Resolution Of Reflectometry Research Articles

Magnetic-field induced flattening of evaporating ferro-nanofluid meniscus for enhanced cooling

This work envisages applying magnetic fields to flatten thin ferro-nanofluid film meniscus for enhanced heat transfer during evaporative cooling process. Experiments are conducted to examine the shape of the evaporating extended meniscus of ferro-nanofluid (Fe304 nanoparticles in water suspension 0.01% v/v) under axisymmetric vertical magnetic fields (∼10−2T) generated by solenoid placed below the heated substrate. The study includes measuring the thickness profile of the meniscus evaporating region using high nano-scale resolution reflectometry and theoretically interpreting meniscus shape in terms of flow and film heat transfer. Profile measurements reveal an increasing influence of magnetic fields in thinning of the adsorbed region and stretching of the transition region, which effectively reduce the thermal resistance across meniscus width. Data reduction based on thickness as well as the derived curvature profiles yields a high-pressure gradient driving flow along the evaporating thin film region. The results imply additional suction induced by disjoining pressure of thinner adsorbed layer which sustains replenishment of lost evaporative mass across a longer transition region interface. Subsequent heat transfer analysis reveals up to 156 % enhancement in overall heat flux and 101 % in average heat transfer with increasing magnetic field intensity. The findings establish proof of concept of applying magnetic field to augment film-based cooling.

Long range and high resolution reflectometry by synthesis of optical coherence function at region beyond the coherence length

A long-range and high-resolution reflectometry by synthesis of optical coherence function at region beyond the coherence length is proposed. We discuss and simulate the principle of the reflectometry system. In basic experiments, the reflectivity distribution is successfully measured at the region beyond the coherence length with a spatial resolution of 19cm and a measurement range of 1km. We have also proposed two methods to improve dynamic range of the system. In the experiments, dynamic range of 45dB is successfully achieved.

High temporal and spatial resolution reflectometry investigations of type-I ELMs induced edge barrier collapse at ASDEX Upgrade

The edge barrier collapse induced by spontaneous and pellet triggered ELMs has been characterized by means of a new technique based on the reflectometry group delay. The analysis of the behaviour of the density layers at the plasma edge revealed small differences between the two types of ELMs. With this technique we are able to detect profile steepening and fuelling effects due to pellet injection, mainly at the high field side. The presence of asymmetries between high and low field sides in the ELM dynamics has also been studied by evaluating the ELM onset time on both sides. The ELM onset on the HFS is observed to be only slightly delayed compared with the LFS onset—the barrier collapses are nearly coincident within the diagnostic time resolution. In our new findings, which apply to both spontaneous and triggered ELMs, there is no clear evidence of long HFS/LFS delays as previously observed for spontaneous ELMs.

Characterization of the density profile collapse of type I ELMs in ASDEX Upgrade with high temporal and spatial resolution reflectometry

This paper characterizes the density profile dynamics during edge localized modes (ELMs), using high temporal and spatial resolution reflectometry, with main emphasis on the dynamics of type I ELMs. Qualitatively, the density profile dynamics of both type I and type III ELM ASDEX Upgrade tokamak discharges shows the same characteristic behaviour. The analysis of the behaviour of the density at the plasma edge allows the identification of three phases of the ELM event: precursor, collapse and recovery phases. For the three phases, the effect of ELMs is analysed both on the high-field side (HFS) and the low-field side (LFS) of the plasma at the ASDEX Upgrade. Asymmetries of the ELM event when comparing the HFS and LFS are found. The ELM event is associated with a sudden loss of particles from the main plasma (inside the last closed flux surface) to the scrape-off layer and then to the divertor. For type I ELMs the relative particle losses (to the pedestal particle content), assuming poloidal symmetry, was found to be of ∼10% using LFS measurements and of ∼5% using the HFS measurements. The type I ELM affected depths are about ∼25% and ∼15% of the plasma minor radius for the LFS and HFS profiles mapped to the outer midplane, respectively.

Elongation of measurement range by successively shifting measurement window in a high spatial resolution reflectometry for optical subscriber networks by synthesis of optical coherence function

A reflectometry system having a high spatial resolution and an elongated measurement range is constructed, considering an application to optical subscriber networks, using a technique of synthesis of optical coherence function (SOCF). In this system, parameters have been adjusted so that the measurement range is elongated by successively shifting the 20 m measurement window while keeping a high spatial resolution. Reflectivity distribution around the end of a 5 km test fibre is successfully measured with a spatial resolution of 11 cm and an elongated measurement range of 1 km.

High-spatial resolution reflectometry by synthesis of optical coherence function for measuring reflectivity distribution at a long distance

A high-spatial resolution reflectometry by synthesis of the optical coherence function is proposed for testing optical devices and circuits at the far end of optical subscriber networks. The system can measure the reflectivity distribution at a long distance without performance degradation resulting from the phase fluctuation in a long-length optical fiber. Reflectivity distribution at a distance of 5 km is measured successfully with the spatial resolution of 6 cm.