Frontiers in High Energy Density Physics The X-Games of Contemporary Science (2003) / Chapter Skim
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4. Laser-Plasma and Beam-Plasma Interactions
4. Laser-Plasma and Beam-Plasma Interactions
Pages 120-148
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From page 120... ...
The answers may, for example, lead to breakthrough progress toward fusion energy, compact high-energy particle accelerators, and novel imaging techniques. They may also help us to understand the mechanism of ultra-high-energy cosmic ray (UHECR)
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From page 121... ...
Then, in the secion on applications of HED beam-plasma physics, three applications are described rather extensively, followed by coverage of seven other applications. The final section discusses the opportunities for furthering this field, both expert mental Iy and theoretical Iy/computational Iy.
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From page 122... ...
· Are the same mechanisms responsible for laboratory plasma accelerators and plasma lenses also operating in the acceleration of particles from supernovae and the collimation of cosmic jets? · Can ion beams produced by relativistic laser-plasma interactions be used as a source for beam-plasma physics, a diagnostic probe, or as a front-end component for accelerators?
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From page 123... ...
At this point, the plasma becomes transparent to the laser pulse it would normally reflect. Other examples of relativistic phenomena accessible with current laser technology include highly nonlinear plasma wakes in which the plasma is driven to complete blowout, ultrastrong plasma lensing of both photons and particles, and intense radiation generation from the terahertz to x-ray frequency range by various mechanisms.
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From page 124... ...
Finally, it is noted that an alternate path to the Schwinger field could be an x-ray free-electron laser. If 1.5-A x rays could be focused to a diffraction-limited spot size of roughly 2 A, the Schwinger field could be reached with an energy of 2 J at a pulse length of 10 fs.
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From page 125... ...
Wakefield accelerators driven by high energy density laser or particle beams promise an entirely new type of technology for building compact highenergy accelerators. Laser pulses propagating in plasmas can generate large-amplitude plasma waves, that is, wakefields, which can be used to trap and accelerate electrons to high energies.
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From page 126... ...
For example, at the SLAC, electron beams have been used to generate wakefields over a meter and to accelerate electrons by as much as 350 MeV. Lasers incident on solid targets can also be used to accelerate heavier particlesprotons and ions.
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From page 127... ...
The laser beams can scatter and/or generate high-energy electrons via a variety of instabilities involving either electron plasma waves (the stimulated Raman instability and the two-plasmon decay) or ion sound waves (the stimulated Brillouin instability)
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From page 128... ...
Fast Ignition In the past decade, the development of short-pulse, ultrahigh-power lasers has motivated another approach to inertial fusion energy called Fast Ignition. In this case, cold deuterium-tritium (DT)
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From page 129... ...
Intense laser pulses made with chirped pulse amplification technology provide a key tool for investigating physics in this regime. Although at lower energy/pulse and shorter pulse lengths than required for Fast Ignition, CPA lasers have already achieved the requisite powers (up to 1045 W)
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From page 130... ...
On . FIGURE 4.4 Three-dimensional particle-in-cell simulations of energetic electron generation and transport with laser pulses in overdense plasmas.
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From page 131... ...
in the driver accelerator can take place through complicated distortions driven by collective processes, imperfect applied fields, image fields from nearby conductors, and interbeam forces. To assist in the final transport through the chamber, plasma lenses, as employed in other accelerator applications, are being studied experimentally and theoretically for heavy ion fusion.
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From page 132... ...
To provide quantitative comparisons of theoretical predictions with experiment, the NTX has been developed at Lawrence Berkeley National Laboratory in collaboration with Princeton Plasma Physics Laboratory. The initial experiment consists of a pulsed metal arc source at the exit of the last pulsed magnet, serving as a "plasma plug," from which electrons are extracted by the positive potential of the traversing beam.
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From page 133... ...
The first optical system, essentially operating as a flashlamp, delivers energy without providing a strong focus. A chirped pulse emerges from a grating at perhaps 40 ps in length, and then is focused beyond the plasma target, so that the plasma is irradiated by fluence on the order of kJ/cm2.
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From page 134... ...
As another significant application, multikilojoule, 5- to 50-ps laser beams will enable high-quality radiography using 20- to 1 00-keV x rays. This has potential importance for NIF, where the x rays produced can reach acceptable brightness for backlighting studies of the implosion physics of capsules or for equation-of-state studies.
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From page 135... ...
free electron laser atJefferson National Laboratory has demonstrated simultaneous production of femtosecond x rays from intracavity Thompson scattering of the wiggler IR radiation off the electron beam, regular IR FEL lasing and terahertz (THz) radiation from the recirculating linac bends, at record fluences in all three parts of the spectrum.
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From page 136... ...
If this mechanism can be made to lase at higher frequencies, it may provide a simple tunable insertion device for FELs. Improved Conventional Accelerator Performance: Control of the Electron Cloud and Two-Stream Instabilities Electron clouds are one of the most significant performance-limiting factors in circular accelerators and storage rings carrying high energy density positively charged beams, and they are a serious concern for future machines such as the Spallation Neutron Source at Oak Ridge National Laboratory, the Large Hadron Collider at CERN, and heavy ion fusion accelerators.
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From page 137... ...
The collective fields created in such cases are not unlike highly nonlinear wakes excited in wakefield accelerators. Advanced plasma and beam modeling tools are being applied to this problem; an improved understanding resulting from simulation studies will play an important role in controlling the electron cloud and two-stream instabilities.
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From page 138... ...
Furman, Lawrence Berkeley National Laboratory. Short-Lifetime Particle "Factories" Laser wakefield acceleration in high-density plasmas produces longitudinal electric fields comparable to the laser transverse field.
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From page 139... ...
, and selected examples are briefly described here. Beam Facilities: The Stanford Linear Accelerator Center Fundamental research into the formation, injection, and propagation of short and possibly shaped bunches in long plasmas appears to hold great promise for advancing toward a future device that can benefit high energy physics and other areas of science.
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From page 140... ...
Furthermore, the diagnostics have become quite sophisticated. For example, Figure 4.10 shows measurements via Thomson scattering of the temporally and spatially resolved amplitudes of both the electron plasma wave due to stimulated Raman scattering and the ion sound wave due to stimulated Brillouin scattering in a laser-plasma experiment.
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From page 141... ...
Michard, 1997, "Interplay Between Ion Acoustic Waves and Electron Plasma Waves Associated with Stimulated Brillouin and Raman Scattering," Phys. Plasmas, 4:423-427, copyright 1997 by the American Institute of Physics.
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From page 142... ...
This program builds on and significantly extends the existing Inertial Fusion Science in Support of Stockpile Stewardship grant program. Chirped Pulse Amplification Laser Facilities The generation and transport of ultrastrong energy flows in matter are clearly a very promising frontier of high energy density physics.
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From page 143... ...
Such sources could be complementary to recent light source facilities such as that at the Jefferson Laboratory infrared free electron laser. The vast potential of these short-pulse, multicolor operating scenarios for materials and other research and development is only just beginning to be explored.
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From page 144... ...
In the mainline approach, laser beams with a pulse length of order 10 ns interact with a target plasma with scale lengths of order 1 cm. The absorption and reflection of the beams are modified by the excitation of plasma waves with maximum frequencies comparable to the laser light frequency (~6 x 1045 so)
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From page 145... ...
and (b) the increase in laser peak power from 1960 to 2010.
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From page 146... ...
center at the Lawrence Berkeley National Laboratory is an IBM SP Powers machine capable of 3.05 Tflops; (d) ASCI Red at Sandia National Laboratories is an Intel processor-based machine capable of 2.37 Tflops; and (e)
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From page 147... ...
The supercomputers developed by the ASCI program represent a powerful enabling technology for the modeling of high energy density science. Figure 4.12 shows the top five supercomputer sites as of November 2001.
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From page 148... ...
Chirped pulse amplification: Allows one to avoid the strong nonlinear effects that can (lestroy an amplifier when attempting to build a high-power laser pulse. To overcome the nonlinearities, the input pulse to the amplifier is stretched in time so that the peak power is decreased.
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