The physics of beat-excited plasmas. Ph.D. Thesis

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1994

OSTI ID:218165

Everett, M J

Physics issues associated with plasma beat-wave acceleration of electrons are studied through experiments, theory, and simulations. In the experiments, a beat-wave is driven in a plasma formed by tunneling ionization with an intense short pulse two frequency CO2 laser (100 Joules in 350 psec (FWHM)). The time evolution of this wave including its amplitude of 33 +/- 11 percent and duration of 100 psec (FWHM) is measured via direct Thomson scattering of a 0.532 micron probe laser. Particle-in-cell (PIC) code simulations with realistic time scales are used to study the dynamics of the wave and pinpoint expulsion of the plasma by the ponderomotive force of the laser and beat-wave as the limiting factor in amplitude and duration of the wave. This wave is used to trap and accelerate an externally injected relativistic electron beam for the first time, producing energy gains of 28 MeV over 1 cm. This is more than 100 times the acceleration gradients of approx. 20 MeV obtained in conventional RF electron accelerators such as the Stanford Linear Accelerator/Collider. Experimental evidence for the coupling of the relativistic phase velocity beat-wave to low phase velocity electron plasma waves associated with the Raman backscatter instability is presented using time and wavenumber resolved spectra of Thomson scattered light from the plasma. The qualitative features of the measured w(t, k) spectra are predicted by a Lagrangian coordinate description and reproduced in particle simulations which show that the daughter waves generated in the mode coupling process take the energy preferentially from the Raman wave without significantly affecting the beat-wave. The evolution of the stimulated Raman backscatter instability of laser light into Compton scattering in an initially cold plasma is also studied through experiments and simulations.

• Research Organization: California Univ., Los Angeles, CA (United States). Dept. of Mechanical, Aerospace and Nuclear Engineering
• OSTI ID: 218165
• Report Number(s): N--96-21382; NIPS--96-34613
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
ACCELERATION
BEAT WAVE ACCELERATORS
COMPUTERIZED SIMULATION
ELECTRONS
PLASMA WAVES
THOMSON SCATTERING