Data taken with the MILOM

Next : Optical module timing precision


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Last update : 01/09/2009

The MILOM line is illustrated in figure 3 (Some views of the MILOM during the deployment). The MILOM was deployed in the sea from the ship CASTOR on 18 March 2005 and connected with the Remote Operated Vehicle VICTOR on 12 April 2005.
The MILOM line is equipped with the latest electronics card versions and enables a complete test of every aspect of the detector design. For the final validation of the design, it is the operation of the optical modules, the optical calibration systems and the acoustic positioning systems which are of primary importance. The other instruments of the line are for special investigations and long term monitoring.

Figure 3. Layout of MILOM line

Data taking started with the MILOM immediately after the connection on 12 April and the data shown in these pages were taken between this date and 21 June. The MILOM operation has provided the opportunity to test and develop all aspects of the data acquisition and analysis software. All results shown in the present document are preliminary glimpses of the data. With the MILOM the full precision of the optical module system has been demonstrated in contrast with the PSL where it was only possible to record the raw counting rate.

In figures 4 and 5, examples of the raw data from the optical modules are shown with typical waveform signals and a typical pulse height spectrum.

Figure 4. Optical Module waveform signals: top recording of an input light pulse and bottom the recording of the reference clock signal.

Figure 5. Photomultiplier charge spectrum, obtained by integrating the waveform signals.

The levels and variations of single photon counting rates seen with the PSL have been confirmed with the MILOM operation. Figure 6 shows an example of the counting rates during a period of four days. The plot shows the baseline, defined as the level between bioluminescence bursts, and the burst rate which is the proportion of the time with bioluminescence bursts. For this, a burst is defined as period when the counting rate increases by 20% above the average level. 

Figure 6. The counting rate in one photomultiplier with a threshold corresponding to 0.5 photo-electrons during a period of 4 days in June 2005. The top plot shows the baseline of the rate outside the periods of bioluminescence bursts and the bottom plot shows the fraction of the time with bursts using the definition in the text.

Next : Optical module timing precision

Author : Thierry Stolarczyk