Intense non-neutral beam propagation in a periodic solenoidal field using a macroscopic fluid model with zero thermal emittance
- Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
A macroscopic fluid model is developed to describe the nonlinear dynamics and collective processes in an intense {ital high-current} beam propagating in the z-direction through a periodic focusing solenoidal field B{sub z}(z+S)=B{sub z}(z), where S is the axial periodicity length. The analysis assumes that space-charge effects dominate the effects of thermal beam emittance, Kr{sub b}{sup 2}{gt}{epsilon}{sub th}{sup 2}, and is based on the macroscopic moment-Maxwell equations, truncated by neglecting the pressure tensor and higher-order moments. Here, K=2N{sub b}Z{sub i}{sup 2}e{sup 2}/{cflx {gamma}}{sub b}{sup 3}m{beta}{sub b}{sup 2}c{sup 2} is the self-field perveance, N{sub b} is the number of particles per unit axial length, and r{sub b} is the characteristic beam radius. Assuming a thin beam with r{sub b}{lt}S, azimuthally symmetric beam equilibria with {partial_derivative}/{partial_derivative}t=0={partial_derivative}/{partial_derivative}{theta} are investigated, allowing for an axial modulation of the beam density n{sub b}(r,z) and macroscopic flow velocity V{sub rb}(r,z){bold {cflx e}}{sub r}+V{sub {theta}b}(r,z){bold {cflx e}}{sub {theta}}+V{sub zb}(r,z){bold {cflx e}}{sub z} by the periodic focusing field. To illustrate the considerable flexibility of the macroscopic formalism, assuming (nearly) uniform axial flow velocity V{sub b} over the beam cross section, beam equilibrium properties are calculated for two examples: (a) uniform radial density profile over the interval 0{le}r{lt}r{sub b}(z), and (b) an infinitesimally thin annular beam centered at r=r{sub b}(z). The analysis generally allows for the azimuthal flow velocity V{sub {theta}b}(r,z) to differ from the Larmor frequency, and the model is used to calculate the (leading-order) correction {delta}V{sub zb}(r,z) to the axial flow velocity for the step-function density profile in case (a) above. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 554217
- Journal Information:
- Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 10 Vol. 4; ISSN PHPAEN; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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