Macroscopic description of pressure-anisotropy-driven collective instability in intense charged particle beams

The macroscopic warm-fluid model developed by Lund and Davidson [Phys. plas mas 5 (1998) 3028] is used in the smooth-focusing approximation to investig ate detailed stability properties of an intense charged particle beam with pressure anisotropy, assuming small-amplitude electrostatic perturbations a bout a waterbag equilibrium. Stability properties are calculated numericall y for the case of extreme pressure anisotropy with P-II(0)( r)= 0 and P-per pendicular to(0) (r) not equal 0, assuming axisymmetric wave perturbations (partial derivative/partial derivative theta = 0) of the form delta phi(x,t )= delta phi(r)exp(ik, z - iwt), where k(z) is the axial wavenumber, and Im omega > 0 corresponds to instability (temporal growth). For sufficiently l arge values of k(z)r(b) where r(b) is the beam radius, the analysis leads t o an anistropy-driven instability (Im omega > 0) provided the normalized De bye length (Gamma(D) = lambda(D perpendicular to)/(r)b) is sufficiently lar ge and the normalized beam intensity (s(b) = <(omega)over cap>(2)(pb)/2 gam ma(b)(2)omega(beta)(perpendicular to)(2)) is sufficiently below the space-c harge limit. (C) 2000 Elsevier Science B.V. All rights reserved.