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Faraday Rotation Measurements in High-Energy-Density Plasmas Using Shaped Laser Beams
Magnetic fields play an important role in plasma dynamics, yet it is a quantity difficult to measure accurately with physical probes, whose presence disturbs the very field they measure. The Faraday rotation of a polarized beam of light provides a mechanism to measure the magnetic field without disturbing the dynamics, and has been used with great success in astrophysics and high energy density plasma science, where physical probes cannot be used. Furthermore, the rotation is typically small, which degrades the accuracy of the measurement. Since polarization cannot be measured directly, detectors rely on a polarizer to measure a small change in beam intensity instead. In this work, we show how beam shaping can improve Faraday rotation measurements using an optical derivative setup. Since the rotation measurement is now strictly proportional to the beam shape and intensity, the system allows to improve the measurement accuracy simply by increasing the laser beam power.
Beam shaping using an ultrahigh vacuum multileaf collimator and emittance exchange beamline
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Preliminary study of photomask pattern inspection by beam-shaped knife-edge interferometry
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Electron beam shaping for actively outcoupling radiation from an x-ray regenerative amplifier free-electron laser
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Ion Channel Laser Based on Direct Laser Acceleration of a Shaped Beam Driver (Final Technical Report)
The main focus of our research was to understand the synergies between an electron bunch and a laser pulse when the two co-propagate through the plasma. We have clearly demonstrated using theoretical and computational modeling that the propagation distance of both the bunch and the laser pulse could be extended. The ability of the combined bunch/pulse system to extend the propagation distance and the size of the plasma bubble enables highly-efficient sources of relativistic electrons. As pointed out by the Plasma Decadal Study, such electron sources can be used for generating extremely bright x-rays for a variety of applications can serve as probes and diagnostics for other plasma experiments: high energy density (HED) sciences, inertial confinement fusion (ICF), and potentially Fusion Materials and Technology (FM&T). Development of advanced diagnostics of plasma-based accelerators is yet another key area identified by recent reports. Even broader security and medical applications of compact accelerator-based radiation sources, such as very high energy electron (VHEE) sources for FLASH radiobiology, have been identified by a recent multi-agency panel. A number of key technical issues were considered and successfully resolved during the course of the grant. Those include: beam loading effect of both the driver and witness bunches on the wake, laser channeling by the bunch, and the direct laser acceleration (DLA) of the driver bunch by the laser pulse. To demonstrate clear synergy, we were able to ascertain that the total energy gain of a witness bunch in the wake of the combined bunch/laser complex is large than the sum of the energy gains in the wake of the laser pulse alone, and the driver bunch alone. We have also demonstrated that not only the energy gain is improved, but the energy spread is not sacrificed. To carry out these simulations, we have to develop a range of in-house computational tools, including a fully-3D code WAND-PIC.
Parametric study of high-energy ring-shaped electron beams from a laser wakefield accelerator
Abstract Laser wakefield accelerators commonly produce on-axis, low-divergence, high-energy electron beams. However, a high charge, annular shaped beam can be trapped outside the bubble and accelerated to high energies. Here we present a parametric study on the production of low-energy-spread, ultra-relativistic electron ring beams in a two-stage gas cell. Ring-shaped beams with energies higher than 750 MeV are observed simultaneously with on axis, continuously injected electrons. Often multiple ring shaped beams with different energies are produced and parametric studies to control the generation and properties of these structures were conducted. Particle tracking and particle-in-cell simulations are used to determine properties of these beams and investigate how they are formed and trapped outside the bubble by the wake produced by on-axis injected electrons. These unusual femtosecond duration, high-charge, high-energy, ring electron beams may find use in beam driven plasma wakefield accelerators and radiation sources.
System and method for grain refinement and general control of grain morphology in laser additive manufacturing
The present disclosure relates to a system for forming a material layer that may make use of an optical light source for generating an optical beam, and a beam shaping subsystem configured to shape the optical beam to generate a complex beam intensity profile. The complex shaped beam may be used to selectively melt at least portions of a bed of powder particles residing on a substrate during formation of the material layer, as the optical light source is moved. A computer may be used to control the optical light source. The complex beam intensity profile enables control over the microstructure of grains formed during melting of the powder particles as the material layer is formed.
Efficient six-dimensional phase space reconstructions from experimental measurements using generative machine learning
Next-generation accelerator concepts, which hinge on the precise shaping of beam distributions, demand equally precise diagnostic methods capable of reconstructing beam distributions within six-dimensional position-momentum spaces. However, the characterization of intricate features within six-dimensional beam distributions using current diagnostic techniques necessitates a substantial number of measurements, using many hours of valuable beam time. Novel phase space reconstruction techniques are needed to reduce the number of measurements required to reconstruct detailed, high-dimensional beam features in order to resolve complex beam phenomena and as a feedback in precision beam shaping applications. In this study, we present a novel approach to reconstructing detailed six-dimensional phase space distributions from experimental measurements using generative machine learning and differentiable beam dynamics simulations. We demonstrate that this approach can be used to resolve six-dimensional phase space distributions from scratch, using basic beam manipulations and as few as 20 two-dimensional measurements of the beam profile. We also demonstrate an application of the reconstruction method in an experimental setting at the Argonne Wakefield Accelerator, where it is able to reconstruct the beam distribution and accurately predict previously unseen measurements 75× faster than previous methods.
Generation of structured coherent extreme ultraviolet beams from an MgO crystal
Short wavelength high-harmonic sources are undergoing intense development for applications in spectroscopy and microscopy. Despite recent progress in peak and average power, spatial control over coherent extreme ultraviolet (XUV) beams remains a formidable challenge due to the lack of suitable optical elements for beam shaping and control. In this work, we demonstrate a robust and precise approach that structures XUV high-order harmonics in space as they are emitted from a nanostructured MgO crystal. Our demonstration paves the way for bridging the numerous applications of shaped light beams from the visible to the short wavelengths, with potential uses for applications in microscopy and nanoscale machining.
FEgen (v.1): Field Emission Distribution Generator Freeware Based on Fowler–Nordheim Equation
This work presents an open-source code, FEgen, that generates initial field emission distributions based on the time-dependent Fowler–Nordheim equation. Current in-demand and open-source beam tracking software—such as ASTRA, IMPACT-T, and GPT—do not contain native distribution generator functions suitable for field emitted electron tracking and phase space analysis. Furthermore, the intuitive graphical user interface of FEgen generates input files shown to be fully compatible with both ASTRA and GPT. Here, detailed application examples demonstrating a subset of FEgen’s capabilities are given by creating a customized emitter pattern with application to transverse beam shaping and longitudinal beam dynamic experiments.
Subsurface Spectroscopy in Heterogeneous Materials Using Self-Healing Laser Beams
Self-healing optical beams are a class of propagation modes that can recover their beam shapes after distortion or partial blockage. This self-healing property makes them attractive for use in applications involving turbid media as they can—in theory—penetrate further into these materials than standard Gaussian beams. In this paper, we characterize the propagation of two different self-healing beams (Bessel and Airy) through a solid scattering material with different scatterer concentrations and find that both beams do recover after scattering for samples below a threshold scatterer concentration. Additionally, we test the applicability of both beam shapes for improved sub-surface spectroscopy in heterogeneous materials using fluorescent particles and find that there is an average fluorescence intensity enhancement of 1.3× using self-healing beams versus a standard Gaussian beam.
Simulating MADMAX in 3D: Requirements for Dielectric Axion Haloscopes
We present 3D calculations for dielectric haloscopes such as the currently envisioned MADMAX experiment. For ideal systems with perfectly flat, parallel and isotropic dielectric disks of finite diameter, we find that a geometrical form factor reduces the emitted power by up to 30% compared to earlier 1D calculations. We derive the emitted beam shape, which is important for antenna design. We show that realistic dark matter axion velocities of 10 -3 c and inhomogeneities of the external magnetic field at the scale of 10% have negligible impact on the sensitivity of MADMAX. We investigate design requirements for which the emitted power changes by less than 20% for a benchmark boost factor with a bandwidth of 50 MHz at 22 GHz, corresponding to an axion mass of 90 μeV. We find that the maximum allowed disk tilt is 100 μm divided by the disk diameter, the required disk planarity is 20 μm (min-to-max) or better, and the maximum allowed surface roughness is 100 μm (min-to-max). We show how using tiled dielectric disks glued together from multiple smaller patches can affect the beam shape and antenna coupling.
Astigmatic electron beam propagation
An astigmatic electron beam with an ellipticity ratio of approximately 2:1 was examined using the Enhanced Modified Faraday Cup (EMFC) diagnostic to measure its properties and show how the power density distribution varies near the beam waist. Results show that the beam has two power density peaks, one on either side of the beam crossover point, resulting from different focal distances of the major and minor axes of the elliptical beam shape. Quantification of the beam properties was used to establish a depth-of-field where the beam diameter and peak power densities are relatively constant. For the 1 kW beam studied here, the depth-of-field measured approximately ±5 mm from the beam crossover point, illustrating how electron beam diagnostics can be used to identify process control limits for repeatable and reliable welds under non-ideal electron beam power density distribution conditions.
Probing strong-field QED in beam-plasma collisions
Ongoing progress in laser and accelerator technology opens new possibilities in high-field science, notably to investigate the largely unexplored strong-field quantum electrodynamics (SFQED) regime where electron-positron pairs can be created directly from light-matter or even light-vacuum interactions. Laserless strategies such as beam-beam collisions have also been proposed to access the nonperturbative limit of SFQED. Here we report on a concept to probe SFQED by harnessing the interaction between a high-charge, ultrarelativistic electron beam and a solid conducting target. When impinging onto the target surface, the beam self fields are reflected, partly or fully, depending on the beam shape; in the rest frame of the beam electrons, these fields can exceed the Schwinger field, thus triggering SFQED effects such as quantum nonlinear inverse Compton scattering and nonlinear Breit-Wheeler electron-positron pair creation. Through reduced modeling and kinetic numerical simulations, we show that this single-beam setup can achieve interaction conditions similar to those envisioned in beam-beam collisions, but in a simpler and more controllable way owing to the automatic overlap of the beam and driving fields. This scheme thus eases the way to precision studies of SFQED and is also a promising milestone towards laserless studies of nonperturbative SFQED.
Beam dynamics challenges in linear colliders based on laser-plasma accelerators
In this paper we discuss design considerations and beam dynamics challenges associated with laser-driven plasma-based accelerators as applied to multi-TeV-scale linear colliders. Plasma accelerators provide ultra-high gradients and ultra-short bunches, offering the potential for compact linacs and reduced power requirements. We show that stable, efficient acceleration with beam quality preservation is possible in the nonlinear bubble regime of laser-plasma accelerators using beam shaping. Ion motion, naturally occuring for dense beams (i.e., low emittance and high energy) severely damps transverse beam instabilities. Coulomb scattering by the background ions is considered and it is shown that the strong focusing in the plasma strongly suppresses scattering-induced emittance growth. Finally, Betatron radiation emission from the transverse motion of the beam in the plasma will result in beam power loss and energy spread growth; however for sub-100 nm emittances, the beam power loss and energy spread growth will be sub-percent for multi-TeV-class plasma linacs.