Selfconsistent field theory of a helix traveling wave tube amplifier
Abstract
A selfconsistent relativistic field theory of a helix traveling wave tube (TWT) is developed on the basis of relativistic fluid equations and Maxwell's equations for a configuration in which a thin annular beam propagates through a sheath helix enclosed within a lossfree wall. The theory is valid for arbitrary azimuthal mode numbers and for backward propagating waves. It is shown that the nearresonant limit for azimuthally symmetric forwardpropagating waves reduces to a Pierce type of coupledwave analysis. A comparison between the complete field theory and the coupledwave theory made for a wide range of beam currents shows that the latter breaks down for sufficiently high currents. Particular attention is given to the ballistic and spacecharge dominated regimes of the Pierce analysis, in which the gain scales as the cube and fourth root of the current, respectively. A discrepancy is found between the Pierce and the field theory which is caused by the dielectric effect of the beam on the helix modes. This can result in the gain increasing faster than the cube root of the current.
 Publication:

IEEE Transactions on Plasma Science
 Pub Date:
 October 1992
 DOI:
 10.1109/27.163592
 Bibcode:
 1992ITPS...20..543F
 Keywords:

 Beam Currents;
 Field Theory (Physics);
 Helices;
 Power Amplifiers;
 Self Consistent Fields;
 Traveling Wave Tubes;
 Boundary Conditions;
 Equilibrium Equations;
 Maxwell Equation;
 Space Charge;
 Electronics and Electrical Engineering