Two- and Multi-bucket X-ray Free-Electron Laser at LCLS

X-ray Free Electron Lasers provide femtosecond X-ray pulses with narrow bandwidth and unprecedented peak brightness. Special modes of operation have been developed to deliver double pulses for X-ray pump, X-ray probe experiments. However, the longest delay between the two pulses achieved with existing single bucket methods is less than 1 picosecond, thus preventing exploration of longer timescales dynamics. We present a novel Two-bucket scheme covering delays from 350 picoseconds to hundreds of nanoseconds in discrete steps of 350 picoseconds. Performance for each pulse can be similar to the one in single pulse operation. The method has been experimentally tested with LCLS-I and LCLS-II hard x-ray undulators.

Bias Polarity Dependent Threshold Switching and Bipolar Resistive Switching of TiN/TaOx/ITO Device

In this work, we demonstrate the threshold switching and bipolar resistive switching with non-volatile property of TiN/TaOx/indium tin oxide (ITO) memristor device. The intrinsic switching of TaOx is preferred when a positive bias is applied to the TiN electrode in which the threshold switching with volatile property is observed. On the other hand, indium diffusion could cause resistive switching by formation and rupture of metallic conducting filament when a positive bias and a negative bias are applied to the ITO electrode for set and reset processes. The bipolar resistive switching occurs both with the compliance current and without the compliance current. The conduction mechanism of low-resistance state (LRS) and high-resistance state (HRS) are dominated by Ohmic conduction and Schottky emission, respectively. Finally, threshold switching and bipolar resistive switching are verified by pulse operation.

Mid IR Holmium, Praseodymium - doped Fluoride Fiber Laser Pulse Operation

Pulsed operation of a novel single-clad mid IR Ho3+, Pr3+ co-doped ZBLAN fiber laser ‎excited by a Nd:YAG laser at 1064 nm has been demonstrated using pulse-pumping. An acousto-optic modulator (AOM) has been used to modulate the CW input pump ‎laser and used in either zero-order or first-order operation. A regular output train of pulses was generated for modulation frequencies over 1 Hz - 100 kHz ‎with zero-order operation of the AOM. A maximum peak power of ~ 50 W and pulse ‎duration of ~200 ns have been obtained for a modulation frequency of 45 kHz and 9.3 ‎W pump power. Single-end and double-end pumping of the ‎first-order AOM operation for the fiber have also been demonstrated to avoid the overheating of the modulator which ‎reduces the modulation efficiency. The same results as the zero AOM operation were obtained when the fiber laser was pumped with a pumping power of about 5 watts. Keywords: Fiber lasers, Pump pulsed operation, Acousto-optic modulator (AOM), Single-end and double-end pumping. PACs: Fiber lasers, 42.55.Wd, Acousto-optical devices, 42.79.Jq.

Performance Improvement of Thermoelectric Air Cooler System by Using Variable-Pulse Current for Building Applications

The thermoelectric air conditioning system (TE-AC) is a small, noiseless alternative to standard vapor compression refrigeration (VCR) systems. The cooling characteristics of a TE-AC system operating under two conditions, i.e., steady current and current pulses, are investigated in this study. This system consists of three thermoelectric modules, a heat sink, and an air circulation fan. The result shows that maximum temperature reduction in cooling side of TE-AC system was achieved at 6 A input current under steady state operation. The optimum performance of the TE-AC system under steady state operation depends upon the combined effect of the cooling load, Joule, Fourier, and Peltier heat. In TE-AC pulse operation, both current width and cooling load applied on the cold side of the thermoelectric module (TEMs) play an important role in achieving optimum cooling performance of the system. When normal input current operation (i.e., no current pulse) was compared to pulse-operated TE-AC system operation, it was found that pulse operation provides an additional average temperature reduction of 3–4 °C on the cold side of TEMs. Although on the hot side, it maintains a temperature in the range of 18 °C to 24 °C to reduce overshoot heat flux. The duration of operation is also important in determining pulse width and pulse amplitude. Minimum and overshoot peak temperature rises during each cycle for longer run operation. In the TE-AC system, the accumulated Joule heat during a current pulse frequently causes a temperature overshoot, which lasts much longer. As a result, the next current pulse was not released until the temperature of TE was restored to its initial value.

Arc Welding Current Control Using Thyristor Based Three-Phase Rectifiers Applied to Gas Metal Arc Welding Connected to Grid Network

The purpose of the welding operation is to ensure the continuity of the materials to be assembled in large industrial sectors. This study aims to suggest a topology of the Thyristor based three-phase rectifiers applied to the Gas Metal Arc Welding (GMAW) process connected to the grid network, the output currents are controlled and using various pulsed forms such as square, annealing, and spike pulse operations and investigate and compare between the effects of the three references welding currents structures on the welding current, welding voltage, droplet diameter, and welding quality. To have the best pulse operation, the amplitude and frequency are kept the same for all operations, the application of meshing graphs in the references of welding currents structures, welding current, welding voltage, and droplet diameter can illustrate a clear comparison between them. The simulation results show that the square pulse operation is the best among them. The Single-Sided Amplitude Spectrum (SSAS) method is also applied to the welding current and droplet diameter of the three operations under slow and rapid droplet detachment rates to estimate the droplet detachment frequency. The results show the great success of the SSAS in estimating the precise frequency.