A cathode of a magnetron having a radial extension to accommodate the cathode terminals is supported by arms which have a greater diameter over the region in which they are supported in the glass thimble than over the region of the free ends. This shifts any vibrations to a higher frequency band, which is less liable to be excited in the event the magnetron is moved rapidly as in a linac used for radiotherapy purposes.
1. A magnetron, comprising:
a cathode having an axis;
a vacuum envelope including a glass portion extending radially relative to the axis of the cathode;
an anode having a cylindrical anode wall surrounding the cathode;
a pair of electrically conducting support arms mounted vacuum-tight in a wall of the glass portion of the vacuum envelope and having free ends located exterior to the cylindrical anode wall; and
leads connecting the free ends of the support arms to the cathode, the support arms supporting the cathode via the leads,
wherein each of the support arms has a first portion having a first diameter extending over a region of mounting in the glass portion, and each of the support arms has a second portion extending from the free ends to the first portion and having a second diameter that is smaller than the first diameter thereby to increase a resonant frequency of the support arms.
2. The magnetron as claimed in claim 1 , wherein each of the support arms is stepped in diameter.
3. The magnetron as claimed in claim 2 , further comprising sleeves connected to a region of greater diameter of the support arms and extending over a region of lesser diameter, to form quarter wavelength chokes.
4. The magnetron as claimed in claim 1 , wherein the support arms include at least one region of tapering diameter.
5. The magnetron as claimed in claim 1 , wherein the support arms terminate outside a profile of an interior of the anode, and the cathode leads are connected during assembly.