recirculating arc. In the electron storage ring, the beam abort or ion clearing gaps or uneven bucket filling can cause large beam phase transients in the (S)RF cavity control systems and even beam loss due to Robinson instability. We have first analyzed the beam stability criteria in steady state and estimate the transient effect in Feedforward and Feedback RF controls. Initial analytical models for these effects are shown for the design of the JLEIC e-ring from 3GeV to 12GeV.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMY003
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WEPMW019	Study of Beam Synchronization at JLEIC	2463
	V.S. Morozov, Y.S. Derbenev, J. Guo, A. Hutton, Y. Zhang JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contracts No. DE-AC05-06OR23177 and DE-AC02-06CH11357. The ion collider ring of Jefferson Lab's Electron-Ion Collider (JLEIC) accommodates a wide range of ion energies, from 20 to 100 GeV for protons or from 8 to 40 GeV per nucleon for lead ions. In this medium energy range, ions are not fully relativistic, which means values of their relativistic beta are slightly below 1, leading to an energy dependence of revolution time of the collider ring. On the other hand, electrons with energy 3 GeV and above are already ultra-relativistic such that their speeds are effectively equal to the speed of light. The difference in speeds of colliding electrons and ions in JLEIC, when translated into a path-length difference necessary to maintain the same timing between electron and ion bunches, is quite large. In this paper, we explore schemes for synchronizing the electron and ion bunches at a collision point as the ion energy is varied.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW019
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WEPMW020	Storage-ring Electron Cooler for Relativistic Ion Beams	2466
	F. Lin, Y.S. Derbenev, D. Douglas, J. Guo, G.A. Krafft, V.S. Morozov, Y. Zhang JLab, Newport News, Virginia, USA R.P. Johnson Muons, Inc, Illinois, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 and DE-AC02-06CH11357 Application of electron cooling at ion energies above a few GeV has been limited due to reduction of electron cooling efficiency with energy and difficulty in producing and accelerating a high-current high-quality electron beam. A high-current storage-ring electron cooler offers a solution to both of these problems by maintaining high cooling beam quality through naturally-occurring synchrotron radiation damping of the electron beam. However, the range of ion energies where storage-ring electron cooling can be used has been limited by low electron beam damping rates at low ion energies and high equilibrium electron energy spread at high ion energies. This paper reports a development of a storage ring based cooler consisting of two sections with significantly different energies: the cooling and damping sections. The electron energy and other parameters in the cooling section are adjusted for optimum cooling of a stored ion beam. The beam parameters in the damping section are adjusted for optimum damping of the electron beam. The necessary energy difference is provided by an energy recovering SRF structure. A prototype linear optics of such storage-ring cooler is presented.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW020
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WEPMW039	JLEIC SRF Cavity RF Design	2522
	S. Wang, J. Guo, R.A. Rimmer, H. Wang JLab, Newport News, Virginia, USA
	The initial design of a low higher order modes (HOM) impedance superconducting RF (SRF) cavity is presented in this paper. The design of this SRF cavity is for the proposed Jefferson Lab Electron Ion Collider (JLEIC). The electron ring of JLEIC will operate with electrons of 3 to 10 GeV energy. The ion ring of JLEIC will operate with protons of up to 100 GeV energy. The bunch lengths in both rings are ~12 mm (RMS). In order to maintain the short bunch length in the ion ring, SRF cavities are adopted to provide large enough gradient. In the first phase of JLEIC, the PEP II RF cavities will be reused in the electron ring to lower the initial cost. The frequency of the SRF cavities is chosen to be the second harmonic of PEP II cavities, 952.6 MHz. In the second phase of JLEIC, the same frequency SRF cavities may replace the normal conducting PEP II cavities to achieve higher luminosity at high energy. At low energies, the synchrotron radiation damping effect is quite weak, to avoid the coupled bunch instability caused by the intense closely-spaced electron bunches, low HOM impedance of the SRF cavities combined with longitudinal feedback system will be necessary.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW039
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Paper

Title

Page

Measurements of Copper RF Surface Resistance at Cryogenic Temperatures for Applications to X-Band and S-Band Accelerators

487

A.D. Cahill, A. Fukasawa, J.B. Rosenzweig
UCLA, Los Angeles, California, USA
G.B. Bowden, V.A. Dolgashev, M.A. Franzi, S.G. Tantawi, P.B. Welander, C. Yoneda
SLAC, Menlo Park, California, USA
J. Guo
JLab, Newport News, Virginia, USA
Y. Higashi
OIST, Onna-son, Okinawa, Japan

Funding: Funding from DOE SCGSR and DOE/SU Contract DE-AC02-76-SF00515
Recent SLAC experiments with cryogenically cooled X-Band standing wave copper accelerating cavities have shown that these structures can operate with accelerating gradients of ~250 MV/m and low breakdown rates. These results prompted us to perform systematic studies of copper rf properties at cryogenic temperatures and low rf power. We placed copper cavities into a cryostat cooled by a pulse tube cryocooler, so cavities could be cooled to 4K. We used different shapes of cavities for the X-Band and S-Band measurements. Properties of the cavities were measured using a network analyzer. We calculated rf surface resistance from measured Q0 and Q external of the cavity at temperatures from 4 K to room temperature. The results were then compared to the theory proposed by Reuter and Sondheimer. These measurements are a part of studies with the goal of reaching very high operational accelerating gradients in normal conducting rf structures.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMW038

Export •

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

MOPMY003

Transient Beam Loading Effects in RF Systems in JLEIC

518

H. Wang, J. Guo, R.A. Rimmer, S. Wang
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The pulsed electron bunch trains generated from the Continuous Electron Beam Accelerator Facility (CEBAF) linac to inject into the proposed Jefferson Lab Electron Ion Collider (JLEIC) e-ring will produce transient beam loading effects in the Superconducting Radio Frequency (SRF) systems that, if not mitigated, could cause unacceptably large beam energy deviation in the injection capture, exceed the energy acceptance of CEBAF's recirculating arc. In the electron storage ring, the beam abort or ion clearing gaps or uneven bucket filling can cause large beam phase transients in the (S)RF cavity control systems and even beam loss due to Robinson instability. We have first analyzed the beam stability criteria in steady state and estimate the transient effect in Feedforward and Feedback RF controls. Initial analytical models for these effects are shown for the design of the JLEIC e-ring from 3GeV to 12GeV.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMY003

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

WEPMW019

Study of Beam Synchronization at JLEIC

2463

V.S. Morozov, Y.S. Derbenev, J. Guo, A. Hutton, Y. Zhang
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contracts No. DE-AC05-06OR23177 and DE-AC02-06CH11357.
The ion collider ring of Jefferson Lab's Electron-Ion Collider (JLEIC) accommodates a wide range of ion energies, from 20 to 100 GeV for protons or from 8 to 40 GeV per nucleon for lead ions. In this medium energy range, ions are not fully relativistic, which means values of their relativistic beta are slightly below 1, leading to an energy dependence of revolution time of the collider ring. On the other hand, electrons with energy 3 GeV and above are already ultra-relativistic such that their speeds are effectively equal to the speed of light. The difference in speeds of colliding electrons and ions in JLEIC, when translated into a path-length difference necessary to maintain the same timing between electron and ion bunches, is quite large. In this paper, we explore schemes for synchronizing the electron and ion bunches at a collision point as the ion energy is varied.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW019

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WEPMW020

Storage-ring Electron Cooler for Relativistic Ion Beams

2466

F. Lin, Y.S. Derbenev, D. Douglas, J. Guo, G.A. Krafft, V.S. Morozov, Y. Zhang
JLab, Newport News, Virginia, USA
R.P. Johnson
Muons, Inc, Illinois, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 and DE-AC02-06CH11357
Application of electron cooling at ion energies above a few GeV has been limited due to reduction of electron cooling efficiency with energy and difficulty in producing and accelerating a high-current high-quality electron beam. A high-current storage-ring electron cooler offers a solution to both of these problems by maintaining high cooling beam quality through naturally-occurring synchrotron radiation damping of the electron beam. However, the range of ion energies where storage-ring electron cooling can be used has been limited by low electron beam damping rates at low ion energies and high equilibrium electron energy spread at high ion energies. This paper reports a development of a storage ring based cooler consisting of two sections with significantly different energies: the cooling and damping sections. The electron energy and other parameters in the cooling section are adjusted for optimum cooling of a stored ion beam. The beam parameters in the damping section are adjusted for optimum damping of the electron beam. The necessary energy difference is provided by an energy recovering SRF structure. A prototype linear optics of such storage-ring cooler is presented.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW020

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WEPMW039

JLEIC SRF Cavity RF Design

2522

S. Wang, J. Guo, R.A. Rimmer, H. Wang
JLab, Newport News, Virginia, USA

The initial design of a low higher order modes (HOM) impedance superconducting RF (SRF) cavity is presented in this paper. The design of this SRF cavity is for the proposed Jefferson Lab Electron Ion Collider (JLEIC). The electron ring of JLEIC will operate with electrons of 3 to 10 GeV energy. The ion ring of JLEIC will operate with protons of up to 100 GeV energy. The bunch lengths in both rings are ~12 mm (RMS). In order to maintain the short bunch length in the ion ring, SRF cavities are adopted to provide large enough gradient. In the first phase of JLEIC, the PEP II RF cavities will be reused in the electron ring to lower the initial cost. The frequency of the SRF cavities is chosen to be the second harmonic of PEP II cavities, 952.6 MHz. In the second phase of JLEIC, the same frequency SRF cavities may replace the normal conducting PEP II cavities to achieve higher luminosity at high energy. At low energies, the synchrotron radiation damping effect is quite weak, to avoid the coupled bunch instability caused by the intense closely-spaced electron bunches, low HOM impedance of the SRF cavities combined with longitudinal feedback system will be necessary.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMW039

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