Jianlun Yang

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 ...

Numerical Simulation of the Interaction Between Z-Pinch Plasma and Foam Converter Using Code MULTI (#18353)

Abstract The interaction between Z-pinch plasma and foam converter has an important effect on the formation of Z-pinch dynamic hohlraums. A new program has been developed to study related physical processes. Numerical results suggest that the interaction on 7–10 MA drivers is strong enough to create dynamic hohlraums with radiation temperature over 100 eV. Simulations also indicate that a radiating shock would appear due to the collision of Z-pinch plasma and foam converter, in good agreement with the measurements on JULONG-I facility. In this technical note, we present the physical model and simulation results, as well as typical experimental results.

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.

Detection of the spectra of multicharged ions with time resolution and the determination of the parameters of the hot component of the plasma in the case of the magnetic implosion of multiwire arrays

The dynamics of the hot component of the plasma of imploding multiwire arrays has been analyzed using the time behavior of the X-ray spectral lines of multicharge ions. The spectra of H- and He-like aluminum ions with nanosecond time resolution have been detected using electron-optical chronography in experiments on the implosion of multiwire arrays by mega-ampere currents. The simultaneous appearance of the resonance lines of H- and He-like ions implies that the hot plasma whose electron temperature is higher than 0.5 keV has existed on the axis before the implosion of the main mass of the liner. The further dynamics of the intensity of the lines is primarily attributed to an increase in the mass of the emitting plasma.

A time-resolved spectroscopic diagnostic based on fast scintillator and optical fiber array for z-pinch plasmas

We report a specially designed type of temporal resolved x-ray spectroscopic diagnostic using a spherically bent quartz crystal for z-pinch plasmas. Registration of time-resolved spectra was accomplished by coupling fast plastic scintillator, an optical fiber array, an optical streak camera, and a charge coupled device as the recording medium of this diagnostic. The diagnostic has been tested in imploding wire array experiments on S-300 pulsed power facility. Time-resolved K-shell lines were successfully obtained for aluminum wire array implosion plasmas.

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.

Measurement of residual carbon in chamber of Shenguang II laser facility

It is reported that in National Ignition Facilitys shock timing campaign, there is a 2 μm layer of residual air condensation on the cold laser entrance hole window, and residual gas level of ∼5×10−6 Torr ( ∼6.6×10−4 Pa) in the chamber [Robey et al., Phys. Plasmas 19, 042706 (2012)]. On Shenguang (SG) II and III laser facilities, a nominal residual gas level in the chamber is ∼10−2 Pa in experiment. In this work, the residual Carbon (C) level in the SG II chamber is investigated experimentally using a transmission grating spectrometer (TGS). The experimental result shows that there is a clear C K edge (280–300 eV), which implies that there is residual C condensation on the charge-coupled device (CCD) silicon oxide layer. The effect of the C condensation on the CCD response is studied with a condensed-C-foil model. With the modified CCD responses, the unfolded spectra by TGS are shown, and the significant C K edge decreases as the C foil thickness increases. Compared to the simulated C K edge depth, the me...

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.