Micro-impulse and plasma plume produced by irradiating aluminum target with nanosecond laser pulses in double-pulse scheme

The micro-impulse generated by ablating an aluminum target in double-pulse laser bursts with different interpulse delays was investigated using a torsion pendulum.The plasma plume was simultaneously visualized using high-speed photography to analyze the coupling mechanism of the ablation impulse.The experiment was carried out using a pulsed laser with a pulse width of 8 ns and a wavelength of 1064 nm.The experimental results show that an impulse with an interpulse delay of 60 ns is roughly 60%higher than that with no delay between the two pulses,when the energy of both laser pulses is 50 m J.Therefore,double-pulse schemes could enhance the ablation impulse under certain conditions.This is because the ablation of the first laser pulse changes the optical properties of the aluminum target surface,increasing the absorptivity.However,the ablation impulse is reduced with a time delay of 20 ns when the energy of both laser pulses is100 mJ or 150 mJ.It can be concluded that the plasma produced by ablating the aluminum with the first pulse shields the second laser pulse.To summarize,the experimental results show that different delay times in a double-pulse scheme have a significant effect on the ablation impulse.The study provides a reference for the optimization of the parameters when laser ablation propulsion with a double-pulse scheme is applied in the fields of space debris removal,laser ablation thrusters,and so on.

Impacts of laser pulse width and target thickness on laser micro-propulsion performance

In order to optimize the laser ablation performance of a micro-thruster with 1U dimensions,which employs a micro semiconductor laser,the impacts of pulse width and glycidyl azide polymer(GAP)thickness on thrust performance were researched.The results showed that with a GAP thickness of 200μm,the single-pulse impulse(I)increased gradually with the increase in the laser pulse width from 50 to 800μs,while the specific impulse(I_(sp)),impulse coupling coefficient(Cm)and ablation efficiency(η)all reached optimal values with a 200μs pulse width.It is worth noting that the optimal pulse width is identical to the ignition delay time.Both Cmandηpeaked with a pulse width of 200μs,reaching 242.22μN W^(-1)and 35.4%,respectively.With the increase in GAP thickness,I and Cmincreased gradually.GAP of different thicknesses corresponded to different optimal laser pulse widths.Under a certain laser pulse width,the optimal GAP thickness should be the most vertical thickness of the ablation pit,and the various propulsion performance parameters at this time were also optimal.With the current laser parameters,the optimal GAP thickness was approximately 150μm,I_(sp)was approximately 322.22 s,andηwas approximately 34.94%.

Numerical Simulation on Laser Propulsion Capability of Polymer Target

A computational model of laser ablated polymer was established. Set the ablation criterion based on threshold energy. Put forward the polymer ablation criterion in the numerical model. It established the energy distribution equation to describe the laser ablation process. When the ablation products ejected, the target gained recoil impulse from ejection process. Get the ejection energy and the recoil momentum of target based on momentum conservation law. The numerical analysis model can reflect the propulsion capability of different polymer propellant, revealed the law of propulsion parameters in laser ablation process.

Design and characterisation of the high-current DC breaker driven by explosive

The development of a high-current DC breaker is very important for the protection of the expensive superconducting magnet.A kind of an economic switch called pyrobreaker,which is driven by explosive detonation waves,has been used as the backup quench protection due to its inherent reliability and fast response.A prototype pyrobreaker with a special structure that can withstand and break 100 kA is discussed.The numerical material model is taken to calculate the fracture demand of contact and the mass demand of explosive.Then,the detonation wave and contact breaking process are simulated by the ANSYS software.The performance of the design and characterisation during dynamic breaking are compared with simulation and no-load experiment test.At the end,the temperature rise test and the breaking test under 100 kA are completed successfully.These results demonstrate that the design of 100 kA pyrobreaker is reliable.