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DOE OSTI2016

Band gap opening in strongly compressed diamond observed by x-ray energy loss spectroscopy

The extraordinary mechanical and optical properties of diamond are the basis of numerous technical applications and make diamond anvil cells a premier device to explore the high-pressure behavior of materials. However, at applied pressures above a few hundred GPa, optical probing through the anvils becomes difficult because of the pressure-induced changes of the transmission and the excitation of a strong optical emission. Such features have been interpreted as the onset of a closure of the optical gap in diamond, and can significantly impair spectroscopy of the material inside the cell. In contrast, a comparable widening has been predicted for purely hydrostatic compressions, forming a basis for the presumed pressure stiffening of diamond and resilience to the eventual phase change to BC8. We here present the first experimental evidence of this effect at geo-planetary pressures, exceeding the highest ever reported hydrostatic compression of diamond by more than 200 GPa and any other measurement of the band gap by more than 350 GPa. We here apply laser driven-ablation to create a dynamic, high pressure state in a thin, synthetic diamond foil together with frequency-resolved x-ray scattering as a probe. The frequency shift of the inelastically scattered x-rays encodes the optical properties and, thus, the behavior of the band gap in the sample. Using the ultra-bright x-ray beam from the Linac Coherent Light Source (LCLS), we observe an increasing direct band gap in diamond up to a pressure of 370 GPa. This finding points to the enormous strains in the anvils and the impurities in natural Type Ia diamonds as the source of the observed closure of the optical window. Our results demonstrate that diamond remains an insulating solid to pressures approaching its limit strength.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Ultrafast Science Opportunities with Electron Microscopy

X-rays and electrons are two of the most fundamental probes of matter. When the Linac Coherent Light Source (LCLS), the world’s first x-ray free electron laser, began operation in 2009, it transformed ultrafast science with the ability to generate laser-like x-ray pulses from the manipulation of relativistic electron beams. This document describes a similar future transformation. In Transmission Electron Microscopy, ultrafast relativistic (MeV energy) electron pulses can achieve unsurpassed spatial and temporal resolution. Ultrafast temporal resolution will be the next frontier in electron microscopy and can ideally complement ultrafast x-ray science done with free electron lasers. This document describes the Grand Challenge science opportunities in chemistry, material science, physics and biology that arise from an MeV ultrafast electron diffraction & microscopy facility, especially when coupled with linac-based intense THz and X-ray pump capabilities.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

DOE OSTI2016

TESLA & ILC Cryomodules

The TESLA collaboration developed a unique variant of SRF cryomodule designs, the chief feature being use of the large, low pressure helium vapor return pipe as the structural support backbone of the cryomodule. Additional innovative features include all cryogenic piping within the cryomodule (no parallel external cryogenic transfer line), long strings of RF cavities within a single cryomodule, and cryomodules connected in series. Several projects, including FLASH and XFEL at DESY, LCLS-II at SLAC, and the ILC technical design have adopted this general design concept. Advantages include saving space by eliminating the external transfer line, relatively tight packing of RF cavities along the beamline due to fewer warm-cold transitions, and potentially lower costs. However, a primary disadvantage is the relative lack of independence for warm-up, replacement, and cool-down of individual cryomodules.

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

Accomplishments in the Trident Laser Facility

Trident has been an extremely productive laser facility, despite its modest size and operating cost in the firmament of high-energy, high-power laser facilities worldwide. More than 150 peer-reviewed journal articles (in 39 different journals) have been published using Trident experimental data, many in high-impact journals such as Nature, Nature Physics, Nature Communications, and Physical Review Letters. More than 230 oral presentations involving research at Trident have been presented at national and international conferences. Trident publications have over 5000 citations in the literature with an h-index of 38. AT least 23 Los Alamos postdoctoral researchers have worked on Trident. In the period since its inception in 1992-2007, despite not issuing formal proposal calls for access nor functioning explicitly as a user facility until later, Trident has 170 unique users from more than 30 unique institutions, such as Los Alamos, Lawrence Livermore, and Sandia national laboratories, various University of California campuses, General Atomic, Imperial College, and Ecole Polytechnique. To reinforce its role as an important Los Alamos point of connection to the external research community, at least 20 PhD students did a significant fraction of their thesis work on Trident. Such PhD students include Mike Dunne (Imperial College, 1995) - now director of LCLS and professor at Stanford; David Hoarty (IC, 1997) - scientist at Atomic Weapons Establishment, UK; Dustin Froula (UC Davis, 2002) - Plasma and Ultrafast Physics Group leader at the Laboratory for Laser Energetics and assistant professor at the Physics and Astronomy Department at the University of Rochester; Tom Tierney (UC Irvine, 2002) - scientist at Los Alamos; Eric Loomis (Arizona State U., 2005) - scientist at Los Alamos; and Eliseo Gamboa (University of Michigan, 2013) - scientist at the Linac Coherent Light Source. The work performed on Trident, besides its scientific impact, has also supported the Inertial Confinement Fusion and Weapons research programs at the Laboratory. It also has advanced technologies and techniques that hold significant promise for Los Alamos initiatives, such as MaRIE (the proposed Matter-Radiation Interactions in Extremes experimental facility), and more generally for important societal applications, such as defense, global security, advanced accelerators, fusion energy, radiotherapy, and laser technology. Specific research contributions based on Trident experiments are listed below.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2016

Computational time-resolved and resonant x-ray scattering of strongly correlated materials

Basic-Energy Sciences of the Department of Energy (BES/DOE) has made large investments in x-ray sources in the U.S. (NSLS-II, LCLS, NGLS, ALS, APS) as powerful enabling tools for opening up unprecedented new opportunities for exploring properties of matter at various length and time scales. The coming online of the pulsed photon source, literally allows us to see and follow the dynamics of processes in materials at their natural timescales. There is an urgent need therefore to develop theoretical methodologies and computational models for understanding how x-rays interact with matter and the related spectroscopies of materials. The present project addressed aspects of this grand challenge of x-ray science. In particular, our Collaborative Research Team (CRT) focused on developing viable computational schemes for modeling x-ray scattering and photoemission spectra of strongly correlated materials in the time-domain. The vast arsenal of formal/numerical techniques and approaches encompassed by the members of our CRT were brought to bear through appropriate generalizations and extensions to model the pumped state and the dynamics of this non-equilibrium state, and how it can be probed via x-ray absorption (XAS), emission (XES), resonant and non-resonant x-ray scattering, and photoemission processes. We explored the conceptual connections between the time-domain problems and other second-order spectroscopies, such as resonant inelastic x-ray scattering (RIXS) because RIXS may be effectively thought of as a pump-probe experiment in which the incoming photon acts as the pump, and the fluorescent decay is the probe. Alternatively, when the core-valence interactions are strong, one can view K-edge RIXS for example, as the dynamic response of the material to the transient presence of a strong core-hole potential. Unlike an actual pump-probe experiment, here there is no mechanism for adjusting the time-delay between the pump and the probe. However, the core hole predominantly decays via Auger processes, thereby providing an internal time-scale, which limits intermediate-state processes to timescales of a few femtoseconds. Accordingly, a number of activities directed at modeling K-, L- and M-edge RIXS in correlated materials were also pursused by our CRT. Our research effort supported by this CMCSN grant substantially advanced the understanding of x-ray scattering processes in the time-domain as well as in the more conventional scattering channels, including time-resolved photoemission, and how such processes can be modeled realistically in complex correlated materials more generally. The modeling of relaxation processes involved in time-domain spectroscopies is important also for understanding photoinduced effects such as energy conversion in photosynthesis and solar cell applications, and thus impacts the basic science for energy needs.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Building a Unified Computational Model for the Resonant X-Ray Scattering of Strongly Correlated Materials

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Technical Design Report for the FACET-II Project at SLAC National Accelerator Laboratory

Electrons can “surf” on waves of plasma – a hot gas of charged particles – gaining very high energies in very short distances. This approach, called plasma wakefield acceleration, has the potential to dramatically shrink the size and cost of particle accelerators. Research at the SLAC National Accelerator Laboratory has demonstrated that plasmas can provide 1,000 times the acceleration in a given distance compared with current technologies. Developing revolutionary and more efficient acceleration techniques that allow for an affordable high-energy collider has been the focus of FACET, a National User Facility at SLAC. FACET used part of SLAC’s two-mile-long linear accelerator to generate high-density beams of electrons and their antimatter counterparts, positrons. Research into plasma wakefield acceleration was the primary motivation for constructing FACET. In April 2016, FACET operations came to an end to make way for the second phase of SLAC’s x-ray laser, the LCLS-II, which will use part of the tunnel occupied by FACET. FACET-II is a new test facility to provide the unique capability to develop advanced acceleration and coherent radiation techniques with high-energy electron and positron beams. FACET-II represents a major upgrade over current FACET capabilities and the breadth of the potential research program makes it truly unique.

43 PARTICLE ACCELERATORS↗

DOE OSTI2017

Estimate of Joule Heating in a Flat Dechirper

We have performed Joule power loss calculations for a flat dechirper. We have considered the configurations of the beam on-axis between the two plates—for chirp control—and for the beam especially close to one plate—for use as a fast kicker. Our calculations use a surface impedance approach, one that is valid when corrugation parameters are small compared to aperture (the perturbative parameter regime). In our model we ignore effects of field reflections at the sides of the dechirper plates, and thus expect the results to underestimate the Joule losses. The analytical results were also tested by numerical, time-domain simulations. We find that most of the wake power lost by the beam is radiated out to the sides of the plates. For the case of the beam passing by a single plate, we derive an analytical expression for the broad-band impedance, and—in Appendix B—numerically confirm recently developed, analytical formulas for the short-range wakes. While our theory can be applied to the LCLS-II dechirper with large gaps, for the nominal apertures we are not in the perturbative regime and the reflection contribution to Joule losses is not negligible. With input from computer simulations, we estimate the Joule power loss (assuming bunch charge of 300 pC, repetition rate of 100 kHz) is 21 W/m for the case of two plates, and 24 W/m for the case of a single plate.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Final Scientific Report: DE-SC0008580

We report scientific, technical, and organizational accomplishments under DE-SC0008580. This includes 10 publications, 5 patent or provisional patent applications, beamtime with important results at both LCLS and APS, and new progress in understanding target design for x-ray heating experiments at x-ray heating facilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

High Power S-Band Vacuum Dry Loads for SLAC Linac

In the beginning of LCLS-1 commission era, an unstable termination mode of the residual RF power on all vacuum dry loads of the SLAC linac was found. The S-Band loads on the current SLAC linac RF system were designed, in some cases, 50+ years ago to terminate stably only 2-3 MW peak power into a thin layer of coated Kanthal material as the high power absorber. The technology of the load design was based on a old flame-sprayed Kanthal wire method onto a base material. During SLAC linac upgrades, the RF power sources dramatically increased from 24 MW peak klystrons to 240 MW peak (with new klystrons and SLED cavities). As a result, the residual RF power on the loads was increased accordingly. The original RF loads were overstressed and cannot stably terminate the residual RF power in the present RF linac layout.

43 PARTICLE ACCELERATORS↗

DOE OSTI2019

LANL Accelerator Activities for C-band

LANL has a range of accelerator activities that would benefit from improvements in RF resonator performance. XFEL (presently using a SRF baseline similar to LCLS-II) would benefit from much higher gradient and long-pulse operation of copper structures. Higher gradient RF structures for lower energy accelerators (~100 MeV) would also provide a path to transportable systems, such as ICS sources. Lastly, the utilization of dielectrics could be exploited for increased efficiency and compactness, e.g. for accelerator in space efforts. A LANL R&D effort aims at systematic improvement of copper structures employing material science simulations to explain and improve breakdown effects, combined with highly optimized designs, integration of cryo-cooling and the use of dielectric insertions. The work is integrated into a High-Gradient collaboration between SLAC, UCLA and LANL.

43 PARTICLE ACCELERATORS↗

DOE OSTI2017

Optimizing the UED beam line design via ImpactT simulation

The high charge low energy compressor system developed at NSLS-II can generate 5MeV electron bunches with 50pC charge (10 -8 electrons) focusing to 30 micron beam size and bunch length of order of 100 fs. NSLS-II plans to build it as part of the existing instrument for the ultra-fast electron diffraction (UED) and ultra-fast electron microscope (UEM) experiments to be installed at ATF-II, BNL. The expected intensity will be several orders of magnitudes higher than achieved previously using current technology (~10 -4 -10 -5 electrons). This type of accelerator based MeV electron microscopes, taking advantage of strong interaction of electrons with matter and overcoming space charge problem, are complementary to XFEL, such as LCLS.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Adaptive Sample Preparation and Target Fabrication for High-Throughput Materials Science

High-repetition-rate brilliant and coherent light sources are significantly increasing the rate at which scientific experiments can be performed. An investment in transformative technologies to make samples of condensed matter could enable a paradigm shift for that field or open new exciting frontiers in high-energy density science (HEDS). This will especially be true for dynamic materials in extremes research or HEDS, where the repetition rate for placing samples into extreme environments is increasing and the samples or targets are irreversibly destroyed in each experiment. Research teams that are able to implement solutions to all aspects of the experimental process and enable a paradigm of high-throughput science will have the greatest success and impact. There are two different directions for adaptive samples. One is research when the number of experiments can be greatly increased with increased volume, such as in high energy density science. The other is when flexibility and agility can aid Bayesian optimization computational methods and speed up the discovery process, as with materials science. Conducting a similar equation-of-state (EOS) experiment took three years on the OMEGA laser facility, compared to five days of shifts at the LCLS XFEL. New materials with improved properties have been found by guided optimization of experimental science. Adaptive sample preparation and target fabrication can create a tremendous return on scientific investment. High-throughput enabling precision science is also a desirable goal. To address these issues, we sought a diverse set of innovative participants who had ideas of how to achieve this paradigm shift. We invited 42 researchers from a variety of disciplines and fields to attend a workshop in College Station, Texas, May 14–16, 2019. Many of the participants had never been in the same room before, and most found it very exciting to hear about new and different research. The goal was twofold: to define the challenges, i.e., “what would we like to be able to do and why it is difficult to do so,” and to describe the progress, approaches and capabilities, as well as the vision, “what we could do if we had more support.”

36 MATERIALS SCIENCE↗

DOE OSTI2010

An Energy Tunable X-ray Delay Device - Phase II

One potential limitation of the LCLS is the maximum frequency—120 Hz— at which the individual pulses are produced. This maximum frequency is dictated by the fundamental design of the original linear accelerator and serves as a limit on the “frames per second” that can be illuminated by the beam. A potential solution for accessing ultrafast dynamics is by temporally splitting the X-ray pulses into two pulses with arbitrary relative intensity and time delay. In this manner, dynamics ranging from the X-ray pulse duration (between one and several hundred femtoseconds) and the maximum relative pulse delay can be explored by evaluating the X-ray response collected as a function of the relative pulse delay.

43 PARTICLE ACCELERATORS↗

DOE OSTI2019

Probing Ultrafast Electron (De)localization Dynamics in Mixed Valence Complexes Using Femtosecond X-ray Spectroscopy (Final Report)

The overall goal of this research program was to understand valence electron and vibrational motion following metal-to-metal charge transfer (MMCT) excitation in the mixed valence complexes dissolved in aqueous solution. The project objectives were (i) to observe the time-dependent re-arrangement of d electrons across two transition metal sites and the bridging ligand following photoinduced MMCT excitation on a sub-50 femtosecond timescale using femtosecond X-ray pulses generated at LCLS (ii) to simulate femtosecond X-ray absorption and emission spectra of solvated, photo-excited, transition metal mixed valence complexes using a realistic treatment of multi-electron correlations/transitions, spin-orbit coupling and final state lifetime effects and to propose and study the feasibility of nonlinear X-ray experiments on solvated transition metal mixed valence systems using future X-FEL light sources and (iii) to determine the role of coupled electronic and vibrational motions during ultrafast photoinduced charge transfer. The final report highlights the scientific results obtained during this funding period.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

APS-TD Helium Cryogenic Facilities

Cryogenic System: • CMTF cryogenic system is supplied by a state of the art Superfluid Cryogenic Plant to supply 40K, 5K, and 2K helium up to 500 W. 2K operations achievable through cold or warm compression systems. Currently Supports: • Cryo Module Test Stand 1 (CMTS1) used to test 1.3 GHz & 3.9 GHz cryomodules for the LCLS-II project. • PIP-II Injection Test Stand (PIP-II IT) program to test the front end of the future PIP-II Linac.and production cryomodules

43 PARTICLE ACCELERATORS↗

DOE OSTI2020

Thermal / structural analysis of the HB 650 thermal shield

Fermilab’s PIP-II project’s superconducting linear accelerator will drive the next generation of particle accelerators through a revolution in beam intensity. Key to beam intensification are the high efficiencies of niobium-tin superconducting radiofrequency (SRF) cavities operating at cryogenic temperatures near 5 Kelvin. A multifaceted approach is employed to achieve and maintain the extreme temperature. Vacuum provides the first barrier to thermal convection. Physical thermal intercept zones further isolate the exterior shell vacuum vessel at 300 Kelvin from the supercooled beamline. The first thermal intercept lies just inside the exterior vacuum vessel forming the 40 Kelvin zone. This 40K thermal shield is the focus of this investigation. In preparation for operation, the thermal shield is cooled from 300K to 40K in a slow process over 2-1/2 days. The factors limiting the cooling rate are a high thermal gradient which produces thermal strain and high mechanical stress. D ecreasing the time required to reach operational temperatures is the desired research goal. Physical testing data and finite element method (FEM) computer models from the Single Spoke Resonator – 1 (SSR1) and Linac Coherent Light Source (LCLS-II) cryomodules will be evaluated to determine needed design changes. The thermal shield design for the High Beta 650 MHz (HB650) will be modified and analyzed using FEM computer models to determine maximum cooling rate with a target of 50 thermal cycles of life. Maximum allowable stress will be determined through low cycle fatigue calculations.

43 PARTICLE ACCELERATORS↗

DOE OSTI2021

Nonlinear X-ray Optics

Novel X-ray free-electron lasers (XFELs) are capable of producing radiation with unprecedented properties. Specifically, their ultrashort coherent X-ray pulses can generate extreme peak intensities where ordinary rules of light-matter interaction may no longer apply, and nonlinear processes start to become important. XFELs have made it possible to observe some of the most important coherent non-sequential nonlinearities, including X-ray-optical sum frequency generation (SFG), X-ray second harmonic generation (XSHG), two-photon absorption (TPA) and nonlinear two-photon Compton scattering (2PCS). In particular, the 2PCS experiment has led to unexpected results, namely the observation of a substantial anomalous red shift in the energy of photons generated by nonlinear two-photon X-ray Compton scattering in beryllium. The energy shift is in addition to the predicted nonlinear Compton shift and was neither expected from extrapolations from linear X-ray interactions nor from nonlinear effects at optical wavelengths. Our results suggest a novel nonlinear scattering mechanism that can only be observed at high fields at X-ray wavelengths, where the photon energy is a significant fraction of the electron rest mass (and thus a significant momentum transfer to the electron occurs during the scattering) and where the interaction is not dominated by the quiver motion of the electron in the field (ponderomotive potential) as is usually the case at longer (optical) wavelengths. The goal of this research project was the investigation of fundamental nonlinear X-ray-matter interactions. As these processes are typically weak, part of this research is the exploration of more efficient nonlinear X-ray processes by studying novel mechanisms including solid-state effects, the assistance of optical radiation and novel phase-matching techniques. These experiments require extremely large X-ray field strengths, such as produced by XFELs. Nonlinear X-ray effects can lead to important applications in many research fields. For example, it could lead to instantaneous plasma diagnostics for materials in extreme conditions, as a method for combining atomic-scale structural sensitivity with chemical specificity, or as a probe of electron dynamics in solids on the attosecond (1 as = 10 -18 s) time- and Ångstrom (10 -10 m) length scales. In addition, a detailed understanding of nonlinear X-ray matter interactions is crucial for understanding and extending the limits of structural determination at high intensity such as in serial femto-crystallography. The results could have a profound impact on advanced XFEL light sources such as the LCLS-II.

47 OTHER INSTRUMENTATION↗