ISSN:
1089-7674
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The rf combined trap for confining a non-neutral plasma by a combination of rf fields and a uniform magnetic field is introduced. The particle motion is studied in such a trap in which the rf fields are given by the TM011 mode. The aim is to determine limits on a focus at the center for low angular momentum particles. Such a focus allows densities in excess of the local Brillouin limit. The motion is described in terms of an effective potential consisting of the ponderomotive potential Vpon(r,z) plus a radial potential mΩc2r2/8 due to the magnetic field Bz plus a centrifugal potential pθ2/2mr2. Near the origin r=0, z=0, the equations reduce to a pair of Mathieu equations for the r and z motions. For certain parameters the system is quasispherically symmetric, i.e. the effective ponderomotive frequencies Ωr, Ωz in r and z are equal. In this case the Brillouin limit for a uniform density plasma is shown to equal the usual cylindrical limit. Numerical integration of the ponderomotive equations is shown for parameters near those giving quasispherical symmetry. There is resonance for Ωr/Ωz=1, giving m=2, n=2 islands. The islands limit the size of the focus at the origin, even for pθ=0. For particles with large effective energy Eeff, there can also be chaos, depending on the elongation L/a of the rf cavity. It is found that the deleterious effect of islands and chaos on the focus is minimized by having the elongation L/a close to unity and having particles trapped deeply in the ponderomotive well. © 1997 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.872303
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