Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session CO8: Laser Plasma Sources of X Rays and Neutrons |
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Chair: Cedric Thaury, Ecole Polytechnique Room: 103/104 |
Monday, November 16, 2015 2:00PM - 2:12PM |
CO8.00001: Compton MeV Gamma-ray Source on Texas Petawatt Laser-Driven GeV Electron Accelerator Joseph M. Shaw, Hai-En Tsai, Rafal Zgadzaj, Xiaoming Wang, Vincent Chang, Neil Fazel, Watson Henderson, M.C. Downer Compton Backscatter (CBS) from laser wakefield accelerated (LWFA) electron bunches is a promising compact, femtosecond (fs) source of tunable high-energy photons. CBS x-rays have been produced from LWFAs using two methods: (1) retro-reflection of the LWFA drive pulse via an in-line plasma mirror (PM) [1,2]; (2) scattering of a counter-propagating secondary pulse split from the drive pulse [3]. Previously MeV photons were only demonstrated by the latter method, but the former method is self-aligning. Here, using the Texas Petawatt (TPW) laser and a self-aligned near-retro-reflecting PM, we generate bright CBS $\gamma $-rays with central energies higher than 10 MeV. The 100 $\mu $m focus of TPW delivers 100 J in 100 fs pulses, with intensity 6x10$^{\mathrm{18}}$ W/cm$^{\mathrm{2}}$ (a0$=$1.5), to the entrance of a 6-cm long Helium gas cell. A thin, plastic PM immediately following the gas cell exit retro-reflects the LWFA driving pulse into the oncoming 0.5 - 2 GeV electron beam to produce a directional beam of $\gamma $-rays without significant bremsstrahlung background. A Pb-filter pack on a thick, pixelated, CsI(Tl) scintillator is used to estimate the spectrum via differential transmission and to observe the beam profile. Recorded beam profiles indicate a low divergence. [1] H.-E. Tsai et al., Phys. Plasmas 22, 023106 (2015). [2] K. Ta Phuoc et al., Nat. Photon. 6, 308 (2012). [3] N.D. Power et al., Nat. Photon. 8, 28(2014). [Preview Abstract] |
Monday, November 16, 2015 2:12PM - 2:24PM |
CO8.00002: Compton X-rays from Self-Generated Backscattered Radiation in a Laser Wakefield Accelerator Antonio Ting, Dmitri Kaganovich, Michael Helle, Yu-hsin Chen, John Palastro, Bahman Hafizi, Daniel Gordon A unique Compton scattering configuration for generating monochromatic, short pulse, and potentially coherent x-rays in a Laser Wakefield Accelerator (LWFA) is being studied at the Naval Research Laboratory. Reflection mechanisms such as stimulated Raman scattering and shock-created density gradients in a plasma can generate the required backward-travelling laser pulse directly from the same laser pulse used in the LWFA, i.e., the high energy electron beam and the counter-propagating photon beam are both self-generated by an ultrashort laser pulse in plasma. Extended interaction distance and automatic alignment of electron beam and backscattered radiation could be beneficial to the amplification of the Doppler upshifted Compton X-rays. Preliminary experiments are ongoing with measurement of Raman backscattering and reflection off a plasma density gradient. Energy resolved X-ray results are also anticipated. [Preview Abstract] |
Monday, November 16, 2015 2:24PM - 2:36PM |
CO8.00003: Thomson Scattering from Electron Plasma Waves in a Raman Plasma Amplifier A. Davies, D. Haberberger, J. Bromage, J.D. Zuegel, D.H. Froula, R. Trines, R. Bingham, J. Sadler, P.A. Norreys, L.O. Silva Electron plasma waves (EPW's) can be used to transfer significant energy from a long-pulse laser to a short-seed pulse. Raman amplification has the potential to amplify intense pulses beyond the capabilities of current laser technology ($\sim 10^{22}$ W/cm$^2$) because of the plasma's ability to sustain large-amplitude plasma waves. Having complete knowledge of the EPW amplitude is essential to establishing optimal parameters for efficient Raman amplification. With Thomson scattering it is possible to measure the spatial and temporal distribution of the EPW amplitude and experimentally determine the effect of the EPW profile on Raman scattering. Moving beyond the initial proof-of-principal experiments at the submillijoule level, to amplifying a 75-mJ, 100-fs seed with a 75-J pump has the potential to produce PW-scale laser pulses with Raman amplification. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Monday, November 16, 2015 2:36PM - 2:48PM |
CO8.00004: Observation of Betatron radiation in the self-modulated regime of laser wakefield acceleration Felicie Albert, Bradley Pollock, Clement Goyon, Arthur Pak, John Moody, Jessica Shaw, Nuno Lemos, Ken Marsh, Christopher Clayton, William Schumaker, Siegfried Glenzer, Alison Saunders, Roger Falcone, Frederico Fiuza, Chan Joshi We observed multi keV Betatron x-rays from a self-modulated laser wakefield accelerator. The experiment was performed at the Jupiter Laser Facility, LLNL, by focusing the Titan short pulse beam (4-150 J, 1 ps) onto the edge of a Helium gas jet at electronic densities around $10^{19}$ cm$^{-3}$. For the first time on this laser system, we used a long focal length optic, which produced a laser normalized potential $a_0$ in the range 1-3. Under these conditions, electrons are accelerated by the plasma wave created in the wake of the light pulse. As a result, intense Raman satellites, which measured shifts depend on the electron plasma density, were observed on the laser spectrum transmitted through the target. Electrons with energies up to 200 MeV, as well as Betatron x-rays with critical energies around 20 keV, were measured. OSIRIS 2D PIC simulations confirm that the electrons gain energy both from the plasma wave and from their interaction with the laser field. [Preview Abstract] |
Monday, November 16, 2015 2:48PM - 3:00PM |
CO8.00005: Self-modulated laser wakefield acceleration as a X-ray source Nuno Lemos, Frank Tsung, Jessica Shaw, Ken Marsh, Felicie Albert, Brad Pollock, Chan Joshi Understanding material properties under extreme conditions of temperature and pressure is critical for different fields of physics such as astrophysics and high energy density (HED) science. The HED science facilities such as OMEGA and the National Ignition Facility are now uniquely able to recreate in the laboratory conditions of temperature and pressure that were thought to be only attainable in the interiors of stars and planets. To diagnose such extreme states of matter, the development of efficient, versatile and fast (sub-picosecond scale) x-ray probes with energies larger than 50 kilo-electronvolts has become essential for HED science experiments on these specific facilities. In this work we explore the betatron radiation generated in self-modulated laser-wakefield accelerators to probe HED plasmas with unprecedented time resolution. Through Osiris 2D particle-in-cell simulations we we will show that this acceleration scheme can produce radiation with energies exceeding 50keV. [Preview Abstract] |
Monday, November 16, 2015 3:00PM - 3:12PM |
CO8.00006: Characterization of Electrons and X-rays Produced using Asymmetric Laser Pulses in the Self-Modulated Laser Wakefield Acceleration Regime Zhen Zhao, Keegan Behm, Anatoly Maksimchuk, John Nees, Victor Yanovsky, Alexander Thomas, Karl Krushelnick The electron injection process into a laser plasma wakefield accelerator can be optimized by modifying the laser pulse parameters. We present an experimental study on the combined effect of the laser pulse duration, frequency chirp, and envelope characteristics on the electron injection process and the associated radiation emission for two different gas types---a 97.5% He and 2.5% N2 mixture and pure He. Our results show that the optimal pulse duration generally produced the highest energy electrons and the most charge. Positively chirped pulses with a fast rising edge sustained electron injection and produced higher charge, but lower energy electrons, compared with negatively chirped pulses with a slow rising edge for similar pulse durations. A similar trend was observed for the X-ray flux. The relationship between the radiant energy and the electron signal followed a power law over a two order magnitude change in the electron density and was not dependent on the pulse duration or sign of the frequency chirp. X-ray spectra showed that ionization injection generally produced more photons than self injection for all pulse durations/chirp and had fewer shot-to-shot fluctuations in the spectra. [Preview Abstract] |
Monday, November 16, 2015 3:12PM - 3:24PM |
CO8.00007: Soft X-ray betatron radiation characterization for warm-dense matter studies at LCLS-MEC W. Schumaker, F. Cordamine, A. Fry, E. Galtier, E. Granados, P. Heimann, J. Kotick, Hae Ja Lee, S.H. Glenzer, B. Barbrel, A. Sanders, R. Falcone, A. Ravarsio, J. Gaudin, B.B. Pollock, F. Albert Laser wakefield acceleration (LWFA) can produce high-energy ($>$100 MeV) electron beams with ultra-short durations ($<$100 fs)[1] in a compact, mm-scale plasma. Transverse motion of the electrons in the wakefield leads to the emission of synchrotron-like X-ray beams, called betatron radiation, with peak photon energies $>$10 keV and source sizes of a few microns [2]. These X-ray beams are presumed to retain the short-pulse characteristic of the electrons, resulting in high peak brightness and peak energy, making the source an excellent candidate for ultrafast temporally resolved pump-probe applications, especially for free-electron laser (FEL) and high-energy density (HED) experiments [3]. Presented here are some of first experimental measurements of betatron in the soft X-ray regime ($<$1 keV) using X-ray mirrors and a grating spectrometer to collect, transport, and focus betatron X-rays for pump-probe experiments at the LCLS Matter-in-Extreme Conditions (MEC) facility.\\[4pt] [1] O. Lundh et al., Nat. Phys. 2011\\[0pt] [2] S. Kneip et al., Nat. Phys. 2010\\[0pt] [3] F. Albert et al., PRL 2013 [Preview Abstract] |
Monday, November 16, 2015 3:24PM - 3:36PM |
CO8.00008: Single-hit spectroscopy of betatron X-ray spectra generated by laser wakefield acceleration using self and ionization injection Florian Condamine, Will Schumaker, Jordan Kotick, Felicie Albert, Benjamin Barbrel, Eric Galtier, Eduardo Granados, Alessandra Ravasio, Alan Fry, Siegfried Glenzer Betatron X-ray created by laser wakefield acceleration (LWFA) are of fundamental interest in plasma physics due to their broadband X-ray spectra, compact source size and ultra short duration. In particular, the femtosecond duration of electrons bunches produced during LWFA offers the opportunity to study warm dense matter (WDM) in detail via pump/probe experiments. In this study, we used the SLAC MEC optical laser (Ti:S 800nm, 1J in 40fs) focused in a gas cell to generate betatron X-ray by using two LWFA techniques : self-injection and ionization-injection. Three different gas types (100\%, 98\% and 90\% helium, doped with nitrogen) were investigated using a single hit detector to characterize X-ray spectra generated by the betatron source. We will compare results with self-injection and ionization-injection for different plasma conditions and several positions of the laser focal spot inside the gas cell. [Preview Abstract] |
Monday, November 16, 2015 3:36PM - 3:48PM |
CO8.00009: Femtosecond probing around the K-edge of a laser heated plasma using X-rays from betatron oscillations in a laser wakefield accelerator Keegan Behm, Tony Zhao, Anatoly Maksimchuk, Victor Yanovsky, John Nees, Stuart Mangles, Karl Krushelnick, Alexander Thomas Presented here are data from a two-beam pump-probe experiment. We used synchrotron-like X-rays created by betatron oscillations to probe a thin metal foil that is pumped by the secondary laser beam. The Hercules Ti:Sapph laser facility was operated with a pulse duration of 34 fs and a power of 65 TW split to drive a laser wakefield accelerator and heat the secondary target. We observed opacity changes around the K-edge of thin foils as they were heated by an ultrafast pump laser. To understand how the opacity is changing with heating and expansion of the plasma, the delay between the two laser paths was adjusted on a fs and ps time scale. Experimental data for polyvinylidene chloride (PVDC) and aluminum show variations in opacity around the Cl and Al K-edges with changes in the probe delay. The transmitted synchrotron-like spectrum was measured using single photon counting on an X-ray CCD camera and was available on a shot-by-shot basis. The success of this work demonstrates a practical application for X-rays produced from betatron oscillations in a wakefield accelerator. The compact size of these ``table-top" accelerators and the ultrashort nature of the generated X-ray pulses allows pump-probe experiments that can probe events that occur on the femtosecond time scale. [Preview Abstract] |
Monday, November 16, 2015 3:48PM - 4:00PM |
CO8.00010: High-resolution and ultrafast imaging using betatron x-rays from laser wakefield accelerators Zulfikar Najmudin Laser wakefield accelerators now routinely produce $\sim$GeV energy gain in $\sim$cm plasmas. and are simultaneously capable of producing high brightness and spatially coherent hard x-ray beams. This unique light-source has been used for medical applications, and also for ultrafast imaging in high energy density science. The experiments were performed with the Astra Gemini laser producing 10 J pulses with duration $\sim 40$ fs focussed to produce a spot of $25 \mu $m (\emph{fwhm}) in a gas-cell of variable length to produce a low divergence beam of x-rays. The length of the gas cell was optimised to produce high contrast x-ray images of radiographed test objects. This source was used for full tomographic imaging of a human trabecular bone sample, with resolution exceeding the $\sim 100\, \mu$m level required for CT applications. Phase-contrast imaging of human prostate and mouse neonates at the micron level was also demonstrated. These studies indicate the usefulness of these sources in research and clinical applications. The ultrafast nature of the source was also demonstrated by performing time resolved imaging of a laser driven shock. The ultrashort duration of the x-ray source essentially freeze the motion of these fast moving transient phenomena. [Preview Abstract] |
Monday, November 16, 2015 4:00PM - 4:12PM |
CO8.00011: Laser Pulse Driven Terahertz Generation via Resonant Transition Radiation (RTR) in inhomogeneous Plasmas Chenlong Miao, John Palastro, Thomas Antonsen Intense, short laser pulses propagating through inhomogeneous plasma can ponderomotively drive THz radiation via a resonant transition radiation mechanism (RTR) for THz generation as the laser pulses cross a plasma boundary [1]. Simulations and theoretical analysis demonstrate that the THz emission is low frequency, broad band, coherent and conical. Simulation results show that this radiation is insensitive to the plasma length and density above 1.5x10$^{18}$ cm$^{-3}$ for the laser parameters we use and assuming a sharp plasma boundary. The effect of density ramps [2] is also considered and shown that an upward ramp enhances the radiated energy while a downward ramp diminishes it. According to the model we developed, the radiation at a given frequency is generated at the resonant point in the plasma ramp where its frequency matches the local plasma frequency. The radiation must then tunnel out of the plasma to the turning point. The results from our model matches well with the simulation using the full format PIC code TurboWAVE, showing that the amount of radiation reaches maximum at a certain ramp length. As an example, a fixed driver pulse (1.66 J) excites THz radiation of 280.7 $\mu$J in a 400 $\mu$m increasing density ramp. [1] L. M. Gorbunov et. al., Plasmas Physics Reports Vol. 32, No. 10 (2006). [2] C. Miao, Proceedings of 6$^{th}$ IPAC, JACoW, in press (2015). [Preview Abstract] |
Monday, November 16, 2015 4:12PM - 4:24PM |
CO8.00012: Ultra-bright laser-driven neutron source M. Roth, A. Favalli, V. Bagnoud, J. Bridgewater, O. Deppert, M. Devlin, K. Falk, J. Fernndez, D. Gautier, N. Guler, D. Henzlova, J. Hornung, M. Iliev, K. Ianakiev, A. Kleinschmidt, K. Koehler, S. Palaniyappan, P. Poth, G. Schaumann, M. Swinhoe, T. Taddeucci, A. Tebartz, Florian Wagner, G. Wurden Short-pulse laser-driven neutron sources have become a topic of interest since their brightness and yield have recently increased by orders of magnitude. Using novel target designs, high contrast - high power lasers and compact converter/moderator setups, these neutron sources have finally reached intensities that make many interesting applications possible. We present the results of two experimental campaigns on the GSI PHELIX and the LANL Trident lasers from 2015. We have produced an unprecedented neutron flux, mapped the spatial distribution of the neutron production as well as its energy spectra and ultimately used the beam for first applications to show the prospect of these new compact sources. We also made measurements for the conversion of energetic neutrons into short epithermal and thermal neutron pulses in order to evaluate further applications in dense plasma research. The results address a large community as it paves the way to use short pulse lasers as a neutron source. This can open up neutron research to a broad academic community including material science, biology, medicine and high energy density physics to universities and therefore can complement large scale facilities like reactors or particle accelerators. [Preview Abstract] |
Monday, November 16, 2015 4:24PM - 4:36PM |
CO8.00013: Spectroscopy of Neutrons Generated Through Nuclear Reactions with Light Ions in Short-Pulse Laser-Interaction Experiments C. Stoeckl, C.J. Forrest, V.Yu. Glebov, T.C. Sangster, W.U. Schroder Neutron and charged-particle production has been studied in OMEGA EP laser-driven light-ion reactions including D--D fusion, D--$^{9}$Be fusion, and $^{9}$Be(D,n)$^{10}$B processes at deuteron energies from 1 to a few MeV. The energetic deuterons are produced in a primary target, which is irradiated with one short-pulse (10-ps) beam with energies of up to 1.25 kJ focused at the target front surface. Charged particles from the backside of the target create neutrons and ions through nuclear reactions in a secondary target placed closely behind the primary interaction target. Angle-dependent yields and spectra of the neutrons generated in the secondary target are measured using scintillator-photomultiplier--based neutron time-of-flight detectors and nuclear activation samples. A Thomson parabola is used to measure the spectra of the primary and secondary charged particles. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944 and DE-FC02-04ER54789. [Preview Abstract] |
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