Bulletin of the American Physical Society
49th Annual Meeting of the Division of Plasma Physics
Volume 52, Number 11
Monday–Friday, November 12–16, 2007; Orlando, Florida
Session QI1: Fast Ignition I |
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Chair: Juan Fernandez, Los Alamos National Laboratory Room: Rosen Centre Hotel Junior Ballroom |
Wednesday, November 14, 2007 3:00PM - 3:30PM |
QI1.00001: Fast ignitor target studies for HiPER Invited Speaker: Recently, a European collaboration has proposed the HiPER facility [1], aimed at the demonstration of laser driven inertial fusion fast ignition. According to the present design, HiPER will have a 3$\omega $, multi-beam, multi-ns-pulse of about 250 kJ and a 2$\omega $ or 3$\omega $ ignition beam delivering 70 kJ in about 15 ps. In this talk, we present studies on fast-ignitor targets directly driven by 100-300 kJ compression pulses, followed by 70-100 kJ ignition pulses. First, we discuss ignition and compression requirements, and present gain curves, based on a model including ablative drive, compression, ignition and burn, and taking the coupling efficiency $\eta _{ig}$ of the igniting beam as a parameter. It turns out that ignition and moderate gain (up to 100) can be achieved, provided that adiabat shaping is used in the compression and the efficiency $\eta _{ig}$ exceeds 20{\%}. According to present understanding, a 2$\omega $ ignition beam is required to make the hot-electron range comparable to the desired size of the hot spot. A reference target family is then presented, based on 1-D fluid simulation of compression, and 2-D fluid and hybrid simulations of fast electron transport, ignition and burn. The sensitivity to compression pulse shape, as well as to hot-electron source location, hot electron range and beam divergence is also discussed. Models and perturbation codes have been used to study the Rayleigh-Taylor instability. Crucial issues that have so far not been studied in detail include high convergence cone-guided implosions, the generation of the hot electron beam and its transport in low-to-moderate density plasmas. However, we have begun studying the hydrodynamics of cone-guided targets with model hydrodynamics simulations and we are tackling aspects of intense laser interaction, hot electron generation and transport with PIC codes. [1] M. Dunne, Nature Phys., \textbf{2}, 2 (2006); HiPER Technical Design Report: http://www.hiper-laser.org/overview/TDR/tdr.asp [Preview Abstract] |
Wednesday, November 14, 2007 3:30PM - 4:00PM |
QI1.00002: Control of the Fast Electron Beam Divergence for Fast Ignition Inertial Fusion Invited Speaker: The fast electron beam divergence in intense laser-plasma interactions is a vital ingredient in determining the success of fast ignition inertial fusion. If it is too large, then the short pulse laser energy required to generate the temperatures needed for hot spark formation becomes impractical to implement on ignition scale facilities. In this talk, I will review the recent experiments performed on the Vulcan PW laser facility to investigate this question. The pulse duration was changed from 0.5 ps - 10 ps and a wide range of plasma diagnostics were fielded. An intensity dependence to the beam divergence has been identified for the first time from these measurements. Two dimensional particle-in-cell simulations reproduce this effect. I will present new ideas on how the divergence can be controlled and the fast electron transport collimated. These are supported by analytic theory and validated by hybrid Vlasov-Fokker-Planck and hybrid particle-in-cell modeling. [Preview Abstract] |
Wednesday, November 14, 2007 4:00PM - 4:30PM |
QI1.00003: Intense Laser Plasma Interactions on the Road to Fast Ignition Invited Speaker: Successful Fast Ignition (FI) offers the prospect of reduced laser driver energy and greater energy gain, which enhances the possibilities for realistic Inertial Confinement Fusion (ICF) energy power plants. The interaction of high intensity laser pulses with hot dense plasma lies at the core of the FI concept. At the most basic level FI relies on converting high energy, high intensity laser light into a beam of electrons which must propagate for 10's to $\sim $100 microns and deposit their energy in the compressed fuel. Thus, the process may be divided into two critical processes: 1) the generation of energetic electrons from the laser-matter interaction, and 2) the transport of energetic electrons through hot dense plasma. Experiments to date have only explored part of the FI relevant parameter space concerning laser energy, intensity, pulse duration, and transport of MeV particles. With the approach of first light on OMEGA EP and then NIF ARC, the field is poised to make crucial measurements that will determine the requirements for full scale FI. This talk will present recent results from high intensity laser-cone interactions that help pave the way to the next generation of experiments. [Preview Abstract] |
Wednesday, November 14, 2007 4:30PM - 5:00PM |
QI1.00004: Hot electron energy coupling in cone-guiding fast ignition Invited Speaker: A critical issue for the fast ignition of inertial fusion targets, where compressed fuel is ignited by injection of an intense short laser pulse, is whether the hot electrons produced in the interaction are in an energy range conducive to efficient heating of the core. The required in-tensity of the ignition laser light becomes greater than $10^{20}$\,W/cm$^2$ to meet the ignition condition. In this talk, we present the result of a ``numerical'' experiment of Cone Guided Fast Ignition with a super-intense laser pulse using a collisional PIC code, {\it PICLS} and challenge this critical issue. Our numerical experiment is the first simulation, which evaluates the complete physics underlying FI self-consistently, excluding nuclear reactions. In particular, this simulation accounts for hot electron generation, fast ion acceleration, energy transport in large density scale coronal plasmas, and collisional energy coupling to the core, i.e. we study a model situation that is as comprehensive and self-consistent as possible today. We found that the while electromagnetic instabilities appear around the cone target where the plasma density is less than a few hundred times critical density, no significant fields are found near the core. This indicates that core heating is mainly provided by collisional processes. In particular, the predominant core heating mechanism has been identified as drag heating between hot and bulk electrons. We also found that after the preplasma inside the cone was blown away, the hot electron temperature observed in the simulation is lower than the ponderomotive scaling. A simple analytic scaling law for the hot electron temperature is obtained which agrees with our simulation results. This temperature scaling indicates that it may be possible to tune the temperature of the hot electrons generated by the super-intense ignition pulse for optimal core heating by manipulating the properties of the material inside the cone target. [Preview Abstract] |
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