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DOE OSTI2020

Generation of ultrafast electron bunch trains via trapping into multiple periods of plasma wakefields

We demonstrate a novel approach to the generation of femtosecond electron bunch trains via laser-driven wakefield acceleration. We use two independent high-intensity laser pulses, a drive, and an injector, each creating their own plasma wakes. The interaction of the laser pulses and their wakes results in a periodic injection of free electrons in the drive plasma wake via several mechanisms, including ponderomotive drift, wake-wake interference, and pre-acceleration of electrons directly by strong laser fields. Electron trains were generated with up to four quasi-monoenergetic bunches, each separated in time by a plasma period. In conclusion, the time profile of the generated trains is deduced from an analysis of beam loading and confirmed using 2D particle-in-cell simulations

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Simulation of shot noise effects in the EIC strong hadron cooling accelerator using real number of electrons

In the electron ion collider design, in order to achieve the peak luminosity 10 34 /cm 2 /s with a reasonable lifetime, an efficient coherent electron cooling scheme was proposed to reduce the hadron beam emittance growth. Such a cooling scheme requires a good electron beam quality with a small energy spread. However, the shot noise in the electron beam through the accelerator might be amplified due to the microbunching instability and degrades the electron beam quality in the modulator section of the strong hadron cooling channel and correspondingly cooling rate. In this study, we report on self-consistent simulations of these effects using a real number of electrons to capture the details of shot noise and analysis of the shot noise growth through the accelerator.

Qiang, Ji↗

DOE OSTI2025

Cyclotron resonance accelerators for industrial applications

Here, this paper describes novel configurations for cyclotron resonance acceleration of electrons and ions that have several attractive features including: a compact robust room-temperature single-cell RF cavity as the accelerator structure; and continuous high current accelerated un-bunched beam output with self-scanning, obviating need for a separate beam scanner. An electron accelerator version, the electron Cyclotron Resonance Accelerator (eCRA), is under development to be an efficient source for high power electron and x-ray beams for medical, research, sterilization, and National Security applications, so as to replace radioactive materials. An ion accelerator version, the ion Cyclotron Auto-Resonance Accelerator (iCARA) is described here, suggesting its potential to produce, as an example, a high-current multi-MeV beam of deuterons which could be highly competitive with that produced either with linacs or cyclotrons. Such a deuteron beam could produce a high flux of fast neutrons via deuteron stripping, for applications including the transmutation of used nuclear fuel, material studies relevant for a fusion reactor inner wall, tritium breeding and medical isotope production. For the high-current, high efficiency simulated performance for eCRA and iCARA as described in this paper, the particle beams produced may not exhibit the low emittance values that are important for most discovery research. Rather, the beams could be useful for industrial applications where higher emittance and some energy spread can be tolerated, in favor of high beam power.

43 PARTICLE ACCELERATORS↗

DOE OSTI2025

Single-Shot Reconstruction of Electron Beam Longitudinal Phase Space in a Laser Wakefield Accelerator

We report on a single-shot longitudinal phase-space reconstruction diagnostic for electron beams in a laser wakefield accelerator via the experimental observation of distinct periodic modulations in the angularly resolved spectra. Such modulated angular spectra arise as a result of the direct interaction between the ultrarelativistic electron beam and the laser driver in the presence of the wakefield. A constrained theoretical model for the coupled oscillator, assisted by a genetic algorithm, can recreate the experimental electron spectra and, thus, fully reconstructs the longitudinal phase-space distribution of the electron beam with a temporal resolution of approximately 1.3 fs. In particular, it reveals the slice energy spread of the electron beam, which is important to measure for applications such as x-ray free electron lasers. In our experiment, the root-mean-square energy spread retrieved is bounded at 9.9 MeV, corresponding to a 0.9%–3.0% relative spread, despite the overall GeV energy beam having approximately 100% relative energy spread.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

Electron beam characterization via quantum coherent optical magnetometry

We present a quantum optics-based detection method for determining the position and current of an electron beam. As electrons pass through a dilute vapor of rubidium atoms, their magnetic field perturbs the atomic spin's quantum state and causes polarization rotation of a laser resonant with an optical transition of the atoms. By measuring the polarization rotation angle across the laser beam, we recreate a 2D projection of the magnetic field and use it to determine the e-beam position, size, and total current. We tested this method for an e-beam with currents ranging from 30 to 110 μA. Our approach is insensitive to electron kinetic energy, and we confirmed that experimentally between 10 and 20 keV. In conclusion, this technique offers a unique platform for noninvasive characterization of charged particle beams used in accelerators for particle and nuclear physics research.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2026

Design of a 915 MHz conduction-cooled cryomodule

High-power, compact, continuous-wave (CW) linear electron accelerators with beam energies of up to 10 MeV are being considered for possible industrial applications. Conduction-cooled, superconducting radio-frequency (SRF) technology allows operating such machines at high electrical efficiency, thereby reducing the operating cost significantly. A prototype conduction-cooled SRF cryomodule has been designed and components are currently being manufactured. The cryomodule features a two-cell, 915 MHz SRF cavity, two cryocoolers, a fundamental power coupler, two magnetic shields, a thermal shield and warm-to-cold transitions. The cryomodule has been designed to be able to provide an energy gain of 3.5 MeV to a CW electron beam with a current of 5 mA. This contribution focusses on thermal and mechanical design aspects of the cryomodule.

Ciovati, G. [Old Dominion Univ., Norfolk, VA (Unit↗

DOE OSTI2025

Design of a 915 MHz conduction-cooled cryomodule

Ciovati, G. [Old Dominion Univ., Norfolk, VA (Unit↗

DOE OSTI2022

200 MV Record Voltage Of vCM And LCLS-II-HE Cryomodules Production Start At Fermilab

The Linac Coherent Light Source (LCLS) is an X-ray science facility at SLAC National Accelerator Laboratory. The LCLS-II project (an upgrade to LCLS) is in the commissioning phase; the LCLS-II-HE (High Energy) project is another upgrade to the facility, enabling higher energy operation. An electron beam is accelerated using superconducting radio frequency (SRF) cavities built into cryomodules. It is planned to build 24 1.3 GHz standard cryomodules and one 1.3 GHz single-cavity Buncher Capture Cavity (BCC) cryomodule for the LCLS-II-HE project. Fourteen of these standard cryomodules and the BCC are planned to be assembled and tested at Fermilab. Procurements for standard cryomodule components are nearing completion. The first LCLS-II-HE cryomodule, referred to as the verification cryomodule (vCM) was assembled and tested at Fermilab. Fermilab has completed the assembly of the second cryomodule. This paper presents LCLS-II-HE cryomodule production status at Fermilab, emphasizing the changes done based on the successes, challenges, mitigations, and lessons learned from LCLS-II; validation of the changes with the excellent vCM results.

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

Multi-objective Bayesian active learning for MeV-ultrafast electron diffraction

Ultrafast electron diffraction using MeV energy beams(MeV-UED) has enabled unprecedented scientific opportunities in the study of ultrafast structural dynamics in a variety of gas, liquid and solid state systems. Broad scientific applications usually pose different requirements for electron probe properties. Due to the complex, nonlinear and correlated nature of accelerator systems, electron beam property optimization is a time-taking process and often relies on extensive hand-tuning by experienced human operators. Algorithm based efficient online tuning strategies are highly desired. Here, we demonstrate multi-objective Bayesian active learning for speeding up online beam tuning at the SLAC MeV-UED facility. The multi-objective Bayesian optimization algorithm was used for efficiently searching the parameter space and mapping out the Pareto Fronts which give the trade-offs between key beam properties. Such scheme enables an unprecedented overview of the global behavior of the experimental system and takes a significantly smaller number of measurements compared with traditional methods such as a grid scan. This methodology can be applied in other experimental scenarios that require simultaneously optimizing multiple objectives by explorations in high dimensional, nonlinear and correlated systems.

43 PARTICLE ACCELERATORS↗

NASA NTRS1993

Ion acceleration and abundance enhancements by electron beam instabilities in impulsive solar flares

We show that a nonrelativistic electron beam in a hydrogen-helium solar flare plasma will excite H(+) electromagnetic ion cyclotron, shear Alfven, and R-X waves, in addition to waves resulting from the two-stream instability. The H(+) electromagnetic ion cyclotron and shear Alfven waves are able to selectively accelerate ambient He-3 and Fe, respectively, to MeV energies through first harmonic gyroresonance, and thereby account for the large (He-3)/(He-4) and Fe/C ratios seen in the energetic particles from impulsive solar flares. In this model, separate heating and acceleration mechanisms for either He-3 or Fe are not required, and Fe acceleration is quite efficient since it does not need to occur by second harmonic gyroresonance. The combination of the other two unstable modes is able to accelerate ions to hundreds of MeV if the particles become trapped in an electrostatic potential well of a two-stream wave.

Miller, James A.↗

NASA NTRS1991

Measurements of the spatial structure and directivity of 100 KeV photon sources in solar flares using PVO and ISEE-3 spacecraft

The objective of this grant was to measure the spatial structure and directivity of the hard X-ray and low energy gamma-ray (100 keV-2 MeV) continuum sources in solar flares using stereoscopic observations made with spectrometers aboard the Pioneer Venus Orbiter (PVO) and Third International Sun Earth Explorer (ISEE-3) spacecraft. Since the hard X-ray emission is produced by energetic electrons through the bremsstrahlung process, the observed directivity can be directly related to the 'beaming' of electrons accelerated during the flare as they propagate from the acceleration region in the corona to the chromosphere/transition region. Some models (e.g., the thick-target model) predict that most of the impulsive hard X-ray/low energy gamma-ray source is located in the chromosphere, the effective height of the X-ray source above the photosphere increasing with the decrease in the photon energy. This can be verified by determining the height-dependence of the photon source through stereoscopic observations of those flares which are partially occulted from the view of one of the two spacecraft. Thus predictions about beaming of electrons as well as their spatial distributions could be tested through the analysis proposed under this grant.

Anderson, Kinsey A.↗

NASA NTRS1987

Rapid temporal evolution of radiation from non-thermal electrons in solar flares

Solutions of the time dependent Fokker-Planck equation was found for accelerated electrons undergoing Coulomb collisions in a magnetized, fully ionized plasma. An exact solution was found for arbitrary pitch angle and energy distribution in a uniform background plasma. Then, for an inhomogeneous plasma, a solution was found for particles with small pitch angles. These solutions were used to calculate the temporal evolution of bremsstrahlung x-rays from short bursts of nonthermal electron beams, and these spectra were compared with observed high time resolution spectra of short timescale solar hard x-ray bursts. It is shown that the observed softening in time of the spectra rules out a homogeneous background and therefore the possibility of electrons being confined to the corona either because of converging magnetic field or high densities. The inhomogeneous solution was also applied to a model with constant coronal density and exponentially rising chromospheric density. The spectra are shown to be consistent with that produced by a collimated beam of electrons accelerated in the corona with certain given conditions. These conditions could be violated if large pitch angle electrons are present.

Lu, Edward T.↗

NASA NTRS1988

Rapid temporal evolution of radiation from nonthermal electrons in solar flares

Solutions of the time dependent Fokker-Planck equation was found for accelerated electrons undergoing Coulomb collisions in a magnetized, fully ionized plasma. An exact solution was found for arbitrary pitch angle and energy distribution in a uniform background plasma. Then, for an inhomogeneous plasma, a solution was found for particles with small pitch angles. These solutions were used to calculate the temporal evolution of bremsstrahlung X-rays from short bursts of nonthermal electron beams, and these spectra were compared with observed high time resolution spectra of short timescale solar hard X-ray bursts. It is shown that the observed softening in time of the spectra rules out a homogeneous background and therefore the possibility of electrons being confined to the corona either because of converging magnetic field or high densities. The inhomogeneous solution was also applied to a model with constant coronal density and exponentially rising chromospheric density. The spectra are shown to be consistent with that produced by a collimated beam of electrons accelerated in the corona with certain given conditions. These conditions could be violated if large pitch angle electrons are present.

Lu, Edward T.↗

DOE OSTI2020

LaserNetUS at the Extreme Light Laboratory. Final report

This is the final report for LaserNetUS, Grant # DE-SC0019419. This project covered the first two annual cycles (2018-2020) of LaserNetUS experiments conducted at the Extreme Light Laboratory, University of Nebraska-Lincoln. The project provided students and scientists from four institutions (BYU, Stanford, UNR, and ARFL) with access to a world-class high-intensity laser facility. Experimental results were obtained on the topics of Nonlinear Thomson scattering, Relativistic vacuum acceleration, and electron beams in relativistic high-energy-density plasma to study x-ray line emission and radio frequencies of ultrashort relativistic electron beam interactions. Another benefit was the training of 10 students (undergraduate or graduate) and 6 young scientists (postdoc or associate/research professors) in critical areas to the future development of high energy density science and high-power laser technology.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2024

An Induction-Type Septum Magnet for the Hadron and Electron Injection of the EIC Complex

The design of the electron Ion Collider (EIC) project is under way to be built at the Brookhaven National Laboratory (BNL) with the collaboration of the Thomas Jefferson National Accelerator Facility (TJNAF). The Rapid Cycling Synchrotron (RCS) which is part of the EIC accelerator complex will accelerate the electron beam up to 18 GeV, and the beam will be injected into the Electron Storage Ring (ESR) to collide with the hadron beam circulating in the Hadron Storage Ring (HSR) which is a modified version of the Relativistic Heavy Ion Collider (RHIC). All three synchrotrons will be located in the same tunnel. This technical note provides information on the latest electromagnetic design of the induction-type septum magnet which will be employed by EIC to Inject the beam into the HSR and RCS and also extract the beam from the RCS.

43 PARTICLE ACCELERATORS↗

DOE OSTI2023

Optics Studies for Multipass Energy Recovery at CEBAF: ER@CEBAF

Energy recovery linacs (ERLs), focus on recycling the kinetic energy of electron beam for the purpose of accelerating a newly injected beam within the same accelerating structure. The rising developments in the super conducting radio frequency technology, ERL technology has achieved several noteworthy milestones over the past few decades. In year 2003, Jefferson Lab has successfully demonstrated a single pass energy recovery at the CEBAF accelerator. Furthermore, they conducted successful experiments with IR-FEL demo and upgrades, as well as the UV FEL driver. This multi-pass, multi-GeV range energy recovery demonstration proposed to be carried out at CEBAF accelerator at Jefferson Lab focuses on demonstrating highest energy recovery in super conducting linac in the low-current range. Continuous electron beam accelerate up to 7.5 GeV within 5-passes and decelerate in the next 5-passes recovering RF energy and dumps at a low energy dump. The beamline optics design for recirculating linacs require special attention to avoid beam instabilities due to RF wakefields. Usually, multi-pass linac beam lines require stronger focusing at lower energies as that is necessary to avoid beam breakup (BBU) instabilities, even with this small beam current. The CEBAF linac optics optimization is focused on balancing over-focusing at higher energies and beta excursions at lower energies. The race-track-shaped geometry of CEBAF accelerator allows its linacs to accommodate multiple energy beams simultaneously, while individual recirculating arcs transporting one beam energy, are shared between accelerating/decelerating beams. For the linac optics optimization process, an extended strategy is used that is originally used in 6-pass Recirculating Linac design of the LHeC, to represent the ten passes through a single linac. Using proper mathematical expressions, linac optics optimization can be achieved with evolutionary genetic algorithms, with Multi-Objective optimization. This thesis introduces a CEBAF optics redesign tailored to accommodates the ER@CEBAF multi-pass ER scheme. The isochronous arcs were retuned to match into optics solutions for optimized 10-pass linacs. Within this work, a single bunch particle tracking analysis presented here focuses on the further improvements of the beamline and beam transportation.

Neththikumara, Isurumali↗

DOE OSTI2021

Picosecond laser generated plasma as a source of singly charged ions for external injection into an EBIS

The focus of this paper is on practical aspects of ion generation by picosecond lasers as a source of low charge state ions for external injection of ions into an electron beam ion source (EBIS). For a ps-laser, compared to a ns-laser currently used at Relativistic Heavy Ion Collier Electron Beam Ion Source (RHIC EBIS), the influence of heat conductivity in the solid target is almost negligible, which results in a lower target consumption rate and less vacuum pressure rise. By using a laser with high repetition rate, it is possible to produce quasi continuous 1+ ion beams for periods of tens of milliseconds, making it possible to take advantage of the ability of the EBIS to accumulate ions in the “slow” injection capture mode. Producing such an ion pulse train is now feasible since ps-lasers with pulse energy up to 10 mJ and rep-rate up to 10 kHz have recently become commercially available. The advantages of this lower current accumulation scheme include: (1) easier beam transport due to lower space charge of lower beam currents required compared to the present single pulse fast injection scheme, (2) better EBIS pulse to pulse ion output stability since pulse to pulse ion variations of the laser source are averaged over a long train of laser pulses, and (3) the possible addition of an isotope separator in which rare beams could be produced and selected at run time from less expensive (unenriched) targets. We studied the properties of plasmas generated by a ps-laser with 1.27 mJ energy within an 8 ps pulse and a repetition rate up to 400 Hz at Argonne National Laboratory to investigate feasibility and specify parameters for a laser ion source for RHIC EBIS using a “slow” injection mode. Al, Ti, Cu, Nb, and Ta targets were tested with various target translation speeds. Here, we demonstrated that a both “slow” and “fast” injection modes are accessible with a single ion source geometry and single injection line, providing the most attractive option for an ion source for external injection into RHIC EBIS trap based on a ps-laser.

43 PARTICLE ACCELERATORS↗

DOE OSTI2019

Producing multi-coloured bunches through beam-induced ionization injection in plasma wakefield accelerator

Our work discusses the properties of electron beams formed in plasma wakefield accelerators through ionization injection. Specifically, the potential for generating a beam composed of co-located multi-colour beamlets is demonstrated in the case where the ionization is initiated by the evolving charge field of the drive beam itself. The physics of the processes of ionization and injection are explored through OSIRIS simulations. Experimental evidence showing similar features are presented from the data obtained in the E217 experiment at the FACET facility of the SLAC National Laboratory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗