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 CI01: Plasma Accelerators and BeamsInvited Live
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Chair: Nick Beier, University of Alberta Room: Ballroom B |
Monday, November 8, 2021 2:00PM - 2:30PM |
CI01.00001: Meter-scale plasma waveguides for laser wakefield acceleration Invited Speaker: Bo Miao Laser wakefield acceleration (LWFA) can deliver electron beams of multi-GeV energies. Achieving such high energy gains, while avoiding dephasing and depletion, typically requires the laser driver to propagate over many Rayleigh lengths at high intensity (normalized vector potential a>1) through low density plasma (~1017 cm-3). We have recently demonstrated two methods, based on optical field ionization (OFI), to generate low-loss, meter-scale plasma waveguides (in hydrogen plasma) where high intensity guided modes can propagate hundreds of Rayleigh lengths [1,2]. The first method uses two time-separated Bessel beam pulses, where the first pulse (a J0 beam) generates the core of the waveguide and the second pulse (a high order Bessel beam) generates the waveguide cladding. The resulting plasma density profile does not rely solely on hydrodynamic expansion and it allows independent control of core and cladding height, which is crucial for reducing guided mode leakage. In the second method, a J0 Bessel beam heats the hydrogen to yield a neutral hydrogen channel with a central density depression. The leading edge of a high intensity laser pulse, injected into the end of this structure, self-generates its own plasma waveguide as it propagates. Both methods employ our recently developed long supersonic hydrogen gas jets. I will describe our recent LWFA experiments employing 20-30 cm long gas jets and injection of multi 100 TW laser pulses and achieving multi-GeV electron acceleration. |
Monday, November 8, 2021 2:30PM - 3:00PM |
CI01.00002: High Intensity Orbital Angular Momentum: Theory, Generation, and Applications Invited Speaker: Andrew M Longman Recently, orbital angular momentum (OAM) beams have demonstrated at relativistic intensities at several high-power laser facilities around the world using off-axis spiral phase mirrors [1,2,3]. The additional angular momentum carried by OAM beams, even when linearly polarized, introduces a new control parameter in laser plasma interactions and has shown promise to introduce new and exciting phenomena not possible with a standard Gaussian beam. |
Monday, November 8, 2021 3:00PM - 3:30PM |
CI01.00003: Two-photon pair creation as a dominant mechanism in a plasma driven by high-intensity lasers Invited Speaker: Yutong He Creation of electrons and positrons from light alone is a basic prediction of quantum electrodynamics, but yet to be observed. Our simulations show that the required conditions are achievable using a high-intensity two-beam laser facility and an advanced target design. Dual laser irradiation of a structured target produces high-density γ rays that then create > 108 positrons at intensities of 2 × 1022 Wcm-2. The unique feature of this setup is that the pair creation is primarily driven by the linear Breit-Wheeler process (γγ→e+e- ), which dominates over the nonlinear Breit-Wheeler and Bethe-Heitler processes. The favorable scaling with laser intensity of the linear process prompts reconsideration of its neglect in simulation studies and also permits positron jet formation at experimentally feasible intensities. Simulations show that the positrons, confined by a quasistatic plasma magnetic field, may be accelerated by the lasers to energies > 200 MeV. The considered geometry has the potential to enable the first experimental measurement of two-photon pair creation, driven entirely by real photons. Such interactions will form a major component of the physics investigated in upcoming high-power laser facilities. From the theory perspective, our results also motivate investigation of field-driven corrections to the two-photon cross section. |
Monday, November 8, 2021 3:30PM - 4:00PM |
CI01.00004: The BELLA PW laser proton beamline: a new platform for ultra-high dose rate radiobiological research Invited Speaker: Lieselotte Obst-Huebl Radiotherapy is the current standard of care for more than 50% of all cancer patients. Improvements in radiotherapy technology have increased tumor targeting and normal tissue sparing. Recently, the beneficial differential effects on tumors versus normal tissues using the delivery of single, high radiation doses of >10 Gy at extremely high dose rates, has received increasing attention and was termed the FLASH effect. However, radiobiological research into radiobiological effectiveness of ultra-high dose rate protons has been limited by the restricted access to proton facilities for experiments. As such, there is much speculation regarding the underlying molecular and cellular mechanisms at play for irradiations with FLASH proton dose rates. We present the first radiobiological results using our new experimental platform to deliver petawatt laser-driven (LD) proton pulses with clinically relevant doses ranging from 5 to 25 Gy at ultra-high instantaneous dose rates of 107 Gy/s with 2 MeV energy at 0.2 Hz repetition rate to prostate cell monolayers grown over a 1 cm diameter field. Dose-dependent cell survival measurements of human normal and tumor prostate cells exposed to either LD protons or conventional X-rays showed significantly higher normal cell survival after LD proton irradiation for total doses >10 Gy. The tumor cells in contrast showed enhanced killing after exposure. These results, in combination with the low-cost and small-footprint nature of LD proton sources, provide evidence to demonstrate the capabilities of this new platform to elucidate the mechanism and optimal conditions of ultra-high dose rate proton therapy. |
Monday, November 8, 2021 4:00PM - 4:30PM |
CI01.00005: Energetic ion acceleration from relativistically transparent prepulse-expanded films driven by ultra-intense femtosecond laser pulses Invited Speaker: Nicholas P Dover State-of-the-art high-power lasers are reaching ever-higher focal intensities, enabling discoveries in high-field science. One key application is the generation of high energy particles from irradiation of solid foils. We have recently investigated laser driven ion acceleration using two different femtosecond-class laser systems operating with ultra-high focal intensities exceeding 1021 W/cm2: J-KAREN-P, at KPSI, and DRACO PW at HZDR. Using advanced pulse characterisation techniques, we tuned both lasers to generate similar intensity and laser contrast profiles, enabling proof-of-principle repeatability experiments. |
Monday, November 8, 2021 4:30PM - 5:00PM |
CI01.00006: Spin and Polarization in High-Intensity Laser-Plasma Interactions Invited Speaker: Daniel Seipt With the ongoing progress of high-power laser developement, high-intensity QED effects are playing an increasingly important role in high-intensity laser plasma interactions. In this talk I will elaborate why electron-spin and photon-polarization will be a relevant subject in high-intensity laser-plasma and laser-beam interactions in the near future due to the fundamental QED processes in strong fields being sensitive to the particle polarization. |
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