Single bunch mode

The prerequisite for such a measurement is information about the starting time. This can be provided by the pulsed time structure of the primary photon beam (single-bunch mode for operating the electron storage ring), or by a reaction product of the photoprocess which is in coincidence with the emitted electron and can be another electron or a photon. More details on time-of-flight electron spectrometry are given in Section 10.1. 

Figure 4.10 The time structure of the X-ray beam derives from that of the electrons (or positrons) in the storage ring. The electrons travel in the ring in bunches and thus the radiation is emitted in pulses. The values shown are for the Daresbury SRS in multibunch mode. In single bunch mode the light pulse occurs each orbital period of 0.321 jus.

This uses a multipole wiggler and will have operational modes for focussed Laue diffraction work and monochromatic experiments. The small source sizes should allow an equivalently small focal spot from a grazing incidence mirror system. Exposure times in the microsecond range for a macromolecular crystal should be feasible. Depending on the current achieved in single bunch mode it may be possible, at least for smaller unit cell sizes, to record a Laue pattern from one of the single bunches with an intrinsic time resolution therefore of the bunch width. (Feasibility experiments of this kind have been conducted at CHESS but on an undulator (Szebenyi et al 1989).)... 

One major advantage of linacs that operate in a single-bunch mode is the short pulse width, typically 30 ps FWHM, which enables the investigation of very fast reactions. A magnetic pulse compression system installed on the 20-MeV electron linac beamline at Argonne National Laboratory generates 5-ps pulses (7). 

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