Pump Limiter Research Articles

Pump-Power-Driven Mode Switching in a Microcavity Device and Its Relation to Bose-Einstein Condensation

We investigate the switching of the coherent emission mode of a bimodal microcavity device, occurring when the pump power is varied. We compare experimental data to theoretical results and identify the underlying mechanism to be based on the competition between the effective gain on the one hand and the intermode kinetics on the other. When the pumping is ramped up, above a threshold the mode with the largest effective gain starts to emit coherent light, corresponding to lasing. In contrast, in the limit of strong pumping it is the intermode kinetics that determines which mode acquires a large occupation and shows coherent emission. We point out that this latter mechanism is akin to the equilibrium Bose-Einstein condensation of massive bosons. Thus, the mode switching in our microcavity device can be viewed as a minimal instance of Bose-Einstein condensation of photons. We, moreover, show that the switching from one cavity mode to the other occurs always via an intermediate phase where both modes are emitting coherent light and that it is associated with both superthermal intensity fluctuations and strong anticorrelations between both modes.

Dynamic Evolution of the Evaporating Liquid-Vapor Interface in Micropillar Arrays.

Capillary assisted passively pumped thermal management devices have gained importance due to their simple design and reduction in energy consumption. The performance of these devices is strongly dependent on the shape of the curved interface between the liquid and vapor phases. We developed a transient laser interferometry technique to investigate the evolution of the shape of the liquid-vapor interface in micropillar arrays during evaporation heat transfer. Controlled cylindrical micropillar arrays were fabricated on the front side of a silicon wafer, while thin-film heaters were deposited on the reverse side to emulate a heat source. The shape of the meniscus was determined using the fringe patterns resulting from interference of a monochromatic beam incident on the thin liquid layer. We studied the evolution of the shape of the meniscus on these surfaces under various operating conditions including varying the micropillar geometry and the applied heating power. By monitoring the transient behavior of the evaporating liquid-vapor interface, we accurately measured the absolute location and shape of the meniscus and calculated the contact angle and the maximum capillary pressure. We demonstrated that the receding contact angle which determines the capillary pumping limit is independent of the microstructure geometry and the rate of evaporation (i.e., the applied heating power). The results of this study provide fundamental insights into the dynamic behavior of the liquid-vapor interface in wick structures during phase-change heat transfer.

Calculation of the Hydraulic Extension Limit of an Extended-Reach Well with Allowance for the Power Limitations of the Available Mud Pumps

A procedure for calculating the pressure and power of a mud pump used in drilling an extendedreach well is described. A method is proposed for determining the hydraulic extension limit length in the drilling process depending on the rated pressure and power of the pump. An example is given of maximum well depth calculation with allowance for the limitations of a specific pump having fixed characteristics.

Development of PM0.1 Personal Sampler for Evaluation of Personal Exposure to Aerosol Nanoparticles

A PM0.1 sampler for the evaluation of the personal exposure to nanoparticles was designed based on a novel approach to a layered mesh inertial filter. Applications to practical environments would include roadsides and highly contaminated workplaces. The separation performances of PM0.1 sampler consisting of a layered mesh inertial filter and pre-separators for the removal of coarse particles were evaluated. The influence of particle loading on the pressure drop and separation performance, which is important from a practical standpoint, was also discussed. The novel personal sampler recorded a cutoff size of 100 nm with a small pressure drop of ~5 kPa. Through the combination of a layered mesh inertial filter for the PM0.1 and pre-cut impactors for the removal of huge or coagulated particles (PM1.4-TSP) along with a pre-cut inertial filter using webbed SUS fibers for the removal of fine particles (PM0.5-PM1.4), the present PM0.1 inlet for the personal sampler was practical for the chemical analysis of collected particles. This sampler was proven effective even under the limitations of a small-capacity portable battery pump, which was rated at less than the minimum change for separation performance. The novel PM0.1 personal sampler is compact and lightweight (under 1 kg including a portable battery pump), which is important for the practical application of a personal sampler.

Evidence of clinical efficacy of counterpulsation therapy methods.

Although heart transplantation remains the ultimate treatment for end-stage heart failure, its epidemiological impact is limited by donor organ availability. Surgical and device-based approaches have been introduced with the aim of increasing systemic perfusion and in some circumstances promoting left ventricular recovery by inducing reverse remodelling. Innovative counterpulsation devices based on the established principle of the intra-aortic balloon pump have been developed, and of these, the CardioVad and the C-Pulse System have been introduced in clinical practice with convincing evidence of haemodynamic efficacy. The evolution from pulsatile to continuous-flow left ventricular assist devices has been associated with improved survival rates during the first 2 years of support with the potential of matching heart transplantation outcomes. However, blood contact with the device remains a significant challenge despite the highly sophisticated technology currently available. Innovative extra-vascular counterpulsation devices have been shown to overcome the limitations of the intra-aortic balloon pump and rend the device suitable for prolonged support. Monitoring of the performance of these novel devices is essential, and carotid Doppler ultrasonography is of utility in assessing the haemodynamic performance of the devices in a clinical setting. Computational modelling has played a role in the simulation of these devices and should continue to assist with their optimisation and implementation in clinical practice.

Bose-Hubbard model: Relation between driven-dissipative steady states and equilibrium quantum phases

We present analytical solutions for the mean-field master equation of the driven-dissipative Bose-Hubbard model for cavity photons, in the limit of both weak pumping and weak dissipation. Instead of pure Mott insulator states, we find statistical mixtures with the same second-order coherence as a Fock state with n photons, but a mean photon number of n/2. These mixed states occur when n pump photons have the same energy as n interacting photons inside the nonlinear cavity and survive up to a critical tunneling coupling strength, above which a crossover to classical coherent state takes place. We also explain the origin of both antibunching and superbunching predicted by P-representation mean-field theory at higher pumping and dissipation. In particular, we show that the strongly correlated region of the associated phase diagram cannot be described within the semiclassical Gross-Pitaevski approach.

Pool boiling CHF of reduced graphene oxide, graphene, and SiC-coated surfaces under highly wettable FC-72

This paper presents the results of a study of enhanced boiling heat transfer (BHT) and critical heat flux (CHF) for a bare indium tin oxide (ITO) surface, a nonporous few-layered graphene-deposited ITO surface, a nonporous SiC layer-deposited ITO surface, and porous graphene and silicon carbide (SiC) layer-deposited ITO surfaces. The experiments were conducted under atmospheric pressure using an FC-72 refrigerant under saturation conditions. Infrared thermometry was used to determine the temperature fields of the heater surfaces and the CHF conditions. The CHF values for the surfaces with highly thermally conductive nonporous graphene layers and nonporous SiC layers were found to be increased by 9% and 15.7%, respectively, compared to that of the bare ITO heating surface. For the heating surfaces with porous graphene layers and SiC layers, the CHF values were increased by 90% and 58%, respectively. All of the heating surfaces exhibited hydrophilic behavior with respect to the FC-72 fluid. The differences in CHF enhancement observed can be explained by differences in the thermal properties of graphene and SiC, their heat dissipation limits, differences in aspects of their surface morphologies, such as their porosities and permeabilities, and the effects of these on their hydrodynamic limits and capillary pumping limits.

Modelling of the micrometric erosion pattern observed on the Tore Supra limiter tiles

Recently, the surface of carbon fibre composite tiles of the toroidal pump limiter of Tore Supra has been analysed by scanning electron and atomic force microscopies. In regions where fibres are perpendicular to the surface, a specific erosion pattern has been observed. It is constituted of a striation oriented with an angle oblique with respect to the magnetic field. The characteristic wavelength of this structure is micrometric, and similar to the fibre size. Modelling has been undertaken to reproduce this micrometric pattern. It is shown to originate from the carbon composite structure, for which it has been found by measurement using laboratory plasma that the erosion rate of the fibres is different from that of the surrounding matrix. Modelling emphasizes the effect of the impinging flux angle distributions of deuterium ions and carbon impurities that are preliminarily determined from computation of the magnetic sheath. In the case of deuterium the sheath is shown to have little effect on the particle trajectories for the simulation parameters considered here, although when impurities are included the sheath deflection is significant. Furthermore this study shows how the fibre organization in the composite influences the striation direction and points out the importance of the angular dependence of the sputtering yield.

Heat flux distribution and gyro-radius smoothing effect on misaligned CFC tile in the Tore Supra tokamak

Understanding heat flux deposition processes is essential for the design of the plasma facing component allowing reliable high power steady state plasma operations. Misalignments up to δ=0.2mm between two adjacent CFC tiles have been reported on the Toroidal Pump Limiter of Tore Supra. Heat flux impinging the top and leading edge of the protruding tile are characterized with both IR thermographic system and numerical modelling using 2D particle-in-cell simulations that accounts for the Larmor radius smoothing effect of incident ions. Numerical heat loads are coupled with a 2D thermal model of the tile and with a specific sensor correction to simulate spatial-resolution related effects (necessary here since the tile misalignment is smaller than the spatial resolution of the IR system). In the experiment depicted here, with a misalignment smaller than an ion gyro-radius, the Larmor radius smoothing effect is maximum and overheating of the leading edge is reduced by a factor of two.

Modelling the erosion/deposition pattern of the Tore Supra Toroidal Pumped Limiter

This paper aims at understanding the main processes responsible for the erosion/deposition pattern observed on the surface of the Toroidal Pumped Limiter of Tore Supra, using the 3D local impurity transport code ERO. The influence of the plasma impurity content, CX-flux and surface temperature on the global carbon balance and erosion/deposition pattern is discussed. Main results are (1) that considering medium-range transport of C ions is mandatory for reproducing the main characteristics of the global C balance and erosion/deposition pattern, (2) that impurities and CX-atoms increase the erosion by a factor⩽2 (without changing the net/gross erosion ratio), and (3) that chemical erosion is governed by the re-erosion of deposits, which depends strongly on the surface temperature.

Turn-on delay of QD and QW laser diodes: What is the difference?

Turn-on delay of laser diodes with quantum-sized active media is investigated both theoretically and experimentally. In this research we show the striking difference in turn-on delay of quantum dot and quantum well laser diodes: With quantum-well lasers turn on delay tends to zero in the limit of high pumping, while with quantum dot lasers turn-on delay has the non-vanishing component which is independent of pumping.

Erosion–deposition mapping of the toroidal pump limiter of Tore Supra

Abstract Analyses of erosion and deposition over the toroidal pump limiter of Tore Supra were performed combining scanning electron microscopy, confocal microscopy and lock-in thermography. The consistency between the different methods allows a complete mapping of the eroded and deposited mass of carbon to be performed. ∼920 g of eroded carbon and ∼520 g of deposited carbon are found, showing that more than half of the eroded carbon is redeposited on the limiter. The highest deposition zones are close to the eroded zones. The gap deposition contribution is estimated at ∼23%, mostly from the erosion zones and with a main contribution from the low field side of the tile toroidal gap surfaces. Raman microscopy and transmission electron microscopy in-depth analyses show that the structure of deposits is non-homogeneous, in agreement with a deuterium impoverishment of the deep layers.

Confocal microscopy: A new tool for erosion measurements on large scale plasma facing components in tokamaks

Abstract A diagnostic based on confocal microscopy was developed at CEA Cadarache in order to measure erosion on large plasma facing components during shutdown in situ in Tore Supra. This paper describes the diagnostic and presents results obtained on Beryllium and Carbon Fibre Composite (CFC) materials. Erosion in the range of 800 μm was found on one sector of the Toroidal Pumped Limiter (TPL) which provides, by integration to the full limiter a net carbon erosion of about 900 g over the period 2002–2007.

Layer removal in gaps by laser process

Abstract The laser ablation technique had been already shown to be well suited to clean the top surface of the Toroidal Pumped Limiter of Tore Supra. The next phase was to apply this technique to the deposits observed in the gaps. This paper focuses on the characterization of gap deposits and the optimization of the laser cleaning process for this application. In general most of the deposits are located inside the gap within the first mm. In the toroidal direction most of the deposits are located on the low field side with thicknesses reaching up to 610 μm, while in the poloidal direction deposits thicknesses up to 450 μm are observed on both sides. The influence of the laser angle has been investigated; an angle of 45° is recommended in the toroidal direction while a perpendicular beam is adopted in the poloidal direction. This study concludes that gap cleaning induces significant additional time for castellated surfaces.

Nonadiabatic electron pumping through interacting quantum dots

We study non-adiabatic charge pumping through single-level quantum dots taking into account Coulomb interactions. We show how a truncated set of equations of motion can be propagated in time by means of an auxiliary-mode expansion. This formalism is capable of treating the time-dependent electronic transport for arbitrary driving parameters. We verify that the proposed method describes very precisely the well-known limit of adiabatic pumping through quantum dots without Coulomb interactions. As an example we discuss pumping driven by short voltage pulses for various interaction strengths. Such finite pulses are particular suited to investigate transient non-adiabatic effects, which may be also important for periodic drivings, where they are much more difficult to reveal.

A high-output-current and low-power-loss thin-film transistor liquid-crystal display (TFT-LCD) driver for portable devices

The application range of traditional thin-film transistor (TFT) liquid-crystal display (LCD) drivers powered by switched-capacitor DC-DC converters (charge pumps) used in portable devices are, to a certain extent, restricted because of their inability to support applications that require high driving current for generating high resolution graphics or powering larger LCD panels. This paper reviews the limitations of charge pumps when used on TFT-LCD drivers fabricated using the chip-on-glass (COG) packaging technology. A high-output-current low-power-loss boost-type DC-DC converter is proposed to replace traditional charge pumps while retaining the existing COG packaging technology in order to reduce production cost. A prototype of the proposed converter is designed with a standard 0.13 µm HV CMOS process. Compared with traditional designs, the proposed converter demonstrates that it is capable of delivering a higher driving current at a much smaller power loss.

Evolution of the bonding defect reported on the tiles of the toroidal pumped limiter of the Tore Supra tokamak with infrared analysis

The bonding of plasma-facing component (PFC) tiles and their possible defects need to be monitored to evaluate the safety during long pulse plasma operations and prevent critical failure, which is very important for ITER and next-step fusion devices. The defect evolutions of two toroidal pumped limiter (TPL) tiles are investigated by analysing the infrared images obtained during Tore Supra experiments from 2006 to 2010 (about 10 000 plasma discharges). The evolution of the defect is characterized by the surface temperature reached in stationary discharge conditions. The comparison of the defect tiles with neighbouring tiles (with no defect) and the evolutions are carried out through the thermal time constants of the tiles. The results show that the two tiles are slowly deteriorating during plasma operation and no plateau of the deterioration is observed in the considered period. By comparing the defect evolutions with the modelling results calculated by CAST3M, the current state of the defect tiles is identified. The defects are significant (about 30% of the tile length or area) and need to be followed and monitored further in the next experimental campaigns of Tore Supra.

Micro-distribution of fuel and metal in carbon-based plasma-facing materials

Surfaces of carbon fibre composite tiles from the toriodal pump limiter of Tore Supra were examined with ion beams to determine simultaneously the distribution of co-deposited deuterium and metallic plasma impurities (i.e. steel components). With a 3He+ ion beam the reaction 2D(3He,p)4He was used for deuterium, 12C(3He,p)14N for carbon, whereas beam-induced x-ray emission and back-scattered ions served for the detection of heavier elements. Measurements were made both with a 1 mm beam and by a micro-beam focused down to 20 μm spot size and scanned over the sample to obtain maps of the different elements. Distribution maps of different elements—fuel and metal species—are presented for four distinct regions on the limiter: erosion zone, shadowed area, thin deposits and thick flaking deposits.

Micro-chemical analysis of high heat loaded CFC–Cu interfaces from Tore Supra and Wendelstein 7-X

A comparison of high-heat-flux tested carbon-fiber reinforced carbon (CFC)/Cu materials of Tore Supra and Wendelstein 7-X plasma-facing components is made in order to understand the different fatigue behavior of the bonding interfaces, in particular for the Tore Supra materials. The elemental distribution around the bonding layer and the chemical composition of the active element titanium are characterized by secondary ion mass spectrometry and x-ray photoelectron spectroscopy. The results show that the improved bonding of the Wendelstein 7-X target elements compared to the Tore Supra pump limiter elements is due to a modified silicon and titanium distribution at the bonding interface. However, the difference in fatigue behavior between the two Tore Supra components cannot be attributed to the bonding interface, since the elemental distribution and chemistry of these components are identical and no degradation is observed after an extended heat flux exposure.

Structural analysis of eroded carbon fiber composite tiles of Tore Supra: insights on ion transport and erosion parameters

As part of the deuterium inventory in the Tore Supra project, a detailed structural analysis of the eroded tiles (carbon fiber composite tiles) of the main plasma-facing component of Tore Supra, the toroidal pump limiter, has been performed. It combines scanning electron microscopy, atomic force microscopy and Raman microscopy. A tile cross-section has been scanned, showing the eroded profile of the tile and allowing the net erosion rate to be determined. Ripples are observed on the surface of the eroded tiles and this pattern gives a clear indication of the ion flux direction. The height profile along the valleys indicates that the fibers are eroded faster than the matrix, the difference in the erosion rates probably originating from differences in microstructure.