Abstract
One important attribute of laser accelerated proton beams is the beam emittance which is a measure of the laminarity of the beam. A low emittance is essential for all kinds of proton imaging experiments. A distinction is drawn between transverse and longitudinal emittance. The transversal emittance delivers a value for the spread in angle, relative to the axes of propagation, caused by random components of transverse velocities [1]. On the other hand the longitudinal emittance considers the “velocity chirp” [2] of the proton beam and is defined by the energy-time product of the beam envelope. Although the energy spread of laser accelerated proton beams is large (e.g. 0–10 MeV), the short acceleration time (at least <10 ps) leads to a longitudinal emittance of less than 10−4 eV s. In [2] the longitudinal emittance was estimated by PIC-simulations being < 10−7 eV s. This is several orders of magnitudes smaller compared to typical values of 0.5 eVs (CERN SPS) [3] for conventional accelerators. Thus, laser accelerated proton beams can be used for time resolved measurements. The longitudinal emittance delivers the upper limit for the time resolution (cf. Sect. 9.3).
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Sokollik, T. (2011). Beam Emittance. In: Investigations of Field Dynamics in Laser Plasmas with Proton Imaging. Springer Theses. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-15040-1_7
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DOI: https://doi.org/10.1007/978-3-642-15040-1_7
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