Jiamin Ning

Numerical and experimental investigations on the interaction of light wire-array Z-pinches with embedded heavy foam converters

The interaction of a light tungsten wire-array Z-pinch with an embedded heavy foam converter, whose mass ratio is typically less than 0.16, is numerically analyzed and experimentally investigated on the 1.3 MA “QiangGuang I” facility. Computational results show that this implosion process can be divided into three stages: acceleration of the tungsten wire-array plasma, collision, and stagnation. The tungsten plasma is accelerated to a high speed by the J × B force and interacts weakly with the foam plasma in the first stage. Strong energy conversions take place in the second collision stage. When the high speed tungsten plasma impacts on the foam converter, the plasma is thermalized and a radial radiation peak is produced. Meanwhile, a shock wave is generated due to the collision. After the shock rebounds from the axis and meets the W/Foam boundary, the plasma stagnates and the second radial radiation peak appears. The collision and stagnation processes were observed and the two-peak radial radiation puls...

Experimental investigation of the ribbon-array ablation process

Ablation processes of ribbon-array loads, as well as wire-array loads for comparison, were investigated on Qiangguang-1 accelerator. The ultraviolet framing images indicate that the ribbon-array loads have stable passages of currents, which produce axially uniform ablated plasma. The end-on x-ray framing camera observed the azimuthally modulated distribution of the early ablated ribbon-array plasma and the shrink process of the x-ray radiation region. Magnetic probes measured the total and precursor currents of ribbon-array and wire-array loads, and there exists no evident difference between the precursor currents of the two types of loads. The proportion of the precursor current to the total current is 15% to 20%, and the start time of the precursor current is about 25 ns later than that of the total current. The melting time of the load material is about 16 ns, when the inward drift velocity of the ablated plasma is taken to be 1.5 × 107 cm/s.

Preliminary investigation on the radiation transfer in dynamic hohlraums on the PTS facility

The radiation transfer in dynamic hohlraums on the PTS facility is preliminarily investigated in this paper. Simulation results show that as the accelerated wire-array plasma impacts onto the foam converter, energy thermalization takes place in a local interaction region near the boundary of the wire-array plasma and the foam converter, and then, high temperature radiation is gradually generated. Its transfer process largely depends on the radiation temperature and the mass density of the converter. When the mass ratio of the wire-array to the converter is near 1.0, the radiation temperature can be increased to about 120 eV with the PTS drive current. In this case, the radiation generated from the interaction region will quickly transfer to the center of the converter. The experimental end-on x-ray images present the overall process of radiation production and transfer of this kind of dynamic hohlraum. As the mass ratio is decreased, the radiation temperature will also be deceased, and the converter will ...

A free-standing thin foil bolometer for measuring soft x-ray fluence

A free-standing thin foil bolometer for measuring soft x-ray fluence in z-pinch experiments is developed. For the first time, we present the determination of its sensitivity by different methods. The results showed great consistency for the different methods, which confirms the validity of the sensitivity and provides confidence for its application in z-pinch experiments. It should be highlighted that the sensitivity of a free-standing foil bolometer could be calibrated directly using Joule heating without any corrections that will be necessary for a foil bolometer with substrate because of heat loss. The difference of the waveforms between the free-standing foil bolometer and that with substrate is obvious. It reveals that the heat loss to the substrate should be considered for the latter in despite of the short x-ray pulse when the peak value is used to deduce the total deposited energy. The quantitative influence is analyzed through a detailed simulation.

Measurements of high energy photons in Z-pinch experiments on primary test stand

High energy photons are measured for the first time in wire-array Z-pinch experiments on the Primary Test Stand (PTS) which delivers a current up to 8 MA with a rise time of 70 ns. A special designed detecting system composed of three types of detectors is used to measure the average energy, intensity, and pulse waveform of high energy photons. Results from Pb-TLD (thermoluminescence dosimeter) detector indicate that the average energy is 480 keV (±15%). Pulse shape of high energy photons is measured by the photodiode detector consisted of scintillator coupled with a photodiode, and it is correlated with soft x-ray power by the same timing signal. Intensity is measured by both TLD and the photodiode detector, showing good accordance with each other, and it is 10(10) cm(-2) (±20%) at 2 m in the horizontal direction. Measurement results show that high energy photons are mainly produced in pinch regions due to accelerated electrons. PTS itself also produces high energy photons due to power flow electrons, which is one order smaller in amplitude than those from pinch region.

Applications of thin film plastic scintillator in measurement of soft x rays generated from Z-pinch implosion

A thin film plastic scintillator detector has been developed for the measurement of radiation power and yield of soft x rays produced from Z-pinch implosion. To enable soft x-ray measurements using plastic scintillators, the detector geometry has been specially designed to minimize visible light and alleviate nonlinear behavior. Energy response has been calibrated, and saturation effects have been explored and described in details. The possibility and limitation of its application to such high-density radiation bursts are analyzed. The detector has been fielded on several meters away in vacuum pipes for hundreds of shots at different Z-pinch facilities, and the measured data in these experiments agreed well with the results from other diagnostics, demonstrating the feasibility and reliability of the detector.

Investigation of ablation of thin foil aluminum ribbon array at 1.5 MA

We present experimental studies of initiation and ablation of a thin foil aluminum ribbon array at the 1.5 MA current level. In contrast to the previous work, we employ ribbon arrays with different ribbon gap parameters to investigate how this affects plasma initiation and foil ablation. Gated narrowband ultraviolet imaging indicated that the current was disorderly distributed at early period of discharge. But later on, it became axially stable and azimuthally symmetrical even for load with a gap as small as 0.1 mm. Using magnetic field probes installed inside and outside the array, we also observed that precursor current at positions with a distance of less than 2.7 mm to the central axis for 4-mm-radius arrays decreased when ribbon gap became small. Results of 0.2 mm gap ribbon array showed an evidence that ribbons can be merged. These observations imply that thin foil ribbon arrays may have potential applications in z-pinch experiments on large scale pulsed power facilities.

Radiation Characteristics of Nested Wire Array Implosions in Sino-Russian Joint Z-Pinch Experiments on Angara-5-1

X-ray radiation characteristics of nested wire array implosions were investigated in the Sino-Russian joint Z-Pinch experiments on Angara-5-1 facility with a load current of 2.5 ~ 3.6 MA. The experimental results indicate that an X-ray power-platform prior to the main peak and a less intensive sub-peak after the main peak in the X-ray power waveform exist for the nested wire array implosions, and the radiation process is relatively faster than that in the case of single array. Laser shadowgraph of the imploding plasma suggests that the prior power-platform is a result of the collision of the inner-outer plasma layers. The faster radiation process of nested array implosion can be explained by analysing the corresponding result of the time-resolved one-dimensional imaging system, which demonstrates a better axial imploding uniformity and synchronization. The sub-peak after the main peak is proposed to be a result of the later-time additional implosion of plasma.

Observation of Axial and Radial Variation of x-ray Radiation Process in Gas-Puff and Wire-Array Implosions

Summary form only given. A sensitive time-resolved one-dimensional X-ray imaging system with linear energy response to 100 eV-2 keV X-rays is developed and applied in Z-Pinch experiments to investigate axial or radial variation characteristics of time dependent X-ray radiation with spatial resolution of 0.1 mm-0.4 mm and temporal resolution of 3 ns. In gas-puff experiment on Qiang-Guang-1 facility, zipper effect investigation is demonstrated and the obtained zipper velocity is typically 5 times 10 cm/s. Zipper-like effect in conical wire-array implosion is also observed. In cylindrical wire-array implosions, observations suggest that X-ray radiation process is basically not simultaneous along the axis of wire-array. Experimental results indicate a much better simultaneousness and uniformity of axial distribution of X-ray radiation process in nested wire-array implosions than in single wire-array implosions, which provides an interpretation of the radiation power increase observed in nested wire-array implosions. Results of radial variation diagnostics of X-ray radiation process suggest similar imploding velocity to that suggested by laser probing multi-frame shadowgraphs.