Hz Operation Research Articles

Numerical Analysis of a Modified Type Pulse Tube Refrigerator

Abstract The loss generated due to direct current gas flow in pulse tube refrigerator (PTR) is one of the major problems which significantly affect the cooling performance. It generates temperature fluctuation at the cold end of the PTR. A new type PTR has been proposed in the present work to diminish the DC flow problem by attaching an additional connection at the hot end from a secondary compressor and investigated numerically using CFD simulation software FLUENT. It is reported a significant enhancement of cooling performance by means of the proposed model. The numerical outcomes of the proposed model are equated with the outcomes of the orifice type pulse tube refrigerator (OPTR) model. The model used for analysis is an axisymmetric model. At 34 Hz operating frequency and 1.2 pressure ratio the numerical simulation is conducted. The proposed model achieves a temperature of 98 K at cold end where as a simple OPTR having same dimension riches a temperature of 130 K. To get an optimum result experimentally for the pulse tube refrigerator, is a very difficult and also high expensive hence the numerical approach is an alternate solution.

Optimized blue-phase liquid crystal for field-sequential-color displays

We report an optimized blue phase liquid crystal (BPLC) mixture JC-BP08 for field-sequential-color (FSC) display applications. JC-BP08 exhibits several attractive features: 1) its fast average gray-to-gray response time enables FSC display, which in turn triples the resolution density and optical efficiency. 2) Its voltage holding ratio is >99.4% at 25°C and >93.2% at 60°C. 3) Its average dielectric constant e’≈87 is still manageable by the bootstrapping driving to enable 240 Hz operation. 4) Using a triangular protrusion electrode structure, the transmittance can reach 74% at 15V, which enables single-TFT driving. 5) With two-domain structure, it offers indistinguishable gamma shift and wide viewing angle. We proposed a voltage charging model and found a linear relationship between the required charging time and e’, which is validated by our experimental results.

Influence of stack geometry on the performance of thermoacoustic refrigerator

The work reported in this paper is focused on the performance of a thermoacoustic refrigerator under various operating conditions. The experiments were conducted with various stack geometries fabricated with epoxy glass and Mylar material. Four stacks with different pore sizes are used to evaluate the performance of the refrigerator. Stack 1 has parallel plates of Mylar material 0.12 mm thick spaced 0.36 mm apart. Stacks 2, 3 and 4 are made of epoxy glass with pores of circular cross-section having 1, 2 and 3 mm diameter, respectively. The entire resonator system was constructed from aluminium material coated with polyurethane material from inside to reduce conduction heat losses. Helium gas was used as a working fluid. The experiments were conducted with different drive ratios ranging from 1.6% to 2% with varying cooling load from 2 to 10 W. For the experiments, operating frequencies from 200 to 600 Hz with mean pressure varying from 2 to 10 bar in steps of 2 bar each were considered. The temperatures of the hot end and cold end of the heat exchangers were recorded using RTDs and a data acquisition system under various operating conditions. The coefficient of performance (COP) and relative COP (COPR) are evaluated. Results show that COP of the refrigerator rises with increase of cooling load and decreases at higher drive ratio. It was also observed that the temperature difference between the hot end and cold end of the stack is higher at 2 W cooling load for 400 Hz operating frequency. The temperature difference between the hot end and cold end of the stack was observed to be 19.4, 17.2, 14 and 12.4°C for stacks 1, 2, 3 and 4, respectively, for 10 bar mean pressure and 2 W cooling load. The temperature difference and COP of the parallel plate stack are better compared with other stack geometries.

Reducing current noise in cryogenic experiments by vacuum-insulated cables.

We measure the current noise of several cryogenic cables in a pulse tube based dilution refrigerator at frequencies between about 1 mHz and 50 kHz. We show that vibration-induced noise can be efficiently suppressed by using vacuum-insulated cables between room temperature and the 2nd pulse tube stage. A noise peak below 4 fA at the 1.4 Hz operation frequency of the pulse tube and a white noise density of 0.44 fA/Hz in the millihertz range are obtained.

High energy, high repetition rate, second harmonic generation in large aperture DKDP, YCOB, and LBO crystals.

We report on type-I phase-matched second harmonic generation (SHG) in three nonlinear crystals: DKDP (98% deuteration), YCOB (XZ plane), and LBO (XY plane), of 8 J, 10 Hz cryogenic gas cooled Yb:YAG laser operating at 1029.5 nm. DKDP exhibited an efficiency of 45% at a peak fundamental intensity of 0.24 GW/cm2 for 10 Hz operation at 10 ns. At the same intensity and repetition rate, YCOB and LBO showed 50% and 65% conversion efficiencies, respectively. Significant improvement in conversion efficiency, to a maximum of 82%, was demonstrated in LBO at 0.7 GW/cm2 and 10 Hz, generating output energy of 5.6 J at 514.75 nm, without damage or degradation. However, no improvement in conversion efficiency was recorded for YCOB at this increased intensity. Additionally, we present theoretically calculated temperature maps for both 10 J and 100 J operation at 10 Hz, and discuss the suitability of these three crystals for frequency conversion of a 100 J, 10 Hz diode pumped solid state laser (DPSSL).

A scalable high-energy diode-pumped solid state laser for laser-plasma interaction science and applications

Laser systems efficiently generating nanosecond pules at kJ energy levels and at multi-Hz repetition rates are required in order to translate laser-plasma interactions into practical applications. We have developed a scalable, actively-cooled diode-pumped solid state laser amplifier design based on a multi-slab ceramic Yb:YAG architecture called DiPOLE (Diode-Pumped Optical Laser for Experiments) capable of meeting such requirements. We demonstrated 10.8 J, 10 Hz operation at 1030 nm using a scaled-down prototype, reaching an optical-to-optical efficiency of 22.5%. Preliminary results from a larger scale version, delivering 100 J pulse energy at 10 Hz, are also presented.

Modeling and Simulation of Electrical Resonance in EHV Transmission Line Case Study in West Java Region 500 kV System

Electrical transmission line can be approached by the second order system with the model of capacitive, inductive, and resistive elements. In the system, the capacitive element is represented by the capacitance value between phases and phase to ground. In the other side, inductance of reactor and phase conductor represent the inductance element, whereas resistance of the phase conductor represents the resistance value of the system. As a second order system, the electrical transmission line is potentially experiencing the resonance phenomena if the natural frequency reaches the 50 Hz operation frequency. This paper explains the study of resonance phenomena in Extra High Voltage (EHV) 500 kV transmission line between two 500 kV Substation in West Java Region by the modeling and simulation. The results show that the transmission line is very vulnerable to the resonance phenomenon which is indicated by the existence of voltage up to 800 kV when this transmission line is not yet energized and causing one of the line arrester broken. The results also show that under the resonance phenomena, single pole auto reclose process is potentially failed. This study is expected to increase the concern for the resonance phenomena in the transmission lines.

Dense Plasma Focus Device Based High Growth Rate Room Temperature Synthesis of Nanostructured Zinc Oxide Thin Films

High-energy-density plasmas in plasma focus device are now routinely being used as nonconventional plasma nanotechnology tool with novel processing and deposition parameters which are not available in conventional lowtemperature plasma facilities. This paper reports the synthesis of multilayered polycrystalline intrinsic defects-free nanostructured zinc oxide (ZnO) thin film onto room-temperature silicon substrates at high growth rates using pulsed high-energy-density dense plasma focus device. The device was operated in pure oxygen environment and the ablation target used was a pure zinc rod fitted onto the anode top. Thin films of ZnO were deposited at room temperature using different numbers of dense plasma focus shots and at different distances from the anode top. The as-deposited ZnO showed the formation of polycrystalline hexagonal phase ZnO thin films with strong c-axis orientation. The scanning electron microscopy results showed either uniformly laid nanoparticles or cauliflower aggregates of nanoparticles on the surface of the thin-film samples with average nanoparticle size varying between 23.3 ± 6.1 and 69.7 ± 16.5 nm. The average thicknesses of the multilayered thin films were measured to be in a range of 1.06 ± 0.14 to about 2.82 ± 0.32 μm. The complete disappearance of deep level emission band in photoluminescence spectrum of ZnO thin-film sample deposited using 30 focus shots at deposition distance of 15 cm showed successful synthesis of high crystalline quality intrinsic defects-free as-deposited ZnO thin film. One of the key features of the ZnO thin-film synthesis using nonconventional plasma focus device is the very high average growth rate of about 0.1 μm/shot. At one plasma focus shot per minute operation, the average growth rate comes out to be 0.1 μm/min, which is either higher or comparable with commonly used ZnO deposition methods; but at 10 Hz operation extreme growth rates of about 60 μm/min could be achieved.

High responsivity of pyroelectric infrared detector based on ultra-thin (10 μm) LiTaO3

Ultra-thin (10 μm) lithium tantalate crystal (LiTaO3) was used as sensitive layer in high responsivity room temperature pyroelectric infrared detector. The responsivity reaches 1.22 × 105 V/W and the noise equivalent power value reaches as low as 7.52 × 10−11 W at 20 Hz operating frequency by using blackbody radiation. The responsivity rate of the pyroelectric infrared detector can be enhanced. It provides a feasible approach for fabricating high response rate pyroelectric infrared sensor and infrared imaging application.

Performance Analysis of Varied Dimensions Piezoelectric Energy Harvester

Thin film piezoelectric material plays a vital role in micro-electromechanical systems (MEMS), due to its low power requirements and the availability of high energy harvesting. Zinc oxide is selected for piezoelectric material because of its high piezoelectric coupling coefficient, easy to deposit on silicon substrate and excellent adhesion. Deposited ZnO and Al improve the electrical properties, electrical conductivity and thermal stability. The design, fabrication and experimental test of fabricated MEMS piezoelectric cantilever beams operating in d33 mode were presented in this paper. PVD (Physical Vapor Deposition) was selected as the deposition method for aluminium while spincoating was chosen to deposit ZnO thin film. The piezoelectric cantilever beam is arranged with self-developed experimental setup consisting of DC motor and oscilloscope. Based on experimental result, the longer length of piezoelectric cantilever beam produce higher output voltage at oscilloscope. The piezoelectric cantilevers generated output voltages which were from 2.2 mV to 8.8 mV at 50 Hz operation frequency. One of four samples achieved in range of desired output voltage, 1-3 mV and the rest samples produced a higher output voltage. The output voltage is adequate for a very low power wireless sensing nodes as a substitute energy source to classic batteries.

Experimental Study of Ejectors’ Effect on the Performance of Pulse Detonation Rocket Engine

Experimental studies were performed to investigate the ejector’s effect on the performance of a pulse detonation rocket engine (PDRE). The PDRE employed in the experiments utilizes gasoline as fuel and air as oxidizer. The operating frequency of the PDRE is 10 and 20 Hz respectively. Performance is quantified by thrust measurements, and the average thrust of the PDRE is obtained by integration of the thrust measured in the experiment. The experimental results show that the PDRE can increase thrust augmentation with an ejector, a maximum thrust augmentation is measured by 18.7% at 10 Hz operating frequency. In the experiment, axial placement (X/DPDRE) of the ejector is varied downstream the PDRE tube of 0.5,1 and 2 respectively. It is found that the thrust augmentation obviously increases when the relative position at 1 and 2, and also the thrust augmentation increases at higher operating frequency. The experiment result is useful for the development of a PDRE producing higher thrust.

Preparation of room temperature terahertz detector with lithium tantalate crystal and thin film

Research on room temperature terahertz (THz) detector is essential for promoting the application of THz science and technology. Both lithium tantalate crystal (LiTaO3) and lithium tantalate thin film were used to fabricate the THz detector in this paper. Polishing process were used to reduce the thickness of LiTaO3 crystal slice by chemical mechanical polishing techniques and an improved sol-gel process was used to obtain high concentration LiTaO3 precursor solution to fabricate LiTaO3 thin film. Three dimension models of two THz detectors were set up and the temperature increasing map of two devices were simulated using finite element method. The lowest noise equivalent power value for terahertz detector using pyroelectric material reaches 6.8 × 10−9 W at 30 Hz operating frequency, which is suitable for THz imaging application.

Paper No P7: A LTPS TFT Compensation Pixel Circuit for Simultaneous Emission Driving High‐Definition AMOLED Display

AbstractWe have proposed a new active organic light‐emitting diode display (AMOLED) pixel design, which is suitable for the simultaneous emission driving high definition AMOLED. In the previous work, the pixel structure could be simplified with the simultaneous emission driving compared to the widely used progressive emission driving. However, the flickering was observed. The proposed pixel circuit can suppress the flickering because 120 Hz operation is possible. The SPICE simulation results show that the proposed pixel successfully compensates Vth.

Low voltage, low energy, and repetitive (4 Hz) operation of a conventional vircator for microwave emission in the range of 4–8 GHz

AbstractIn this paper, we are presenting the microwave emission results of a vircator that emits its radiation lying well-within the microwave range of electromagnetic spectrum viz 4–8 GHz and the energy needed per shot is as low as 25 Joules only. In this reported experiment, the pulse forming line is charged to a voltage of 160 kV and the measured diode voltage is 50 kV in the experiment. The primary energy is nearly 50 Joules only and hence the energy efficiency of the high voltage pulse transformer and pulse forming line combination for the given experiment is nearly 50%. The experiment is the first of its kind in establishing (experimentally) the low voltage operation of a conventional vircator, which has a planar cylindrical cathode and stainless steel mesh anode, for the microwave emission purpose. Moreover, because of the low voltage and low energy operation we could operate the whole system in repetitive mode and we could achieve as high as 4 Hz operation with this device. Interestingly, the current density of the velvet cathode used in the present experiment is nearly 300 A/cm2 in the present reported set of experiments. One interesting observation emerging out from the present experiment is that in the low voltage operation of the vircator the beam acceleration potential is relatively low and hence the axial velocities of reflexing electrons (trapped between cathode and virtual cathode) is also limited and far less than 1.8 × 108 m/s and hence with small anode cathode gaps like that of 3 mm, which is the case of present experiments, it becomes feasible to achieve radiation frequency of 4–8 GHz from the vircator.

Design Optimization, Series Production, and Testing of the SIS100 Superconducting Magnets for FAIR

SIS100, the core machine of the FAIR project, is being realized now, with the dipole series already ordered. This machine uses fast ramped superconducting dipole magnets (4 T/s, 1 Hz operation cycle), which were optimized to reduce the ac loss and to provide adequate end fields. We present the actual status of the design optimization for the superconducting main magnets as well as of the corrector magnet units. Their series production is now launched and the testing strategy is clarified. The key issues of ac loss minimization, hydraulic resistance, and test facility built is discussed.

Apodized distributed feedback fiber laser with asymmetrical outputs for multiplexed sensing applications

The spectral characteristics of four different types of apodized fiber Bragg gratings with a single π phase shift are analyzed based on the simulation. The 2-discrete Gaussian apodization is proved to have the most effective suppression to grating side mode. A novel asymmetrical distributed feedback fiber laser based on this apodization structure is presented and fabricated as well. The grating has a -20 dB side-mode suppression. The laser exhibits a high power ratio of backward to forward outputs. It has a relative intensity noise of -90 dB/Hz and a linewidth of 20k Hz operating in a single polarization longitudinal mode.

Driving Scheme Using Bootstrapping Method for Blue-Phase LCDs

We present a new pixel circuit on glass using hydrogenated amorphous silicon (a-Si:H) for driving polymer-stabilized blue-phase liquid crystal displays (BPLCDs). Different from conventional nematics, BPLC demands a large dielectric anisotropy in order to lower the operation voltage. As a result, the pixel's capacitance is increased by ~ 10×, which seriously limits the charging capability and optical efficiency. Simulation results show that the average error rate of storage voltage in pixel circuit is below 5.14% for 180 Hz operating frequency.

Frequency Dependency of Multi-layer OLED Current Density-voltage Shift and Its Application to Digitally-driven AMOLED

We report, for the first time, operation frequency dependence of current density-voltage (<TEX>$J_{OLED}-V_{OLED}$</TEX>) shift for multi-layer organic light-emitting diodes (OLEDs). When the OLEDs were electrically stressed for 21 hours with 50% duty voltage pulses at 60, 120, 240, and 360 Hz, the JOLED-VOLED shifts were suppressed by half for 360 Hz operation compared with 60 Hz operation, but with little change in emission efficiencies. This frequency dependent <TEX>$J_{OLED}-V_{OLED}$</TEX> shift is believed to be commonly observed for typical multi-layer OLEDs and can be used to further improve lifetime of digitally-driven active-matrix OLED displays.

Low energy prepulse for 10 Hz operation of a soft-x-ray laser

The influence on Nickel-like Molybdenum soft-x-ray laser performance and stability of a low energy laser prepulse arriving prior to the main laser pumping pulses is experimentally investigated. A promising regime for 10 Hz operation has been observed. A four times increase in soft-x-ray laser operation time with a same target surface is demonstrated. This soft-x-ray laser operation mode corresponds to an optimum delay between the prepulse and the main pulses and to a prepulse energy greater than 20 mJ. We also show that this regime is not associated with a weaker degradation of the target or any reduced ablation rate. Therefore the role of preplasma density gradient in this effect is discussed.

Segment side-pumped Q-switched Nd:YAG laser

In the design of conduction-cooled lasers, a side-pumped configuration is an attempt to solve the space conflict between pump and heat removal. The pump radiation always competes with the heat removal and mechanical support device for the lateral surface of a laser rod. This space conflict can be addressed by a segment side-pumped configuration in which circular laser diode arrays and heat-conducting rod holders alternate periodically along the length of the laser rod. This scheme permitted 11 Hz operation of a 190 mJ Q-switched laser at the wavelength of 1064 nm without the use of liquid cooling for both the laser rod and laser diode arrays and the corresponding optical-optical conversion efficiency of 23.1%. Thus, it has great potential to be used in compact and miniature laser systems.