Experiments requiring time resolution compatible with single X-ray pulse duration (~250ps after APS-U, currently ~100ps)
These experiments are currently conducted by isolating a single ~100ps X-ray pulse by the BioCARS shutter system. This can be done in 24-bunch mode or hybrid mode of the APS storage ring.
After the APS-U, these experiments will be conducted in 48-bunch mode (timing mode). Hybrid mode is not part of the current APS-U plan.
Single X-ray pulse FWHM will be ~250ps after the APS-U. This determines the best time resolution achievable at 14-ID after the APS upgrade.
X-ray flux per single 250ps pulse in 48-bunch mode will be about the same as the current single pulse flux in 24-bunch mode.
Experiments compatible with multi-pulse exposure times (100ns and longer time resolution after the APS-U, currently 200ns and longer time resolution)
These experiments are currently conducted in 24-bunch and 324-bunch modes of the APS storage ring.
After the APS-U, these experiments will be conducted in the 48-bunch mode (timing mode) and 324-bunch mode (brightness mode).
For a given exposure time, X-ray flux will be 2X higher after the APS-U as ring current is increased from 100mA to 200mA.
Best time resolution for such experiments will be ~100ns, determined by the minimum open time of the ultra-fast BioCARS X-ray chopper. Minimum open time is currently ~200ns.
X-ray Beam size at the sample
Smallest X-ray beam size at 14-ID is currently 20 µm (h) x 20 µm (v)
We anticipate that the smallest beam size with the current optics after the APS-U will be:
<10 um (h) x 20 um (v) in 48-bunch mode
<10um (h) x <10um (v) in 324-bunch mode
We are exploring options to reduce the beam size further.
Most of current experiments are conducted with 5% bandwidth (crystallography) and 2.5% bandwidth (solution scattering).
Following the APS-U, we anticipate that we will be able to use 2% bandwidth for most experiments without a significant loss in flux.
Benefits for BioCARS user experiments
We expect that both serial crystallography and solution scattering time-resolved experiments will benefit from the smaller X-ray beam size and 2X higher X-ray flux per exposure (except in cases where a single X-ray pulse exposure is necessary). Benefits include faster data collection, use of smaller crystals and reduced solution sample consumption.
Reduced undulator bandwidth will be of a significant benefit for Laue crystallography users.