High gain free electron laser for heating and current drive in the ALCATOR-C tokamak

We have used the free electron laser particle simulation code FRED to examine the design of an FEL for amplifying radiation in the 1–2 mm wavelength range for use in electron heating and current drive in a tokamak device such as ALCATOR-C. We have used as a desired design goal a peak output power of 8 GW, with a minimum input power in the 1–100 W range. We have examined the effects of electron beam current, energy and brightness, laser frequency and input power as well as wiggler wavelength and overall wiggler length on performance of the FEL. We find that to obtain the desired power output, we require a 3 kA electron beam with a brightness of about 1 × 105 A/cm2. For a 1 mm wavelength system, the beam energy must be at least 10 MeV, the laser input power must be at least 100 W, and the wiggler wavelength is 8 cm, with an overall length of at least 6 m. For a 2 mm wavelength system, the output power goals can be met with a 7 MeV electron beam, with 10 W of input laser power, and a wiggler with an 8 cm wavelength and total length of at least 6 m. The beam and laser requirements to meet the design criteria are less stringent for the 2 mm wavelength system. The magnet requirements to meet the design power level goal is more difficult to meet with a wiggler wavelength of 8 cm compared to a 9.8 cm wiggler wavelength. With the 10 MeV beam energy of the 1 mm system and the 7 MeV beam energy of the 2 mm system, the peak magnetic field changes from about 0.4 to 0.6 T when the wiggler wavelength changes from 9.8 to 8 cm.