Sub-thresholds analysis

A systematic search for sub-threshold UFO events (i.e. events which have not initiated beam dump) has been launched after July 7th. A collection of 111 such events has been gathered in 2010 data during the periods when beams were declared stable [6]. The data have been extracted from the Logging Database using the following criteria:

• Signal is observed on primary collimators (TCP).

• Signal is observed in at least three neighbouring BLM monitors.

• Loss duration is in the millisecond scale.

Additional analyses with loosen conditions are ongoing.

The analysis of this sample revealed the following properties of the UFO events:

• The UFO event rate increases linearly with the beam intensity, as shown in Figure 4; the rate expected at beam of 1000 bunches, extrapolated from the linear tendency, is about 1 event every half hour.

  Figure 4: Dependence of the UFO event rate on the beam intensity.

  

• The observed signal length becomes shorter with increasing beam intensity, as shown in Figure 5.

  Figure 5: Dependence of duration of the UFO event signal on the beam intensity.

  

• The BLM signal amplitude, measured as a signal accumulated in $\rm 40~\mu s$ integration time, is independent on the beam intensity, as shown in Figure 6.

  Figure 6: Dependence of the amplitude of the UFO event signal on the beam intensity.