Electron gun device of field emission type

Claim 2

In an electron gun device of the field emission type for generating an electron beam having a cathode tip of needle shape, means for heating said cathode tip, a first anode, a second anode, and means for applying an electric voltage between said cathode tip and said first anode so as to produce an electric field therebetween which causes electrons to be emitted from said tip, the improvement which comprises a shield electrode disposed to surround said first anode between said first and second anode and means for applying to said shield electrode the same voltage as that applied to said anode, whereby said shield electrode shields said anode from ground potential portions of said device.

Claim 3

An electron gun device as defined in claim 1, wherein said anode and said shield electrode are substantially concentric cup-shaped elements.

Claim 4

An electron gun device as defined in claim 1, wherein said means for heating said cathode tip includes a pair of terminals connected to said cathode tip for applying a heating current thereto and an insulator for supporting said pair of terminals, and further including an additional shield electrode disposed between said insulator and said anode and being connected to one of said pair of terminals.

Claim 5

An electron gun device as defined in claim 3, wherein said means for applying a voltage to said shield electrode includes an electrical connection between said shield electrode and said additional shield electrode.

Claim 6

An electron gun device as defined in claim 1, wherein said shield electrode is a substantially cylindrical element disposed concentrically to said anode.

Claim 7

An electron gun device of the field emission type comprising: a cathode tip of needle shape capable of being heated and having a large negative electric potential with respect to ground potential portions of said gun device; an anode applied with an accelerating voltage with respect to said tip so as to produce therebetween an electric field which causes field emission of electrons from said tip; and a shield electrode disposed to surround said anode and interposed between said anode and said ground potential portions of the gun device, said shield electrode being rendered in the same potential as that of said tip, whereby said shield electrode shields said anode from the ground potential portions to thereby prevent undesired discharge therebetween.

Claim 8

An electron gun device of the field emission type comprising: a cathode tip of needle shape capable of being heated and having a large negative electric potential with respect to ground potential portions of said gun device; an anode applied with an accelerating voltage with respect to said tip so as to produce therebetween an electric field which causes field emission of electrons from said tip; and a shield electrode disposed to surround said anode and interposed between said anode and said ground potential portions of the gun device, said shield electrode being rendered in the same potential as that of said tip, whereby said shield electrode shields said anode from the ground potential portions to thereby prevent undesired discharge therebetween.

Claim 9

An electron gun device as defined in claim 6, wherein said anode and said shield electrode are substantially concentric cup-shaped elements.

Claim 10

An electron gun device as defined in claiM 6, wherein said shield electrode is a substantially cylindrical element disposed concentrically to said anode.

Claim 11

An electronic gun device as defined in claim 6, further including means for heating said cathode tip including a pair of terminals connected to said cathode tip for applying a heating current thereto and an insulator for supporting said pair of terminals, and an additional shield electrode disposed between said insulator and said anode and being connected to one of said pair of terminals.

Claim 12

An electron gun device as defined in claim 9, wherein said means for applying a voltage to said shield electrode includes an electrical connection between said shield electrode and said additional shield electrode.