Analysis of ultra-short bunches in free-electron lasers

Campbell, L T and Freund, H P and Henderson, J R and McNeil, B W J and Traczykowski, P and van der Slot, P J M (2020) Analysis of ultra-short bunches in free-electron lasers. New Journal of Physics, 22 (7). 073031. ISSN 1367-2630 (https://doi.org/10.1088/1367-2630/ab9850)

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Abstract

Free-electron lasers (FELs) operate at wavelengths from millimeter waves through hard x-rays. At x-ray wavelengths, FELs typically rely on self-amplified spontaneous emission (SASE). Typical SASE emission contains multiple temporal 'spikes' which limit the longitudinal coherence of the optical output; hence, alternate schemes that improve on the longitudinal coherence of the SASE emission are of interest. In this paper, we consider electron bunches that are shorter than the SASE spike separation. In such cases, the spontaneously generated radiation consists of a single optical pulse with better longitudinal coherence than is found in typical SASE FELs. To investigate this regime, we use two FEL simulation codes. One (MINERVA) uses the slowly-varying envelope approximation (SVEA) which breaks down for extremely short pulses. The second (PUFFIN) is a particle-in-cell simulation code that is considered to be a more complete model of the underlying physics and which is able to simulate very short pulses. We first anchor these codes by showing that there is substantial agreement between the codes in simulation of the SPARC SASE FEL experiment at ENEA Frascati. We then compare the two codes for simulations using electron bunch lengths that are shorter than the SASE slice separation. The comparisons between the two codes for short bunch simulations elucidate the limitations of the SVEA in this regime but indicate that the SVEA can treat short bunches that are comparable to the cooperation length.

ORCID iDs

Campbell, L T ORCID logoORCID: https://orcid.org/0000-0003-1375-1551, Freund, H P, Henderson, J R, McNeil, B W J ORCID logoORCID: https://orcid.org/0000-0002-7267-611X, Traczykowski, P ORCID logoORCID: https://orcid.org/0000-0003-4746-7698 and van der Slot, P J M;
  • Item type:Article
    ID code:72568
    Dates:
    Date
    Event
    21 July 2020
    Published
    1 June 2020
    Published Online
    1 June 2020
    Accepted
    Subjects:Science > Physics
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:04 Jun 2020 11:03
    Last modified:11 Nov 2024 12:42
    URI:https://strathprints.strath.ac.uk/id/eprint/72568
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