Simulation of the acoustic pulse expected from the interaction of ultra-high energy neutrinos and seawater

Abstract

The purpose of this thesis was to design, build, and test a device capable of simulating the acoustic pulse expected from the interaction between an Ultra-High Energy (UHE) neutrino and seawater. When a neutrino interacts with seawater, the reaction creates a long, narrow shower of sub-atomic particles. The energy from this reaction causes nearly instantaneous heating of the seawater on an acoustic timescale. The acoustic pulse created by the resulting thermal expansion of the water is predicted to be bipolar in shape. This work was undertaken to support a Stanford experiment, the Study of Acoustic Ultra-high energy Neutrino Detection (SAUND), that uses existing hydrophone arrays to detect UHE neutrinos from the acoustic pulse generated by their rare interactions with seawater. The device fabricated for this thesis uses the discharge current from a 4 microFarads capacitor charged to 2.5kV to heat the seawater between two copper plates. The anode and cathode plates of this "zapper" design were 6 cm in diameter and 20 cm apart. The acoustic pulse generated by the zapper was measured both in a small test tank at NPS and at the Acoustic Test Facility located at NUWC Keyport. Bipolar pulses observed at NPS on two separate test dates had average pulse lengths of 110 microseconds +/- 10 microseconds and 160 +/- 20 microseconds and average amplitudes at 1m of 1.9 +/- 0.3Pa and 4.7 +/- 0.6Pa. The average pulse length recorded at Keyport was 49 +/- 6 microseconds and the average amplitude at 1m was 6.4 +/- 0.9Pa. The pulse lengths recorded at NPS were reasonably consistent with theory, however all pressure amplitudes were about 100 times lower than predicted. The cause of the amplitude discrepancy is not completely understood at this time.