An emittance exchange (EEX) beamline may provide a unique capability in transferring a transverse beam density modulation into longitudinal bunching. This process can be advantageous for achieving coherent bunches at below the micron level. This can provide conditions of super-radiance in a radiating system, or a large input signal for a high gain in the FEL process. This mechanism has been proposed to enable FEL action down to the few nm scale for future facilities. We investigate the feasibility of creating longitudinal density modulation at the Argonne Wakefield Accelerator, beginning with the case of 200-800 nm bunching in a pC-level beam. We discuss plans for modulated beam creation, also addressing collective and nonlinear effects in the EEX beamline and subsequent radiation-based diagnosis via CTR or FEL processes.

We report theoretical calculations of plasma wave generation in the whistler modes and in the extraordinary modes, by pulsed electron beams in a magnetized plasma. The numerical simulations of the wave generation take into account the longitudinal expansion of the electron beam due to the space charge force and the energy spread. The work presented in this article provides predictions for the wave generation performance of the beam plasma interactions experiment (Beam PIE), where pulsed electron beams were produced by a spaceborne radio frequency (RF) linear accelerator. We also theoretically explore the desirable properties of the pulsed electron beam for future space experiments, which will be the next step toward eventually demonstrating the radiation-belt remediation (RBR).

A new instrument for electron beam characterization has been developed, based on measuring the range of beam electrons in different thicknesses of aluminum, to determine both the current and energy of an electron beam traveling in open air. This instrument is referred to as a ‘plate spectrometer’ as the thickness of the spectrometer is adjusted by adding or removing alu- minum plates. This spectrometer was assembled and then characterized at the Idaho Accelerator Center (IAC) with three different beam energies and with one beam energy at the University of Maryland Radiation Facilities. The plate spectrometer was able to match the median energies and provide a reasonable constraint to the beam distributions seen in the IAC magnetic spectrometer. In a separate experiment, the plate spectrometer was also seen to agree with a dosimetry characterization of the beam at the University of Maryland Radiation Facilities and improved upon the uncertainties of this measurement.

Summary: An experiment to fly an accelerator in space recently concluded successfully. Discuss the objectives, differences from terrestrial accelerators, and results from the flight. Accelerators have the potential to play a major role in space-based activities. These can range from investigation of the Earth’s magnetic field, to helping mitigate the effects of increased solar activity (e.g. by helping drain the Earth’s radiation belts of charged particles), to deep-space missions. There are many challenges associated with operating accelerators in a space-based environment, however, ranging from high-voltage systems, to thermal management, to spacecraft charging. The Beam-Plasma Interaction Experiment – BeamPIE – was a small electron accelerator launched on a sounding rocket in 2023, to both explore the interaction of an electron beam with the near-earth plasma environment, and to test several new approaches to accelerator design in a space environment. This talk presents an overview of the BeamPIE accelerator design, mission objectives, and results from its flight.

Dielectric materials are foundational to our modern-day communications, defense, and commerce needs. Although dielectric breakdown is a primary cause of failure of these systems, we do not fully understand this process. We analyzed the dielectric breakdown channel propagation dynamics of two distinct types of electrical trees. One type of these electrical trees has not been formally classified. We observed the propagation speed of this electrical tree type to exceed 10 million meters per second. These results identify substantial gaps in the understanding of dielectric breakdown, and filling these gaps is paramount to the design and engineering of dielectric materials that are less susceptible to electrostatic discharge failure.

Insufficiently accurate magnetic-field-line mapping between the equatorial magnetosphere and the ionosphere prevents us from determining the cause of many types of aurora and ionospheric phenomena and from knowing many of the connections in the magnetosphere-ionosphere-thermosphere system.The bold MIO mission concept is to operate a powerful 1-MeV electron accelerator on a main spacecraft in the equatorial nightside magnetosphere: with the beam directed into the atmospheric loss cone the accelerator deposits energy of ionizing electrons in the atmosphere sufficient to optically illuminate the magnetic footpoint of the spacecraft while 4 nearby daughter spacecraft make equatorial magnetospheric measurements.A network of ground-based imagers in Alaska and Canada will locate the optical beamspot thereby unambiguously establishing the connection between equatorial magnetospheric measurements and ionospheric phenomena.Critical gradient and boundary measurements will be made to discern magnetospheric generator mechanisms and boundary mapping.This enables the magnetospheric drivers of various aurora, ionospheric phenomena, and field-aligned currents to be determined.

Although planar beams appears to be the ultimate solution for realizing high frequency vacuum electron devices, it is very challenging to form a sheet beam that exhibits high transport characteristics and low beam loss. Typically, a circular/elliptical beam from thermionic cathode is compressed to a high compression ratio using high magnetic focusing. The compression often causes rapid increase of transverse momentum, increasing emittance. The emittance growth in turn leads to beam interceptions at the narrow aperture of SWS/cavities. To mitigate this, we propose to use planar array of field emitters that will eventually provide a uniform planar electron beam. Field emitters are electron emitters capable of emitting electrons after the application of high voltage. The idea is to form a sheet beam from a planar array Field Emitter Arrays (FEAs), obviating the need for high magnetic compression of the beam, with the hypothesis that there will be no anomalous emittance growth. The emittance behavior of the Diamond FEAs has been analyzed and demonstrated at LANL before. This presentation will focus on beam coalescing effect of multiple beamlets emitted from field emitters and how they form sheet beam from a planar array of these beamlets.

We report the start-to-end modeling of our accelerator lattice design employing a laser-assisted bunch compression (LABC) scheme in an X-ray free electron laser (XFEL), using the proposed Matter-Radiation Interactions in Extremes (MaRIE) XFEL parameters. The accelerator lattice utilized a two-stage bunch compression scheme, with the first bunch compressor performing a conventional bulk compression enhancing the beam current from 20 A to 500 A, at 750 MeV. The second bunch compression was achieved by modulating the beam immediately downstream of the first bunch compressor by a laser with 1-μm wavelength in a laser modulator, accelerating the beam to the final energy of 12 GeV, and compressing the individual 1-μm periods of the modulated beam into a sequence of microbunches with 3-kA current spikes by the second bunch compressor. The LABC architecture presented had been developed based on the scheme of enhanced self-amplified spontaneous emission (ESASE), but operated in a disparate regime of parameters. Enabled by the novel technology of the cryogenic normal conducting radiofrequency photoinjector, we investigated an electron beam with ultra-low emittance at the starting point of the lattice design. Our work aimed at mitigating the well-known beam instabilities to preserve the beam emittance and suppress the energy spread growth.

voltage variation across the induction cells is shown to be nearly unchanged for end-point energies above 10 MeV.

Flat-beam transforms (FBTs) provide a technique for controlling the emittance partitioning between the beam's two transverse dimensions. To date, nearly all FBT studies have been in regimes where the beam's own space-charge effects can be ignored, such as in applications with high-brightness electron linacs where the transform occurs at high, relativistic, energies. Additionally, FBTs may provide a revolutionary path to high-power generation at high frequencies in vacuum electron devices where the beam emittance is currently becoming a limiting factor, which is the motivation for this paper. Electron beams in vacuum electron devices operate both at a much lower energy and a much higher current than in accelerators and the beam's space-charge forces can no longer be ignored. Here we analyze the effects of space charge in FBTs and show there are both linear and nonlinear forces and effects. The linear effects can be compensated by retuning the FBT and by adding additional quadrupole elements. The nonlinear effects lead to an ultimate dilution of the lower recovered emittance and may lead to an eventual power limitation for high-frequency traveling-wave tubes and other vacuum electron devices.

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamics code is developed based on a Lagrangian method for the calculation of the particles' radiation near-fields using wavefront/wavelet meshes via the Green's function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in 2D/3D simulations at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. The current 2D implementation of CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed. Extension of the core algorithms to 3D is possible and planned.

Los Alamos National Laboratory has developed an incoherent, long-range, sub-centimeter resolution (LIDAR) with which we achieve centimeter-scale reflection holography at extremely long ranges. The system consists of a pulsed laser and photon-counting receiver. This combination yields round-trip time of flight data to illuminate parts of the object of interest. The aggregation of these data for many LIDAR pulses yields a plot with a range on the X axis and reflectance on the Y axis, which we refer to as a range profile. Observing that the range profile is a projection of the reflection map of the object onto the view vector, we collect profiles from a variety of viewing angles and invert these data to form an image. We adapt imaging algorithms from the field of computer aided tomography to suit our application and present results from imaging demonstrations at a 10 km range.

A workshop on The Next Generation Gamma-Ray Sources sponsored by the Office of Nuclear Physics at the Department of Energy, was held November 17--19, 2016 in Bethesda, Maryland. The goals of the workshop were to identify basic and applied research opportunities at the frontiers of nuclear physics that would be made possible by the beam capabilities of an advanced laser Compton beam facility. To anchor the scientific vision to realistically achievable beam specifications using proven technologies, the workshop brought together experts in the fields of electron accelerators, lasers, and optics to examine the technical options for achieving the beam specifications required by the most compelling parts of the proposed research programs. An international assembly of participants included current and prospective $\gamma$-ray beam users, accelerator and light-source physicists, and federal agency program managers. Sessions were organized to foster interactions between the beam users and facility developers, allowing for information sharing and mutual feedback between the two groups. The workshop findings and recommendations are summarized in this whitepaper.

In this article, we report theoretical and design studies on the application of an electrostatic potential depression (EPD) on two types of traditional microwave sources, the klystron and the inductive output tube (IOT), both operating in the UHF band. The EPD is implemented by a section of the metallic beam pipe on which a direct current (dc) negative high voltage is applied. Inside the EPD section, the modulated electron beam develops into bunches over a very short longitudinal distance, indicating a possible design approach for a compact device. With the application of an EPD, the peak value of the first harmonic current in a microwave tube can be further increased compared to that in a conventional design, suggesting higher circuit efficiency. As the electron beam leaves the EPD section, the reacceleration of the beam provides a longitudinal cooling effect. With the addition of an EPD, circuit power extraction efficiency above 80% is achieved in both the modified design of the IOT and the novel conceptual circuit design of the klystron.

The preservation of low-emittance electron beams will continue to be a challenge and an objective in rflinac-driven accelerators where off-axis steering can lead to both transverse long-range wakefields (LRWs) and short-range wakefields (SRWs) that dilute the emittance [1]. Earlier experimentalists using normal conducting S-band and L-band accelerators have mitigated these effects by steering the beam optimally through the cavities while watching downstream imaging screens [2] or streak camera images [3]. One can even tune the wakefields to cancel some of the effects in a few normal conducting L-band structures by not centering the beam on a screen or BPM after each structure in simulations [4]. Since the transverse wakefields depend on 1/a where a is the cavity bore radius, it was somewhat surprising to identify both LRWs including higher order modes (HOMs) [5] and SRWs [6] in the superconducting rf TESLA-type cavities with their larger 35-mm radii. These cavities are used in major accelerator facilities (FLASH and the European XFEL), the under-construction LCLS-II XFEL, the Superconducting Test Facility in Japan, and proposed for the conceptual International Linear Collider (ILC) in Japan. Recent tests at Fermilab showed that near-resonance conditions of an HOM frequency with a beam harmonic resulted in submacropulse centroid oscillations at 100 kHz that diluted macropulse-averaged beam size [5]. More importantly, the same off-axis steering resulted in the generation of SRWs whose submicropulse transverse head-tail kicks produced projected beam size dilutions of 40% and greater in the sampled distributions, an effect at least 5x larger than that of the HOMs [6]. Such effects would also dilute the emittance values, and they would be a particular problem for ultra-low emittance preservation. These effects were seen after only two TESLA-type cavities with beam injected at 4.5 MeV and a final energy of 41 MeV. The transverse wakes depend on charge, beam offset, and the SQRT of bunch length, but inversely on beam energy. Thus, the emittance dilution threat is highest at the lower energies in the first accelerator cavities after the gun such as occurs in the LCLS-II injector with <1 MeV into the cryomodule. This same principle applies to all accelerators in labs around the country at Fermilab, SLAC, and Argonne. In the case of the SC rf cavities, HOM couplers provide online signals of dipolar modes dependent on beam offset and downstream streak camera images or a rf transverse deflecting cavity (TDC) plus screen provide submicropulse information. Such a scenario of multiple options for steering and tracking beam effects should be a prime application for machine learning techniques with extensions to virtual diagnostics [7].

We propose a new method for the precise measurement of dielectric permittivity of ceramics and polymers at millimeter-wave frequencies that employs the TE01 mode of a circular waveguide. At higher frequencies, accurately measuring the dielectric permittivity of materials becomes extremely challenging by using the fundamental TE10 mode of a rectangular waveguide. As the frequency increases, the dimensions of the dielectric sample that has to be fit into the waveguide become very small. Therefore, small fabrication imperfections that produce air gaps between the sample and the wall of the waveguide result in significant errors during measurements. In contrast, the TE01 mode of the circular waveguide that does not have an electric field at the surface of the waveguide is insensitive to small imperfections during fabrication. We measured the dielectric permittivity in small samples of alumina (Al2O3), magnesium calcium titanate (MCT) ceramics, and Teflon placed in a circular waveguide. The results showed that the method was very robust with respect to manufacturing imperfections: when dimensions of the alumina and Teflon samples varied by as much as 10% and 20%, the differences in the computed dielectric permittivity of the alumina were only 1.26% and 3.06%, respectively, and those of Teflon were 1.98% and 2.12%. In addition, when the high-dielectric permittivity material MCT samples were deformed by 5% and 10%, the differences were just 0.04% and 0.14% each, respectively. We believe that this new proposed method is also applicable to even higher frequencies in the THz regime and at a very high relative dielectric permittivity of larger than 10.

Ganguli and Crabtree have written a comment about a recent article by the authors listed above on radiation-belt remediation. They have objected to our evaluation of the Naval Research Laboratory’s chemical release concept which states that this concept may be impractical due to an apparently low overall efficiency. In their comment, they provide a scientific argument and refer to the published literature to counter our statement. Here, we provide more details on our numerical calculations and experimental results which led to this evaluation.

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 −1 . 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 m. 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. The emittance, we note, is the effective area in transverse phase space ( x , p x / m e c ) or ( y , p y / m e c ) occupied by the beam distribution, and it is relevant to achievable beam sizes as well as setting a limit on FEL wavelength. 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—including the imaging of virus particles—which may profit from this new model of performing XFEL science.