Shaotong Zhou

Preliminary experimental results of tungsten wire-array Z-pinches on primary test stand

The Primary Test Stand (PTS) developed at the China Academy of Engineering Physics is a 20 TW pulsed power driver, which can deliver a ∼10 MA, 70 ns rise-time (10%–90%) current to a short-circuit load and has important applications in Z-pinch driven inertial confinement fusion and high energy density physics. Preliminary results of tungsten wire-array Z-pinch experiments on PTS are presented. The load geometries investigated include 15-mm-tall cylindrical single and nested arrays with diameter ranging from 13 mm to 30 mm, consisting of 132–300 tungsten wires with 5–10 μm in diameter. Multiple diagnostics were fielded to characterize the x-ray radiation from wire-array Z pinches. The x-ray peak power (∼50 TW) and total radiated energy (∼500 kJ) were obtained from a single 20-mm-diam array with 80-ns stagnation time. The highest x-ray peak power up to 80 TW with 2.4 ns FWHM was achieved by using a nested array with 20-mm outer diameter, and the total x-ray energy from the nested array is comparable to that of single array. Implosion velocity estimated from the time-resolved image measurement exceeds 30 cm/μs. The detailed experimental results and other findings are presented and discussed.

Diagnosing x-ray power and energy of tungsten wire array z-pinch with a flat spectral response x-ray diode

Fast z-pinch is a very efficient way of converting electromagnetic energy to radiation. With an 8-10 MA current on primary test stand facility, about 1 MJ electromagnetic energy is delivered to vacuum chamber, which heats z-pinch plasma to radiate soft x-ray. To develop a pulsed high power x-ray source, we studied the applicability of diagnosing x-ray power from tungsten wire array z-pinch with a flat spectral response x-ray diode (FSR-XRD). The detector was originally developed to diagnose radiation of a hohlraum in SG-III prototype laser facility. It utilized a gold cathode XRD and a specially configured compound gold filter to yield a nearly flat spectral response in photon energy range of 0.1-4 keV. In practice, it was critical to avoid surface contamination of gold cathode. It is illustrated that an exposure of an XRD to multiple shots caused a significant change of response. Thus, in diagnosing x-ray power and energy, we used each XRD in only one shot after calibration. In a shot serial, output of FSR-XRD was compared with output of a nickel bolometer. In these shots, the outputs agreed with each other within their uncertainties which were about 12% for FSR-XRD and about 15% for bolometer. Moreover, the ratios between the FSR-XRD and the bolometer among different shots were explored. In 8 shots, the standard deviation of the ratio was 6%. It is comparable to XRD response change of 7%.

A simple model for a shock wave in a dynamic hohlraum

The dynamic hohlraum (DH) is an approach to Inertial Confinement Fusion, and its X-ray radiation can be widely used in high energy density physics. The shock wave in dynamic hohlraum is important because it heats the foam to high radiation temperatures. Here, we proposed a simple model to describe the shock wave in the dynamic hohlraum. Based on the Rocket ablation model, this simple shock model connects the wire-array implosion phase and the shock formation phase. We also use the experimental result of dynamic hohlraum with a heavy foam mass acquired on primary test stand to verify this model. This simple shock model helps researchers to estimate when and where the collision happens so that researchers could understand the physics in DH more clearly.

The magnetically driven plasma jet produces a pressure of 33 GPa on PTS

We report on experiments in which a magnetically driven plasma jet was used to hit a 500 μm thick planar aluminum target. The plasma jet was produced by using a 50 μm thick aluminum radial foil, which was subjected to 4 MA, 90 ns rising time current on the primary test stand pulsed power facility. The subsequent magnetic bubbles propagate with radial velocity reaching 200 km/s and an axial velocity of 230 km/s. After the plasma knocks onto the target, a shock forms in the target. When the shock gets to the backside of the target, we measure the velocity of the moving surface using dual laser heterodyne velocimetry. By using the Hugoniot relations, we know that the plasma jet produced a pressure of 33 GPa. According to the measured pressure and the velocity of the plasma jet, the density of the jet can be also roughly estimated.

Design and primary results of x-ray heating aluminum foil experiments at PTS facility

Summary form only given. The strong X-ray radiations produced by mega-ampere-current-level fast Z-pinch plasmas offer valuable and indispensible opportunities to create hot and dense radiation-heated plasmas1, serving the laboratory investigations of radiation sciences in the fields of opacity measurements, photon-ionized plasmas and so on. Recently, experiments of x-ray heating aluminum foil has been designed and is being carried out at the Primary Test Stand (PTS) facility2, a 8-10 MA, 70 ns pulsed power driver being able to generate x-ray bursts of 80 TW peak power and 3-5 ns FWHM3. In this paper, we present the simulation results of the aluminum foils heated by x-rays using a 1D radiation hydrodynamic code, the design of the sample foils with CH coatings on each side and the diagnostic results of x-ray power and energy in different spectral regions, transmission spectra through the foils and so on. By analyzing the measurements, the states and properties of the radiation-heated aluminum plasmas are estimated and discussed.

Conditions for supersonic bent Marshak waves

Supersonic radiation diffusion approximation is an useful method to study the radiation transportation. Considering the 2-d Marshak theory, and an invariable source temperature, conditions for supersonic radiation diffusion are proved to be coincident with that for radiant flux domination in the early time when exf/L≪1. However, they are even tighter than conditions for radiant flux domination in the late time when exf/L≫1, and can be expressed as M>4(1+e/3)/3 and τ>1. A large Mach number requires the high temperature, while the large optical depth requires the low temperature. Only when the source temperature is in a proper region the supersonic diffusion conditions can be satisfied. Assuming a power-low (in temperature and density) opacity and internal energy, for a given density, the supersonic diffusion regions are given theoretically. The 2-d Marshak theory is proved to be able to bound the supersonic diffusion conditions in both high and low temperature regions, however, the 1-d theory only bounds i...

Diagnostics forz-pinch on PTS facility

Summary form only given. An extensive diagnostics with spatial and temporal resolution for Z-pinch was developed on the PTS facility at Key Labora tory of Pulsed Power, CAEP. PTS facility can generate a curr ent rising to 8-10 MA in 90 ns, which was used to drive wire array Z pinches. Diagnostics including soft X-ray power meter, DANTE, transmission grating spectrometer, time-resolved X-ray pinhole camera, optical/X-ray streak cameras, X-ray crystal spectrometer, laser differential interferometer and some experimental results are described in this paper.

PPPS-2013: Optical and x-ray diagnostics time-resolved K-shell line spectra measu rement of the imploding al wire array

Summary form only given. A device that integrates a Johann-type spectrometer with the x-ray PIN diodes, positioned accurately on the rowland circle of the cylindrical bent crystal with different Bragg angles to aim at different spectral lines, has been developed for measuring th e time-resolved K-shell line emissions of the imploding Al wire array. Four typical channels respectively keyed to the Al ion hydrogen-like (H_α, 0.7171 nm and H_β, 0.6052 nm) and helium-like (He_α, 0.7757 nm and H_β, 0.6634 nm) resonance lines are designed and the signal ratios of the H_α line to the He_α line has been used to retrieve the time-dependent electron temperature. The designing principle of the spectrometer is described and the preliminary experimental results on the YANG and PTS accelerator are presented and analyzed.

Tungsten wire-array Z pinches at 7–10 MA PTS facility

Experimental results of Z pinches conducted on PTS facility at Institute of Fluid Physics are presented here. Tungsten wire arrays driven by current with peak value of ~7 MA and zero-to-peak rise time of ~100 ns generate an x-ray power of ~50 TW, x-ray energy of ~0.5 MJ and color temperature of ~150 eV. Axial kinetic energy induced by m=0 like instability was proposed to solve the discrepancy that the kinetic energy built up in implosion is too low to contribute to the x-ray radiation. Changes in wavelength of instability in Z pinches might be explained by equivalence of plasma column to plasma waveguide to some extent. The role of magnetic reconnection in corona acceleration and precursor forming in the case of low-wire-number Z pinches has been pointed out. Estimation demonstrates the generation of electromagnetic pulse of 1 GW in peak power and 0.5 J in radiated energy from motion of plasma column with energy conversion efficiency of ~10-7.

The Plasma Column Evolution in Gas-Puff Z-Pinches on the Yang Accelerator

The plasma column evolution in gas‐puff z‐pinch was investigated on the Yang accelerator. The pinch process was significantly influenced by the initial gas distribution. Uniformity of the gas‐puff distribution resulted in the asymmetry of the initially load current through the main channels of the plasma layer. The zipper velocity and implosion speed under “trumpet” distribution was given, it was observed the pinch speed and the temperature of the plasma near cathode increased when the rise time of the load current was shortened.