Patent ID: 8823263

Claim:
An electron tube comprising: a microwave structure ( 10 , 30 ) having an evacuated envelope ( 12 , 32 ) comprising two ends, the microwave structure being at a reference potential (E), an electron gun ( 34 ) comprising a cathode ( 36 ) for providing a beam ( 16 , 38 ) of electrons, along an axis ZZ′, at one end of the evacuated envelope, an electron collector ( 40 ) for gathering electrons of the beam at the other end of the evacuated envelope, at least one high-voltage power supply for applying to the cathode ( 36 ) a negative high-voltage potential (HT) with respect to the reference potential (E), between the cathode ( 36 ) and the microwave structure, a device (Pe) for extracting positive ions comprising at least one electrode e 2 carried to a negative potential (Vp) with respect to the reference potential (E) so as to extract positive ions (In) from the evacuated envelope, these positive ions being produced by the impacting of the electrons of the electron beam with molecules of residual gas in the evacuated envelope, wherein the device for extracting positive ions comprises another electrode el forming with the electrode e 2 a pair (Pe) of electrodes e 1 , e 2 , the electrodes of the pair facing one another on either side of the electron beam, the other electrode el of the pair being carried to the reference potential (E), the electrode e 2 being carried to the negative potential (Vp) with respect to the reference potential (E) so as to create between the two electrodes an ion-extracting electric field (Ech), wherein each electrode e 1 , e 2 of the pair (Pe) has a cylindrical half-plate shape, the two electrodes being symmetric on either side of the axis ZZ′.