Wiggler taper optimization for free-electron-laser amplifiers with moderate space-charge effects

Conference · Thu Jan 01 04:00:00 EST 1987

OSTI ID:5704791

Jong, R A; Scharlemann, E T; Fawley, W M

The standard synchronous tapering method used to design the wiggler magnetic field for free-electron-laser (FEL) amplifiers operating in the Compton regime will not work for amplifier systems where space-charge effects are important. The space-charge effects lower the overall gain in the amplifier system and, even more importantly, shift the peak in the gain curve to magnetic field values that are significantly less than the synchronous magnetic field value. As a result, the overall predicted gain using the synchronous tapering method is too low. Moreover, the synchronous magnetic field corresponds to the peak in the gain curve for a frequency below the fundamental frequency. Consequently, shot noise at frequencies below the fundamental frequency can grow to levels that may prevent amplification of the fundamental. We have developed a new tapering strategy that improves the predicted amplifier gain and circumvents the shot-noise growth for systems with moderate space-charge effects. For this new strategy, we hold the wiggler magnetic field constant at a value below the synchronous value but near the peak of the gain curve for the fundamental frequency, for some optimized length at the front end of the wiggler. Beyond this constant wiggler section, the field is tapered using the standrd synchronous tapering algorithm. This new tapering scheme results in significant improvement in predicted amplifier gains and limits the growth of shot noise to insignificant levels. We demonstrate the effectiveness of this new tapering algorithm using the tapered wiggler design for the proposed microwave heating experiment (MTX) at the Lawrence Livermore National Laboratory (LLNL). 4 refs., 8 figs.

• Research Organization: Lawrence Livermore National Lab., CA (USA)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5704791
• Report Number(s): UCRL-96735; CONF-8709110-15; ON: DE88003758
• Country of Publication: United States
• Language: English

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AMPLIFIERS
BEAMS
DESIGN
ELECTRICAL EQUIPMENT
ELECTROMAGNETS
ELECTRON BEAMS
ELECTRONIC EQUIPMENT
EQUIPMENT
FREE ELECTRON LASERS
FREQUENCY DEPENDENCE
HEATING
LASERS
LEPTON BEAMS
MAGNETIC FIELDS
MAGNETS
MATHEMATICAL SPACE
MICROWAVE AMPLIFIERS
MICROWAVE EQUIPMENT
MICROWAVE HEATING
OPTIMIZATION
PARTICLE BEAMS
PHASE SPACE
SPACE
SPACE CHARGE
WIGGLER MAGNETS