On the use of the FEL to produce high transient spacecharge potentials in a magnetized plasma
Abstract
A recently developed approximate theory is used to estimate the magnitude of the spacecharge potentials and electric fields that could be produced within a plasma column exposed to the focussed microwave beam from the Livermore freeelectron laser (FEL). The plasma, composed of electrons and singly charged high mass ions, is assumed immersed in a solenoidal magnetic field with a strong longitudinal gradient. Cyclotron resonance of the electrons in the magnetic field leads to rapid heating and an associated strong axial expelling force resulting from the interaction of the electrons' magnetic moment with the magnetic field gradient. Ion inertia, together with the quasineutrality constraint, leads to the development of a flatbottomed potential well, thereby forcing the electron loss rate to equal the inertiadominated rate of the ions. This phenomenon, first observed experimentally in the 1960's, is made much more effective by the high power levels of the FEL. At present FEL power levels (2 GW), positive potentials of 4 MV and associated sheath electric fields approaching 1 GV/meter are predicted, with columnaveraged fields of order 50 MV/meter. At projected FEL power levels, potentials of 15 MV, and sheath fields of 1.6 GV/meter are predicted. These figures are much higher than the corresponding figures for conventional RF or inductiontype ion accelerators. Plasma parameters appropriate for a proofofprinciple experiment are given.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 June 1989
 Bibcode:
 1989STIN...8928814P
 Keywords:

 Electric Fields;
 Free Electron Lasers;
 Plasma Potentials;
 Plasma Sheaths;
 Plasmas (Physics);
 Space Charge;
 ChildLangmuir Law;
 Cyclotron Resonance;
 Magnetic Fields;
 Mathematical Models;
 Microwaves;
 Photoionization;
 Lasers and Masers