Abstract
Active longitudinal beam optics can help FEL facilities achieve cutting edge performance by optimizing the beam to: produce multi-color pulses, suppress caustics, or support attosecond lasing. As the next generation of superconducting accelerators comes online, there is a need to find new elements which can both operate at high beam power and which offer multiplexing capabilities at Mhz repetition rate. Laser heater shaping promises to satisfy both criteria by imparting a programmable slice-energy spread on a shot-by-shot basis. We use a simple kinetic analysis to show how control of the slice energy spread translates into control of the bunch current profile, and then we present a collection of start-to-end simulations at LCLS-II in order to illustrate the technique.
Highlights
Facility scale electron accelerators regularly produce high-current, high-brightness electron bunches by accelerating and compressing the bunch from an rf photoinjector
In the context of x-ray free-electron laser facilties (XFELs) [1,2,3,4,5,6,7], modulation of the current profile can lead to optimized beam brightness, suppressed horn formation [8], two-color operation [9], and attosecond x-ray pulses [10,11,12,13]; while in plasma-wakefield accelerators, shaping of the current profile can lead to maximization of the energy transfer to the witness bunch in high-transformer ratio experiments [14,15]
We provide a series of numerical case studies in which a temporally shaped laser heater provides useful control of the current profile at an XFEL
Summary
Facility scale electron accelerators regularly produce high-current, high-brightness electron bunches by accelerating and compressing the bunch from an rf photoinjector. The interaction in the wiggler produces a periodic energy modulation which is effectively washed out by the chicane dispersion, such that the net result is a controlled increase in the energy spread of the beam [19,20] This heating is used to suppress the collective instabilities that develop during acceleration and bunch compression (namely the microbunching instability) [21,22,23,24,25]. If instead the laser heater intensity profile is modulated as a function of time, we can create a time-dependent energy spread which can be used to shape the bunch current profile (see Fig. 1) Such temporal laser shaping was initially proposed to control the temporal properties of XFELs [26] and multicolor generation in a seeded FEL [9].
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