IPAC2017 - List of Authors (Dolgashev, V.A.)

Paper	Title	Page
MOPVA033	A Compact Thermionic RF Injector with RF Bunch Compression fed by a Quadrupole-Free Mode Launcher	924
	F. Toufexis, V.A. Dolgashev, C. Limborg-Deprey, S.G. Tantawi SLAC, Menlo Park, California, USA
	Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515, and the National Science Foundation under Contract No. PHY-1415437. We present a design for a compact X-Band RF thermionic injector consisting of two iris-loaded accelerator structures. Both structures are fed by a single quadrupole-free TM01 mode launcher. In the first structure the electron bunches are extracted from a thermionic cathode. The second structure creates an energy chirp in the bunch for its further ballistic compression. This injector can produce short electron bunches without the need for a magnetic bunch compressor. We are developing this injector as part of a linac-based 91.392 GHz RF power source, which further comprises a booster linac and a mm-wave decelerator structure that extracts 91.392 GHz RF power from the electron beam. This source will be used to power a short-period RF undulator with 1.75 mm period. F. Toufexis and S.G. Tantawi, A 1.75 mm Period RF-Driven Undulator, these proceedings.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA033
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MOPVA034	A Compact EUV Light Source Using a mm-Wave Undulator	928
	F. Toufexis, V.A. Dolgashev, C. Limborg-Deprey, S.G. Tantawi SLAC, Menlo Park, California, USA
	Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515, and the National Science Foundation under Contract No. PHY-1415437. We are building an Extreme Ultra Violet (EUV) light source based on a 1.75 mm period RF undulator. We will use a thermionic X-Band injector which utilizes RF bunch compression. The beam is accelerated using an X-Band traveling wave accelerating structure followed by a high shunt impedance standing wave accelerating structure up to 129 MeV. The beam then goes through a 91.392 GHz RF undulator with a period of 1.75 mm, producing EUV radiation around 13.5 nm. The RF undulator is powered by a 91.392 GHz decelerating structure, which extracts the RF power from the spent electron beam. The length of the entire beam line from the cathode to the beam dump is approximately 6 m. We describe the design and projected operating parameters for this EUV light source. F. Toufexis and S.G. Tantawi, A 1.75 mm Period RF-Driven Undulator, these proceedings.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA034
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TUPAB139	Design of an X-Band Photoinjector Operating at 1 kHz	1659
	W.S. Graves, A.C. Goodrich, M.R. Holl, N.J. O'Brien Arizona State University, Tempe, USA V. Bharadwaj, P. Borchard Tibaray Inc., Stanford, USA V.A. Dolgashev, E.A. Nanni SLAC, Menlo Park, California, USA
	A kHz repetition rate RF photoinjector with novel features has been designed for the ASU CXLS project. The photoinjector consists of a 9.3 GHz 4.5 cell standing-wave RF cavity that is constructed from 2 halves. The halves are brazed together, with the braze joint bisecting the irises and cells, greatly simplifying its construction. The cathode is brazed onto this assembly. RF power is coupled into the cavity through inline circular waveguide using a demountable TM01 mode launcher. The mode launcher feeds the power through 4 ports distributed azimuthally to eliminate both dipole and quadrupole field distortions. The brazed-in cathode and absence of complex power coupler result in a very inexpensive yet high performance device. The clean design allows the RF cavity to sit entirely within the solenoid assembly. The cathode gradient is 120 MV/m at 3 MW of input power. The cathode cell is just 0.17 RF wavelength so that laser arrival phase for peak acceleration is 70 degrees from zero crossing resulting in exit energy of 4 MeV. The photoinjector will operate with 1μs pulses at 1 kHz, dissipating 3 kW of heat. Details of the design are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPAB139
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WEPAB115	Normal Conducting CW Transverse Crab Cavity For Producing Short Pulses In SPEAR3	2840
	Z. Li, V.A. Dolgashev, M. Dunham, K.J. Gaffney, R.O. Hettel, X. Huang, N. Kurita, J.A. Safranek, J.J. Sebek, K. Tian SLAC, Menlo Park, California, USA
	Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515. The ability to produce short pulse X-rays on the scale of 1-10 ps fwhm in the SPEAR3 storage ring light source would enable enhanced timing mode studies of dynamic processes in materials as they occur. The crab cavity approach appears to be optimal for SPEAR3 to produce short pulse X-rays. Furthermore, by using a two-frequency crabbing scheme, SPEAR3 would be able to produce short-pulse bunches while supplying the high average flux needed for regular users. While supercon-ducting RF (SCRF) technology could be a natural choice for the CW crab cavity, the deflecting voltage for SPEAR3 crabbing appears to be within reach of more affordable normal conducting RF (NCRF). In this paper, we present a preliminary NCRF CW crab cavity design for SPEAR3.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB115
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WEPAB138	Prototyping High-Gradient mm-Wave Accelerating Structures	2902
	E.A. Nanni, V.A. Dolgashev, A.A. Haase, J. Neilson, S.G. Tantawi SLAC, Menlo Park, California, USA S.C. Schaub MIT, Cambridge, Massachusetts, USA B. Spataro INFN/LNF, Frascati (Roma), Italy R.J. Temkin MIT/PSFC, Cambridge, Massachusetts, USA
	We present single-cell accelerating structures designed for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures are pi-mode standing-wave cavities fed with a TM01 circular waveguide. The structures are fabricated using precision milling out of two metal blocks, and the blocks are joined with diffusion bonding and brazing. The impact of fabrication and joining techniques on the cell geometry and RF performance will be discussed. First prototypes had a measured Qo of 2800, approaching the theoretical design value of 3300. The geometry of these accelerating structures are as close as practical to single-cell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. The structures will be powered with short pulses from a MW gyrotron oscillator. RF power of 1 MW may allow us to reach an accelerating gradient of 400 MeV/m.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB138
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THPIK125	Ultra High Gradient Breakdown Rates in X-Band Cryogenic Normal Conducting Rf Accelerating Cavities	4395
SUSPSIK097	use link to see paper's listing under its alternate paper code
	A.D. Cahill, J.B. Rosenzweig UCLA, Los Angeles, California, USA V.A. Dolgashev, S.G. Tantawi, S.P. Weathersby SLAC, Menlo Park, California, USA
	Funding: Work Supported by DOE/SU Contract DE-AC02-76-SF00515, US NSF Award PHY-1549132, the Center for Bright Beams, and DOE SCGSR Fellowship. RF breakdown is one of the major factors limiting the operating accelerating gradient in rf particle accelerators. We conjecture that the breakdown rate is linked to the movements of crystal defects induced by periodic mechanical stress. Pulsed surface heating possibly creates a major part of this stress. By decreasing crystal mobility and increasing yield strength we hope to reduce the breakdown rate for the same accelerating gradient. We can achieve these properties by cooling a copper accelerating cavity to cryogenic temperatures. We tested an 11.4 GHz cryogenic copper accelerating cavity at high power and observed that the rf and dark current signals are consistent with Q₀ changing during rf pulses. To take this change in Q₀ into account, we created a non-linear circuit model in which the Q₀ is allowed to vary inside the pulse. We used this model to process the data obtained from the high power test of the cryogenic accelerating structure. We present the results of measurements with low rf breakdown rates for surface electric fields near 500 MV/m for a shaped rf pulse with 150 ns of flat gradient.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK125
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THPIK126	Design of a Field-Emission X-Band Gun Driven by Solid-State RF Source	4399
	E.A. Nanni, V.A. Dolgashev, J. Neilson, S.G. Tantawi SLAC, Menlo Park, California, USA B.E. Carlsten, J.W. Lewellen, D.C. Nguyen LANL, Los Alamos, New Mexico, USA M. Othman UCI, Irvine, California, USA
	We present the design of a field-emission X-band gun designed to be powered using a solid-state RF source. The source of the electron beam is a field emission nano-tip array. The RF gun is intended to be a beam source for 1 MeV solid-state driven linac for deployment on a satellite to map magnetic fields in the magnetosphere. The gun has to satisfy strict requirements on both average and peak power consumption, as well as rapid turn on time. In order to achieve low power consumption, the RF gun operates at relatively low accelerating gradient of 2 MeV/m. The beam exit energy is ~20 keV for an RF power 1.5 kW. Each cell of the RF gun is separately powered by commercially available, GaN high electron mobility transistors. In proof of principle experiments we successfully powered a 9.3 GHz accelerating cavity with a 100 W transistor and a 1% duty cycle.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK126
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

A Compact Thermionic RF Injector with RF Bunch Compression fed by a Quadrupole-Free Mode Launcher

924

F. Toufexis, V.A. Dolgashev, C. Limborg-Deprey, S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515, and the National Science Foundation under Contract No. PHY-1415437.
We present a design for a compact X-Band RF thermionic injector consisting of two iris-loaded accelerator structures. Both structures are fed by a single quadrupole-free TM01 mode launcher. In the first structure the electron bunches are extracted from a thermionic cathode. The second structure creates an energy chirp in the bunch for its further ballistic compression. This injector can produce short electron bunches without the need for a magnetic bunch compressor. We are developing this injector as part of a linac-based 91.392 GHz RF power source, which further comprises a booster linac and a mm-wave decelerator structure that extracts 91.392 GHz RF power from the electron beam. This source will be used to power a short-period RF undulator with 1.75 mm period*.
* F. Toufexis and S.G. Tantawi, A 1.75 mm Period RF-Driven Undulator, these proceedings.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA033

Export •

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

MOPVA034

A Compact EUV Light Source Using a mm-Wave Undulator

928

F. Toufexis, V.A. Dolgashev, C. Limborg-Deprey, S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: This project was funded by U.S. Department of Energy under Contract No. DE-AC02-76SF00515, and the National Science Foundation under Contract No. PHY-1415437.
We are building an Extreme Ultra Violet (EUV) light source based on a 1.75 mm period RF undulator*. We will use a thermionic X-Band injector which utilizes RF bunch compression. The beam is accelerated using an X-Band traveling wave accelerating structure followed by a high shunt impedance standing wave accelerating structure up to 129 MeV. The beam then goes through a 91.392 GHz RF undulator with a period of 1.75 mm, producing EUV radiation around 13.5 nm. The RF undulator is powered by a 91.392 GHz decelerating structure, which extracts the RF power from the spent electron beam. The length of the entire beam line from the cathode to the beam dump is approximately 6 m. We describe the design and projected operating parameters for this EUV light source.
* F. Toufexis and S.G. Tantawi, A 1.75 mm Period RF-Driven Undulator, these proceedings.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA034

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

TUPAB139

Design of an X-Band Photoinjector Operating at 1 kHz

1659

W.S. Graves, A.C. Goodrich, M.R. Holl, N.J. O'Brien
Arizona State University, Tempe, USA
V. Bharadwaj, P. Borchard
Tibaray Inc., Stanford, USA
V.A. Dolgashev, E.A. Nanni
SLAC, Menlo Park, California, USA

A kHz repetition rate RF photoinjector with novel features has been designed for the ASU CXLS project. The photoinjector consists of a 9.3 GHz 4.5 cell standing-wave RF cavity that is constructed from 2 halves. The halves are brazed together, with the braze joint bisecting the irises and cells, greatly simplifying its construction. The cathode is brazed onto this assembly. RF power is coupled into the cavity through inline circular waveguide using a demountable TM01 mode launcher. The mode launcher feeds the power through 4 ports distributed azimuthally to eliminate both dipole and quadrupole field distortions. The brazed-in cathode and absence of complex power coupler result in a very inexpensive yet high performance device. The clean design allows the RF cavity to sit entirely within the solenoid assembly. The cathode gradient is 120 MV/m at 3 MW of input power. The cathode cell is just 0.17 RF wavelength so that laser arrival phase for peak acceleration is 70 degrees from zero crossing resulting in exit energy of 4 MeV. The photoinjector will operate with 1μs pulses at 1 kHz, dissipating 3 kW of heat. Details of the design are presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPAB139

Export •

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

WEPAB115

Normal Conducting CW Transverse Crab Cavity For Producing Short Pulses In SPEAR3

2840

Z. Li, V.A. Dolgashev, M. Dunham, K.J. Gaffney, R.O. Hettel, X. Huang, N. Kurita, J.A. Safranek, J.J. Sebek, K. Tian
SLAC, Menlo Park, California, USA

Funding: This work was supported by DOE Contract No. DE-AC02-76SF00515.
The ability to produce short pulse X-rays on the scale of 1-10 ps fwhm in the SPEAR3 storage ring light source would enable enhanced timing mode studies of dynamic processes in materials as they occur. The crab cavity approach appears to be optimal for SPEAR3 to produce short pulse X-rays. Furthermore, by using a two-frequency crabbing scheme, SPEAR3 would be able to produce short-pulse bunches while supplying the high average flux needed for regular users. While supercon-ducting RF (SCRF) technology could be a natural choice for the CW crab cavity, the deflecting voltage for SPEAR3 crabbing appears to be within reach of more affordable normal conducting RF (NCRF). In this paper, we present a preliminary NCRF CW crab cavity design for SPEAR3.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB115

Export •

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

WEPAB138

Prototyping High-Gradient mm-Wave Accelerating Structures

2902

E.A. Nanni, V.A. Dolgashev, A.A. Haase, J. Neilson, S.G. Tantawi
SLAC, Menlo Park, California, USA
S.C. Schaub
MIT, Cambridge, Massachusetts, USA
B. Spataro
INFN/LNF, Frascati (Roma), Italy
R.J. Temkin
MIT/PSFC, Cambridge, Massachusetts, USA

We present single-cell accelerating structures designed for high-gradient testing at 110 GHz. The purpose of this work is to study the basic physics of ultrahigh vacuum RF breakdown in high-gradient RF accelerators. The accelerating structures are pi-mode standing-wave cavities fed with a TM01 circular waveguide. The structures are fabricated using precision milling out of two metal blocks, and the blocks are joined with diffusion bonding and brazing. The impact of fabrication and joining techniques on the cell geometry and RF performance will be discussed. First prototypes had a measured Qo of 2800, approaching the theoretical design value of 3300. The geometry of these accelerating structures are as close as practical to single-cell standing-wave X-band accelerating structures more than 40 of which were tested at SLAC. This wealth of X-band data will serve as a baseline for these 110 GHz tests. The structures will be powered with short pulses from a MW gyrotron oscillator. RF power of 1 MW may allow us to reach an accelerating gradient of 400 MeV/m.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPAB138

Export •

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

THPIK125

Ultra High Gradient Breakdown Rates in X-Band Cryogenic Normal Conducting Rf Accelerating Cavities

4395

SUSPSIK097

use link to see paper's listing under its alternate paper code

A.D. Cahill, J.B. Rosenzweig
UCLA, Los Angeles, California, USA
V.A. Dolgashev, S.G. Tantawi, S.P. Weathersby
SLAC, Menlo Park, California, USA

Funding: Work Supported by DOE/SU Contract DE-AC02-76-SF00515, US NSF Award PHY-1549132, the Center for Bright Beams, and DOE SCGSR Fellowship.
RF breakdown is one of the major factors limiting the operating accelerating gradient in rf particle accelerators. We conjecture that the breakdown rate is linked to the movements of crystal defects induced by periodic mechanical stress. Pulsed surface heating possibly creates a major part of this stress. By decreasing crystal mobility and increasing yield strength we hope to reduce the breakdown rate for the same accelerating gradient. We can achieve these properties by cooling a copper accelerating cavity to cryogenic temperatures. We tested an 11.4 GHz cryogenic copper accelerating cavity at high power and observed that the rf and dark current signals are consistent with Q₀ changing during rf pulses. To take this change in Q₀ into account, we created a non-linear circuit model in which the Q₀ is allowed to vary inside the pulse. We used this model to process the data obtained from the high power test of the cryogenic accelerating structure. We present the results of measurements with low rf breakdown rates for surface electric fields near 500 MV/m for a shaped rf pulse with 150 ns of flat gradient.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK125

Export •

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

THPIK126

Design of a Field-Emission X-Band Gun Driven by Solid-State RF Source

4399

E.A. Nanni, V.A. Dolgashev, J. Neilson, S.G. Tantawi
SLAC, Menlo Park, California, USA
B.E. Carlsten, J.W. Lewellen, D.C. Nguyen
LANL, Los Alamos, New Mexico, USA
M. Othman
UCI, Irvine, California, USA

We present the design of a field-emission X-band gun designed to be powered using a solid-state RF source. The source of the electron beam is a field emission nano-tip array. The RF gun is intended to be a beam source for 1 MeV solid-state driven linac for deployment on a satellite to map magnetic fields in the magnetosphere. The gun has to satisfy strict requirements on both average and peak power consumption, as well as rapid turn on time. In order to achieve low power consumption, the RF gun operates at relatively low accelerating gradient of 2 MeV/m. The beam exit energy is ~20 keV for an RF power 1.5 kW. Each cell of the RF gun is separately powered by commercially available, GaN high electron mobility transistors. In proof of principle experiments we successfully powered a 9.3 GHz accelerating cavity with a 100 W transistor and a 1% duty cycle.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-THPIK126

Export •

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