arXiv subjects

S. Tantawi

Publications and source records attributed to S. Tantawi.

12 recordsLinked to original sources

arXiv2025

A Compact Low-level RF Control System for Advanced Concept Compact Electron Linear Accelerator

A compact low-level RF (LLRF) control system based on RF system-on-chip (RFSoC) technology has been designed for the Advanced Concept Compact Electron Linear-accelerator (ACCEL) program, which has challenging requirements in both RF performance and size, weight and power consumption (SWaP). The compact LLRF solution employs the direct RF sampling technique of RFSoC, which samples the RF signals directly without any analogue up and down conversion. Compared with the conventional heterodyne based architecture used for LLRF system of linear accelerator (LINAC), the elimination of analogue mixers can significantly reduce the size and weight of the system, especially with LINAC requires a larger number of RF channels. Based on the requirements of ACCEL, a prototype LLRF platform has been developed, and the control schemes have been proposed. The prototype LLRF system demonstrated magnitude and phase fluctuation levels below 1% and 1 degree, on the flat top of a 2 microseconds RF pulse. The LLRF control schemes proposed for ACCEL are implemented with a prototype hardware platform. This paper will introduce the new compact LLRF solution and summarize a selection of experimental test results of the prototype itself and with the accelerating structure cavities designed for ACCEL.

physics.acc-ph↗

arXiv2023

LLRF System Considerations for a Compact, Commercial C-band Accelerator using the AMD Xilinx RF-SoC

This work describes the LLRF and control system in use for a novel accelerator structure developed for a compact design operating in C-band developed by SLAC, with collaboration from RadiaBeam and RadiaSoft. This design is a pulsed RF/pulsed beam system that only provides minimal monitoring for control of each two-cavity pair. Available signals include only a forward and reflected signal for each pair; such a design requires careful consideration of calibration and power-on routines, as well an understanding of how to correct for disturbances caused by the entire RF signal chain, including a new SSA, klystron, and distribution system. An AMD Xilinx RF-SoC with a separate supervisory computer is the LLRF system core, with on-board pulse-to-pulse feedback corrections. This work presents the current status of the project, as well as obstacles and manufacturing plans from the viewpoint of developing for larger-volume manufacturing. This material is based upon work supported by the Defense Advanced Research Projects Agency under Contract Numbers 140D0423C0006 and 140D0423C0007. The views, opinions, and/or findings expressed are those of the author(s) and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.

physics.acc-ph↗

arXiv2023

XCC: An X-ray FEL-based $γγ$ Compton Collider Higgs Factory

This report describes the conceptual design of a $γγ$ Higgs factory in which 62.8 GeV electron beams collide with 1 keV X-ray free electron laser (XFEL) beams to produce colliding beams of 62.5 GeV photons. The Higgs boson production rate is 80,000 Higgs bosons per 10$^7$ second year, roughly the same as the ILC Higgs rate at $\sqrt{s}$=250 GeV. The electron accelerator is based on cold copper distributed coupling (C$^3$) accelerator technology. Unlike the center-of-mass energy spectra of previous optical wavelength $γγ$ collider designs, the sharply peaked $γγ$ center-of-mass energy spectrum of XCC produces model independent Higgs coupling measurements with precision on par with $e^+e^-$ colliders. For the triple Higgs coupling measurement, the XCC center-of-mass energy can be upgraded to 380 GeV, where the cross section for $γγ\rightarrow HH$ is twice that of $e^+e^- \rightarrow ZHH$ at $\sqrt{s}$=500 GeV. Design challenges are discussed, along with the R\&D to address them, including demonstrators.

physics.acc-ph↗

arXiv2022

An Impartial Perspective for Superconducting Nb3Sn coated Copper RF Cavities for Future Accelerators

This Snowmass21 Contributed Paper encourages the Particle Physics community in fostering R&D in Superconducting Nb3Sn coated Copper RF Cavities instead of costly bulk Niobium. It describes the pressing need to devote effort in this direction, which would deliver higher gradient and higher temperature of operation and reduce the overall capital and operational costs of any future collider. It is unlikely that an ILC will be built in the next ten years with Nb as one of the main cost drivers of SRFs. This paper provides strong arguments on the benefits of using this time for R&D on producing Nb3Sn on inexpensive and thermally efficient metals such as Cu or bronze, while pursuing in parallel the novel U.S. concept of parallel-feed RF accelerator structures. A technology that synergistically uses both of these advanced tools would make an ILC or equivalent machines more affordable and more likely to be built. Such a successful enterprise would readily apply to other HEP accelerators, for instance a Muon Collider, and to accelerators beyond HEP. We present and assess current efforts in the U.S. on the novel concept of parallel-feed RF accelerator structures, and in the U.S. and abroad in producing Nb3Sn films on either Cu or bronze despite minimal funding.

physics.acc-ph↗

arXiv2020

An Ultra-Compact X-Ray Free-Electron Laser

In the field of beam physics, two frontier topics have taken center stage due to their potential to enable new approaches to discovery in a wide swath of science. These areas are: advanced, high gradient acceleration techniques, and x-ray free electron lasers (XFELs). Further, there is intense interest in the marriage of these two fields, with the goal of producing a very compact XFEL. In this context, recent advances in high gradient radio-frequency cryogenic copper structure research have opened the door to the use of surface electric fields between 250 and 500 MV/m. Such an approach is foreseen to enable a new generation of photoinjectors with six-dimensional beam brightness beyond the current state-of-the-art by well over an order of magnitude. This advance is an essential ingredient enabling an ultra-compact XFEL (UC-XFEL). In addition, one may accelerate these bright beams to GeV scale in less than 10 meters. Such an injector, when combined with inverse free electron laser-based bunching techniques can produce multi-kA beams with unprecedented beam quality, quantified by ~50 nm-rad normalized emittances. These beams, when injected into innovative, short-period (1-10 mm) undulators uniquely enable UC-XFELs having footprints consistent with university-scale laboratories. We describe the architecture and predicted performance of this novel light source, which promises photon production per pulse of a few percent of existing XFEL sources. We review implementation issues including collective beam effects, compact x-ray optics systems, and other relevant technical challenges. To illustrate the potential of such a light source to fundamentally change the current paradigm of XFELs with their limited access, we examine possible applications in biology, chemistry, materials, atomic physics, industry, and medicine which may profit from this new model of performing XFEL science.

physics.acc-ph↗

arXiv2018

Next Generation High Brightness Electron Beams From Ultra-High Field Cryogenic Radiofrequency Photocathode Sources

Recent studies of the performance of radio-frequency (RF) copper cavities operated at cryogenic temperatures have shown a dramatic increase in the maximum achievable surface electric field. We propose to exploit this development to enable a new generation of photoinjectors operated at cryogenic temperatures that may attain, through enhancement of the launch field at the photocathode, a significant increase in five-dimensional electron beam brightness. We present detailed studies of the beam dynamics associated with such a system, by examining an S-band photoinjector operated at 250 MV/m peak electric field that reaches normalized emittances in the 40 nm-rad range at charges (100-200 pC) suitable for use in a hard X-ray free-electron laser (XFEL) scenario based on the LCLS. In this case, we show by start-to-end simulations that the properties of this source may give rise to high efficiency operation of an XFEL, and permit extension of the photon energy reach by an order of magnitude, to over 80 keV. The brightness needed for such XFELs is achieved through low source emittances in tandem with high current after compression. In the XFEL examples analyzed, the emittances during final compression are preserved using micro-bunching techniques. Extreme low emittance scenarios obtained at pC charge, appropriate for significantly extending temporal resolution limits of ultrafast electron diffraction and microscopy experiments, are also reviewed. While the increase in brightness in a cryogenic photoinjector is mainly due to the augmentation of the emission current density via field enhancement, further possible increases in performance arising from lowering the intrinsic cathode emittance in cryogenic operation are also analyzed. Issues in experimental implementation, including cavity optimization for lowering cryogenic thermal dissipation, external coupling, and cryo-cooler system are discussed.

physics.acc-ph↗

arXiv2018

SLAC Microresonator Radio Frequency (SMuRF) Electronics for Read Out of Frequency-Division-Multiplexed Cryogenic Sensors

Large arrays of cryogenic sensors for various imaging applications ranging across x-ray, gamma-ray, Cosmic Microwave Background (CMB), mm/sub-mm, as well as particle detection increasingly rely on superconducting microresonators for high multiplexing factors. These microresonators take the form of microwave SQUIDs that couple to Transition-Edge Sensors (TES) or Microwave Kinetic Inductance Detectors (MKIDs). In principle, such arrays can be read out with vastly scalable software-defined radio using suitable FPGAs, ADCs and DACs. In this work, we share plans and show initial results for SLAC Microresonator Radio Frequency (SMuRF) electronics, a next-generation control and readout system for superconducting microresonators. SMuRF electronics are unique in their implementation of specialized algorithms for closed-loop tone tracking, which consists of fast feedback and feedforward to each resonator's excitation parameters based on transmission measurements. Closed-loop tone tracking enables improved system linearity, a significant increase in sensor count per readout line, and the possibility of overcoupled resonator designs for enhanced dynamic range. Low-bandwidth prototype electronics were used to demonstrate closed-loop tone tracking on twelve 300-kHz-wide microwave SQUID resonators, spaced at $\sim$6 MHz with center frequencies $\sim$5-6 GHz. We achieve multi-kHz tracking bandwidth and demonstrate that the noise floor of the electronics is subdominant to the noise intrinsic in the multiplexer.

astro-ph.IM↗

arXiv2018

Ultra-High Brightness Electron Beams from Very-High Field Cryogenic Radio-frequency Photocathode Sources

Recent investigations of RF copper structures operated at cryogenic temperatures performed by a SLAC-UCLA collaboration have shown a dramatic increase in the maximum surface electric field, to 500 MV/m. We examine use of these fields to enable very high field cryogenic photoinjectors that can attain over an order of magnitude increase in peak electron beam brightness. We present beam dynamics studies relevant to X-ray FEL injectors, using start-to-end simulations that show the high brightness and low emittance of this source enables operation of a compact FEL reaching a photon energy of 80 keV. The preservation of beam brightness in compression, exploiting micro-bunching techniques is discussed. While the gain in brightness at high field is due to increase of the emission current density, further increases in brightness due to lowering of the intrinsic cathode emittance in cryogenic operation are also enabled. While the original proposal for this type of cryogenic, ultra-high field photoinjector has emphasized S-band designs, there are numerous potential advantages that may be conferred by operation in C-band. We examine issues related to experimental implementation in C-band, and expected performance of this type of device in a future hard X-ray FEL such as MaRIE.

physics.acc-ph↗

arXiv2014

Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz

A design for a compact x-ray light source (CXLS) with flux and brilliance orders of magnitude beyond existing laboratory scale sources is presented. The source is based on inverse Compton scattering of a high brightness electron bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency standing-wave linac and RF photoinjector powered by a single ultrastable RF transmitter at x-band RF frequency. The high efficiency permits operation at repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating with trains of 100 bunches of 100 pC charge, each separated by 5 ns. The entire accelerator is approximately 1 meter long and produces hard x-rays tunable over a wide range of photon energies. The colliding laser is a Yb:YAG solid-state amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as the accelerator. The laser pulse is frequency-doubled and stored for many passes in a ringdown cavity to match the linac pulse structure. At a photon energy of 12.4 keV, the predicted x-ray flux is $5 \times 10^{11}$ photons/second in a 5% bandwidth and the brilliance is $2 \times 10^{12}\mathrm{photons/(sec\ mm^2\ mrad^2\ 0.1\%)}$ in pulses with RMS pulse length of 490 fs. The nominal electron beam parameters are 18 MeV kinetic energy, 10 microamp average current, 0.5 microsecond macropulse length, resulting in average electron beam power of 180 W. Optimization of the x-ray output is presented along with design of the accelerator, laser, and x-ray optic components that are specific to the particular characteristics of the Compton scattered x-ray pulses.

physics.acc-ph↗

arXiv2012

Molybdenum sputtering film characterization for high gradient accelerating structures

Technological advancements are strongly required to fulfill the demands of new accelerator devices with the highest accelerating gradients and operation reliability for the future colliders. To this purpose an extensive R&D regarding molybdenum coatings on copper is in progress. In this contribution we describe chemical composition, deposition quality and resistivity properties of different molybdenum coatings obtained via sputtering. The deposited films are thick metallic disorder layers with different resistivity values above and below the molibdenum dioxide reference value. Chemical and electrical properties of these sputtered coatings have been characterized by Rutherford backscattering, XANES and photoemission spectroscopy. We will also present a three cells standing wave section coated by a molybdenum layer $\sim$ 500 nm thick designed to improve the performance of X-Band accelerating systems.

physics.acc-ph↗

arXiv2009

X-band crab cavities for the CLIC beam delivery system

The CLIC machine incorporates a 20 mrad crossing angle at the IP to aid the extraction of spent beams. In order to recover the luminosity lost through the crossing angle a crab cavity is proposed to rotate the bunches prior to collision. The crab cavity is chosen to have the same frequency as the main linac (11.9942 GHz) as a compromise between size, phase stability requirements and beam loading. It is proposed to use a HE11 mode travelling wave structure as the CLIC crab cavity in order to minimise beam loading and mode separation. The position of the crab cavity close to the final focus enhances the effect of transverse wake-fields so effective wake-field damping is required. A damped detuned structure is proposed to suppress and de-cohere the wake-field hence reducing their effect. Design considerations for the CLIC crab cavity will be discussed as well as the proposed high power testing of these structures at SLAC.

physics.acc-ph↗

arXiv2001

Room temperature accelerator structures for linear colliders

Early tests of short low group velocity and standing wave structures indicated the viability of operating X-band linacs with accelerating gradients in excess of 100 MeV/m. Conventional scaling of traveling wave traveling wave linacs with frequency scales the cell dimensions with l. Because Q scales as l1/2, the length of the structures scale not linearly but as l3/2 in order to preserve the attenuation through each structure. For NLC we chose not to follow this scaling from the SLAC S-band linac to its fourth harmonic at X-band. We wanted to increase the length of the structures to reduce the number of couplers and waveguide drives which can be a significant part of the cost of a microwave linac. Furthermore, scaling the iris size of the disk-loaded structures gave unacceptably high short range dipole wakefields. Consequently, we chose to go up a factor of about 5 in average group velocity and length of the structures, which increases the power fed to each structure by the same factor and decreases the short range dipole wakes by a similar factor. Unfortunately, these longer (1.8 m) structures have not performed nearly as well in high gradient tests as the short structures. We believe we have at least a partial understanding of the reason and will discuss it below. We are now studying two types of short structures with large apertures with moderately good efficiency including: 1) traveling wave structures with the group velocity lowered by going to large phase advance per period with bulges on the iris, 2) pi mode standing wave structures

physics.acc-ph↗