Bulletin of the American Physical Society
58th Annual Meeting of the APS Division of Plasma Physics
Volume 61, Number 18
Monday–Friday, October 31–November 4 2016; San Jose, California
Session TO6: Laser-plasma Ion Acceleration |
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Chair: Stepan Bulanov, Lawrence Berkeley National Laboratory Room: 230 C |
Thursday, November 3, 2016 9:30AM - 9:42AM |
TO6.00001: Progress toward a practical laser driven ion source using variable thickness liquid crystal targets Patrick Poole, Ginevra Cochran, Karl Zeil, Josephine Metzkes, Lieselotte Obst, Thomas Kluge, Hans-Peter Schlenvoigt, Irene Prencipe, Tom Cowan, Uli Schramm, Douglass Schumacher Ion acceleration from ultra-intense laser interaction has been long investigated in pursuit of requisite energies and spectral distributions for applications like proton cancer therapy. However, the details of ion acceleration mechanisms and their laser intensity scaling are not fully understood, especially the complete role of pulse contrast and target thickness. Additionally, target delivery and alignment at appropriate rates for study and subsequent treatment pose significant challenges. We present results from a campaign on the Draco laser using liquid crystal targets that have on-demand, in-situ thickness tunability over more than three orders of magnitude, enabling rapid data collection due to \textless 1 minute, automatically aligned target formation. Diagnostics include spectral and spatial measurement of ions, electrons, and reflected and transmitted light, all with thickness, laser focus, and pulse contrast variations. In particular we discuss optimal thickness vs. contrast and details of ultra-thin target normal ion acceleration, along with supporting particle-in-cell studies. [Preview Abstract] |
Thursday, November 3, 2016 9:42AM - 9:54AM |
TO6.00002: Experiments and PIC simulations on liquid crystal plasma mirrors for pulse contrast enhancement G. E. Cochran, P.L. Poole, A. Krygier, P.S. Foster, G.G. Scott, L.A. Wilson, J. Bailey, N. Bourgeois, C. Hernandez-Gomez, R. Heery, J. Purcell, D. Neely, P.P. Rajeev, R.R. Freeman, D.W. Schumacher High pulse contrast is crucial for performing many experiments on high intensity lasers in order to minimize modification of the target surface by pre-pulse. This is often achieved through the use of solid dielectric plasma mirrors which can limit laser shot rates. Liquid crystal films, originally developed as variable thickness ion acceleration targets (P. L. Poole \textit{et al}., PoP \textbf{21}, 063109 (2014)), have been demonstrated as effective plasma mirrors for pulse cleaning, reaching peak reflectivities over 70{\%}. These films were used as plasma mirrors in an ion acceleration experiment on the Scarlet laser and the resultant increase in peak proton energy and change in acceleration direction will be discussed. Also presented here are novel 2D3V, LSP particle-in-cell simulations of dielectric plasma mirror operation. By including multiphoton ionization and dimensionality corrections, an excellent match to experiment is obtained over 4 decades in intensity. Analysis of pulse shortening and plasma critical surface behavior in these simulations will be discussed. Formation of thin films at 1.5 Hz will also be presented. [Preview Abstract] |
Thursday, November 3, 2016 9:54AM - 10:06AM |
TO6.00003: LPWA using supersonic gas jet with tailored density profile O. Kononenko, S. Bohlen, J. Dale, R. D'Arcy, M. Dinter, J.H. Erbe, G. Indorf, L. di Lucchio, L. Goldberg, J.N. Gruse, S. Karstensen, V. Libov, K. Ludwig, A. Martinez de la Ossa, F. Marutzky, A. Niroula, J. Osterhoff, M. Quast, L. Schaper, J.-P. Schwinkendorf, M. Streeter, G. Tauscher, S. Weichert, C. Palmer, Taras Horbatiuk Laser driven plasma wakefield accelerators have been explored as a potential compact, reproducible source of relativistic electron bunches, utilising an electric field of many GV/m. Control over injection of electrons into the wakefield is of crucial importance in producing stable, mono-energetic electron bunches. Density tailoring of the target, to control the acceleration process, can also be used to improve the quality of the bunch. By using gas jets to provide tailored targets it is possible to provide good access for plasma diagnostics while also producing sharp density gradients for density down-ramp injection. OpenFOAM hydrodynamic simulations were used to investigate the possibility of producing tailored density targets in a supersonic gas jet. Particle-in-cell simulations of the resulting density profiles modelled the effect of the tailored density on the properties of the accelerated electron bunch. Here, we present the simulation results together with preliminary experimental measurements of electron and x-ray properties from LPWA experiments using gas jet targets and a 25 TW, 25 fs Ti:Sa laser system at DESY. [Preview Abstract] |
Thursday, November 3, 2016 10:06AM - 10:18AM |
TO6.00004: Dynamics of laser driven proton beams exhibited by experimentally determined laser absorption and reflection Jianhui Bin, Klaus Allinger, Konstantin Khrennikov, Paul Bolton, Joerg Schreiber Plasma expansion driven by irradiation of targets by intense laser pulses has attracted scientific interest for decades; especially with laser intensities beyond the threshold for heating electrons to relativistic energies (\textgreater 1.37*10$^{\mathrm{18}}$W/cm$^{\mathrm{2}})$. Expansion velocities of at least ten percent of the speed, yield tens of MeV ion kinetic energies. Improving our understanding of the physics of ion acceleration is crucial for its various potential applications. Here we show the experimental investigation of proton acceleration from nanometer thin foils with intense laser pulses. We analyzed the laser absorption by parallel monitoring laser transmissivity and reflectivity with different laser intensities when moving the targets along the laser axis. A direct correlation between laser absorption and maximum proton energy is observed. Experimental results are interpreted via analytical estimation, exhibiting a coexistence of plasma expansion and radiation pressure acceleration (RPA) mechanisms in the whole proton acceleration based on the measured laser absorption and reflectivity. The result enhances understanding of the underlying physics underlying laser-driven ion acceleration and can guide for further optimization. [Preview Abstract] |
Thursday, November 3, 2016 10:18AM - 10:30AM |
TO6.00005: Achieving Stable Radiation Pressure Acceleration of Heavy Ions via Successive Electron Replenishment from Ionization of a High-Z Material Coating X. F. Shen, B. Qiao, H. X. Chang, S. Kar, C. T. Zhou, M. Borghesi, X. T. He Generation of monoenergetic heavy ion beams aroused more scientific interest in recent years. Radiation pressure acceleration (RPA) is an ideal mechanism for obtaining high-quality heavy ion beams, in principle. However, to achieve the same energy per nucleon (velocity) as protons, heavy ions undergo much more serious Rayleigh-Taylor-like (RT) instability and afterwards much worse Coulomb explosion due to loss of co-moving electrons. This leads to premature acceleration termination of heavy ions and very low energy attained in experiment. The utilization of a high-Z coating in front of the target may suppress the RT instability and Coulomb explosion by continuously replenishing the accelerating heavy ion foil with co-moving electrons due to its successive ionization under laser fields with Gaussian temporal and spatial profiles. Thus stable RPA can be realized. Two-dimensional and three-dimensional particles-in-cell simulations with dynamic ionization show that a monoenergetic Al$^{13+}$ beam with peak energy 4.0GeV and particle number 10$^{10}$ (charge $>$ 20nC) can be obtained at intensity 10$^{22}$ W/cm$^2$. [Preview Abstract] |
Thursday, November 3, 2016 10:30AM - 10:42AM |
TO6.00006: Spectral control of laser accelerated ions via deuterium vapour deposition onto cryogenically cooled targets Graeme Scott A widely perceived criticism of the best understood laser driven ion acceleration mechanism, TNSA, is that the energy spectra routinely obtained are Maxwellian in nature, and are non-ideal for some of the long term envisaged applications of a laser accelerated ion source such as ion driven fast ignition or hadrontherapy. We, however, demonstrate a novel method to accelerate a quasi-monoenergetic deuterium beam in the TNSA regime of ion acceleration. This is made possible by recent developments in cryogenic targetry at the Central Laser Facility, and is achieved by cooling a gold target to approximately 7-8 K and introducing overcoats of isotopic deuterium layers on top of the hydrogen contaminant layer present on the original target. The presence of a lower charge to mass ion on top of the high charge to mass hydrogen, alters the sheath dynamics during the acceleration such that the high energy portion of the deuterium beam exhibits a full width at half maximum energy spread of $\delta \varepsilon $/$\varepsilon $ \textasciitilde 0.3-0.5. Experimental results and multidimensional numerical modelling will be presented describing this effect. Further than this, experimental results show that the accelerated deuterium beam is found to significantly enhance the number of neutrons produced when fielded in a pitcher/catcher configuration, and provides avenues for investigation on the production of a high brightness neutron source. [Preview Abstract] |
Thursday, November 3, 2016 10:42AM - 10:54AM |
TO6.00007: Kinetic effects on the transition to relativistic self-induced transparency in laser-driven ion acceleration Evangelos Siminos, Benjamin Svedung Wettervik, Mickael Grech, T\"unde F\"ul\"op We study kinetic effects responsible for the transition to relativistic self-induced transparency in the interaction of a circularly-polarized laser-pulse with an overdense plasma and their relation to hole-boring and ion acceleration. It is shown, using particle-in-cell simulations and an analysis of separatrices in single-particle phase-space, that this transition is mediated by the complex interplay of fast electron dynamics and ion motion at the initial stage of the interaction. It thus depends on the ion charge-to-mass ratio and can be controlled by varying the laser temporal profile. Moreover, we find a new regime in which a transition from relativistic transparency to hole-boring occurs dynamically during the course of the interaction. It is shown that, for a fixed laser intensity, this dynamic transition regime allows optimal ion acceleration in terms of both energy and energy spread. [Preview Abstract] |
Thursday, November 3, 2016 10:54AM - 11:06AM |
TO6.00008: Proton acceleration by multi-terawatt interaction with a near-critical density hydrogen jet Andy Goers, Linus Feder, George Hine, Fatholah Salehi, Daniel Woodbury, J.J. Su, Dennis Papadopoulos, Arie Zigler, Howard Milchberg We investigate the high intensity laser interaction with thin, near critical density plasmas as a means of efficient acceleration of MeV protons. A promising mechanism is magnetic vortex acceleration, where the ponderomotive force of a tightly focused laser pulse drives a relativistic electron current which generates a strong azimuthal magnetic field. The rapid expansion of this azimuthal magnetic field at the back side of the target can accelerate plasma ions to MeV scale energies. Compared to typical ion acceleration experiments utilizing a laser- thin solid foil interaction, magnetic vortex acceleration in near critical density plasma may be realized in a high density gas jet, making it attractive for applications requiring high repetition rates. We present preliminary experiments studying laser-plasma interaction and proton acceleration in a thin ($<200$ $\mu$m) near-critical density hydrogen gas jet delivering electron densities $10^{20}-10^{21} cm^{-3}$. [Preview Abstract] |
Thursday, November 3, 2016 11:06AM - 11:18AM |
TO6.00009: kHz Ion Acceleration Under Variable Background Pressure John T. Morrison, S. Feister, K. Frische, D.R. Austin, G.K. Ngirmang, A.C. Peterson, J. Smith, A. Klim, C. Orban, E.A. Chowdhury, W.R. Roquemore High-repetition rate, ultra-high intensity lasers are coming online, opening new possibilities for statistical approaches and applications to High Energy Density Physics (HEDP) research through relativistic laser-plasma interactions (RLPI). A new experimental framework including high-repetition rate solid-density targets, high-acquisition rate detectors, data acquisition, and analysis is needed to take advantage of these new possibilities. At the Extreme Light Laboratory at AFRL, development of a liquid target system has enabled us to perform 1kHz RLPI experiments in 0.03-20 mbar background pressures and intensities up to 5 \textbf{\textbullet }10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}}$. However, RLPI studied here transpires within a moderate vacuum, which may affect the strength of the electrostatic coupling between the energetic electrons and target ions, altering expected results for both the detected electrons and accelerated ions. Both the experimental methods and measurements of the ion acceleration from sub-micron solid density targets with variable background pressures will be presented. [Preview Abstract] |
Thursday, November 3, 2016 11:18AM - 11:30AM |
TO6.00010: Analysis of efficient ion acceleration with multi-picosecond LFEX laser Natsumi Iwata, Akifumi Yogo, Kunioki Mima, Shota Tosaki, Keisuke Koga, Hideo Nagatomo, Yasuaki Kishimoto, Hiroaki Nishimura, Horishi Azechi We demonstrate an efficient proton acceleration reaching 30 MeV by using high contrast, kilojoule, picosecond laser LFEX at the peak intensity of $2.3\times10^{18}$ W/cm$^{2}$ [1]. Owing to the large spot size of 70 $\mu$m FWHM, the target foil expands one-dimensionally during the multi-picosecond pulse duration time, which yields the electron heating beyond the ponderomotive scaling observed in the experiment. We present by a 1D PIC simulation that the electron temperature evolves in time while the electrons recirculate between the front and rear surfaces of the expanding plasma. A theoretical calculation for the ion maximum energy that takes the temperature evolution into account agrees with the experimental result quantitatively. Being supported by the experiment and simulation, our theoretical model for the non-isothermal plasma expansion dynamics will provide an important basis for understanding the multi-picosecond high intensity laser-plasma interactions and for various applications such as energetic ion beam generation for medical applications and fast ignition-based laser fusion. [1] A. Yogo, K. Mima, N. Iwata et al., submitted to Nat. Comm. [Preview Abstract] |
Thursday, November 3, 2016 11:30AM - 11:42AM |
TO6.00011: Generation of Energetic Particles in Intense Laser Matter Interaction Bhuvanesh Ramakrishna, Tayyab Muhammad, Suman Bagchi, Tirtha Mandal, Juzer Chakera, Prasad Naik, Parshotam Dass Gupta The acceleration of high energy ion beams up to several tens of MeV per nucleon following the interaction of an ultra-short (t \textless 50 fs), intense (I$\lambda^{\mathrm{2}}$ \textgreater 10$^{\mathrm{18}}$ W.cm$^{\mathrm{-2}}$.$\mu $m$^{\mathrm{-2}})$ laser pulse with solid targets, is one of the burgeoning fields of research in the last few years. Mechanisms leading to forward-accelerated, high quality ion beams, operating at currently accessible laser intensities (up to 10$^{\mathrm{21}}$ W/cm2) in laser-matter interactions, are mainly associated with large electric fields set up at the target rear interface by the laser-accelerated electrons leaving the target. In this paper, we present our recent experimental results on MeV ion generation by mildly relativistic (10$^{\mathrm{19\thinspace }}$W/cm$^{\mathrm{-2}})$ short-pulse (45 fs) laser interaction with foil targets of varying thicknesses, structured / uniform targets (e.g. nano structures on thin metallic foils, sandwich targets). Spectral modification / bunching, and divergence from structured targets will be discussed. [Preview Abstract] |
Thursday, November 3, 2016 11:42AM - 11:54AM |
TO6.00012: Enhancing Target Normal Sheath Accelerated Ions with Micro-structured Targets Kevin George, Joseph Snyder, Liangliang Ji, Trevor Rubin, Abraham Handler, Patrick Poole, Christopher Willis, Rebecca Daskalova, Ginevra Cochran, Douglass Schumacher Laser driven target normal sheath acceleration (TNSA) of ions has been widely studied due to its fundamental importance, use as a probe, and for possible applications such as cancer therapy and neutron generation. Much of this work has been conducted on thin foils with peak ion energy and yield optimized using laser parameters such as energy and spot size. Micro-structured targets, however, have demonstrated increased peak ion energy and yield by controlling and enhancing mechanisms preferential to TNSA. Novel micro-structured targets were developed using optical lithography techniques on thin substrates at the OSU NanoSystem Laboratory. Variable structure height (0.5-2 micron) and transverse patterning (up to 1 micron resolution) permit the survey of a range of structured target variables in the study of ion acceleration. We describe the development of these targets and an experiment investigating the enhancement of TNSA ions from lithography produced micro-structured targets conducted at the Scarlet Laser Facility. Experimental results show increased proton and Carbon yield \textgreater 2 MeV and higher peak Carbon energy from structured targets. [Preview Abstract] |
Thursday, November 3, 2016 11:54AM - 12:06PM |
TO6.00013: Front surface structured targets for enhancing laser-plasma interactions Joseph Snyder, Kevin George, Liangliang Ji, Sasir Yalamanchili, Ethan Simonoff, Ginevra Cochran, Rebecca Daskalova, Patrick Poole, Christopher Willis, Nathan Lewis, Douglass Schumacher We present recent progress made using front surface structured interfaces for enhancing ultrashort, relativistic laser-plasma interactions. Structured targets can increase laser absorption and enhance ion acceleration through a number of mechanisms such as direct laser acceleration and laser guiding. We detail experimental results obtained at the Scarlet laser facility on hollow, micron-scale plasma channels for enhancing electron acceleration. These targets show a greater than three times enhancement in the electron cutoff energy as well as an increased slope temperature for the electron distribution when compared to a flat interface. Using three-dimensional particle-in-cell (PIC) simulations, we have modeled the interaction to give insight into the physical processes responsible for the enhancement. Furthermore, we have used PIC simulations to design structures that are more advantageous for ion acceleration. Such targets necessitate advanced target fabrication methods and we describe techniques used to manufacture optimized structures, including vapor-liquid-solid growth, cryogenic etching, and 3D printing using two-photon-polymerization. [Preview Abstract] |
Thursday, November 3, 2016 12:06PM - 12:18PM |
TO6.00014: Dynamics of laser-driven proton beam focusing and transport into solid density matter J. Kim, C. McGuffey, F. Beg, M. Wei, D. Mariscal, S. Chen, J. Fuchs Isochoric heating and local energy deposition capabilities make intense proton beams appealing for studying high energy density physics and the Fast Ignition of inertial confinement fusion. To study proton beam focusing that results in high beam density, experiments have been conducted using different target geometries irradiated by a kilojoule, 10 ps pulse of the OMEGA EP laser. The beam focus was measured by imaging beam-induced Cu K-alpha emission on a Cu foil that was positioned at a fixed distance. Compared to a free target, structured targets having shapes of wedge and cone show a brighter and narrower K-alpha radiation emission spot on a Cu foil indicating higher beam focusability. Experimentally observed images with proton radiography demonstrate the existence of transverse fields on the structures. Full-scale simulations including the contribution of a long pulse duration of the laser confirm that such fields can be caused by hot electrons moving through the structures. The simulated fields are strong enough to reflect the diverging main proton beam and pinch a transverse probe beam. Detailed simulation results including the beam focusing and transport of the focused intense proton beam in Cu foil will be presented. This work was supported by the National Laser User Facility Program through award DE-NA0002034 [Preview Abstract] |
Thursday, November 3, 2016 12:18PM - 12:30PM |
TO6.00015: Physics of Double Pulse Irradiation of Targets For Proton Acceleration S. Kerr, M. Mo, R. Masud, L. Manzoor, H. Tiedje, Y. Tsui, R. Fedosejevs, A. Link, P. Patel, H. McLean, A. Hazi, H. Chen, L. Ceurvorst, P. Norreys Experiments have been carried out on double-pulse irradiation of um-scale foil targets with varying preplasma conditions. Our experiment at the Titan Laser facility utilized two 700 fs, 1054 nm pulses, separated by 1 to 5 ps with a total energy of 100 J, and with 5-20{\%} of the total energy contained within the first pulse. The proton spectra were measured with radiochromic film stacks and magnetic spectrometers. The prepulse energy was on the order of 10 mJ, which appears to have a moderating effect on the double pulse enhancement of proton beam. We have performed LSP PIC simulations to understand the double pulse enhancement mechanism, as well as the role of preplasma in modifying the interaction. A 1D parameter study was done to isolate various aspects of the interaction, while 2D simulations provide more detailed physical insight and a better comparison with experimental data. [Preview Abstract] |
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