On the plasma constriction close to the electrodes of high-pressure mercury and sodium lamps

Abstract

The arc attachment on electrodes is investigated in 50 Hz high-pressure mercury and sodium discharges between 50 and 150 W. In the cathode and also in the anode phase the discharges are constricted towards the electrodes, and in case of mercury a spot is formed at the electrode. For sodium a diffuse attachment is found in both phases. Side-on intensities in the electrode region are measured with an intensified CCD camera connected to a spectrograph. This leads to a spatial resolution of ~10 µm. The plasma temperature is determined from absolute line intensities of optically thin lines. A rapid temperature increase to nearly 11 000 K is found for mercury within 200 µm in front of the cathode. The same tendency is found in case of sodium but the sheath is smaller and the temperatures are lower compared to mercury.

Time-dependent simulation of plasma and electrodes in high-intensity discharge lamps with different electrode shapes

“…Considering that j and grad σ are constant on a path perpendicular to the cathode surface within the skin one gets 13 :…”

“…This deformation changes electrode and plasma temperatures as well as the electrode fall voltages. A detailed analysis of the range of variation of computed results caused by different geometries of the electrode tip will be presented in section 3 (see especially figures [8][9][10][11][12][13][14][15]. There are two reasons for this investigation.…”

“…Results for the plasma hot-spot temperature depending on electrode tip geometry and lamp current I are given in figure 11 (near cathode tip) and figure 12 (near anode tip). The differences in the plasma hot-spot temperature for different shapes of the electrode tip can be up to 2500 K. Again, this might be difficult to measure due to the uncertainty in the experimental data (±500 K in plasma temperature measurements at the hot plasma spot would be a small error [13]) and the small distances of the hot plasma spot to the electrode tip (at I = 1 A: 160 µm for the flat cathode tip, 21 µm for the conical cathode tip (90˚apex angle), 190 µm for the flat anode tip, 49 µm for the conical anode tip (90˚apex angle)).…”

Color shift of head lamps for automotive lighting over lifetime

“…The plasma temperature was determined according to Bartels [2] from the radiance of the self-reversal maxima of the optically thick Hg spectral line at 546 nm [3][4][5][6]. A thermographic system was used to measure temperature profiles of the discharge tube (see fig.…”

Investigation of acoustic resonances in high-power lamps

“…Spectroscopic plasma diagnostic measurements [16,17] were carried out in the middle of the lamp with a 0.5 m-spectrograph (SpectraPro 500i, Acton) combined with a 2048x2048 CCD-camera (Pixis, Roper). Two different gratings with 600 l/mm and 2400 l/mm were used in order to obtain overview spectra and high resolution lineshapes necessary for optical temperature measurements.…”