Shenghai Xiang

Diagnosis of electromagnetic properties and light flash characteristics created by hypervelocity impact\m{1}

In order to diagnose electromagnetic properties and light flash characteristics generated by hypervelocity impact, the diagnostic systems of sweep Langmuir probe(SLP) and triple Langmuir probe (TLP) for electron temperature and electron density in plasma were established, properties of magnetic field were obtained by using coil measurement system established, and characteristics of light flash were also acquired through optical pyrometer measurement system during the whole physical process in hypervelocity impact, Experimental results showed that the average electron temperature of the triple Langmuir probe was near 0.75 eV on the whole physical process, the average electron density in the experiment was about. However, the electron temperature and electron density of plasma acquired by using t he sweep Langmuir probe were lower than the values by using triple Langmuir probe. The peak value of magnetic induction intensity induced by plasma was 9.8 × 10/cm during the hypervelocity impacts, and light flash intensity peak value was 40–50 mW.cm−2.nm−1 in the experimental conditions in the paper.

The signal characteristics of light flash generated by hypervelocity impact natural dolomite plate

To investigate light flash produced during hypervelocity impact in the laboratory, we have conducted a series of experiments on a two-stage light gas gun at different impact velocities and the same impact angle. Light flash were acquired through optical fiber pyrometer measurement system during the whole physical process in hypervelocity impact, Experimental results showed that the maximum light flash intensity decreases with impact velocity increasing, and maximum light flash intensity should exist a critical impact velocity for polycarbonate projectile impacting natural dolomite plate, which may be between 2.52 km/s and 4.21 km/s at the wavelength of 550 nm–700 nm. In addition, the light flash intensity peak value was 0.4∼0.5 mW.cm−2.nm−1 in the experimental conditions in the paper.

Triple Langmuir probe diagnosis of transient plasma created by hypervelocity impact

To acquire the characteristic parameters of plasma generated by hypervelocity impact, experimental system and a new Triple Langmuir probe diagnostic system are established in the paper. Triple Langmuir probe diagnostic technology does not require a voltage or frequency sweep compared to other Langmuir probe methods. The system allows the direct display of electron temperature and semidirect display of electron density by appropriate display system, this method eliminates the time consuming in data analysis required in curve-fitting current-voltage characteristics. As an example of application to timedependent plasmas measurement, the electron temperature and electron density of plasmas were measured in hypervelocity impact experiments. Experimental results show that the Triple Langmuir probe diagnostic technology can be well used to measure electron temperature and electron density of time-evolution plasma.

Research on the Ionization Degree of the Plasma Generated by 2A12 Aluminum Target During Hypervelocity Impact

The theories of impact dynamics and adiabatic temperature change were adopted to investigate the ionization degree of the plasma generated by the 2A12 aluminum target during 2A12 aluminum projectile hypervelocity impact, and the radiant temperature was also estimated during hypervelocity impact. A two-stage light gas gun combined with the plasma characteristic parameters measured by a triple Langmuir probe was applied, and then the fitting relationship between the plasma ionization degree and the theoretical impact temperature as well as the fitting relationship between the maximum electron density and impact velocity were obtained with the aid of the theoretical derivation of the plasma ionization degree and the electron temperature and electron density extracted from experiments.

Characterization of light flash signatures using optical-fiber pyrometer detectors during hypervelocity impact

Impact light flash is an intense light flash released when a target is impacted by a hypervelocity projectile. Light flash is caused by emissions from a jet of shocked material which is thrown from the impact site. Impact light flash phenomenology is now being considered for applications where remote diagnostics are required to observe and diagnose impacts on satellites and spacecraft. Additionally, this phenomena and remote diagnostics are under consideration for deep space exploration and missile defense applications. Currently, optical signatures created from hypervelocity impact can be utilized as the basis for detectors (spectrometers, pyrometers), which characterize the material composition and temperature. To establish this capability technically in the laboratory, we have conducted a series of experiments on a two-stage light gas gun at impact velocities ranging from 1.96 to 4.21 km/s. The focus of this work is to develop a flash signatures collected methods for use as a reliable light flash, and late time radiating evolution to characterize material behavior in the shocked and expanding state; ascertain scaling of light flash with impact velocity, and determine the temperature of the impact flash resulting from radiating emissions when photomultiplier tube (PMT) are used in conjunction with narrow band pass filtering at specific wavelengths as a pyrometer. The results of these experiments are discussed in detail using natural dolomite target.

Electrostatic Discharge of Plasma Created by Hypervelocity Impact 2A12 Aluminum Targets With Gradient Potential

Based on the objective reality of gradient potential existence in spacecraft surface caused by charging particles in space-plasma environment or solar wind activities, electrostatic discharge of spacecraft with surface charging or deep dielectric charging would be induced by debris or meteoroids impact. To simulate the gradient potential on the spacecraft surface in the laboratory, spacecraft surface was segmented into different parts, which different spacing reserved in two adjacent surfaces was added resistance to create different potential surfaces, and the highest potential surface as a target in the segmented surface. Circuit system realizing different gradient potential, discharge test system, as well as ultrahigh-speed camera acquired system was built by ourselves; combining with two-stage light gas gun loading system, four set experiments have been performed about hypervelocity impact on 2A12 aluminum target with gradient potential. In the experiments, spacings of 2A12 aluminum target were the same among different potential parts in every experiment, and the spacings of four set experiments were 2, 5, 10, and 15 mm, and high-potential 2A12 aluminum as the target, respectively. The experiments were performed at the impact velocity of about 3 km/s and the incidence angles of 60° (between projectile flying trajectory and target plane). Voltage probes and current probes were used to acquire discharge voltages and currents during the process of the impact. The experimental results showed that the discharge induced by impact plasma was generated between high- and low-potential targets by forming a plasma discharge channel, the gaps with 2–15 mm can evoke discharge among different targets, and the variations of the discharge current along the high- and low-potential targets did not obviously. However, the discharge duration decreased with an increasing of distance between high- and low-potential targets at the near collision velocities and the same incidence angle of the projectile. The whole physical process of discharge had experienced four stages in general, which created by hypervelocity impact 2A12 aluminum targets with gradient potential. The first stage was plasma generated by hypervelocity impact, the second stage was complex mixed plasma including plasma generated by hypervelocity impact and discharge plasma induced by split targets with gradient potential, the third stage was discharge plasma induced by hypervelocity impact, and the fourth stage was the discharge between charging particles due to the reciprocating motion of charging particles in the electromagnetic field.

Analysis of luminous efficiency for light flash created by hypervelocity impact natural dolomite plate

In order to understand luminous efficiency of the visible wavelength and the infrared wavelength range generated by hypervelocity impact natural dolomite plate, experimental measurement of the light flash created by hypervelocity impact natural dolomite plate were performed in the visible wavelength range by using the optical transient pyrometer measurement system and two-stage light gas gun loading system at the different impact velocity and the projectile incident angles of 45◦ and 60◦ (with the angle along the target plane), respectively. Based on the Planck’s blackbody continuous radiation law in the visible wavelength range, luminous efficiency extrapolate to infrared wavelength range by combining with Matlab computer programming, the calculated results of the luminous efficiency showed that the luminous efficiency of the light flash created by hypervelocity impact natural dolomite plate in the infrared wavelength range was approximately 1∼1.5 times in the visible wavelength range.