1. Autonomous Rate Measuring System Theodoros Athanasopoulos Representing the KM3NeT Consortium Nestor Institute For Astroparticle Physics VLV v T09 Athens 13 th – 15 th October 2009 13/10/2009VLVvT09 Theodoros Athanasopoulos1

2. Autonomous Rate Measuring System Target of the experiment To measure the effect of sedimentation and bio-fouling on the glass surface of optical modules deployed in the deep sea. How do we measure? We will periodically measure and record the singles at ½ spe and doubles (in a 10ns window) PMT rates caused mainly by K 40 decays and monitor the gain by recoding the single photoelectron pulse height. 13/10/2009VLVnT09 Theodoros Athanasopoulos2

3. Autonomous Rate Measuring System An Autonomous System The PMT Rate Measuring System is an autonomous system, battery powered, designed to operate for more than 1 year with data recorded in memory and monthly transfers acoustically to surface. Due to limited battery life of the acoustic modem, data transmitted has been designed to be only 40kB per month. Battery life is also an issue for the rest of the electronics so low power electronics have been designed and developed for this system. The system will be in sleep mode most of the time. It will turn on only for 1 hour every week to take the measurement, store the data and go to sleep mode again. It will also wake up to transmit the data upon acoustical request. System total power consumption is: On Mode: 40W=> 40W x 52h = 2080Wh Total power consumption = 3219Wh Off Mode: 130mW => 130 x 8760h = 1139Wh Total power supplied = 8400Wh Use of alkaline batteries 13/10/2009VLVnT09 Theodoros Athanasopoulos3

4. System Description (Mechanical) 13/10/2009VLVnT09 Theodoros Athanasopoulos4 APPARATUS LAYOUT (Side View) Battery bank x 4 8 Optical Modules (4 pairs )

5. 8ch HV Control System Description (Electronics) 13/10/2009VLVnT09 Theodoros Athanasopoulos5 OM 1 OM 2 OM 3 OM 4 OM 5 OM 6 OM 7 OM 8 4 Channel Discriminator MAX964 4 Channel ADC AD7476 4 Channel Discriminator MAX964 4 Channel ADC AD7476 FPGA Spartan 3E FPGA Spartan 3E SD 1GB SD 1GB μController PIC18F4550 μController PIC18F4550 Slow Controls Power Regulation & Power Distribution System Power Regulation & Power Distribution System Board to FPGA buses 8ch HV Monitor Acoustic Modem 14bit bus

6. Assembled System 13/10/2009VLVnT09 Theodoros Athanasopoulos6 Power Regulation and Power Distribution Unit FPGA Board

7. Front End Electronics 13/10/2009VLVnT09 Theodoros Athanasopoulos7 Discriminator ½ SPE Discriminator ½ SPE AMP Peak and Hold To Singles Rate Counter ADC PMT Pulse Inverted and amplified PMT Pulse Discriminator Pulse Coincidence Logic To Doubles Rate Counter From Other Discriminators

8. Conclusion We have designed a low power autonomous system to measure the K 40 rate to stay in the sea for more than one year. It will be sensitive to reductions in the singles and doubles rate at single photoelectron conditions due to sediment adhesion. Data will be retrieved periodically acoustically. Expected deployment end of this month. System is currently being tested at the Nestor Lab. 13/10/2009VLVnT09 Theodoros Athanasopoulos8