Theory and Modeling of Petawatt Laser Pulse Propagation in Low Density Plasmas

Technical Report · Thu Dec 08 00:00:00 EST 2016

DOI:https://doi.org/10.2172/1334788· OSTI ID:1334788

Shadwick, Bradley A. ^[1]; Kalmykov, S. Y. ^[1]

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1. Univ. of Nebraska, Lincoln, NE (United States). Dept. of Physics and Astronomy

Report describing accomplishments in all-optical control of self-injection in laser-plasma accelerators and in developing advanced numerical models of laser-plasma interactions. All-optical approaches to controlling electron self-injection and beam formation in laser-plasma accelerators (LPAs) were explored. It was demonstrated that control over the laser pulse evolution is the key ingredient in the generation of low-background, low-phase-space-volume electron beams. To this end, preserving a smooth laser pulse envelope throughout the acceleration process can be achieved through tuning the phase and amplitude of the incident pulse. A negative frequency chirp compensates the frequency red-shift accumulated due to wake excitation, preventing evolution of the pulse into a relativistic optical shock. This reduces the ponderomotive force exerted on quiescent plasma electrons, suppressing expansion of the bubble and continuous injection of background electrons, thereby reducing the charge in the low-energy tail by an order of magnitude. Slowly raising the density in the pulse propagation direction locks electrons in the accelerating phase, boosting their energy, keeping continuous injection at a low level, tripling the brightness of the quasi-monoenergetic component. Additionally, propagating the negatively chirped pulse in a plasma channel suppresses diffraction of the pulse leading edge, further reducing continuous injection. As a side effect, oscillations of the pulse tail may be enhanced, leading to production of low-background, polychromatic electron beams. Such beams, consisting of quasi-monoenergetic components with controllable energy and energy separation, may be useful as drivers of polychromatic x-rays based on Thomson backscattering. These all-optical methods of electron beam quality control are critically important for the development of future compact, high-repetition-rate, GeV-scale LPA using 10 TW-class, ultra-high bandwidth pulses and mm-scale, dense plasmas. These results emphasize that investment into new pulse amplification techniques allowing for ultrahigh frequency bandwidth is as important for the design of future LPA as are the current efforts directed to increasing the pulse energy.

• Research Organization: Univ. of Nebraska, Lincoln, NE (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• DOE Contract Number: SC0008382
• OSTI ID: 1334788
• Report Number(s): DE-SC0008382; TRN: US1700814
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
WAKEFIELD ACCELERATORS
ELECTRON BEAMS
PLASMA
ELECTRONS
PLASMA DENSITY
PLASMA GUNS
QUALITY CONTROL
BEAM INJECTION
PULSES
LASER RADIATION
WAVE PROPAGATION
MATHEMATICAL MODELS
PETAWATT POWER RANGE
BRIGHTNESS
GEV RANGE
COMPUTERIZED SIMULATION
AMPLIFICATION
AMPLITUDES
BUBBLES
INTERACTIONS
OSCILLATIONS
TUNING
BEAM DYNAMICS
self-injection
bubble regime
macro-particle
symplectic integration