Blochdocs (January 2023)

Warning

As of January 2023, previous restrictions around the allowable photon energy range in some polarization modes have lifted considerably. The only restriction now relates to degradation of the lifetime in the 1.5GeV ring. As long as the lifetime stays above 5h, the conditions are considered acceptable. Estimates of what this corresponds to are listed below.

Mode	EPU Phase	Allowed gap range (mm)	Allowed hv range (eV)
Horizontal	0	No restrictions	>10
Vertical	42	>15	>14
Circular +	0 .. 42	>18*	>15
Circular -	0 .. -42	>18*	>15

*Conservative estimate. To be verified.

Maximum countrate

Excessive countrates will damage the MCP in the detector assembly, and at BLOCH it is very easy to generate unsafe countrates. Respect the following rules:

1. Maximum 1 million counts per second if everything is in a narrow stripe (for example transmission mode or graphene’s Dirac cone)

2. Maximum 10 million counts per second if intensity is evenly distributed across the detector

3. Core levels should be measured in an angular lens mode, except where lens table limits make this impossible.

Warning

There is no background process in SES to monitor countrates, so you must verify that the countrate is safe while in voltage calibration mode. If you will perform an angle scan or photon energy scan, check the intensity over the whole scan range, not just your starting position. If you will measure in swept mode, ensure that the intensity slightly below your starting point is also safe.