Some facilities are very flexible to compensate users for long beam outages. Either some of the machine development shifts are sacrificed after a beam outage, or pre-scheduled blocks of shifts are used to re-schedule users when problems with the accelerator prevent them to finish their experiments. These compensation times are currently accounted for in very different ways, depending on the facility.
We propose to define a set of a unified metrics to account for user operation times. User operation should be distinguished in two categories:
Scheduled User Time: time allocated for user experiments at least one month in advance.
User Backup Time: time that was originally not allocated for experiments, but was later provided to re-schedule users that could not finish their measurements.
The sum of these is the User Time; operation failures should be recorded during all of this time. If Scheduled User Time: is converted into shutdown time less than one month before this user time time, then this time has to be recorded as a “no-beam” failure. This rule takes care that all beam outages are visible in the statistics: some facilities do not count outages of several days for the beam availability, because they re-schedule all users to a newly allocated time and declare the downtime to be a shutdown time. This is very good for the users: better to be re-scheduled than losing all beam time. But it prevents the comparison with facilities that handle such outages differently.
The following example will illustrate the proposed scheduling procedure: A facility has 4000 hours Scheduled User Time. A vacuum leak occurs in the storage ring and causes a beam outage of seven days. Management decides to declare these seven days to be shutdown time and to shorten the following shutdown time in two weeks time by seven days to re-schedule all users.
According to our proposal this will be accounted for as a seven day or 168 hours “no-beam” event. The extra seven days are User Backup Time. The total user time will be 4168 hours. This still allows each facility to calculate “beam-availability” according to their own definitions. But at the same time it provides statistical data that can be compared to other facilities.
A clear and dependable accounting of the user operation time is a prerequisite for a meaningful operation reliability evaluation of each accelerator. To draw an extreme picture: if all beam outages are declared to be shutdowns retroactively then the beam is always 100% available during user operation. It is important that only those times can be counted as User Time where the failures are recorded and evaluated. If failure modes within the extra time for the users are not analyzed, then this time must not be accounted as User Time in the common operation metrics data.
At BESSY II the extra time given to the users has traditionally been provided with an unmanned control room during the night. In this mode small failures can lead to long outages. These failures have been counted separately, since it was a different operation mode. This allows one to evaluate the accelerator reliability for the scheduled time and the extra user time separately. By user request BESSY changed this policy in 2015. Now all usable beam time is manned by operations staff.