Measurement of emission current and temperature profile of emissive probe materials using CO2 LASER

Temperature response of laser heated emissive probe materials under vacuum and free atmospheric conditions

“…Equation ( 3) is used for estimating rise in probe temperature with respect to incident laser power [9,15,18], while taking care of all three modes of heat transfer such as conduction, convection and radiation, respectively. For LaB 6 , specific heat and conductivity are 1974 (J K −1 kg −1 ) and 47.7 (W m −1 K −1 ) and for graphite these value are 707 (J K −1 kg −1 ) and 100 (W m −1 K −1 ) respectively [9,15].…”

“…For LaB 6 , specific heat and conductivity are 1974 (J K −1 kg −1 ) and 47.7 (W m −1 K −1 ) and for graphite these value are 707 (J K −1 kg −1 ) and 100 (W m −1 K −1 ) respectively [9,15]. During calculations, reflectivity of LaB 6 and graphite are considered as 57% [18,24] and 22.7% [18], respectively at 10.6 µm wavelength.…”

“…On the other hand, cerium hexaboride (CeB 6 ), with a Richardson constant of 3.6 A K −2 cm −2 [16,17] and a work function of 2.59 eV [16], requires to operate at temperature of ∼2200 K [16]. Also, LaB 6 with Richardson constant of 29 A K −2 cm −2 [17] and a work function of 3.6 eV [18], should operate at a temperature of ∼2350 K. Interestingly, at this temperature, both material CeB 6 and LaB 6 are mechanically stable and thus more suitable emitter for such high density, high temperature plasmas like tokamak. It has been reported that CeB 6 is more resistive to carbon contamination and has a lower evaporation rate than LaB 6 [17,19] and hence there is a possibility that CeB 6 will have longer lifetime than LaB 6 as LHEP tip.…”

“…It has been reported that CeB 6 is more resistive to carbon contamination and has a lower evaporation rate than LaB 6 [17,19] and hence there is a possibility that CeB 6 will have longer lifetime than LaB 6 as LHEP tip. Until recently LaB 6 and graphite were more common candidates to be chosen as LHEP tip [14,15,18,[20][21][22] and CeB 6 is emerging now as popular candidate for LHEP [16]. A high density small diameter (1.0 mm) high power laser light (in this case, coherent-make, CW CO 2 laser @10.6 µm wavelength having maximum output power 55 W) is used to heat the probe tip.…”

Laser Heated Emissive Probes Design and Development under National Fusion Program and Potential Measurement

“…1. [9] The setup consists of a cylindrical chamber 50 cm in length and 20 cm in diameter with ports for viewing and inserting probes, gauges and electrodes. Helium plasma was produced by filament discharge at 3.0×10 −3 mbar pressure.…”