IPAC2018 - List of Authors (Tantawi, S.G.)

Paper	Title	Page
MOPML052	The Path to Compact, Efficient Solid-State Transistor-Driven Accelerators	520
	D.C. Nguyen, C.E. Buechler, G.E. Dale, R.L. Fleming, M.A. Holloway, J.W. Lewellen, D. Patrick LANL, Los Alamos, New Mexico, USA V.A. Dolgashev, E.N. Jongewaard, E.A. Nanni, J. Neilson, A.V. Sy, S.G. Tantawi SLAC, Menlo Park, California, USA
	Funding: Research presented in this work is supported by (LANL) Laboratory Directed Research and Development 20170521ER and by (SLAC) Department of Energy contract DE-AC02-76SF00515. Small, lightweight, few-MeV electron accelerators that can operate with low-voltage power sources, e.g., solid-state transistors running on 50 VDC, instead of high-voltage klystrons, will provide a new tool to enhance existing applications of accelerators as well as to initiate new ones. Recent advances in gallium nitride (GaN) semiconductor technologies * have resulted in a new class of high-power RF solid-state devices called high-electron mobility transistors (HEMTs). These HEMTs are capable of generating a few hundred watts at S-, C- and X-bands at 10% duty factor. We have characterized a number of GaN HEMTs and verified they have suitable RF characteristics to power accelerator cavities *. We have measured energy gain as a function of RF power in a single low-beta C-band cavity. The HEMT powered RF accelerators will be compact and efficient, and they can operate off the low-voltage DC power buses or batteries. These all-solid-state accelerators are also more robust, less likely to fail, and are easier to maintain and operate. In this poster, we present the design of a low-beta, 5.1-GHz cavity and beam dynamics simulations showing continuous energy gain in a ten-cavity C-band prototype. See for example, http://www.wolfspeed.com/downloads/dl/file/id/463/product/174/cghv59350.pdf ** J.W. Lewellen et al., Proceedings of LINAC2016, Paper MO3A03
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPML052
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUYGBD5	A 2D Steady-State Space Charge Solver for Azimuthally Symmetric Problems of Arbitrary Degree
	A.R. Gold, A. R. Gold, S.G. Tantawi SLAC, Menlo Park, California, USA
	Student poster award talk
	Slides TUYGBD5 [4.665 MB]
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUZGBE4	Toward High-Power High-Gradient Testing of mm-Wave Standing-Wave Accelerating Structures	1224
	E.A. Nanni, V.A. Dolgashev, A.A. Haase, J. Neilson, S.G. Tantawi SLAC, Menlo Park, California, USA S. Jawla, R.J. Temkin MIT/PSFC, Cambridge, Massachusetts, USA S. C. Schaub MIT, Cambridge, Massachusetts, USA B. Spataro INFN/LNF, Frascati (Roma), Italy
	Funding: This work is supported in part by Department of Energy contract DE-AC02-76SF00515 (SLAC) and DE-SC0015566 (MIT). We will preliminary testing results for single-cell accelerating structures intended 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 consist of pi-mode standing-wave cavities fed with TM01 circular waveguide mode. We fabricated of two structures one in copper and the other in CuAg alloy. Cold RF tests confirm the design RF performance of the structures. The geometry and field shape of these accelerating structures is 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 a MW gyrotron oscillator that produces microsecond pulses. One megawatt of RF power from the gyrotron may allow us to reach a peak accelerating gradient of 400 MeV/m.
	Slides TUZGBE4 [4.644 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUZGBE4
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPAK086	A 2D Steady-State Space Charge Solver for Azimuthally Symmetric Problems of Arbitrary Degree	3431
SUSPF072	use link to see paper's listing under its alternate paper code
	A.R. Gold, A. R. Gold, S.G. Tantawi SLAC, Menlo Park, California, USA
	Correctly and rapidly simulating the steady-state interaction between particle beams and electromagnetic fields is crucial to the design and optimization of accelerator and radiofrequency (RF) source components. Iteratively solving for the self-consistent interaction between particles and fields can prove challenging and highly susceptible to numerical noise and mesh induced instabilities. We present herein two new approaches to solving the self-consistent trajectories of particles in the presence of external and self fields. The first method reformulates the integrated self field contribution as a path integral. The second method uses a hybrid Eulerian framework and produces an interpolated continuous current density, resulting in 1-2 orders of magnitude fewer particles required to obtain an accurate solution. We conclude with benchmarking results which show this method is as accurate as state of the art PIC solvers, while running 80-120X faster.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK086
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPAL080	Parallel-Feed SRF Accelerator Structures	3835
	P.B. Welander, Z. Li, M.H. Nasr, S.G. Tantawi SLAC, Menlo Park, California, USA
	Funding: This work is supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515. Development of SRF accelerator technology that enables both higher gradient and higher efficiency is crucial for future machines. While much of the recent R&D focus has been on materials and surface science, our aim is to optimize the cavity geometry to maximize performance with current materials. The recent demonstration of a highly efficient parallel-feed NCRF structure at SLAC has served as a proof-of-concept. Applied to SRF, such a structure could dramatically reduce power consumption while boosting the achievable gradient. Instead of coupled elliptical cells, our structure employs isolated reentrant cells. To feed RF power to the cavities, each cell is directly coupled to an integrated manifold. The structure is made in two parts, split along the beam axis, which are then joined. Such a structure has been fabricated from bulk Cu and tested at SLAC - designed for X-band, it operates at a record gradient of 150 MV/m. Adapting to SRF at 1.3 GHz and fabricating from Nb, such a cavity could achieve more than 50% lower RF loss and 40% higher gradient compared to the TESLA cavity. We will describe our simulations and propose an experimental roadmap for demonstrating this technology.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL080
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMF090	Linac Design Elements for Spaceborne Accelerators	4291
	J.W. Lewellen, C.E. Buechler, G.E. Dale, M.A. Holloway, D.C. Nguyen, D. Patrick LANL, Los Alamos, New Mexico, USA V.A. Dolgashev, E.N. Jongewaard, J. Neilson, S.G. Tantawi SLAC, Menlo Park, California, USA J-.M. Lauenstein NASA Goddard Space Flight Center, Greenbelt, USA
	Funding: Los Alamos National Laboratory LDRD and Program Development Los Alamos National Laboratory, in collaboration with SLAC and Goddard Space Flight Center, have begun developing a high-duty-factor, MeV-range linear accelerator intended for use on satellites, specifically to probe the magnetosphere-ionosphere linkage. The design makes use of low-beta C-band cavities operating at moderate gradients, individually powered by 500-W RF amplifier chips. We present the current state of the design, and technology maturation efforts including RF amplifier performance studies, cavity tuner design and an initial acceleration test using a DC beam source and single RF cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF090
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMK048	The Design and Construction of a Novel Dual-Mode Dual-Frequency Linac Design	4391
SUSPF045	use link to see paper's listing under its alternate paper code
	M.H. Nasr, S.G. Tantawi SLAC, Menlo Park, California, USA
	One promising approach in boosting accelerators efficiency is dual-mode simultaneous operation. In our work, the topic of dual-mode acceleration is studied from a wider perspective with new approaches and tools. We present a new type of accelerator structures that operates simultaneously with two modes and two frequencies. The frequencies are not constrained to be harmonically related, but rather have a common sub-harmonic. These designs will utilize a newly developed parallel-feeding network that feeds each individual accelerating cell independently using a distributed feeding network. As a result, the design problem converges to a single-cell design with identical cells. The cells are designed for maximum efficiency using new geometrical optimization that utilizes nonuniform rational B-spline (NURBS) with a series of control points. We will present a study on the topic for S-band simultaneous operation with C-band or X-band.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK048
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMK049	New Geometrical-Optimization Approach using Splines for Enhanced Accelerator Cavities' Performance	4395
	M.H. Nasr, S.G. Tantawi SLAC, Menlo Park, California, USA
	Over the past decades accelerator scientists made a huge effort in advancing the technology of particle accelerators, which lead to state-of-the-art fabrication techniques as well as simulation tools. Combining these advancements with the large boosting in computing speed provides large flexibility and motivation to investigate new accelerator geometries. In this paper, we describe a new optimization approach for the geometry of accelerating cells. This approach uses a set of control points with variable positions to control a non-uniform rational B-spline (NURBS), which describes the cavity shape. The positions of the control points are then optimized using differential-evolution optimization to maximize/minimize a defined optimization function, which is defined by the user and depends on the cavity parameters such as the shunt impedance, wall losses, peak surface fields…etc. This optimization approach leads to accelerator geometries with enhanced performance and very smooth surface fields.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK049
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

The Path to Compact, Efficient Solid-State Transistor-Driven Accelerators

520

D.C. Nguyen, C.E. Buechler, G.E. Dale, R.L. Fleming, M.A. Holloway, J.W. Lewellen, D. Patrick
LANL, Los Alamos, New Mexico, USA
V.A. Dolgashev, E.N. Jongewaard, E.A. Nanni, J. Neilson, A.V. Sy, S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: Research presented in this work is supported by (LANL) Laboratory Directed Research and Development 20170521ER and by (SLAC) Department of Energy contract DE-AC02-76SF00515.
Small, lightweight, few-MeV electron accelerators that can operate with low-voltage power sources, e.g., solid-state transistors running on 50 VDC, instead of high-voltage klystrons, will provide a new tool to enhance existing applications of accelerators as well as to initiate new ones. Recent advances in gallium nitride (GaN) semiconductor technologies * have resulted in a new class of high-power RF solid-state devices called high-electron mobility transistors (HEMTs). These HEMTs are capable of generating a few hundred watts at S-, C- and X-bands at 10% duty factor. We have characterized a number of GaN HEMTs and verified they have suitable RF characteristics to power accelerator cavities **. We have measured energy gain as a function of RF power in a single low-beta C-band cavity. The HEMT powered RF accelerators will be compact and efficient, and they can operate off the low-voltage DC power buses or batteries. These all-solid-state accelerators are also more robust, less likely to fail, and are easier to maintain and operate. In this poster, we present the design of a low-beta, 5.1-GHz cavity and beam dynamics simulations showing continuous energy gain in a ten-cavity C-band prototype.
* See for example, http://www.wolfspeed.com/downloads/dl/file/id/463/product/174/cghv59350.pdf
** J.W. Lewellen et al., Proceedings of LINAC2016, Paper MO3A03

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPML052

Export •

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

TUYGBD5

A 2D Steady-State Space Charge Solver for Azimuthally Symmetric Problems of Arbitrary Degree

A.R. Gold, A. R. Gold, S.G. Tantawi
SLAC, Menlo Park, California, USA

Student poster award talk

Slides TUYGBD5 [4.665 MB]

Export •

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

TUZGBE4

Toward High-Power High-Gradient Testing of mm-Wave Standing-Wave Accelerating Structures

1224

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

Funding: This work is supported in part by Department of Energy contract DE-AC02-76SF00515 (SLAC) and DE-SC0015566 (MIT).
We will preliminary testing results for single-cell accelerating structures intended 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 consist of pi-mode standing-wave cavities fed with TM01 circular waveguide mode. We fabricated of two structures one in copper and the other in CuAg alloy. Cold RF tests confirm the design RF performance of the structures. The geometry and field shape of these accelerating structures is 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 a MW gyrotron oscillator that produces microsecond pulses. One megawatt of RF power from the gyrotron may allow us to reach a peak accelerating gradient of 400 MeV/m.

Slides TUZGBE4 [4.644 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUZGBE4

Export •

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

THPAK086

A 2D Steady-State Space Charge Solver for Azimuthally Symmetric Problems of Arbitrary Degree

3431

SUSPF072

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

A.R. Gold, A. R. Gold, S.G. Tantawi
SLAC, Menlo Park, California, USA

Correctly and rapidly simulating the steady-state interaction between particle beams and electromagnetic fields is crucial to the design and optimization of accelerator and radiofrequency (RF) source components. Iteratively solving for the self-consistent interaction between particles and fields can prove challenging and highly susceptible to numerical noise and mesh induced instabilities. We present herein two new approaches to solving the self-consistent trajectories of particles in the presence of external and self fields. The first method reformulates the integrated self field contribution as a path integral. The second method uses a hybrid Eulerian framework and produces an interpolated continuous current density, resulting in 1-2 orders of magnitude fewer particles required to obtain an accurate solution. We conclude with benchmarking results which show this method is as accurate as state of the art PIC solvers, while running 80-120X faster.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAK086

Export •

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

THPAL080

Parallel-Feed SRF Accelerator Structures

3835

P.B. Welander, Z. Li, M.H. Nasr, S.G. Tantawi
SLAC, Menlo Park, California, USA

Funding: This work is supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
Development of SRF accelerator technology that enables both higher gradient and higher efficiency is crucial for future machines. While much of the recent R&D focus has been on materials and surface science, our aim is to optimize the cavity geometry to maximize performance with current materials. The recent demonstration of a highly efficient parallel-feed NCRF structure at SLAC has served as a proof-of-concept. Applied to SRF, such a structure could dramatically reduce power consumption while boosting the achievable gradient. Instead of coupled elliptical cells, our structure employs isolated reentrant cells. To feed RF power to the cavities, each cell is directly coupled to an integrated manifold. The structure is made in two parts, split along the beam axis, which are then joined. Such a structure has been fabricated from bulk Cu and tested at SLAC - designed for X-band, it operates at a record gradient of 150 MV/m. Adapting to SRF at 1.3 GHz and fabricating from Nb, such a cavity could achieve more than 50% lower RF loss and 40% higher gradient compared to the TESLA cavity. We will describe our simulations and propose an experimental roadmap for demonstrating this technology.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL080

Export •

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

THPMF090

Linac Design Elements for Spaceborne Accelerators

4291

J.W. Lewellen, C.E. Buechler, G.E. Dale, M.A. Holloway, D.C. Nguyen, D. Patrick
LANL, Los Alamos, New Mexico, USA
V.A. Dolgashev, E.N. Jongewaard, J. Neilson, S.G. Tantawi
SLAC, Menlo Park, California, USA
J-.M. Lauenstein
NASA Goddard Space Flight Center, Greenbelt, USA

Funding: Los Alamos National Laboratory LDRD and Program Development
Los Alamos National Laboratory, in collaboration with SLAC and Goddard Space Flight Center, have begun developing a high-duty-factor, MeV-range linear accelerator intended for use on satellites, specifically to probe the magnetosphere-ionosphere linkage. The design makes use of low-beta C-band cavities operating at moderate gradients, individually powered by 500-W RF amplifier chips. We present the current state of the design, and technology maturation efforts including RF amplifier performance studies, cavity tuner design and an initial acceleration test using a DC beam source and single RF cavity.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF090

Export •

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

THPMK048

The Design and Construction of a Novel Dual-Mode Dual-Frequency Linac Design

4391

SUSPF045

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

M.H. Nasr, S.G. Tantawi
SLAC, Menlo Park, California, USA

One promising approach in boosting accelerators efficiency is dual-mode simultaneous operation. In our work, the topic of dual-mode acceleration is studied from a wider perspective with new approaches and tools. We present a new type of accelerator structures that operates simultaneously with two modes and two frequencies. The frequencies are not constrained to be harmonically related, but rather have a common sub-harmonic. These designs will utilize a newly developed parallel-feeding network that feeds each individual accelerating cell independently using a distributed feeding network. As a result, the design problem converges to a single-cell design with identical cells. The cells are designed for maximum efficiency using new geometrical optimization that utilizes nonuniform rational B-spline (NURBS) with a series of control points. We will present a study on the topic for S-band simultaneous operation with C-band or X-band.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK048

Export •

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

THPMK049

New Geometrical-Optimization Approach using Splines for Enhanced Accelerator Cavities' Performance

4395

M.H. Nasr, S.G. Tantawi
SLAC, Menlo Park, California, USA

Over the past decades accelerator scientists made a huge effort in advancing the technology of particle accelerators, which lead to state-of-the-art fabrication techniques as well as simulation tools. Combining these advancements with the large boosting in computing speed provides large flexibility and motivation to investigate new accelerator geometries. In this paper, we describe a new optimization approach for the geometry of accelerating cells. This approach uses a set of control points with variable positions to control a non-uniform rational B-spline (NURBS), which describes the cavity shape. The positions of the control points are then optimized using differential-evolution optimization to maximize/minimize a defined optimization function, which is defined by the user and depends on the cavity parameters such as the shunt impedance, wall losses, peak surface fields…etc. This optimization approach leads to accelerator geometries with enhanced performance and very smooth surface fields.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK049

Export •

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