A highhyphen;power Gaussian laser beam exerts a strong ponderomotive force on the electrons of a plasma, pushing them away from the axial region. This provides a passage to the beam through an otherwise overdense plasma. The depth of penetration, in the typical case of a linear density profile, increases with the power of the beam up to some critical value of power, beyond which the depth of penetration increases abruptly to very large values. The critical value of power corresponds tovd=vth, wherevdandvthare the oscillatory velocity and thermal velocity of electrons, respectively. For a CO2laser this corresponds to a power quest;1011W for fusion parameters. The effect of selfhyphen;generated magnetic fields is to reduce the depth of penetration and to enhance the critical power.
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