Effects of sawtooth heat pulses on edge flows and turbulence in a tokamak plasma

Enhancements of edge zonal flows,radial electric fields,and turbulence are observed in electron cyclotron resonance heating-heated plasmas(Zhao et al 2013 Nucl.Fusion 53083011).In this paper,the effects of sawtooth heat pulses on flows and turbulence are presented.These experiments are performed using multiple Langmuir probe arrays in the edge plasmas of the HL-2A tokamak.The edge zonal flows,radial electric fields,and turbulence are all enhanced by sawteeth.Propagation of the zonal flow and turbulence intensities is also observed.The delay time of the maximal intensity of the electric fields,zonal flows,and turbulence with respect to the sawtooth crashes is estimated as~1 ms and comparable to that of the sawtooth-triggered intermediate phases.Not only the zonal flows but also the radial electric fields lag behind the turbulence.Furthermore,the intensities of both the zonal flows and electric fields nearly linearly increase/decrease with the increase/decrease of the turbulence intensity.A double-source predator-prey model analysis suggests that a relatively strong turbulence source may contribute to the dominant zonal flow formation during sawtooth cycles.

Analysis of heat pulse signals determination for sediment-water interface fluxes

The heat pulse signal is analyzed in a new way with the goals of clarifying the relationships between the variables in the heat transfer problem and simplifying the procedure for calculating sediment-water interface fluxes J. Only three parameters x0 λand pc l are needed to calculate J by the heat pulse data for this analysis method.The results show that there is a curvilinear relationship between the peak temperature arrival time and sediment-water interface fluxes and there exists a simple linear relationship between sediment-water interface fluxes and the natural log of the ratio of the temperature increase downstream from the line heat source to the temperature increase upstream from the heat source.The simplicity of this relationship makes the heat pulse sensors an attractive option for measuring soil water fluxes.

Heating pulse tests under constant volume on Boom clay

Boom clay formation is a potential natural host rock for geological disposal of high-level nuclear waste in Belgium.Heating pulse tests with controlled power supply（maximum temperature was limited to 85℃） and controlled hydraulic boundary conditions were performed under nearly constant volume conditions to study the impact of thermal loading on the clay formation.Selected test results of intact borehole samples retrieved in horizontal direction are presented and discussed.The study focuses on the time evolution of temperature and pore water pressure changes along heating and cooling paths,i.e.pore pressure build-up during quasi-undrained heating and later dissipation at constant temperature.

Thermal Analysis of Melting Occurring Inside a Finned Rectangular Enclosure Equipped with Discrete Pulsed Protruding Heat Sources

This paper numerically investigates the effect of the location of a horizontal fin on the melting of a phase change material(PCM)inside a rectangular enclosure heated by multiple discrete pulsed protruding heat sources.The fin and the phase change material filling the enclosure store the thermal energy extracted from the heat sources,in sensible and latent forms.The heat sources are assumed to simulate electronic components undergoing a superheating technical issue.By extracting heat from the electronics,the PCM plays the role of a heat sink.To analyze the thermal behavior and predict the cooling performance of the proposed cooling system,we derive a nonlinear mathematical model based on mass,momentum and energy conservation laws.Several numerical investigations are conducted to quantify the influence of the fin position on the thermal behavior and the cooling performance of the heat sink.Predictions include the transient maximum temperature occurring inside the heat sources and the liquid volume.A comparison between our numerical results and experimental data selected from the literature shows a good agreement.The main conclusion is that the presence of the fin leads to a slight increase in the melting time.

Heating of Nanosized Liquid Water in High-Intensity Terahertz Pulses

Non-equilibrium molecular dynamics simulations of liquid water in picosecond high-power terahertz pulses are performed by using a non-polarizable potential model. Numerical results show that the energy absorption of water molecules exhibits a pronounced resonance with THz pulses in the frequency range of 14-17 THz. With the THz pulse at resonant frequencies, the maximum temperature is about 562 K by heating the water at room temperature. Further investigation indicates that the results are independent of the size of the nanoscale water box. The efficiency of energy transfer by resonant absorption is more than seven times of microwave heating. These studies show promising applications of ultrashort THz pulses.

Heat Exchanging Process of Metal Target under Millisecond Pulsed Laser Shocking

Laser plays an important role in synthesizing nanometer material. A three-dimensional mathematical model is established in this paper when single pulsed millisecond laser shocks the surface of the metal target at a liquid-solid interface. By changing laser power density and target size, the temperature field variation of the metal target is investigated. Results show that the generation process of nanoparticles includes heating, melting and boiloff.

Uncertainty in sap flow of Brazilian mahogany determined by the heat ratio method

The tropical arboreal species Brazilian mahogany(Swietenia macrophylla) is very important economically and ecologically,for which understanding ecophysiological variables such as sap flow will improve understanding of the species and its cultivation.This paper aims to measure uncertainties(U) involved in the application of the heat ratio method for determining sap flow in Brazilian mahogany using sets of heating probes and thermometers installed on plants of 18 months of age,cultivated in Yellow Latosol,under a weighing lysimeter and located in a protected environment.The uncertainty in sap flow was calculated as the combination of uncertainty in the thermal diffusivity(U_(k)),conductive section(U_(Sc)) and corrected sap velocity(U_(Vc)).U_(k) had greater weight in determining the flow of sap in Brazilian mahogany,when compared to U_(Sc) and U_(Vc).The thermal diffusivity during the cycle,or period evaluated,must be adjusted to improve the accuracy of the heat ratio method because the sap flow overestimated transpiration by 15.0%.When soil water was optimal In addition,the vapor pressure deficit linearly and indirectly influenced the SF with a difference of 14.6%.

Preliminary Results of Sawtooth Behaviour and Electron Heat Transport During ECRH Experiment on HL-2A

An electron cyclotron resonance heating （ECRH） system with a maximum output power of 1 MW, a frequency of 68 GHz and a duration of ls was operated on HL-2A tokamak. The temperature profile control and the sawtooth behaviour during ECRH experiments are investigated. ‘Density pumpout＇ during on-axis ECRH is analysed. Features of confinement and electron heat transport during ECRH are studied.

Behaviors of Electron Heat Transportation in HT-7 Sawtoothing Plasma

It is found that in HT-7 ohmic plasma, main energy loss comes from electron heat conduction, hence quantitative data of electron heat diffusivity is a very important issue for investigation of electron heat transportation behavior in different target plasmas so as to get high performance plasma. A time-to-peak method of the heat pulse propagation originating from the sawtooth activity on the soft x-ray intensity signal has been adopted to experimentally determine electron heat diffusivity XeHP on the HT-7 tokamak. Aiming to improve the signal-to-noise (S/N) ratio of the original signal to get a stable and reasonable electron heat diffusivity XeHD value, some data processing methods, including average of tens of sawteeth, is discussed. The electron heat diffusivity XeHP is larger than XePB which is determined from the balance of background plasma power. Based on variation of the measured electron heat diffusivity XeHP, performances of different high confinement plasmas are analyzed.

Primary Results of ECRH Experiment and Electron Heat Transport on the HL-2A Tokamak

As an ordinary mainly auxiliary heating on tokamak plasma, electron cyclotron resonance heating （ ECRH ） is an useful method to the study of electron heat transport and confinement performance. In this work, primary results of ECRH experiments on the HL-2A tokamak are presented. The features of confinement and electron heat transport during ECRH are analyzed.

The nonlinear response of Cattaneo-type thermal loading of a laser pulse on a medium using the generalized thermoelastic model

The nonlinear thermoelastic responses of an elastic medium exposed to laser generated shortpulse heating are investigated in this article. The thermal wave propagation of generalized thermoelastic medium under the impact of thermal loading with energy dissipation is the focus of this research. To model the thermal boundary condition(in the form of thermal conduction),generalized Cattaneo model(GCM) is employed. In the reference configuration, a nonlinear coupled Lord-Shulman-type generalized thermoelasticity formulation using finite strain theory(FST) is developed and the temperature dependency of the thermal conductivity is considered to derive the equations. In order to solve the time-dependent and nonlinear equations, Newmark’s numerical time integration technique and an updated finite element algorithm is applied and to ensure achieving accurate continuity of the results, the Hermitian elements are used instead of Lagrangian’s. The numerical responses for different factors such as input heat flux and nonlinear terms are expressed graphically and their impacts on the system’s reaction are discussed in detail.The results of the study are presented for Green–Lindsay model and the findings are compared with Lord-Shulman model especially with regards to heat wave propagation. It is shown that the nature of the laser’s thermal shock and its geometry are particularly determinative in the final stage of deformation. The research also concluded that employing FST leads to achieving more accuracy in terms of elastic deformations;however, the thermally nonlinear analysis does not change the results markedly. For this reason, the nonlinear theory of deformation is required in laser related reviews, while it is reasonable to ignore the temperature changes compared to the reference temperature in deriving governing equations.

Quantitative Evaluation of Fatigue Crack Size Using Eddy Current Pulsed Thermography

A set of metallic specimens containing fatigue cracks with different sizes were tested using eddy current pulsed thermography(ECPT),therefore the relations between heating response of the crack area and the crack length was studied.The numerical and experimental results both showed that the increase of the crack length enhanced the crack heating response under specific test conditions.A particular form of calculated response signal,which is linearly related to the crack length,was introduced to provide a quantitative evaluation of crack length.

INVESTIGATION OF PULSED-WIRE TECHNIQUE FOR WALL PARAMETERS MEASUREMENT IN SEPARATED FLOWS

A pulsed-wire wall probe measurement system was developed in this paper,which can be used for measuring wall Parameters in separated flow- The operating princi-ple was described and the way of probe calibration was given. Wall parameters of back-ward-facing and forward-facing step flow were measured,and the wall nows structure andcharacters were revealed.

An ultra-fast charging strategy for lithium-ion battery at low temperature without lithium plating

Conventional charging methods for lithium-ion battery(LIB)are challenged with vital problems at low temperatures:risk of lithium(Li)plating and low charging speed.This study proposes a fast-charging strategy without Li plating to achieve high-rate charging at low temperatures with bidirectional chargers.The strategy combines the pulsed-heating method and the optimal charging method via precise control of the battery states.A thermo-electric coupled model is developed based on the pseudo-twodimensional(P2D)electrochemical model to derive charging performances.Two current maps of pulsed heating and charging are generated to realize real-time control.Therefore,our proposed strategy achieves a 3 C equivalent rate at 0℃ and 1.5 C at-10℃ without Li plating,which is 10–30 times faster than the traditional methods.The entropy method is employed to balance the charging speed and the energy efficiency,and the charging performance is further enhanced.For practical application,the power limitation of the charger is considered,and a 2.4 C equivalent rate is achieved at 0℃ with a 250 kW maximum power output.This novel strategy significantly expands LIB usage boundary,and increases charging speed and battery safety.

Phase structure of sputtered Ta coating and its ablation behavior by laser pulse heating(LPH)

Phase structure of sputtered Ta coating in the negative glow space and LPH effect were explored.The whole coating/substrate system is substrate→physically gas-absorbed Fe surface→oxygen-enriched TaOx layer→amorphous Ta→αandβdual phase→singleαphase.After LPH course,micro structure of Ta coating shows intact,only a few cracks emerge after 100 laser pulses,exhibiting thin HAZ but thick Fe/Ta ICZ,without martensitic transformation.For the electrodeposited Cr coating,continuous thermal stresses produce many extra micro-crack,substrate oxidation and martensitic transformation,leading to crack propagations and final bulk delamination,without any ICZ.

Difference Scheme for Hyperbolic Heat Conduction Equation with Pulsed Heating Boundary

In this paper, the authors have analyzed the second-order hyperbolic differential equation with pulsed heating boundary, and tried to solve this kind of equation with numerical method. After analyzing the error of the difference scheme and comparing the numerical results with the theoretical results, the authors present some examples to show how the thermal wave propagates in materials. By analyzing the calculation results, the conditions to observe the thermal wave phenomena in the laboratory are conferred. Finally the heat transfer in a complex combined structure is calculated with this method. The result is quite different from the calculated result from the parabolic heat conduction equation.

Efficient Cooling System Using Electrocaloric Effect

The electrocaloric effect in thin films of an electrocaloric material has the potential to be used for efficient cooling systems for high power electronic devices. We numerically calculated the effect of parameters in electrocaloric refrigeration with a thermal switch of fluid motion on the thermal performance. The system of changing air and water flow with the pulse generation of cold energy increased the heat transfer efficiency to 67% at a frequency of 5 Hz. The optimum time delay of water flow to increase the heat transfer efficiency was zero at low frequency and became half of the time period to change heat for a high frequency of 100 Hz. When the heat transfer efficiency was high, the final temperature change in water flow was not the maximum temperature change.

Effects of laser pulse heating of copper photocathodes on high-brightness electron beam production at blowout regime

Producing high-brightness and high-charge（〉100 pC） electron bunches at blowout regime requires ultrashort laser pulses with high fluence. The effects of laser pulse heating of the copper photocathode are analyzed in this paper. The electron and lattice temperature is calculated using an improved two-temperature model, and an extended Dowell-Schmerge model is employed to calculate the thermal emittance and quantum efficiency. A timedependent growth of the thermal emittance and the quantum efficiency is observed. For a fixed amount of charge,the projected thermal emittance increases with decreasing laser radius, and this effect should be taken into account in laser optimization at blowout regime. Moreover, laser damage threshold fluence is simulated, showing that the maximum local fluence should be less than 40 mJ/cm^2 to prevent damage to the cathode.

Experimental Study and Heat Transfer Analysis on the Boiling of Saturated Liquid Nitrogen under Transient Pulsed Laser Irradiation

The boiling behavior of the liquid nitrogen (LN2) under the transient high heat flux urgently needs to be researched systematically. In this paper, the high power short pulse duration laser was used to heat the saturated LN2 rapidly, and the high-speed photography aided by the spark light system was employed to take series of photos which displayed the process of LN2's boiling behavior under such conditions. Also, a special temperature measuring system was applied to record the temperature variation of the heating surface. The experiments indicated that an explosive boiling happened within LN2 by the laser heating, and a conventional boiling followed up after the newly-defined changeover time. By analyzing the temperature variation of the heating surface, it is found that the latent heat released by the crack of the bubbles in the bubble cluster induced by the explosive boiling is an important factor that greatly influences the boiling heat transfer mechanism.

Temperature of the Limiter Surface Measured by IR Camera in HT-7 Tokamak

Temperature measurement by IR （infrared） camera was performed oll HT-T tokamak. particularly during long pulse discharges, during which the temperature of the hot spots on the belt limiter exceeded 1000℃. The heat load on the surface of the movable limiter could be obtained through ANSYS with the temperature measured by IR-camera. This work could be important for the temperature measurement and heat load study on the first wall of EAST device.