Accelerating Structures

Oscillating fields in tree space, far from all sources (i.e., at distances r very much larger than the wavelength X of the radiation), consist of a sum of all possible traveling electromagnetic waves. Provided the particles to be accelerated are traveling less than the velocity of light, acceleration2 can occur. Once the velocity approaches that of light, only waves traveling in the same direction as the particles remain in phase with the particles. Unfortunately, since free radiation is transversely polarized, no continuous acceleration is possible. Despite claims,3 no juggling with holograms, phase plates or foci can change this. In the presence of a magnetic field, the particle’s direction can be perturbed in such a way as to allow continuous acceleration ,4 but this too decreases as the particle’s momentum increases and significant perturbations become impractical. In5 or near6 a dielectric, the inverse eerenkov effect will accelerate, but the field that can be used is limited, because the dielectric cannot be allowed to break down. At high fields any dielectric becomes a plasma and the situation becomes very complicated. Acceleration within such a plasma is certainly possible7 but the practicality of such acceleration remains to be determined.