Small Experimental Device Research Articles

A novel plasma source concept for negative ion generation in neutral beam injectors for fusion applications

Abstract A low-temperature plasma can very well be confined by a simple magnetic dipole, such as in the Van Allen belts of Earth’s magnetoshpere. This configuration can be reproduced in laboratory as a small experimental device, designed in such a way that the magnetic field lines remain within a vacuum-tight container and are virtually not intercepted by the container wall. In this paper we propose to use a dipole field for the realization of an efficient negative Ion source. To this purpose, we analyze the plasma confinement capabilities of such plasma source, in order to assess the equilibrium pressure and estimate the particle trajectories and drifts.

Heat leak of cryogenic pipe for superconducting dc power transmission line (SCDC)

Main loss of the superconducting DC power transmission line (SCDC) comes from the heat leak of the cryogenic pipe because of no internal heat generation in the dc cable. It should be minimized to realize the high performance of SCDC. The heat leak of the cryogenic pipe depends on the ambient temperature, and when it is high, the heat leak is also high. Therefore, we estimated the sensitivity of the heat leak for the ambient temperature at first, and estimated the effect of this for the distance between the cryogenic stations. The major process of the heat leak is the heat transfer through the multi-layer insulation (MLI) and the second process is the thermal conduction of the support leg of the inner pipe in our design. The MLI is made from the multi-layers of the aluminium-coated thin film (ACTF) with the spacer, and the support leg is made of the glass fiber reinforced plastic (GFRP). The aluminium layer reflects the infrared light highly to reduce the heat transfer by radiation, and the spacer can prevent the direct contact with the ACTF. Therefore, the weight of the MLI should be light to minimize the thermal transfer of the spacer. We tested various types of MLI to find the optimum MLI structure experimentally. Usually, the measurement of the heat leak is not easy in an actual cryogenic pipe and we need the long experiment time and a relatively large instrument to evaluate the heat leak. However, since we need to evaluate many MLIs, we developed the different way to estimate the heat leak through the MLI by a small experimental device. To find the optimum MLI, we started to test three samples of the MLI supplied from Kaneka Corp., and measured the temperature of the MLI. Since the heat capacity of MLI is low, we used the 50-micron meters thermocouple (TC) and attached it to measure the temperature of the MLI carefully. The result of the experiment shows that we found that the net type of the spacer is better than the spacer used in Ishikari project, and the heat leak would be half of the Ishikari project. We also measured the thermal conductivity of two test samples of GFRP to reduce the heat conductions of the support leg. The thermal conduction of these two GFRPs are almost 1/2 to 1/4 of the recommended values of the NIST. Because of these efforts to reduce the heat leak of the cryogenic pipe, we can expect the target values of the heat leak is a half of the Ishikari project in the next project, and if we can reach this value, we can extend the distance of the cryogenic stations to ∼100km actually on the earth. The values of this distance is important to transfer the electricity for all over the world like the gas and oil pipeline in the present time.

Influence of thermal stratification by fire on heat-mass coupling response mechanism of the liquefied tank

In order to study the explosion-inducing process and thermal response of fire-induced BLEVE(boiling liquid expanding vapor explosion), a small experimental device was established. The radiant heating source was used to simulate the external fire heat effect, and superheated water was used as the medium. The pneumatic ball valve was used to simulate the leakage action. The gas-liquid flow, internal pressure and temperature transient response of the tank during the heating and venting processes were measured, and the superheated process of the medium in the tank was analyzed. The temperature-pressure coupling response after the explosion was traced to investigate the thermal action of the fire on the tank. The experiment found that the heating of the storage tank was the generation and gradual disappearance of temperature stratification. The crack action would result in the breaking of phase equilibrium and pressure rebound. There was an overheat delay in the detonation, and the temperature stratification would prolong the overheat time of the medium. There was a lower limit for the occurrence of the BLEVE accident, the critical stratification degree was used to quantify the limit and the limit of this experimental condition was ξ≤2.33.

Challenges facing high-field tokamaks

David Kramer wrote an interesting report on high-magnetic-field fusion devices for the August 2018 issue of Physics Today (page 25). The high magnetic field certainly does shrink the device’s plasma volume, but high magnetic field is a double-edged sword. It has significant disadvantages. The story points out only one: the increased pressure on the field coils.Another disadvantage is that as one shrinks the device, the neutron wall loading increases. Take SPARC, the tokamak being developed by Commonwealth Fusion Systems (CFS). It has 1/70 the volume of ITER, the international prototype fusion energy reactor, but 10 times the power density. Whereas ITER hopes to achieve 500 MW of neutron power, SPARC hopes to achieve about 70 MW. If one assumes surface area scales as the 2/3 power of volume, SPARC’s surface area is about 1/17 of ITER’s. Hence SPARC, a small experimental device, will have about 2.5 times ITER’s wall loading of about 1 MW/m2! The problem will only get worse as CFS moves to devices like the ARC (affordable, robust, compact) reactor, which will produce commercially interesting amounts of power. Wall loading is a big issue, not a minor detail, in fusion physics.In addition, whereas the plasma scales to smaller size with increasing magnetic field, the fusion blanket does not. No matter what the magnetic field, the blanket has to prevent leakage of uncharged neutrons out the other end. The minimum blanket thickness I have seen is about one and a half meters thick. The blanket alone dictates some minimum size for a power-producing fusion device. It is difficult to see how shrinking the minor radius to below a meter buys you very much if the blanket thickness is one and a half meters. That could be a problem especially for the Tokamak Energy device, a spherical tokamak, which relies on a thin center post that must remain superconducting in the presence of an intense neutron flux.To me, the most important advantage of using high-temperature superconductors (HTS), whether at 5 T or 10 T, is a point Kramer mentions in passing at the end. Namely, the magnets could be disassembled and reassembled rather easily. Since I first heard of tokamaks a half century ago, the story has always been that because of the interlocking coil arrangement, one could not do maintenance on them. The new HTS magnets, in one fell swoop, may have solved that issue. To me, that is the really big deal. Section:ChooseTop of page <<CITING ARTICLES© 2019 American Institute of Physics.

Specifics of phytomass combustion in small experimental device

A wood pellet combustion carries out with high efficiency and comfort in modern pellet boilers. These facts help to increase the amount of installed pellet boilers in households. The combustion process quality depends besides the combustion conditions also on the fuel quality. The wood pellets, which don`t contain the bark and branches represent the highest quality. Because of growing pellet demand, an herbal biomass (phytomass), which is usually an agricultural by-product becomes economically attractive for pellet production. Although the phytomass has the net calorific value relatively slightly lower than the wood biomass, it is often significantly worse in view of the combustion process and an emission production. The combustion of phytomass pellets causes various difficulties in small heat sources, mainly due to a sintering of fuel residues. We want to avoid the ash sintering by a lowering of temperature in the combustion chamber below the ash sintering temperature of phytomass via the modification of a burner design. For research of the phytomass combustion process in the small boilers is constructed the experimental combustion device. There will investigate the impact of cooling intensity of the combustion chamber on the combustion process and emissions. Arising specific requirements from the measurement will be the basis for the design of the pellet burner and for the setting of operating parameters to the trouble-free phytomass combustion was guaranteed.

Research on forming precision of flexible rolling method for three-dimensional surface parts through simulation

Flexible rolling is a novel forming process for three-dimensional surface parts using a pair of bendable rolls. By controlling the distribution of the gap between the upper and lower forming rolls in the rolling process, the sheet metal is nonuniformly thinned in the thickness direction and the longitudinal elongation is different in the width direction of the sheet metal, which makes the sheet metal deform in rolling direction. With the rotation of the bendable rolls, the sheet metal is deformed consecutively and a three-dimensional surface part could be obtained. A small experimental device has been designed. Finite element analysis (FEA) model is established. Spherical surface and saddle surface are simulated, and their experimental results are presented. The major purpose of the present work is to analyze the forming precision of flexible rolling and the reasons for the shape errors through simulated and experimental results. The results demonstrate that the proposed process is a feasible and effective way of forming three-dimensional surface parts.

Flow Behaviors Study on Superheated Steam Fluidized Bed Drying

In the paper, we theoretical analysis the gas-particle flow behaviors in the drying chamber. Then establish a small experimental device and conduct a comparative fluidization experiment with superheated steam and hot air, which the dried rapeseed particles are the experimental material. The critical fluidizing velocity of the rapeseed particles in superheated steam is 1.26 m/s in the experimental condition. The experimental results show that the inlet operating flow velocity of superheated steam fluidized bed drying is greater than which of the traditional hot air fluidized bed dying under the same conditions.

Research on the Oil-Gas-Water Three-Phase Flow Experimental Apparatus

The oil-gas-water three-phase flow experimental apparatus in key laboratory of process monitoring and control in Tianjin University is a set of indoor small experimental device, which can simulate oil wells, simulate the pipeline transport of multiphase flow and study the experiment of multiphase flow. The device includes energy power dynamic systems, measurement pipelines systems, multiphase flow test pipelines system, control valves, sampling and control system platform. The software of the control system is mixed programming between the configuration software MCGS and the Visual Basic.

Development of a four-grade and four-segment electrodialysis setup for desalination of polymer-flooding produced water

An electrodialysis (ED) setup with an 11 m 3/h water treatment scale was designed based on a small experimental device. The setup adopts four-grade and four-segment (four-GS) reversal electrodialysis (EDR) technology to desalinate polymer-flooding produced water (PFPW). The removal rate of total dissolved solids (TDS) with different flow rates was measured with different grades and segments. The operating performance of this setup was determined to meet design standards. The maximum treatment capacity and the optimal operation conditions of the tested setup were studied. The design standards were met only by adopting a four-GS ED setup. The maximal capacity of the four-GS ED setup for treating PFPW was 5 m 3/h. The optimal operating condition and results were at an operating electric current of 86 A, 62.5% production rate of diluted treated PFPW, 0.89 kW∙h/m 3 energy consumption, and 78.7% TDS removal rate. Under optimal conditions, the treated PFPW has two beneficial uses. First, the diluted treated PFPW is feasible for preparing polymer solutions. Second, the concentrated treated PFPW is feasible for replacing the original PFPW as the injecting water in the water-flooding process for high permeability layers.

Demonstration of the stress-minimized force-balanced coil concept for SMES

Strong electromagnetic force caused by high magnetic field and coil current is a serious problem in SMES systems. In facing this problem, we proposed the concept of Force-Balanced Coil (FBC) which is a helically wound toroidal coil. Based on the virial theorem, the FBC can minimize structure requirements for energy storage by selecting an optimal number of poloidal turns. We designed and fabricated a small experimental device which is composed of inner and outer helical coils mutually wound in opposite toroidal directions using NbTi superconductors. The distribution of the working stresses in this device can be changed by selecting the optimal current ratios between inner and outer coil currents. From the experimental results, we demonstrated the validity of the FBC concept.

Magnetic circuit switching element with superconducting coil

In an existing power system, high-current circuit breakers are widely used. Meanwhile, we propose a new switching device using a switching of magnetic paths. It is a magnetic circuit switch activated by on/off of superconducting coils wound on iron core-legs. We have carried out an experiment using a small experimental device with two superconducting coils (control coils). When the control coil is shorted, the voltage of the output coil in the shorted side becomes 0 V because the magnetic flux is blocked completely by the induced shielding current of the superconducting coil. It was confirmed that the current of the superconducting coil is decided by the turn-ratio of the coils both experimentally and theoretically. Therefore, it was assured that any tremendous overcurrent does not flow in the shorted superconducting control coils. After this, we applied this device into a model of two-circuit transmission system and confirmed the fundamental behavior in case of a line fault. The experimental result shows that the fault current is suppressed almost perfectly and the transmission system can continue the power transmission without any intermission.

Stability improvement of AC superconducting magnet by forced-convection cooling

The authors propose a new improved cooling system of an AC(50/60 Hz) superconducting magnet introducing a forced-convection flow of liquid helium. In this system, the flow through the cooling channel between the winding layers is generated by a screw rotating in a cylinder surrounding the magnet. A small experimental device composed of an AC superconducting magnet and a rotating screw was manufactured. The screw was rotated by an extended driving shaft. The experimental result shows that the stability of the magnet is improved by the rotation of the screw. That is, the thermal disturbance (heater input power) which generates the quench of the magnet increases as the rotational speed of the screw does. It is expected that this technique can be successfully applied to superconducting AC power apparatuses as transformers or reactors.