On the measurement of energy fluxes in plasmas using a calorimetric probe and a thermopile sensor

Abstract

Two different diagnostics for the determination of the energy influx in plasma processes were used to characterize an ion beam source and an asymmetric RF discharge. The related energy fluxes were measured in dependence on the ion energy and on the RF power, respectively. The first sensor, called HFM (Heat Flux Microsensor) is a thermopile which allows for direct energy flux measurements. With the second sensor, a calorimetric probe, the energy influx has been calculated from the temporal temperature evolution preliminary registered. Although the working principle of both sensors is different, the obtained results are in good agreement. In the ion beam ( < 1,5keV)) rather high energy influxes are achieved (up to 700mW/cm²), whereas the values measured in the asymmetric RF discharge were lower than 50mW/cm² for discharge powers in the range of 10 to 100 W. The performances and limitations of both sensors are compared and discussed.

A Heat Flux Microsensor for Direct Measurements in Plasma Surface Interactions

“…Comparison that we have done in previous work has evidenced drawbacks and advantages of both sensors [22]. The main advantage of the calorimetric probe is its low cost, simplicity and sturdiness.…”

Energy influx measurements with an active thermal probe in plasma-technological processes

“…Active probes are also established, constructed as a planar substrate or as a rotationallysymmetric membrane, whereby the energy influx is determined by the measurement of a temperature gradient [3][4][5]. However, the temperature of these probes is not freely adjustable and its distribution along the surface is not constant.…”

“…Different methods are established for determination the energy flux at plasmatechnological processes: for example by measuring the temperature difference generated on a substrate [1,6], by measuring the increasing temperature in the centre of a membrane being exposed to an energy flux and clamped and cooled by a guard ring [4,7], or by recording the temporal heating and cooling temperature course of a dummy substrate [5,8,9].…”

“…Ellmer et al carried out measurements with a Gardon sensor and tried to minimize the errors by blackening the probe [4,7]. However, the calibration results deviated strongly from the expected value because of the heat conduction of the thermal probe.…”

“…However, the calibration results deviated strongly from the expected value because of the heat conduction of the thermal probe. [4] Even through calibrating the passive thermal probe, errors of at least 20% were estimated [5,10,11].…”