Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session UO05: Laser and Accelerator DiagnosticsOn Demand
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Chair: Mathieu Bailly-Grandvaux, UCSD Room: Rooms 306-307 |
Thursday, November 11, 2021 2:00PM - 2:12PM |
UO05.00001: K-shell spectroscopy of nanowire plasmas heated with highly relativistic laser pulses Reed C Hollinger, Shoujun Wang, Huanyu Song, Ryan Nedbailo, Vyacheslav Shlyaptsev, Jorge J Rocca, Jerry Clark, Ronnie L Shepherd, Jim A Emig, Ed Magee, Matthew P Hill, Riccardo Tommasini, Alexander Pukhov, Christoph Baumann, Brian F Kraus, Lan Gao, Philip C Efthimion, Kenneth W Hill, Manfred L Bitter The K-shell emission from Ni and Ti near-solid density nanowire array plasmas and solid foils is measured with high spectral resolution at the ALEPH laser facility at Colorado State University using a suite of high-resolution x-ray spectrometers for time-integrated measurements. The addition of a sub-picosecond resolution x-ray streak camera allows for time-resolved measurements of the spectral line emission. The targets are irradiated at highly relativistic intensities, ao ~ 20, with ultra-high contrast 400 nm laser pulses of ~50 fs duration. The plasma density is varied using arrays of 100 nm diameter nanowire arrays with different wire spacings which allows us to vary the target density from 7% to 30% of solid density. The x-ray yield of the lower density nanowire arrays exceeds that of the solid density foil by a factor of ~5x. Time-resolved x-ray emission reveals that the lower density nanowire arrays reach higher temperatures and radiate for longer durations of time (~25 ps) whereas the higher density nanowire arrays radiate for shorter times, converging with the x-ray emission of solid density foils. The experimental results will be compared to three-dimensional particle-in-cell simulations. |
Thursday, November 11, 2021 2:12PM - 2:24PM |
UO05.00002: High-repetition-rate X-ray imaging of hydrodynamic shock waves using a laser wakefield accelerator Mario Balcazar, Yong Ma, Paul T Campbell, Matthew Trantham, Rachel Young, John Nees, Alexander G Thomas, Carolyn C Kuranz, Hai-En Tsai, Tobias M Ostermayr, Robert Jacob, Sahel Hakimi, Anthony J Gonsalves, Jeroen van Tilborg, Carl B Schroeder, Eric Esarey, Cameron R Geddes, Paul King, Elizabeth S Grace, Raspberry A Simpson, Felicie Albert, Nuno Lemos, Brendan Kettle, Eva E Los, Stuart Mangles Betatron X-ray sources from laser wakefield accelerators provide a promising alternative for generating bright and ultrafast radiation at a fraction of the size and cost of conventional synchrotron facilities. The oscillation of plasma electrons in the wake bubble results in the emission of X-ray bursts with sub-micron source size, low beam divergence, and femtosecond duration. These radiation characteristics, in combination with a phase-contrast imaging technique and a high-repetition-rate accelerator, allow for capturing the complete time evolution of sub-micron scale dynamic systems. In this work we present the rst demonstration of high-repetition-rate phase-contrast imaging of dynamic phenomena using betatron X-rays. For this purpose we captured the interaction of a long laser pulse (200 ps, 1J) with a 30m stream of water. By taking advantage of the high-repetition-rate and high-resolution properties of the BELLA HTW betatron source we captured the full evolution of the propagating hydrodynamic shock, as well as experimentally observed multi-wave generation within the water target. Moreover, unprecedented experimental measurements of sheet-generated electric elds in the vicinity of the water jet have been made using electron beam radiography. Preliminary hydrodynamic simulations using CRASH and particle-in-cell simulations in FBPIC are used to complement the experimental measurements. This work paves the way tobetter diagnostic systems in High-energy-density physics experiments, where higher resolution and lower signal-to-noise ratio X-ray sources are needed. |
Thursday, November 11, 2021 2:24PM - 2:36PM Not Participating |
UO05.00003: Tomographic imaging with an intense laser-driven multi-mev photon source Donald C Gautier, james hunter, Sasi Palaniyappan, juan c fernandez, Brian J Albright, Reed C Hollinger, Shoujun Wang, Jorge J Rocca
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Thursday, November 11, 2021 2:36PM - 2:48PM |
UO05.00004: MeV x-ray sources from dual compound parabolic concentrator targets Shaun M Kerr, Ginevra E Cochran, David Alessi, Jeff Bude, Hui Chen, Jared C Delora-Ellefson, David N Fittinghoff, Matt Hamamoto, Daniel H Kalantar, Andreas J Kemp, Nuno Lemos, Andy J Mackinnon, Andrew G MacPhee, David A Martinez, Arthur E Pak, Matt Prantil, Dean R Rusby, Craig W Siders, Scott Wilks, Jackson J Williams, Matthew P Hill, Kevin Meaney, Yongho Kim, Hermann Geppert-Kleinrath, Paul Fitzsimmons, Mario J Manuel, William Hoke, Michael Mauldin, Scott Vonhoff, Matthew Quinn Experiments using the NIF Advanced Radiographic Capability (ARC) laser and compound parabolic concentrator (CPC) cone targets1 have demonstrated >10x enhancement in coupling to relativistic electrons and MeV photons, compared to flat targets. To generate multiple x-ray bursts, we are investigating using dual CPC cone targets with nanosecond delays between the cone interactions. Target features to mitigate the degradation of the second, delayed cone source have been tested, including different shielding and spatial configurations. The experimental results of this campaign will be presented, as well as multi-stage hydro and PIC simulation studies of the delayed cone interaction. |
Thursday, November 11, 2021 2:48PM - 3:00PM |
UO05.00005: Characterizing the X-ray spectra from scraping relativistic electrons in linear accelerators La Moyne T Mix, Joshua E Coleman Finite rise and fall times in linear induction accelerators produce off energy electrons, which are 10% or more of the electron pulse. These lower energy, relativistic electrons are over focused by transport magnets and strike the stainless steel beam pipe, producing Bremsstrahlung X-rays. Some of the low energy electrons may exit the beam pipe into the accelerator hall. On the DARHT Axis-I accelerator we are performing a series of experimental measurements supplemented calculations to characterize the X-ray spectra from the lower energy electrons incident on the beam pipe after the acceleration cells. The nominal energy of the 1.7 kA beam is 19.8 MeV at this point ~30 m downstream of the injector. Greater than 107 photons are produced by both the head and tail of the beam, a dose equivalent of ~10 mrad at a distance of 1 m. The X-rays may be dominated by Fe K-edge emission on top of a Bremsstrahlung continuum. We will distinguish the contribution of the stray electrons to the scattered signal with magnetic dipoles and characterize the X-ray spectra using filtered and diffractive X-ray optic techniques. |
Thursday, November 11, 2021 3:00PM - 3:12PM |
UO05.00006: Scintillator-based calorimetry of multi-MeV X-rays from GeV laser wakefield accelerators José A Franco-Altamirano, Andrea Hannasch, Isabella M Pagano, Thanh Ha, Constantin Aniculaesei, B M Hegelich, Rafal Zgadzaj, Michael C Downer We reconstruct spectra of >100 MeV Bremsstrahlung x-rays from a GeV laser wakefield electron accelerator driven by the Texas Petawatt Laser. We measure from single-shot X-ray depth-energy measurements in a compact (7.5 x 7.5 x 10 cm), modular X-ray calorimeter made of alternating layers of absorbing materials and plastic scintillators [1]. Geant4 simulations of energy deposition of single-energy X-rays in the stack generate an energy-vs-depth response matrix for a given stack configuration. An iterative reconstruction algorithm based on Kramers’ law photon energy distribution was used to unfold X-ray spectra within a minute. The unfolded X-ray spectra agree with GEANT4 simulations using independently-measured electron spectra. The results demonstrate the viability of stack calorimetry for unfolding spectra of secondary plasma-accelerator-based x-rays of photon energies well beyond the range previously demonstrated [1]. We discuss uncertainties and limitations of the unfolding process at multi-MeV photon energies, and the performance of slab- and fiber-based scintillators that enable prompt data readout |
Thursday, November 11, 2021 3:12PM - 3:36PM |
UO05.00007: Charged particle deflectometry of strong magnetic field generation driven by intense laser-solid interactions Paul T Campbell, Brandon K Russell, Gennady Fiksel, Philip M Nilson, Jason A Cardarelli, Qian Qian, Karl M Krushelnick, Louise Willingale, Alexander G Thomas In experiments performed at the OMEGA EP laser facility, proton deflectometry was used to capture the spatial and temporal evolution of magnetic fields generated during both moderate (IL ~ 1014 Wcm-2) and high (IL > 1018 Wcm-2) intensity laser-solid interactions. The strong fields and short timescales associated with high intensity interactions pose a significant challenge to proton image interpretation methods, especially as large deflections result in proton trajectory crossing and caustic formation. Consequently, we investigate the application of relativistic electron beams from laser-wakefield accelerators for ultrafast deflectometry measurements of large amplitude laser-driven magnetic fields. In addition to attractive imaging properties (ultrashort bunch duration and low emittance), laser-wakefield sources readily scale to high-repetition rate experiments. A conceptual design for relativistic electron deflectometry experiments will be presented, along with considerations of realistic beam parameters, such as energy spread and finite emittance, and incorporating magnetic beam optics. |
Thursday, November 11, 2021 3:36PM - 3:48PM |
UO05.00008: Probing the fields of an LWFA in blowout regime using a relativistic electron beam Navid Vafaei-Najafabadi, Kyle G Miller, Thamine Dalichaouch, Nolan Maher, Nicholas Manzella, Irina Petrushina, Apurva Gaikwad, Rafal Zgadzaj, Igor Pogorelsky, Marcus Babzien, Mikhail Fedurin, Rotem Kupfer, Karl Kusche, Mikhail Polyanskiy, Mark A Palmer, Roman V Samulyak, Chaojie Zhang, Warren B Mori, Michael C Downer, Chandrashekhar Joshi, Vladimir N Litvinenko The large stable bubbles created by a sub-ps, long-wave infrared laser in low density ~1016 cm-3) plasma provide ideal conditions for accelerating electrons with low emittance and energy spread [1]. Variation and evolution of the fields inside such a structure may be examined using a relativistic electron beam as a probe. Direct interaction of a particle beam with the fields, rather than the index of refraction in the case of a laser probe, enables the examination of low-density wakefield details with high sensitivity. Here, we explore the interaction of a relativistic beam with a plasma bubble using the analytical expressions for the fields in the blowout regime. This theoretical exploration will be focused on two limits: first, where the electron beam traverses the fields at a grazing incident angle and second, where the beam’s momentum is primarily transverse to the wakefield propagation. Application of the resulting expressions to the simulated fields of an LWFA in a blowout regime, particularly targeting the conditions that will be available at the Accelerator Test Facility (ATF) of Brookhaven National Laboratory (BNL) will be presented. |
Thursday, November 11, 2021 3:48PM - 4:00PM |
UO05.00009: Proton Beam Imaging Energy Spectrometer (PROBIES) for high repetition rate laser plasma experiments Elizabeth S Grace, Derek Mariscal, Ghassan Zeraouli, Graeme G Scott, Raspberry A Simpson, Kelly Swanson, Blagoje Z Djordjevic, Huanyu Song, Ryan Nedbaillo, Jaebum Park, John Morrison, Reed C Hollinger, Shoujun Wang, Jorge J Rocca, Tammy Ma High-intensity (>10^18 W/cm2) laser interactions with thin foils have long been known to accelerate high-energy, high-flux proton beams via the target normal sheath acceleration mechanism [1,2]. To spatially and spectrally characterize these beams, radiochromic film (RCF) stacks have been widely employed due to their accuracy and reliability [3,4]. In practice, the size of the target holder and the time required to prepare and scan the films limit the number of films that can be fielded in the stack, and the films must be removed from the vacuum chamber and replaced between shots. These constraints may be eliminated without sacrificing spatial or spectral information with the use of a proton energy step wedge and scintillator combination that allows the same information to be collected on a single camera frame. Building on previous work [5], the step wedge consists of a set of repeating periodic filters so that for each energy, the beam profile is discretely sampled at an array of spatial locations. This array of spatial samples is interpolated to obtain the spatial profile for each energy. An organic scintillator [6] is used to detect MeV protons, and an optical imaging setup collects the emerging light on a CCD, enabling high repetition rate (>1 Hz) data collection with a spectral resolution of 1.2 MeV and spatial imaging resolution of 20 microns. Preliminary results from commissioning experiments at the ALEPH laser facility at CSU will be presented, including cross-calibration with RCF and automated analysis for spatio-spectral proton beam retrieval. |
Thursday, November 11, 2021 4:00PM - 4:12PM |
UO05.00010: Determining plasma parameters from laser-driven THz radiation Kathryn A Wolfinger, Valentina Lee, Gregory R Werner, Michael D Litos, John R Cary In numerical simulations, the creation of a wakefield by a laser pulse propagating through neutral gas results in the radiation of an axially polarized electromagnetic pulse (EMP), which initial calculations indicate may carry off 10-20% of the wakefield energy. Frequencies of 10 - 90 THz have be observed, with peak amplitudes on the order of 10 - 100s MV/m. The VSim/Vorpal computational application has been used to produce full PIC, 2D simulations of neutral gas ionization, axial current generation, and EMP propagation. A reduced model for EMP generation and evolution, driven by the ponderomotive potential, is shown to accurately represent this phenomenon, with significantly shorter run-times than full PIC simulations. Also, the reduced model is noise-free, while PIC simulations require averaging techniques to fully extract the EMP. From this reduced model, we see that the EMP's temporal profile depends on plasma density, ionization radius, and the laser's normalized vector potential. As such, the THz EMP may act as a diagnostic for plasma parameter extraction. A detailed comparison of the EMP's energy with the wakefield's will be presented for a range of plasma densities. In addition, 2D PIC simulations of plasma channel formation will be presented for several plasma densities. |
Thursday, November 11, 2021 4:12PM - 4:24PM |
UO05.00011: PWFA Plasma Source Density and Width Measurement by Robust Optical Methods Valentina Lee, Robert Ariniello, Christopher E Doss, Keenan D Hunt-Stone, Kathryn A Wolfinger, Michael D Litos The quality of the accelerated electron beam of an electron beam-driven plasma wakefield accelerator (PWFA) depends significantly on the density profile of the plasma source. Therefore, proper plasma diagnostic methodologies are essential. The PWFA plasma source is a long narrow, laser-ionized gas filament formed ahead of the arrival of the electron beam. It is less than 1 mm in diameter and up to 1 m in length with a typical core density of 10^(16-18) cm^-3. Its geometry and density range make it challenging to diagnose. Laser shadowgraphy and plasma afterglow optical imagery are two easily implemented experimental methods that hold complementary strengths and allow for coarse diagnosis of the PWFA plasma source. The former has an ultrafast response but presents a longitudinally integrated signal. The latter provides fine-scale longitudinal resolution, but its signal is time-integrated. To interpret such time-integrated signals correctly, the temporal evolution of the plasma filament formation and decay processes are modeled. Multiple linear regression is performed on the simulated data to select the heavy-weighted first-order and second-order dependence of the experimental signals on the initial plasma density and width. Experimental results supported by simulations are presented. |
Thursday, November 11, 2021 4:24PM - 4:36PM Not Participating |
UO05.00012: A new diagnostic framework for optimizing high-repetition rate short-pulse-laser plasma experiments Raspberry A Simpson, Derek Mariscal, Jackson J Williams, Graeme G Scott, Blagoje Z Djordjevic, Elizabeth S Grace, Andreas J Kemp, Scott Wilks, Tammy Ma High-intensity (>10^18 W/cm^2) short-pulse ( |
Thursday, November 11, 2021 4:36PM - 4:48PM |
UO05.00013: Characterization of short-pulse laser produced fast electrons by using 3-D hybrid particle-in-cell simulations Lei Chen, Hiroshi Sawada, Tyler Daykin, Farhat N Beg, Hui Chen, Anthony J Link, Jackson J Williams, Yuan Ping, Harry S McLean Characteristics of fast electrons produced in intense short-pulse laser-solid interaction were experimentally and numerically investigated. The experiment was carried out using a 50 TW Leopard laser (15J, 0.35 ps, 2×1019 W/cm2) at UNR. The laser-target interaction generates relativistic electrons predominantly by the ponderomotive potential. Subsequently, the electron transport in a target produces bremsstrahlung and escaping electrons that were recorded by two absolutely calibrated filter stack spectrometers and a magnet electron spectrometer, respectively. The angularly resolved bremsstrahlung was then modeled with a 3-D hybrid particle-in-cell code, LSP, by varying divergence angles and electron beam energies, while the slope temperature was estimated from an exponential fit to the measured electron spectrum. The fitting was performed for a 100 μm Cu foil with and without a CH backing. The divergence angle and conversion efficiency from laser to electrons producing bremsstrahlung are found to be ∼55° and ∼7% for the Cu-CH target. While a similar conversion efficiency is obtained for both targets, it is found that the calculated bremsstrahlung at the detector positions is relatively independent of the divergence angle for the Cu target due to strong refluxing. |
Thursday, November 11, 2021 4:48PM - 5:00PM |
UO05.00014: Ion Velocity Distributions Functions in an Inductively Coupled Plasma's Meniscus David D Caron, Thomas E Steinberger, Earl Scime By increasing aspect ratios and fitting more features onto chips, semiconductors have continued to increase the processing power of modern electronics. This requires a great amount of precision in the processing techniques as the features are only a few dozen silicon atoms in size and are more prone to defects. To better understand the ion dynamics for etching and doping, we used laser induced fluorescence (LIF) to obtain ion velocity distribution functions inside an inductively coupled plasma (ICP) source. The ICP was fitted with graphite extraction optics that allowed for beam formation through a 5 mm aperture. A wafer was placed 12 mm away and biased so that a plasma meniscus was formed on the inside of the extraction optics. This meniscus boundary acts as an electrostatic lens and affects ion trajectories. Therefore, the focal spot of the beam is dependent on the meniscus’s spatial structure. This boundary can be affected by changing source parameters such as applied extraction bias and rf antenna power. A confocal LIF system was used to investigate this boundary and the background plasma. We report non-perturbative, localized measurements up to 25 mm into an ICP for ion velocity and temperature. We also measured the meniscus extraction region in order to characterize the extracted ion properties’ relation to controllable source parameters. |
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