Mechanical and Aerospace Engineering


Interferometry and Vibration Compensation on NSTX-U
By: Evan Scott Advisor: Professor Bahram Ravani 

Controlled nuclear fusion offers a nearly unlimited supply of clean energy if it can be achieved. One fusion research device, National Spherical Torus Experiment (NSTX) located at the Princeton Plasma Physics Laboratory (PPPL), has recently undergone an extensive upgrade to NSTX-U. The Far-infrared Tangential Interferometer/Polarimeter (FIReTIP) system, previously installed on NSTX before the upgrade, is an important laser-based plasma diagnostic for line-integrated plasma density measurements with high time resolution. Due to extensive changes to NSTX during the upgrade process, the FIReTIP system has been dramatically altered from its previous configuration. The modification and reinstallation of FIReTIP on NSTX-U are presented.

One of the primary goals of FIReTIP on NSTX-U is to provide real-time density measurements for density feedback control of the tokamak plasma. By nature, FIReTIP is susceptible to noise from mechanical vibrations. In FIReTIP’s new configuration, mechanical vibration isolation cannot be used on a particularly sensitive component, a retroreflector, because the retroreflector is mounted to the inside wall of the NSTX-U vacuum vessel. To compensate for the effects of vibrations, two methods are proposed. A visible light heterodyne interferometer system will be employed on FIReTIP to measure mechanical vibrations independently of the plasma, allowing the effects of vibrations to be subtracted from the measured plasma density in real-time. Additionally, the use of active noise cancellation via Kalman filtering has been explored for use with FIReTIP alongside the visible light interferometer. Both the accuracy and feasibility of active noise cancellation on the FIReTIP system are discussed.

Date(s) - 07/18/2017
10:00 am - 12:00 pm

2050 Academic Surge


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