Free electron oscillator

1. An oscillator, comprising:

a source of charged particles for generating a beam of charged particles;

a first electrode which selectively receives the beam of charged particles;

a first deflector electrically coupled to the first electrode; and

a charged particle removing circuit electrically connected to at least one of the first electrode and the first deflector and configured to remove charged particles from at least one of the first electrode and the first deflector at least when the first electrode is not receiving the beam of charged particles, wherein an accumulation of charge on the first electrode causes the beam of charged particles to be directed away from the first electrode by the first deflector.

2. The oscillator as claimed in claim 1 , wherein the charged particles comprise electrons and the accumulation of charge on the first electrode is an accumulation of a negative charge.

3. The oscillator as claimed in claim 1 , wherein the first deflector and the first electrode are on the same side of the beam of charged particles with reference to a direction of travel of the beam of charged particles.

4. The oscillator as claimed in claim 1 , further comprising a focusing element for receiving the beam of charged particles when the beam of charged particles is not being received by the first electrode.

5. The oscillator as claimed in claim 1 , further comprising:

a second electrode; and

a second deflector, wherein the first deflector and the first electrode are on the same side of the beam of charged particles with reference to a direction of travel of the beam of charged particles, and the second deflector and the second electrode are on a different side of the beam of charged particles with reference to the direction of travel of the beam of charged particles.

6. An oscillator, comprising:

a source of charged particles for generating a beam of charged particles; and

first and second electrodes disposed in a direction of travel of the beam of charged particles, wherein an accumulation of charge on the first electrode causes the beam of charged particles to be directed towards the second electrode and vice versa such that the beam of charged particles oscillates between the first and second electrodes; and

a charged particle removing circuit electrically connected to at least one of the first and second electrodes and configured to remove charged particles from the at least one of the first and second electrodes when said beam of charged particles is not directed towards said at least one of the first and second electrodes.

7. The oscillator as claimed in claim 6 , wherein the charged particles comprise electrons and the accumulation of charge on the first electrode is an accumulation of a negative charge.

8. The oscillator as claimed in claim 6 , further comprising first and second deflectors interposed between the source of charged particles and the first and second electrodes,

wherein the first deflector is coupled to the second electrode and the second deflector is connected to the first electrode, and

wherein the accumulation of charge on the first electrode is an accumulation of a positive charge and causes an accumulation of positive charge on the second deflector.

9. The oscillator as claimed in claim 6 , wherein the first and second electrodes are separated by a gap through which a portion of the beam of charged particles can periodically pass as the beam of charged particles oscillates.

10. The oscillator as claimed in claim 6 , further comprising first and second deflectors interposed between the source of charged particles and the first and second electrodes,

wherein the first deflector is coupled to the first electrode and the second deflector is connected to the second electrode, and

wherein the accumulation of charge on the first electrode is an accumulation of a negative charge and causes an accumulation of negative charge on the first deflector.