• A. Nause, E. Dyunin, A. Gover
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv

The possibility to control optical frequency current shot-noise by longitudinal collective interaction in an electron beams was suggested recently, based on an extended 1D (single Langmuir mode) model.[1] This model predicts the possibility to reduce the beam current-noise below the classical shot-noise level. 3D simulations in GPT were executed in order to verify the predicted current shot noise reduction. It was verified numerically that minimal current shot-noise is attainable in a drift length of quarter wavelength oscillation. However the attainment of the effect requires proper setting of the beam geometrical and current density parameters to avoid interference of higher order Langmuir modes.[2] The parameters range of which the single mode model is valid and the deterioration effects out of this range were determined. Parameters for future experiments are suggested. This process may be applicable for controlling microbunching instabilities and FEL coherence enhancement.

[1] A. Gover, PRL 102, 154801 (2009).
[2] M. Venturini, Phys. Rev. ST Accel. Beams 11, 034401(2008).

• H. S. Marks, E. Dyunin, A. Gover, M. Volshonok
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
• Y. Lasser, R. Shereshevsky, A. Yahalom
  Ariel University Center of Samaria, Faculty of Engineering, Ariel

Deviations in the electron beam trajectory through the planar wiggler of the Israeli Electrostatic Accelerator FEL were found to be primarily caused by small variations in the strength and angle of polarisation of lateral focussing bar magnets which are positioned on both sides of the wiggler, and provide a quadrupole guiding field on axis. The field of the wiggler on axis was measured using a Labview controlled automated system built in our lab, based on a 2-axis Hall Effect magnetic sensor driven by a stepper motor. Polarisation field components of the individual focussing magnets were measured separately. Then, using an algorithm, the focussing magnets were paired, such that their non-uniformities were utilised to not only cancel out each other's error, but also to cancel out the field errors on axis due to variation in strength and polarisation angle of the wiggler magnets. The quality of the predicted electron beam transport was evaluated by 3-D simulation with the General Particle Tracer code which allowed the input of all the measured fields.