A simple replacement of tungsten filament hot cathodes by DC heated LaB6 rod and its noise characteristics with laser-induced fluorescence

Hot cathode discharges are common plasma sources for fundamental plasma physics studies and other applications due to their quiescent and relatively simple properties, and tungsten filaments are commonly used for the ease of heating them. Recently, tungsten filaments are increasingly being replaced by less luminous alternatives, such as barium oxide or lanthanum hexaboride. These materials can emit electrons at temperatures close to 1000 K lower than tungsten, greatly reducing their blackbody radiations. This results in significant improvement in signal recovery for active spectral diagnostic, such as laser-induced fluorescence. However, these less luminous cathodes often come in vastly more complicated designs than those of tungsten hot cathodes and are much more expensive to procure and difficult to operate. In this paper, we present a simple, low cost direct current heated design of a LaB6 cathode that is manufactured at suitable dimensions and make a comparison of the laser-induced fluorescence (LIF) signal-to-noise ratio of this LaB6 hot cathode discharge with that of a typical tungsten filament discharge, revealing that LaB6 has, indeed, an improved LIF signal-to-noise ratio compared with the tungsten filament. Published under an exclusive license by AIP Publishing.

Automated summary

Hot cathode discharges using tungsten filaments are commonly used in plasma physics studies and applications for their simplicity, but less luminous alternatives like barium oxide or lanthanum hexaboride can provide improved signal recovery for active spectral diagnostic. However, these alternatives come with more complex designs and higher costs to procure and operate. An experiment comparing the signal-to-noise ratio of laser-induced fluorescence from a LaB6 hot cathode discharge with that of a typical tungsten filament found that LaB6 does indeed have an improved ratio.