Xiao-dong Ren

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.

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...

Role of magnetic fluctuations in mode selection of magnetically driven instabilities

The influences of magnetic fluctuations on quasiperiodic structure formation and fundamental wavelength selection of the instability have been studied using two 25-μm-diameter tungsten wires on a 100 ns rise time, 220 kA pulsed power facility. Two different load configurations were adopted to make end surfaces of electrodes approximately satisfy reflecting and absorbing boundary conditions, respectively. The experimental results that the fundamental wavelength in the case of absorbing boundary condition is about one half of that in the case of reflecting boundary condition have demonstrated that magnetic fluctuations appear to play a key role in mode selection of magnetically driven instabilities. The dominant wavelength should be proportional to magnetic field and inversely proportional to square root of mass density, provided that the magnetosonic wave propagating perpendicular to magnetic fields provides a leading candidate for magnetic fluctuations. Therefore, magnetic fluctuation is one of the three key perturbations, along with surface contaminants and surface roughness, that seeds magnetically driven instabilities.

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.