Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session GO7: Relativistic Laser Plasma Interaction and Particles (ions, electrons, positrons, neutrons) II |
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Chair: Derek Mariscal, Lawrence Livermore National Lab Room: OCC B117-119 |
Tuesday, November 6, 2018 9:30AM - 9:42AM |
GO7.00001: High charge ion beams with achromatic divergence by the BELLA petawatt laser Jianhui Bin, Sven Steinke, Jaehong Park, Qing Ji, Kei Nakamura, Anthony J Gonsalves, Stepan Bulanov, Csaba Toth, Jean-Luc Vay, Carl B Schroeder, Cameron Guy Robinson Geddes, Eric Esarey, Thomas Schenkel, Wim Pieter Leemans We report on an experimental study of ion acceleration from micrometer thick metallic targets using the BELLA petawatt laser. Here, we show that for the first time, high quality ion beams can be generated under 0.5 Hz high repetition rate with a petawatt laser system, delivering unprecedented single shot doses up few 1000s Gy. By using a large focal spot size (r0=53 um), proton beams with a significant reduced divergence (<250 mrad) are observed. In addition, the proton beams present a remarkable thickness-dependent achromatic feature in high energy range, for example, in case of 2 um Ti target, the proton beams present constant divergence angle of ~100 mrad beyond 3.2 MeV. Such ion beams are of particularly interest for applications that require high ion charge density. |
Tuesday, November 6, 2018 9:42AM - 9:54AM |
GO7.00002: Sweeping acceleration of high charge ion beams in the large spot size regime with the high repetition rate BELLA petawatt laser Sven Steinke, Jianhui Bin, Jaehong Park, Qing Ji, Kei Nakamura, Anthony J Gonsalves, Stepan Bulanov, Csaba Toth, Jean-Luc Vay, Carl B Schroeder, Cameron Guy Robinson Geddes, Eric Esarey, Thomas Schenkel, Wim Pieter Leemans We present an experimental study of ion acceleration using the BELLA petawatt laser. Enabled by the high repetition rate (1 Hz) of the laser, targetry and diagnostic we were able to conduct parameter scans involving >100 shots. In the large laser spot size regime, where the laser pulse length is much shorter than the laser spot size on target and is obliquely incident, the laser pulse duration needs to be optimized to obtain uniform plasma heating across the focal plane. Proton spectra from laser pulse duration scans (35 -600fs) reveal such a geometric optimization of the Target Normal Sheath Acceleration (TNSA). The field dynamics inferred from Particle-in-Cell simulations are used to unravel the interaction dynamics and provide further insights into the ion acceleration process. |
Tuesday, November 6, 2018 9:54AM - 10:06AM |
GO7.00003: Scaling Laws of Ion Acceleration in Ultrathin Foils Driven by Laser Radiation Pressure Xiaofei Shen, Bin Qiao, Hao He, Yu Xie, Hua Zhang, Cangtao Zhou, Shaoping Zhu, Xian T He Scaling laws of laser-driven ion acceleration can be used to evaluate the laser and target parameters needed to produce ion beams of interest, which are very important for the construction of laser facilities. The scaling laws of target normal sheath acceleration have been investigated widely, however, that of radiation pressure acceleration (RPA) is still not very clear, especially for that of the maximum energy. Considering the instabilities are inevitable during laser plasma interaction, the maximum energy of ion beams in RPA should have two contributions: the bulk acceleration driven by radiation pressure and the sheath acceleration in the moving foil reference induced by hot electrons. A theoretical model is proposed to quantitatively explain the results that the cutoff energy and energy spread are larger than the predictions of the “light sail” model, which have been observed in simulations and experiments for a large range of laser and target parameters. Scaling laws derived from this model and supported by the simulation results are verified by the previous experiments. |
Tuesday, November 6, 2018 10:06AM - 10:18AM |
GO7.00004: Effects of background pressure on high repetition rate, relativistic laser-driven MeV ion and electron acceleration Joseph Snyder, John T Morrison, Kevin M George, Gregory K. Ngirmang, Scott B Feister, Joseph R Smith, Manh S Le, Kyle Frische, Enam A Chowdhury, Chris M Orban, William M Roquemore The relativistic laser-plasma interaction (LPI) can produce energetic electrons, ions, and photons. LPI studies are increasingly moving towards high repetition rate in order to collect more data and demonstrate real world applicability. Liquid targets can provide repeatable, thin targets for high repetition rate LPI experiments, but may require higher vacuum pressure than what is commonly used. Therefore, it is important to understand how the chamber pressure effects particle acceleration and determine necessary pressure limits for target development. We present results from a series of experiments on the effect of background pressure on particle acceleration with pressures ranging from 30 mTorr to >10 Torr. In particular, we show a substantial increase in conversion efficiency to target normal ions when the chamber pressure drops below ~1 Torr. These studies facilitate future experimental design on particle acceleration and inform target development for high repetition rate LPI experiments. |
Tuesday, November 6, 2018 10:18AM - 10:30AM |
GO7.00005: Generation of high energy and well-collimated ion beams by laser-driven magnetized electron sheath acceleration with kilotesla magnetic fields Kathleen Weichman, Joao J Santos, Toma Toncian, Alexey Arefiev Recent progress in laser-driven magnetic field generation enables using kilotesla-level fields to influence hot electron transport over the length and time scales relevant to sheath-based ion acceleration. I will present 2D and 3D particle-in-cell simulations demonstrating that the magnetic field can beneficially alter the topology of the sheath electric field compared to conventional target normal sheath acceleration. In particular, the magnetization of hot electrons creates a robust focusing effect that can produce high energy, well-collimated beams of multiple ion species. |
Tuesday, November 6, 2018 10:30AM - 10:42AM |
GO7.00006: Ion Acceleration from Near-Critical-Density Plasmas via Magnetic Vortex Acceleration in 3D Particle-in-cell Simulations Jaehong Park, Stepan Bulanov, Jean-Luc Vay, Sven Steinke, Jianhui Bin, Qing Ji, Cameron Guy Robinson Geddes, Carl B Schroeder, Eric Esarey, Thomas Schenkel, Wim Pieter Leemans We explored laser-driven ion acceleration via the Magnetic Vortex Acceleration scheme using 3D Warp+PICSAR and WarpX PIC simulation codes. In this scheme a high intensity and short pulse laser pulse propagates in near critical density plasma targets, making a channel in both electron and ion density. When the laser pulse exits the plasma, it establishes strong longitudinal electric fields that can accelerate the ions, which are pinched by the electrons in a thin filament along the laser propagation axis. We found that under the optimum conditions of the target thickness and density [1], the maximum ion energy in 3D is about 50% lower than that in 2D due to the smaller channel size in 3D. Particle tracking method is used to understand the acceleration process in more detail. [1] S. S. Bulanov, et al, Phys. Plasmas 17,043105(2010) |
Tuesday, November 6, 2018 10:42AM - 10:54AM |
GO7.00007: Collisionless shock acceleration of carbon ions in 1μm-laser-driven near-critical plasma Chengkun Huang, Sasi Palaniyappan, Donald Gautier, Frederico Fiuza, Wenjun Ma, Jörg Schreiber, Juan Carlos Fernandez, Abel Raymer, Russel Mortensen, Raymond Gonzales, Sha-Marie L Reid, Tom Shimada, Randall Johnson Collisionless shock acceleration of charged particles is ubiquitous in the cosmos and its successful adaptation in the laboratory using laser-driven plasmas has the potential for compact particle accelerators suitable for several applications. We report collisionless shock acceleration of narrow-energy-spread carbon ions to 30 MeV with 4% conversion efficiency. This is achieved using a 100 TW linearly polarized laser interacting with a carbon nanofoam target of near-critical density for the 1μm-wavelength laser. The use of nanofoam near-critical target improves upon previous experiments with gas jets leading to low conversion efficiency or with exploding solid foils for which target pre-expansion needs to be optimized empirically. The variations in the accelerated ion spectra among different carbon ion species and proton radiography of the laser-driven near-critical plasma, together with kinetic simulations, provide detailed insight into the dynamics of the laboratory laser-driven collisionless shocks. |
Tuesday, November 6, 2018 10:54AM - 11:06AM |
GO7.00008: Absolute calibration of GafChromic film for high-flux laser-driven ion beams Jianhui Bin, Qing Ji, Peter Anthony Seidl, David Raftrey, Sven Steinke, Thomas Schenkel, Wim Pieter Leemans We report on the calibration of GafChromic HD-v2 radiochromic film at extremely high dose up to 100 kGy. The absolute calibration was done with nanosecond ion bunches at the Neutralized Drift Compression Experiment II (NDCX-II) at Lawrence Berkeley national laboratory (LBNL) with doses ranging from 100 to 100 kGy. The films were scanned using EPSON V600 scanner in separate RGB channels, as well as Grayscale channel. An absolutely calibrated optical density filter was used as a reference to transfer our one-time absolute calibration curve to different experimental setups. The calibration curve is further applied to a laser driven ion experiment at the BELLA petawatt laser facility at LBNL, to reconstruct the spatial and energy distribution of the laser-accelerated proton beams. The result was compared to the measured spectrum with a Thomson spectrometer using microchannel plate as the detector, showing fair agreement in proton beam energy and intensity. |
Tuesday, November 6, 2018 11:06AM - 11:18AM |
GO7.00009: Distinguishing between ion acceleration regimes at oblique incidence with particle-in-cell simulations G. E. Cochran, P. L. Poole, T. Cowan, T. Kluge, J. Metzkes-Ng, L. Obst, I. Principe, H.-P. Schlenvoigt, U. Schramm, K. Zeil, D. W. Schumacher A recent high-contrast experiment using the Draco laser (~3 J, 1021 W/cm2) at 45 degrees angle of incidence on liquid crystal targets showed predominantly target normal directed ions for all target thicknesses from >1 μm down to 10 nm. Target normal ions are often considered to be an indication of the target normal sheath acceleration (TNSA) mechanism, but the thinner targets in this experiment are well under the predicted theoretical transition to radiation pressure acceleration (RPA). We present 3D particle-in-cell simulations which reproduce the dominance of target normal acceleration as well as the transparency onset as a function of target thickness. Particle tracking shows that high energy ions from the thinnest targets are accelerated volumetrically, in contrast to originating at the rear surface as in thicker targets. We show that target normally directed ions are produced by TNSA for thick targets, but by RPA for thin targets. A simple analytical model for RPA-driven target deformation is presented, which agrees well with 2D and 3D simulation results. |
Tuesday, November 6, 2018 11:18AM - 11:30AM |
GO7.00010: Laser-Driven Proton Acceleration and Focusing using the Orion laser facility Adam Higginson, Christopher S McGuffey, Ross J Gray, Gabriel Schaumann, Thomas Hodge, Steve Gales, Matthew P Hill, Steven F James, Jonas Ohland, Christopher Spindloe, David Neely, Colin Danson, Mingsheng Wei, Markus Roth, Farhat N Beg, Paul McKenna The study of ion acceleration driven by intense (>1020 Wcm-2) laser-solid interactions has received considerable interest over the past decade, motivated by potential applications of the resulting compact ion source in sectors including industry, medicine and defence. Specifically, the work detailed here is of broad relevance to multiple avenues of high energy density physics, as well as the proton fast ignition (PFI) approach to inertial confinement fusion. Presented is a study of laser-driven proton acceleration and focusing using conical targets. Using the Orion laser system at AWE in the UK, delivering a peak intensity of 1021 Wcm-2, a spectrally broad focused component in the range 10 - 30 MeV is measured, with a clear annular structure in the proton beam's spatial distribution near the cut-off energy. An auxiliary laser-driven proton beam, generated using a second short pulse beam, is used to transversely probe the target, to characterize the field structure responsible for the focusing. To close in on a realistic PFI scenario, multiple long pulsed beams are used to induce plasma expansion around the cone walls, to measure the effect of a dense, long scale-length plasma on the focusing of the proton beam. This is found to quench any focusing effect. |
Tuesday, November 6, 2018 11:30AM - 11:42AM |
GO7.00011: Proton Acceleration in a Laser-driven Relativistic Electron Vortex Longqing Yi, Tunde M Fulop We show that when a solid plasma foil with a density gradient in the front surface is irradiated by an intense laser pulse at a grazing angle ~ 10o, a relativistic electron vortex is excited in the near-critical-density layer after the laser pulse depletion. Due to the asymmetry introduced by nonuniform background density, the vortex drifts at a constant velocity, typically 0.2 - 0.3 of the speed of the light. The strong magnetic fields inside the vortex lead to significant charge separation where the initially stationary protons can be captured and accelerated to twice of the drifting velocity (100-200 MeV). A representative case with laser intensity at 1021 W/cm2 is discussed, in which a 140 MeV quasi-monoenergetic proton beam (energy spread ~10%) is obtained. We demonstrating the vortex velocity, and therefore the maximum proton acceleration energy, are determined by E x B drift of the laser-driven electrons in the self-generated fields. We derive an analytical model that can describe the main findings of the simulations. |
Tuesday, November 6, 2018 11:42AM - 11:54AM |
GO7.00012: Laser-driven acceleration of titanium ions and the calibration of the ion beam diagnostic Joseph Strehlow, Pierre Forestier-Colleoni, Jun Li, George M Petrov, Christopher S McGuffey, Jonathan L Peebles, Shu Zhang, Farhat N Beg A super-intense laser pulse, incident on a thin foil target, can create plasma structures with accelerating fields on the order of TV/m, accelerating ions to multi-MeV energies. The 1020 W/cm2, linearly polarized Texas Petawatt Laser (TPW) facility was employed to accelerate high energy titanium ions from ultrathin (60 to 200 nm) planar titanium foil targets. A clear optimum target thickness is observed, with Ti19+ ions exceeding 200 MeV from 80 nm targets. Two Thomson parabolas, spectrometers that separate ions by their charge-to-mass ratio, were aligned to target normal and close to the laser propagation axis. In the spectrometers, BAS-TR image plates were used to detect the ions. A plastic grid of CR-39 was mounted in front of the image plates to measure absolute counts from the deposited titanium ions. This calibration enables the extraction of absolute energy spectra of the titanium ions. Established analytical models, such as target normal sheath acceleration (TNSA) and radiation pressure acceleration (RPA) are applied, along with the fully relativistic 2-D particle-in-cell code EPOCH, to provide insight into the underpinning physics responsible for ion acceleration in this ultrathin target regime. |
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