Excitation of the l=12 cyclotron resonance in the NRL modified betatron accelerator

The basic periodicity in the NRL device is twelve-fold. There are twelve toroidal field coils, twelve sectors, and so on. For a long time, the l equals 12 resonance was the dominant resonance in the experiment. To test the importance of the l equals 12 resonance, we have intentionally introduces an l equals 12 field error using twelve resonant coils. By activating these coils when the resonance is observed, the duration of x-rays produced by beam loss was reduced from 900 microsecond(s) to 5.5 microsecond(s) , while the amplitude of the signal increased from 0.5 to approximately 40 volts. The full width of the x-ray pulse at half maximum is inversely proportional to the current through the resonant coils and proportional to the risetime of the pulse. Work is in progress with a set of twelve internal coils that have a risetime of 300 - 400 ns. The results with these coils have confirmed the importance of the l equals 12 resonance. In addition, it has been shown experimentally that by adding a (Delta) B(theta ) such that the ratio of the total toroidal magnetic field to the vertical field is not an integer, the cyclotron resonance is not excited. These experiments have extended the beam lifetime by more than 100 microsecond(s) , which is approximately equal to the risetime of the applied (Delta) B(theta ) pulse. In the presence of such a pulse, the beam lifetime is 1 ms and the electron beam energy is 22 MeV, while the trapped current is in excess of 1 kA.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.