THE HIGH-FREQUENCY ELECTRIC AND MAGNETIC-FIELDS OF A SOLENOID

General and simplified expressions for the electric and magnetic fields of a solenoid at frequencies up to 100 MHz are obtained from first principles for both an empty and a plasma-filled solenoid. For the empty solenoid, the field amplitudes usually differ only slightly from their low-frequency expressions, but there is a significant change in the phase of the fields with respect to the driving current in the solenoid, as the frequency increases. The expression found for the ratio of the longitudinal component of the electric field to the azimuthal component differs significantly from that which has previously been published. When the solenoid contains a moderately dense plasma, there is an even more pronounced change in both the amplitudes and phases.