Near Infrared Radiation from Heated Nanostructured Tungsten

Abstract

Helium plasma irradiation to metals leads to morphology changes in nanometer scales by the formation of helium bubbles. The nanostructure significantly alters the optical property of the metal. In this study, near infrared radiations from a heated nanostructured tungsten are measured with a spectrometer. Energy balance between the influx of plasma and radiation from the sample is discussed in terms of the optical emittance. It is shown that the optical emittance is increased considerably by the morphology change in the range from visible to near infrared, and the efficiency of radiation is increased by two to three times.

Accelerated/reduced growth of tungsten fuzz by deposition of metals

“…At the contact surface, a temperature gap can be formed [26], and the temperature gap is a product of the heat flux and the thermal contact resistance. The heat load from the plasma can be expressed as [27]…”

Optical properties of nanostructured tungsten in near infrared range

“…As discussed in [16], the total emittance increased from 0.3 to almost unity during the helium irradiation. The increase in the total emittance increased the emission at the same temperature, and a decrease in the surface temperature by more than 200 • K occurred, consequently.…”

“…Helium plasmas were produced by dc arc discharge, and the length of the plasma was approximately 2 m. A tungsten sample, which was installed to the downstream of the plasma, was exposed to the helium plasma at an elevated temperature, typically higher than 1000 K. The sample was connected to a tungsten wire, and the incident ion energy was controlled by electrically biasing the sample. In this situation, the heat conduction to the connecting wire is negligible; the temperature is determined from the balance between the radiation and the heat influx from the plasma [16]. The nanostructure formation proceeded only when the sample was negatively biased sufficiently, because the incident ion energy is a critical parameter for the formation of the nanostructure [10,17].…”

“…The reflectance was measured using an integrating sphere and a laser diode, as shown in figure 5(b), at the wavelength of 1550 nm, which almost corresponds to the wavelength of the radiation pyrometer. In the formation process, the evolutions of R and at 1550 nm under a similar experimental condition measured previously [16] were used. The surface temperature and the incident ion energy were 1380 K and 60 eV, respectively, and the evolutions are shown in figure 5(c).…”

Experimental investigation on the effect of surface electric field in the growth of tungsten nano-tendril morphology due to low energy helium irradiation

“…The control W sample was mounted onto a ceramic heater that maintains the sample temperature using feedback from a thermocouple mounted inside the heater. The heater was taken to 1273 K. At this temperature, the heat flux from the plasma when the sample is biased to -50 V is comparable to the thermal radiation of polished W. At the beginning of the exposure, the temperature of the surface of the W sample is 1273 K. As the surface morphology changes to W fuzz, the emissivity increases to 1 [26], and the surface temperature is calculated to be 20 K lower than the heater temperature. Helium plasma was generated with an electron density of 6 x 10 17 m -3 and an electron temperature of 2.8 eV as determined from a double Langmuir probe.…”