Electron discharge image tube with electrostatic field shaping electrode

Claim 1

An electron discharge tube including: a. an input portion including an electron emissive cathode capable of emitting electrons as an electron-image in response to a radiation image impinging thereon, b. an output means for receiving said electron-image and for providing a read-out of said electron-image; said output means including an electron-image receiving member in spaced-apart facing relation to said cathode; c. hermetically sealed envelope means fixably supporting and electrically isolating said cathode and said output means at opposing ends of a tubular envelope portion whereby an electron accelerating cavity extends within the interior of said tubular envelope means between said cathode and said electron-image receiving member; d. an electron lens system capable of accelerating electrons emitted from said cathode to impinge upon a surface portion of said electron-image receiving member as an electron-image; said electron lens system including at least two electrically isolated electron focussing electrodes secured within said cavity at opposing ends of the tube by said envelope means; said focussing electrodes being electrically isolated from each other by a tubular insulating member of said tubular envelope portion having an interior wall surface facing said cavity within said tube; e. a tubular electrostatic field shaping electrode extending coaxially about the entire interior wall surface of said tubular insulating member facing said cavity; said field shaping electrode being capable of substantially preventing electron bombardment of said interior wall surface by divergent electrons and of substantially avoiding, during operation of the tube, spurious output signals resulting from the generation of positive ions from that surface as a consequence of such electron bombardment; and f. a housing surrrounding said envelope means; said housing including a conductive shield which coaxially surrounds said envelope means and said field shaping electrode; said shield being capable of establishing a ground plane electrically isolated from electrical potentials which may be applied to said focussing electrodes, field forming electrode, said cathode, and said receiving member.