Characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation

Kneip, S. and McGuffey, C. and Martins, J. L. and Bloom, M. S. and Chvykov, V. and Dollar, F. and Fonseca, R. and Jolly, S. and Kalintchenko, G. and Krushelnick, K. and Maksimchuk, A. and Mangles, S. P. D. and Najmudin, Z. and Palmer, C. A. J. and Phuoc, K. Ta and Schumaker, W. and Silva, L. O. and Vieira, J. and Yanovsky, V. and Thomas, A. G. R. (2012) Characterization of transverse beam emittance of electrons from a laser-plasma wakefield accelerator in the bubble regime using betatron x-ray radiation. Physical Review Special Topics: Accelerators and Beams, 15 (2): 021302. ISSN 1098-4402

Abstract

We propose and use a technique to measure the transverse emittance of a laser-wakefield accelerated beam of relativistic electrons. The technique is based on the simultaneous measurements of the electron beam divergence given by v(perpendicular to)/v(parallel to), the measured spectrum gamma, and the transverse electron bunch size in the bubble r(perpendicular to). The latter is obtained via the measurement of the source size of the x rays emitted by the accelerating electron bunch in the bubble. We measure a normalized rms beam transverse emittance <0.5 pi mm mrad as an upper limit for a spatially Gaussian, spectrally quasimonoenergetic electron beam with 230 MeV energy in agreement with numerical modeling and analytic theory in the bubble regime.