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Heat-flux sensors are widely used in industry to test building products and designs for resistance to bushfire, to test the flammability of textiles and in numerous applications such as concentrated solar collectors. In Australia, such detectors are currently calibrated by the National Measurement Institute Australia (NMIA) at low flux levels of 20 W $$\cdot $$ m $$^{-2}$$ . Estimates of the uncertainty arising from nonlinearity at industrial levels (e.g. 50 kW $$\cdot $$ m $$^{-2}$$ for bushfire testing) rely on literature information. NMIA has developed a facility to characterize the linearity response of these heat-flux sensors up to 110 kW $$\cdot $$ m $$^{-2}$$ using a low-power $$\hbox {CO}_2$$ laser and a chopped quartz tungsten-halogen lamp. The facility was validated by comparison with the conventional flux-addition method, and used to characterize several Schmidt-Boelter-type sensors. A significant nonlinear response was found, ranging from ( $$3.2 \pm 0.9$$ )% at 40 kW $$\cdot $$ m $$^{-2}$$ to more than 8 % at 100 kW $$\cdot $$ m $$^{-2}$$ . Additional measurements confirm that this is not attributable to convection effects, but due to the temperature dependence of the sensor's responsivity. [ABSTRACT FROM AUTHOR]

A new laser-based technique to examine heat transfer and energetics of phase transitions in metal-carbon fixed points and potentially to improve the quality of phase transitions in furnaces with poor uniformity is reported. Being reproducible below 0.1 K, metal-carbon fixed points are increasingly used as reference standards for the calibration of thermocouples and radiation thermometers. At NMIA, the Co-C eutectic point is used for the calibration of thermocouples, with the fixed point traceable to the International Temperature Scale (ITS-90) using radiation thermometry. For thermocouple use, these cells are deep inside a high-uniformity furnace, easily obtaining excellent melting plateaus. However, when used with radiation thermometers, the essential large viewing cone to the crucible restricts the furnace depth and introduces large heat losses from the front furnace zone, affecting the quality of the phase transition. Short $$\hbox {CO}_{2}$$ laser bursts have been used to illuminate the cavity of a conventional Co-C fixed-point cell during various points in its melting phase transition. The laser is employed to partially melt the metal at the rear of the crucible providing a liquid-solid interface close to the region being observed by the reference pyrometer. As the laser power is known, a quantitative estimate of $$(166 \pm 30) \hbox { J}{\cdot }\hbox {g}^{-1}$$ can be made for the Co-C latent heat of fusion. Using a single laser pulse during a furnace-induced melt, a plateau up to 8 min is observed before the crucible resumes a characteristic conventional melt curve. Although this plateau is satisfyingly flat, well within 100 mK, it is observed that the plateau is laser energy dependent and elevates from the conventional melt 'inflection-point' value. [ABSTRACT FROM AUTHOR]

Platinum resistance thermometers (PRTs) are capable of providing reliable measurements at the millikelvin level, and are widely used in both industry and research applications. However, the intrinsic thermal noise associated with their resistance requires the use of a measurement current of typically around a milliampere to determine their resistance. Unfortunately, this same current also dissipates heat into the thermometer element, causing the well-known 'self-heating' effect of typically a few millikelvins. Performing measurements in terms of the ratio to the resistance at the ice point provides some level of cancelation of this error around this temperature: If the thermal resistance between the sensor and environment were constant, this cancelation would work over a much wider temperature range. However, there is little evidence on the effectiveness of this strategy in practice. This paper reports on an extensive set of systematic measurements of the self-heating of six standard platinum resistance thermometers (SPRTs) and six industrial platinum resistance thermometers (IPRTs) of different designs, as a function of temperature, over the range from $$-190~^{\circ }\mathrm{C}$$ to $$420\,^{\circ }\mathrm{C}$$ , in a range of intercomparison baths and blocks. The measurements show that PRT self-heating varies from being almost constant with temperature to being nearly proportional to temperature. The assumption of a roughly temperature-independent thermal resistance is thus not justified in general. The results allow estimation of appropriate uncertainty terms for SPRT and IPRT self-heating for the two scenarios of 'working in $$R$$ ' and 'working in $$W$$ .' [ABSTRACT FROM AUTHOR]

In this paper, the spectrum of fast Alfvén eigenmodes is examined for a cylindrical, current-carrying, inhomogeneous plasma, at frequencies above the ion cyclotron frequency. Although the spectrum for m=0 and m=±1 modes in a current-free plasma has been studied extensively, the influence of a steady plasma current and the properties of high m modes have not received as much attention. It is shown that there exists a wide spectrum of positive m modes that propagate in the ion cyclotron range of frequencies, regardless of the plasma density or device size. These modes propagate, as surface waves, in the plasma edge region. Mode splitting, caused by the finite plasma current, is sufficiently large in tokamak devices that high m modes propagate in only one direction parallel to the equilibrium Bz field. High m modes are guided along the steady magnetic field lines in the plasma edge and are therefore potentially very dangerous from an edge heating point of view. [ABSTRACT FROM AUTHOR]