Initial testing of ohmic heating through double flux swing during electron cyclotron start-up in the QUEST spherical tokamak

A power-supply system was developed for Ohmic heating(OH)to double×10^(18)the amount of change magnetic flux in the primary central solenoid(CS)on the QUEST spherical tokamak.Two power supplies are connected with stacks of insulated-gate bipolar transistors,and sequentially operated to generate positive and negative CS currents.This bipolar power-supply system is controlled via a field-programmable gate array,which guarantees the safety of the entire system operation.The new OH system,assisted by electron cyclotron heating,enables the stable generation of plasma currents exceeding 100 k A.Moreover,the achieved electron density over the wide range in the major radial direction exceeds the cut-off density for one of the highpower microwave sources in QUEST.This strategy yields target plasmas for future experiments with the electron Bernstein wave.

Study on Matching a 300 MVA Motor Generator with an Ohmic Heating Power Supply in HL-2M

A new 300 MVA/1350 MJ motor generator （MG） will be built to feed all of the poloidal field power supplies （PFPS） and auxiliary heating power supplies of the HL-2M tokamak. The MG has a vertical-shaft salient pole 6-phase synchronous generator and a coaxial 8500 kW induction motor. The Ohmic heating power supply （OHPS） consisting of 4-quadrant DC pulsed convertor is the one with the highest parameters among the PFPS. Therefore, the match between the generator and the OHPS is very important. The matching study with Matlab/Simulink is described in this paper. The simulation results show that the subtransient reactance of the generator is closely related to the inversion operation of the OHPS. By setting various subtransient reactance in the simulation generator model and considering the cost reduction, the optimized parameters are obtained as xd＂ = 0.405 p.u. at 100 Hz for the generator. The models built in the simulation can be used as an important tool for studying the dynamic characteristics and the control strategy of other HL-2M PFPSes.

Simultaneous effects of chemical reaction and Ohmic heating with heat and mass transfer over a stretching surface: A numerical study

In this article, we have considered the simultaneous influence of ohmic heating and chemical reaction on heat and mass transfer over a stretching sheet. The effects of applied magnetic field are also taken into consideration while the induced magnetic field is not considered due to very small magnetics Reynolds number. The governing flow problem comprises of momentum, continuity, thermal energy and concentration equation which are transformed into highly nonlinear coupled ordinary differential equations by means of similarity transforms, which are then, solved numerically with the help of Successive Linearization method(SLM) and Chebyshev Spectral collocation method. Numerical values of skin friction coefficient, local Nusselt number, and Sherwood number are also taken into account with the help of tables. The physical influence of the involved parameters of flow velocity, temperature and concentration distribution is discussed and demonstrated graphically. The numerical comparison is also presented with the existing published results and found that the present results are in excellent agreement which also confirms the validity of the present methodology.

Hall and ion slip effects on peristaltic flow and heat transfer analysis with Ohmic heating

The peristaltic transport of a magnetohydrodynamic （MHD） fluid is exam- ined for both symmetric and asymmetric channels. Hall and ion slip effects are taken into account. The heat transfer is analyzed by considering the effects of viscous and Ohmic dissipations. The relevant flow problems are first modeled, and then the closed form solutions are constructed under the assumptions of long wavelength and low Reynolds number. The solutions are analyzed through graphical illustration. It is noted that the velocity increases but the temperature decreases with the increases in the Hall and ion slip parameters. The axial pressure gradient is less in magnitude in the presence of Hall and ion slip currents. The Hall and ion slip effects are to decrease the maximum pres- sure against which peristalsis works as a pump. The free pumping flux decreases with the increases in the Hall and ion slip parameters. The increases in the Hall and ion slip parameters result in an increase in the size of the trapped bolus.

Modelling and Simulation of an Ohmic Heating Process

Ohmic Heating (OH) is one of the emerging thermal technologies used in food processing which can produce rapid and uniform heating with close to 100% energy transfer efficiency. Although mathematical modelling for OH processes has been studied by many researchers in recent years, systematic simulations of OH have not been developed for model-based control of the processes. In this paper, mathematical model for a Colinear Ohmic Heater is presented, analyzed, and studied based on the selected configuration. A numerical solution for the mathematical equations has been defined and proposed. MATLAB/Simulink model is hence developed and validated against the available data. Simulation results have shown that MATLAB/Simulink model can produce robust outputs at low computational costs with an accuracy of up to 99.6% in comparison to the analytical solution. This model can be used in further studies for analysis of the OH processes and development of advanced controllers.

Changes in electrical conductivity of liquid foods during ohmic heating

Ohmic heating is a food processing method in which alternating current(AC)went through a food sample and resulted in internal energy generation in foods.It is an alternative fast heating technique.Its principal advantage is the ability to rapidly and uniformly heat food materials of various densities.During ohmic heating,change in electrical conductivity was observed.The intensity of food materials’electrical conductivity or overall resistance critically controls ohmic heating rate.An ohmic heating set-up was prepared under this project.Tomato juice was heated(about 32℃ to 80℃)in a batch type ohmic heater at different voltage gradients in the range of 50-70 V/cm.It was statistically found that the voltage gradient had significant impact on conductivity and system performance coefficient(SPC)(P<0.05).It was concluded that the electrical conductivity values linearly increased with temperature.The SPCs of the system ranged between 0.779 and 0.943.The value of R2 of the linear model was greater than 0.98.

On radiative-magnetoconvective heat and mass transfer of a nanofluid past a non-linear stretching surface with Ohmic heating and convective surface boundary condition

In this paper magnetoconvective heat and mass transfer characteristics of a two-dimensional steady flow of a nanofluid over a non-linear stretching sheet in the presence of thermal radiation,Ohmic heating and viscous dissipation have been investigated numerically.The model used for the nanofluid incorporates the effects of the Brownian motion and the presence of nanopanicles in the base fluid.The governing equations are transformed into a system of nonlinear oidinary differential equations by using similarity transformation.The numerical solutions are obtained by using fifth order Runge-Kutta-Fehlberg method with shooting technique.The non-dimensional parameters on velocity,temperature and concentra­tion profiles and also on local Nusselt number and Sherwood number are discussed.The results indicate that the local skin friction coefficient decreases as the value of the magnetic parameter increases whereas the Nusselt number and Sherwood number increase as the values of the Brownian motion parameter and magnetic parameter increase.

Hall,ion slip and ohmic heating effects in thermally active sinusoidal channel

In this paper Carreau fluid is taken into account to study its peristaltic flow with Hall and ion-slip effects.The study is carried out in a wave frame of reference for both asymmetric and symmetric channel.Analysis of heat transfer is accomplished by taking the effects of viscous dissipation and ohmic heating into our consideration.Modeling of fundamental equations is followed by the construction of closed form solutions for pressure gradient,stream function and temperature while assuming Reynold's number is very low and wavelength very long.The closed form solutions are generated with the help of perturbation technique considering Weissenberg number to be very small.The effects of emerging parameters on pumping,trapping,axial pressure gradient,pressure rise,velocity profile and temperature are analyzed through the graphical representation.

Energy Confinement of both Ohmic and LHW Plasma on EAST

Study on the characters of energy confinement in both Ohmic and lower hybrid wave （LHW） discharges on EAST is conducted and the linear Ohmic confinement （LOC）, saturated ohmic confinement （SOC） and improved Ohmic confinement （IOC） regimes are investigated in this paper. It is observed that an improved confinement mode characterized by both a drop of IDa line intensity and an increase in line average density can be triggered by a gas puffing pulse.

Magnetic probe diagnostics of nonlinear standing waves and bulk ohmic electron power absorption in capacitive discharges

It is recognized that standing wave effects appearing in large-area,very-high-frequency capacitively coupled plasma(CCP)reactors cause center-high plasma non-uniformity.Using a high-frequency magnetic probe,we present a direct experimental diagnostic of the nonlinear standing waves and bulk ohmic electron power absorption dynamics in low pressure CCP discharges for different driving frequencies of 13.56,30,and 60 MHz.The design,principle,calibration,and validation of the probe are described in detail.Spatial structures of the harmonics of the magnetic field,determined by the magnetic probe,were used to calculate the distributions of the harmonic current and the corresponding ohmic electron power deposition,providing insights into the behavior of nonlinear harmonics.At a low driving frequency,i.e.13.56 MHz,no remarkable nonlinear standing waves were identified and the bulk ohmic electron power absorption was observed to be negligible.The harmonic magnetic field/current was found to increase dramatically with the driving frequency,due to decreased sheath reactance and more remarkable nonlinear standing waves at a higher driving frequency,leading to the enhancements of the ohmic heating and the plasma density in the bulk,specifically at the electrode center.At a high driving frequency,i.e.60 MHz,the high-order harmonic current density and the corresponding ohmic electron power absorption exhibited a similar node structure,with the main peak on axis,and one or more minor peaks between the electrode center and the edge,contributing to the center-high profile of the plasma density.

Novel heating technologies to improve fermentation efficiency and quality in wheat products:A short review

Identifying novel processing methods is an important research direction in the field of food engineering.Fermented flour products have been popular all over the world for a long time because of their unique flavor and texture.Whether for yeast or sourdough,the accurate temperature control is essential for the fermentation process.Some novel heating methods have shown potential in the processing of fermented flour products.Microwave heating(MWH),radiofrequency heating(RFH),and ohmic heating(OH)are undoubtedly the most promising heating methods.MWH affects the fermentation time of the dough by affecting the water molecules in the dough,and may also improve the fermentation quality of wholewheat flour products.RFH contributes to the control of harmful substances in the fermentation process and has shown potential for the production of sourdough bread.OH has superiority in accurately controlling the temperature,enzymes,microorganisms,etc.in the fermentation process,and it is beneficial to shortening the fermentation time.Researchers have applied these heating methods with different properties to different uses.This article summarized the application and potential of these three novel heating methods in the production of fermented flour products.The application scenarios and parameter settings of novel heating technologies in dough fermentation process need further research.It is reasonable to believe that novel heating methods can become an important tool to improve the efficiency of dough fermentation and the quality of fermented dough in the future.

Sawtooth Activity in Ohmically Heated Plasma on HT-7 Tokamak

Sawtooth activity on HT-7 tokamak has been investigated experimentally mainly by using soft x-ray diode array and magnetic probes. Their behaviors and occurrences are correlated closely to the discharge conditions: the electron density Ne, the electron temperature Te, the safety factor qa on plasma boundary and wall condition etc. When central line-averaged electron density Ne(0) is over 2.0×1013cm-3 , major sawtooth activity emerges with a period of up to 6.5 ms and a fluctuation amplitude of up to 2-30 % of SXR radiation signal. In some cases such as the safety factor between 4.2-4.7 and Zeff=3.0-6.0, a monster sawtooth activity often emerges without apparent deterioration of plasma confinement and without major disruption. During these events, abundant MHD phenomena are observed including partial sawtooth oscillations. In this paper, the observed sawtooth behaviors and their dependence on the and their dependence density Ne and wall condition in ohmically heated plasma are introduced, the results are discussed and presented.

Monster Sawtooth Activity in Ohmically Heated HT-7 Plasma

Experimental properties of monster sawtooth activities in ohmic HT-7 plasma are presented in this paper. The monster sawtooth activities belong to global fluctuations and are characterized with a series of large core collapses on SXR intensity traces with a long period, a large amplitude fluctuation and a large inversion radius. However, they emerge without apparent deterioration of plasma confinement and without major plasma disruption. During the events, long partial sawtooth collapses and abundant MHD phenomena are also observed.

Initial Plasma Startup Test on SUNIST Spherical Tokamak

The goal of the Sino-United Spherical Tokamak (SUNIST) at Tsinghua University is to extend the understanding of toroidal plasma physics at a low aspect ratio (R/a≈1.3) and to demonstrate a maintainable target plasma by non-inductive startup. The SUNIST device is designed to operate with up to 13 kA of ohmic heating field current, and to 0.15 T of toroidal field at 10 kA of discharge current. All of the poloidal fields can provide 30 mVs of Volt-seconds transformer. Experimental results of plasma startup show that SUNIST has remarkable characteristics of high ramp rate (dIp/dt≈50 MA/s ), high normalized current In of about 2.8 (In = Ip/αBt), and high-efficiency (Ip/Irod ≈0.4) production of plasma current while operating at a low toroidal field. Major disruption phenomena have not been observed from magnetic diagnostics of all testing shots. Initial discharges with 52 kA of plasma current (exceeding the designed value of 50 kA), 2 ms of pulse length and 50 MA/s of ramp rate have been achieved easily with pre-ionized filament.

Estimation model for electrical conductivity of red grape juice

The equations for predicting the electrical conductivities of red grape juice at different concentrations have been evaluated in this study.Three samples of red grape juice having concentrations of 10.5,12.5 and 14.5°Brix were ohmically heated by applying three different voltage gradients(10,12 and 15 V/cm)in the temperature range of 25-80℃.The mathematical models using multiple linear regression analysis indicated that electrical conductivity depended on temperature and concentration.The predictions of electrical conductivities using the mathematical models was found to be highly accurate with R2 value of 0.9975 when compared with the experimental data of red grape juice with concentration of 11.5°Brix.The reducing chi-square(χ^(2))and the root mean square error(RMSE)from the mathematical models were calculated and compared with the experimental data.As the results,multiple linear regressions on the coefficients of the mathematical model of electrical conductivity prediction have given highest values of the R2 and lowestχ^(2)and RMSE so the established model was confirmed as highly accurate when estimating electrical conductivities of red grape juice.

STUDY OF FREE BURNING ARC CHARACTERISTICS BY DIMENSIONAL ANALYSIS AND COMPUTER SIMULATION

This paper deals with the study of experimental current intensity/voltage characteristicsof a free burning arc that appears to be singular:At low intensity current,the arc voltagedecreases until a minimum value,corresponding to a critical current intensity Ic.Forcurrent intensities higher than Ic,there is an increase of the arc voltage with the currentintensity.Dimensional analysis and Pi theorem coupled with a large set of experimentaldata allow us to evaluate the main physical processes responsible for the characteristicsshape.At low current intensity,the plasma is mostly driven by thermal conduction effectswhile at high current intensity,it is principally governed by radiation losses.Finally,theresults obtained from dimensional analysis allow to propose a 1D numerical simulationof the plasma column that gives rather good qualitative results.