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The performance of high voltage gas circuit breakers depends on the temperature distribution of hot gas or plasma from the arc zone mixed with cold gas that is present, for example, in the exhausts and mixing volume. Understanding the details of the mixing process is imperative to estimate the temperature distribution within the entire breaker volume. Design studies rely on computational fluid dynamics (CFD) simulations to search for the best way to achieve satisfactory mixing. One key uncertainty in the CFD simulations is the role of turbulence in this process and how to properly account for it. To gain knowledge of the mixing process between hot and cold gases, we have constructed a simplified breaker geometry that is flexible and accessible to diagnostics. Apart from standard measurements of current and arc voltage, we measure pressure in the arc zone and the mixing volume. Further, the mixing volume is specially designed to be transparent, allowing us to make shadowgraphy measurements of the turbulent mixing during and after the arcing phase. We report on experiments performed in air at atmospheric pressure.

A polarimetric Fabry-Perot fiber laser sensor for fluid pressure up to 100 MPa is investigated. The fluid acts on one of two elliptical-core fiber sections in the laser cavity, producing a shift in the differential phase of the two orthogonal polarization modes and thus a variation in the beat frequencies of the corresponding longitudinal laser modes. The second fiber section, with a 90 degrees offset in the core orientation, compensates for temperature-induced phase shifts. The dispersion in the birefringent fiber Bragg grating reflectors is employed to remove the near degeneracy of the polarization mode beat frequencies of a given order and to improve substantially the resolution of the sensor to a few parts in 10(6) of the free spectral range. Further investigations address the effect of the fluid on the integrity of the fiber, the influence of various fiber coatings on the sensor response, and the intrinsic stability of erbium-doped and undoped sensing fibers under fluid pressure.