Zeping Xu

Simulation of the quasi-spherical wire-array implosion dynamics based on a multi-element model

The implosion dynamics of quasi-spherical wire arrays with different initial aspect ratios are investigated with a multi-element model, and the simulated results are compared with experimental results in the Qiangguang-1 Facility in 2011. According to the simulation, the pinch plasmas implode in different modes when the aspect ratios of the initial wire arrays are different. The aspect ratio of the wire array in shot 11259 is 0.76, and the simulated pinch plasma implodes onto the equatorial surface. In shot 11268, the aspect ratio is 1.33 and the plasma implodes onto the central axis. In shot 11270, the aspect ratio is 1.05 and the plasma implodes toward the central point of the load. The simulated shapes of the plasma shells are in good accordance with the experimental time-resolved x-ray framing images. The simulated imploding times are consistent with the experimental x-ray peak times. The quasi-spherical implosion is more effective in driving inertial controlled fusion.

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.

Measurement of axial radiation properties in Z-pinch dynamic hohlraum at Julong-1

Axial radiation properties in Z-pinch dynamic hohlraum is investigated experimentally for the first time at Julong-1 facility in China, employing a load that contains a cylindrical CHO foam placed at the central axis position of the nested tungsten wire array. Time-resolved axially radiating images indicate that the velocity of the radiating shock is 31.9 ± 5.6 cm/μs in shot 0181. At t = −6.5 ns with respect to the peak of radially radiated power at stagnation, the annular width is estimated to be ∼1 mm and the intensities distribution in the shock implies a good azimuthal symmetry of radiation pressure. Axial power is found to peak prior to the arrival of the shock to the axis, which is explained by the balance between shock heating and radiating cooling. Utilizing the end-on radiation images and axial power, the peak radiation temperature in dynamic hohlraum is obtained to be ∼65 eV.

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.

A novel extreme ultraviolet four channels normal incidence imaging system for plasma diagnostics of Z-pinch facility

A novel EUV four channels normal incidence imaging system for plasma diagnostics of Z-pinch facility was presented in this paper, which consists of four concave mirrors and one convex mirror used for focusing an object onto four different positions with about 30 μm resolution on the same image plane. In addition, this imaging system can work at the energies of 50 eV, 95 eV, 150 eV, and broadband of 50-100 eV by using different multilayer films deposited on the concave and convex mirrors. This instrument, combined with framing camera, can achieve the power of two-dimensional spatial and temporal resolution, as well as the ability to imaging the plasma at the specific temperature. In the paper, the four channels microscope centering at multi-energies was developed.

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.