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The Axisymmetric Instability of a Self-Pinched Beam with a Rounded Radial Density Profile,

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The axisymmetric perturbations sausage and Hollowing modes of an intense relativistic self-pinched electron beam propagating in a resistive plasma background are studied, especially for a beam with rounded radial density profile. The Bennett profiles are assumed for both the equilibrium beam current J sub brJ sub b01 r to the second powerR to the second power sub b to the - second power and plasma return current J sub pr-fJ sub b01 r to the second powerR to the second power sub p to the - second power, where R sub b and R sub p are the characteristic radii of the beam and plasma return currents respectively. It is further assumed that the electric conductivity 0r of the plasma channel is proportional to the return current. For a paraxial electron beam with complete space-charge neutralization by the ambient plasma, the axisymmetric modes can be destabilized by the phase lag between the magnetic field and beam current, even without the plasma return current. The plasma return current significantly modifies the growth rate of the instability such that the ratio of plasma to beam current -I sub pI sub bfR to the second power sub pR to the second power sub b largely determines the stability character of the beam. Furthermore, for the same fractional current neutralization f, the modes are highly unstable for smaller ratio of plasma to beam radius R sub pR sub b. As comparing to the resistive hose instability, the growth rates for hollowing mode could be larger than those of hose mode, while the sausage mode is much stabler than the hose mode. Stability properties are illustrated in detail for various system parameters.

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  • Particle Accelerators
  • Plasma Physics and Magnetohydrodynamics

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