Design and Characterization of Compact Discharge Units for Advanced LIGO

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One of the remaining risks for the success of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) is excess noise due to charge accumulation on the mirrors used as test masses in the interferometer. Research funded by this award will lead to the construction of compact discharge units (CDUs) that can be used to mitigate the charge on the test masses. Each unit features a steerable, low-energy electron beam to neutralize positive charges and a wide angle UV beam to photo-eject negative charges. The CDUs will be optimized for size, reliability, and discharge current within the UV-radiation level tolerable for the optical coating of the Advanced LIGO test masses. Testing of the units will be performed with an existing torsion balance that can measure the absolute charge on an insulator with conducting surface.In fact, charge mitigation is important for a variety of precision mechanical experiments, including Advanced LIGO, torsion balances, and inertial masses in satellites. In all these systems, a sensitive test mass is electrically isolated from its surroundings. Charge accumulation can lead to spurious coupling between a test mass and nearby surfaces. This unwanted coupling leads to excess noise, degrading the performance of the experiments. The compact discharge unit can be used to reduce this extraneous noise by neutralizing charge on the test mass. Graduate students will participate in this project.