Tomographic Methods for the Determination of Electron Beam Phase Space Distributions

(TU-2-02) Presenting Author: Vitaly Yakimenko (Invited)

Vitaly Yakimenko  

BNL

High-brightness electron beams are critical for many applications; in particular, free-electron lasers. A diagnostic that measures the multi-dimensional phase-space density of the electron bunch is extremely valuable for characterizing such beams. The emittance determined by the second moments of the beam distribution is not always sufficient to accurately predict FEL gain for realistic non-Gaussian beams. More detailed phase space information must be used to distinguish between the core of the beam and its tails. Measurement of a slice emittance has been achieved [1]. Tomographic reconstruction of phase space was suggested [2] and implemented [3,4] using a single quadrupole scan. In the present work special attention was given to the accuracy of the phase space reconstruction. An analysis using a transport line with nine focusing magnets and techniques to control optical functions and phases was utilized. Combining the slice emittance and tomography diagnostics has led to an unprecedented visualization of phase space distributions in 5 dimensional phase-space. The first results of this work are represented by dramatic improvements in understanding and control, including improvements in stability of photo-injector subsystems. Tomographic diagnostics, coupled with control of the radial charge distribution presents an opportunity in the near future to further improve electron beam brightness by performing high-order emittance corrections.

[1] X. Qiu, K. Batchelor, I. Ben-Zvi and X.J. Wang, Phys. Rev. Let. 76 No. 20, 3723, (1996)

[2] J.S. Fraser, IEEE Trans. Nucl. Sci. NS-26, No. 1, 1641 (1979)

[3] C.B. McKee, P.G. O'Shea and J.M.J. Madey, Nucl. Inst. And Meth. In Phys.Res. A358, 264 (1995)

[4] I. Ben-Zvi, J.X. Qiu and X.J. Wang, Proc. PAC'97, Vancouver BC Canada, May 12-16, 1997