High-speed three-dimensional plasma temperature determination of axially symmetric free-burning arcs

Abstract

In this paper we introduce an experimental technique that allows for high-speed, three-dimensional determination of electron density and temperature in axially symmetric free-burning arcs. Optical filters with narrow spectral bands of 487.5–488.5 nm and 689–699 nm are utilized to gain two-dimensional spectral information of a free-burning argon tungsten inert gas arc. A setup of mirrors allows one to image identical arc sections of the two spectral bands onto a single camera chip. Two-different Abel inversion algorithms have been developed to reconstruct the original radial distribution of emission coefficients detected with each spectral window and to confirm the results. With the assumption of local thermodynamic equilibrium we calculate emission coefficients as a function of temperature by application of the Saha equation, the ideal gas law, the quasineutral gas condition and the NIST compilation of spectral lines. Ratios of calculated emission coefficients are compared with measured ones yielding local plasma temperatures. In the case of axial symmetry the three-dimensional plasma temperature distributions have been determined at dc currents of 100, 125, 150 and 200 A yielding temperatures up to 20000 K in the hot cathode region. These measurements have been validated by four different techniques utilizing a high-resolution spectrometer at different positions in the plasma. Plasma temperatures show good agreement throughout the different methods. Additionally spatially resolved transient plasma temperatures have been measured of a dc pulsed process employing a high-speed frame rate of 33000 frames per second showing the modulation of the arc isothermals with time and providing information about the sensitivity of the experimental approach.

Characterization of a copper spark discharge plasma in argon atmosphere used for nanoparticle generation

“…The emission spectroscopic analysis of arc discharges in argon is investigated in detail for tungsteninert gas (TIG) welding. Recently a thorough study was published on the temperature distribution of TIG arcs in the current range of 100-200 A, where peak temperatures of about 17000-19500 K were reported near the cathode [42]. These values agree fairly well with the temperature obtained here in the 0.5-2.0 μs time range in which the peak current is also around 100-200 A.…”

Influence of the Surface Structure on the Anode Boundary of High Current Moving Arcs in Atmosphere

“…The mirror arrangement enables the observation of the arc from two orthogonal directions using only one camera. The 3D-reconstruction for the determination of the arc volume is done by calculating ellipses based on the maxima in each row of the two orthogonal images and a threshold for the brightness [15,16]. The example in Fig.…”

Time-Resolved Emission Spectroscopy Measurements during the Restrike Period in Arc Plasma Torch

“…Although CCD-based high-speed cameras are still more frequently used and also their speed quickly increases, they are still relatively expensive. Nevertheless, attempts to combine high-speed CCD and spectroscopy measurements have been done exactly on the arc discharges [4,5]. On the other hand, photomultipliers offer usually well temporal but lower spatial and spectral resolution.…”