Fabrication of phased array microwave waveguides windows

In thermonuclear fusion research, RF power is used to heat the plasma and accelerate particles in order to drive steady-state currents in the plasma. In the range of frequencies near lower hybrid resonance, between 1 and 8 GHz, RF power can be successfully coupled to the plasma only by launching waves with a refraction index greater than unity along the confining toroidal field. This is achieved by using an array of waveguides in which each element is properly phased with respect to the element adjacent to it and the width and separation of the elements are such as to achieve the desired k-spectrum. The higher the number of elements, the narrower the k-spectrum becomes. In most experiments, this narrowing of the spectrum produces a higher efficiency. Because of the potentially large number of elements in an array and the desirability of placing the array as close to the vacuum vessel as possible, it is convenient to make the vacuum seal on the array assembly. This is much more desirable than making individual vacuum seals for each element. This problem has been approached by fabricating a long, tight array of elements and brazing the elements into a vacuum flange. Fabrication of the array is described