Speckle measurements of density and temperature profiles in a model gas circuit breaker

Optical Diagnostics of Switching Arcs Near Current-zero: Speckle Imaging and Interferometry

“…The speckle and interferometry experimental setups are described in detail in [3] and [4], respectively. Here we only briefly present the two techniques; a schematic of the speckle imaging setup is provided in Figure 1; the experimental setup for interferometry is given in Figure 2.…”

“…Shifts in the speckle pattern produced by scattering from the diffuser and observed on the camera (with respect to a reference image in the absence of an arc and/or gas flow) were used to determine the line-of-sight integrated gradient in the refractive index at each point. The approach used to calculate the density and temperature from such measurements is given in [3]. For the interferometry measurements, a reference beam was added to the experimental setup and the probe beam and the reference beam were re-combined at a slight angle using a vol.…”

“…It is important to note that the circuit breaker test devices used to obtain speckle and interferometric images differed considerably. The test device used in the former tests, described in detail in [3] is shown in Figure 3. Briefly, this test device consisted of two fixed contacts (a hollow contact and a solid contact) and a nozzle system used to guide the flow of gas (synthetic air in the case of the tests discussed in this work) from a high pressure tank through the arc zone.…”

“…This led to an arc that moved within the arc zone and did not always remain parallel to the axis of the test device. As discussed in detail in [3] the instability and asymmetry in the arc sometimes prevented reconstruction of the index of refraction profile from the measured line-integrated deflection angles (corresponding to the line integrated refractive index). This is because a three-dimensional reconstruction based on a single projection is only possible for an object with defined symmetry, such as axi-symmetry (temporal and spatial fluctuations can also wash out features, but this effect is negligible for single, nanosecond laser pulses).…”

“…Such information can be obtained from computational fluid dynamics (CFD) simulations [1], but such models often lack experimental validation (aside from comparison with the measured current, voltage, and pressure). For this reason, several spatially resolved optical diagnostic methods based on well-established techniques that measure the index of refraction (or its gradient) were recently developed or adapted to image circuit breaker arcs near current zero [2][3][4][5]. The advantages and disadvantages of interferometric techniques compared to other optical methods (such as emission spectroscopy) are discussed in detail in those studies.…”