Keeping track of how much useful beam is delivered to experiments (i.e., "time accounting") is especially important here at Jefferson Lab. The Lab's contract with the Department of Energy is a "performance based" contract, where success is gauged at least in part on how much beam is delivered to experiments. Thus, careful attention is given to monitoring how the beam is used. Each of the experimental halls plays an important role in the time-accounting process.
Keeping Track of ABU (Available Beam in Use)
The most important concern for the halls is keeping track of ABU (i.e., when the beam is being used to perform a part of the hall's scheduled program). It is important to note that there are occasionally times when ABU is not just the delivery of CW beam to a target. An energy measurement or current calibration may need to be performed, and that time should also be counted as ABU.
It is also important to understand the time spans used to record ABU. The Control Room Crew Chief's shift begins and ends an hour earlier than the rest of the crew. For example:
- Swing Shift Crew Chief hours: 1500-2300
- Swing Shift Operator hours: 1600-0000.
Time accounting for accelerator shifts is based on the CREW CHIEF's hours. Therefore, at the end of the shift, when the Crew Chief calls the halls and asks for the "Available Beam in Use" (ABU) hours for the shift, the Crew Chief needs to know the number of hours that acceptable beam was used during the Crew Chief's shift. In the above example for Swing shift, that would be from 1500-2300.
Up time is just a little bit different than ABU. Up time is actually measured automatically by a program called "BOOM" which counts Up time whenever it sees CW beam on a hall-specific beam-current monitor (BCM). BOOM feeds this number directly into the Crew Chief shift log, where it is only edited by the Crew Chief if it is blatantly wrong.