PWT Linac Structure

The Plane Wave Transformer (PWT) Linac Structure is a high-beta, standing-wave, linac structure with an effective shunt impedance (ZT2) of 150 MW/m at 3 GHz. The structure consists of a cylindrical tank with an array of washers along the axis. The outer part of the structure is excited in a TEM-like mode, which propagates power back and forth along the structure, at the speed of light, to provide coupling between the individual cells. This standing wave drives a TM02-like mode in the space between the washers. Thus the washers serve to transform the transverse electric field of the TEM-mode (a plane wave) in the outer part of the structure to a bi-directional longitudinal electric field along the axis for acceleration of particles hence the name "plane wave transformer".

The PWT linac structure offers advantages over other known linac structures in the areas of power efficiency, field stability, weight, fabrication simplicity, and costs. The exceptional efficiency and stability of this structure should translate into significant commercial advantages in most of the scientific, medical, and industrial applications. The structure offers higher output energies and/or higher beam currents for the same input power, or requires less input power for the same energies and currents than other linac structures. Relatively large temperature differences are allowed with the structure, thereby simplifying the cooling systems. The structure is relatively light weight, simple to fabricate, simple to evacuate, easy to tune, and easy to excite.

Specific areas where this new linac structure might find application include medical therapy and diagnostics, including the relatively new application of intraoperative radiation therapy (IORT), industrial radiography for non-destructive testing of thick metal parts, munitions, and rocket motors, materials modification as in crosslinking of polymers, sterilization of waste products, radiation processing of food and medical products, and pest control in grain, fruit, etc. As the applications mature, the demand for higher energy (more penetrating) radiation will increase, underscoring the advantages of the electron linac as the source of the radiation.

The PWT linac structure offers many advantages over other known electron linac structures. The most fundamental advantage is the exceptionally high shunt impedance, which translates into performance advantages and reduced operational costs. Many of the practical advantages relate to the ease of fabrication, assembly, handling, tuning, cooling, evacuation, and excitation, which translate into reduced capital costs. This structure should find its way into many existing electron linac application, and may, because of its economical format, open the door to new electron linac applications.