Theory of low voltage annular beam free-electron lasers

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:238823

Blank, M; Freund, H P; Jackson, R H ^[1]

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1. Naval Research Lab., Washington, DC (United States); and others

An nonlinear analysis of an annular beam propagating through a cylindrical waveguide in the presence of a helical wiggler and an axial guide field is presented. The analysis is based upon the ARACHNE simulation which is a non-wiggler-averaged slow-time-scale simulation code in which the electromagnetic field is represented as a superposition of the TE and TM modes in a vacuum waveguide, and the beam space-charge waves are represented as a superposition of Gould-Trivelpiece modes. The DC self-electric and self-magnetic fields are also included in the model. ARACHNE has been extensively benchmarked against experiments at MIT and NRL in the past with good agreement, but all of these experiments have dealt with solid electron beams and beam voltages in excess of 200 kV. In seeking to reduce the beam voltage requirements we now consider the effect of operation with an annular beam. One advantage to be obtained by using an annular beam is that, for a fixed beam current, the effect of the DC selffields (i.e., the space-charge depression in beam voltage) will be reduced relative to that of a solid beam. This facilitates beam transport in short period wigglers in which the transverse dimensions are also small. A specific example is under study which makes use of 55 kV/5A electron beam with inner and outer radii of 0.27 cm and 0.33 cm respectively. The wiggler amplitude is 250 G with a period of 0.9 cm. and guide fields up to 3 kG corresponding to Group I trajectories. The waveguide radius is chosen to correspond to grazing incidence for the fundamental mode in Ku-Band (12-18 GHz). Preliminary results indicate that efficiencies upwards of 10% are possible with no wiggler taper. In addition, the energy spread must be held below 0.1%, and the instantaneous bandwidth is found to be greater than 20%.

• Research Organization: Brookhaven National Lab., Upton, NY (United States)
• OSTI ID: 238823
• Report Number(s): BNL--61982-Absts.; CONF-9508156--Absts.; ON: DE96002729
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
43 PARTICLE ACCELERATORS
BEAM DYNAMICS
ELECTRON BEAMS
FREE ELECTRON LASERS
SPACE CHARGE
WAVEGUIDES
WIGGLER MAGNETS