Constructing a field-emission (FE) x-ray tube

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This project aimed at constructing an x-ray camera equipped with a multiple field cathode (MFC) as the electron source. The construction of the x-ray camera and its test were completed before March 1, 1999.The total system of our x-ray camera is basically composed of camera chamber, electron source and pumping system. The respective components are outlined as follows.1) x-ray cameraThe x-ray camera is entirely composed of a stainless-steel cylindrical chamber with seven viewing and connection ports. Inside the chamber are installed an Al target and a Grazer lense, the latter of which is water-cooled.2) Electron sourceThe FE emitter, or the electron source, is exchangeable without breaking the main vacuum. Its position adjustment is done with the aid of a manipulator, and electrons emitted from it are focused onto the target through the Glazer lense.3) Pumping systemThe camera chamber is pumping down to -10^<-7> Torr, with the aid of two turbomolecular pumps. The field cathode employed were Mo meshes simply cut by a scissor. It is emphasized that sharp x-ray images were obtained using such a simple mesh emitter. This is really "epoch-making" because no x-ray image has been recorded so far by using field electrons. One undesirable result is that the chamber pressure remained at the order of 10^<-7> Torr because of an 0-ring to combine the chamber and the high-voltage insulator. Since field emission is a typical surface phenomenon, a ultrahigh vacuum (UHV) is demanded to maintain a stable operation of the electron source. Our next step is thus to construct a UHV x-ray camera based on a variety of experiences that we had in the present project.