Abstract
Longitudinal bunch shaping is gaining increasing attention due to the large impact it has on modern accelerators. The existing methods for controlling the density profile fall into three categories: laser shaping, emittance exchange, or correlations between the energy and one of the other coordinates. These methods require either (i) dispersive elements (e.g., dipole magnet), which generate coherent synchrotron radiation, or (ii) shaping near the cathode, which can distort the profile due to space-charge effects. These collective effects significantly decrease shaping quality as the bunch charge increases. None of the existing methods are currently capable of shaping high-charge bunches. In this paper, we introduce a transverse deflecting cavity-based shaping method to avoid the impact of collective effects on the shaping process. In this method, a transverse deflecting cavity introduces the $z\ensuremath{-}x$ correlation, and a transverse mask tailors the longitudinal density profile. This method provides high-quality shaping regardless of charge level and preserves the beam quality.
Highlights
Over the past decade, the electron linear accelerator community has explored several methods of longitudinal bunch shaping with the common goal of accurate shaping over a broad ranges of bunch parameters while maintaining beam quality
These previous shaping methods can be categorized into three groups: laser shaping, emittance exchange (EEX), and correlation-based methods, which we describe below
This is a new method of shaping a bunch’s longitudinal profile that is free from collective effects, which is a major advantage over existing methods
Summary
The electron linear accelerator community has explored several methods of longitudinal bunch shaping (hereafter, shaping) with the common goal of accurate shaping over a broad ranges of bunch parameters (charge, bunch length, etc.) while maintaining beam quality. The second method, EEX-based shaping, first shapes the transverse dimension of the bunch and is followed by an exchange of the transverse and longitudinal phase spaces to create the desired longitudinal profile [4,5] This method can generate high-quality shapes at moderate charges, the EEX beam line requires dipole magnets. To overcome the limitations of the collective effects present in existing shaping methods, we introduce a transverse deflecting cavity (TDC)-based shaping method This shaping concept was inspired by our earlier work on gigahertz laser-free time-resolved transmission electron microscopy [12] and a similar concept proposed in Ref. II, but we leave details of those topics for future work
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