Abstract
DC photoguns are used to produce high-quality, high-intensity electron beams for accelerator driven applications. Ion bombardment is believed to be the major cause of degradation of the photocathode efficiency. Additionally to ions produced in the accelerating cathode-anode gap, the electron beam can ionize the residual gas in the transport line. These ions are trapped transversely within the beam and can drift back to the accelerating gap and contribute to the bombardment rate of the cathode. This paper proposes a method to reduce the flow of ions produced in the beam transport line and drifting back to the cathode-anode gap by introducing a positive potential barrier that repels the trapped ions. The reduced ion bombardment rate and increased life time of photocathodes will reduce the downtime required to service photoinjectors and associated costs.
Highlights
Pozdeyev*Brookhaven National Laboratory, Upton, New York 11973-5000, USA (Received 19 June 2007; published 6 August 2007)
The successful demonstration of high power energy recovery at JLAB FEL [1] has led to a great interest in developing high average current, high brightness photoinjectors for such applications as energy recovery linac (ERL)-based synchrotron radiation facilities [2,3], FELs [3], electron cooling [4], and colliding beams for nuclear and high energy physics [5]
While conventional radio frequency (RF) guns can reach higher accelerating gradients and potentially a lower beam emittance, they have to operate in a pulsed regime to maintain RF power losses under control that limits the average beam current
Summary
Brookhaven National Laboratory, Upton, New York 11973-5000, USA (Received 19 June 2007; published 6 August 2007). Ions produced in collisions of the electron beam with residual gas in the cathode-anode gap are accelerated towards the cathode and bombard the cathode surface, reducing its quantum efficiency. In addition to ions produced in the accelerating gap, there is another source of ions that has been overlooked so far in existing models of ion bombardment: ions produced in a beam transport line beyond the anode and trapped in the electron beam. These ions can drift back to the cathode and increase the rate of ion bombardment. The paper describes a simple and effective solution to the problem of trapped ions, a positive potential barrier
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