We present a theory for the acceleration of monoenergetic protons, trapped in a self-organized double layer, by short pulse laser irradiation on a thin foil with the specific thickness suggested by the simulation study of Yan et al (2008 Phys. Rev. Lett. 100 135003). The laser ponderomotive force pushes the electrons forward, leaving the ions behind until the space charge electric field balances the ponderomotive force at a distance . For the optimal target thickness D = > c/ω p , the electron sheath is piled up at the rear surface and the sheath electric field accelerates the protons until they are reflected by the inertial force in the accelerated frame. These protons are therefore trapped by the combined forces of the electrostatic field of the electron sheath and the inertial force of the accelerating target. Together with the electron layer, they form a double layer and are collectively accelerated by the laser ponderomotive force, leading to monoenergetic ion production.
Laser guiding in an axially nonuniform plasma channel c. s.A plasma channel produced by a short laser pulse is axially nonuniform due to self-defocusing of the laser. When a delayed second laser pulse propagates through the channel, diffraction and refraction effects do not balance each other exactly, resulting in periodic beam radius variation with the distance of propagation.
Lower-hybrid waves of finite wavenumber in a tokamak are susceptible to parametric instabilities when a certain threshold in density and power is exceeded. For typical tokamak temperatures, the channel of decay with a large growth rate is found to be due to the nonlinear ion-cyclotron damping of the beat wave generated by the pump and the lower-hybrid sideband. We furthermore compute the spectrum of the sideband at ω0−nωci through the nonlinear cascade of parametric interaction. The resonant decay into ion-cyclotron waves is also considered and shown to have a lower density threshold close to the critical density above which there is no current drive and occurs preferentially in a narrow region near the edge.
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