Z-pinch Plasma Research Articles

Design of Apparatus in Z-Pinch Plasma Neutron Sources for Fusion-Fission Breeders

In the fast Z-pinch experiments, the beam-target neutrons, the Deuterium-Deuterium neutrons and Deuterium-Tritium neutrons can be generated. It is a good idea to use deuterium Z-pinch plasmas to generate fusion neutrons which can be used in the fusion-fission breeders. The common design of Z-pinch plasmas apparatuses was introduced. The design of Z-pinch apparatuses for fusion-fission breeders is proposed.

Separating the Z-pinch plasma X-ray radiation and attaining the electron temperature

According to the experimental results of spectrum diagnosis made on Qiang-Guang-I generator, we report a method to separate and diagnose Z-pinch plasma radiation spectrum. Spectral lines and different continuums are separated from experimental results and electron temperatures can be acquired. Results show that continuums are superposed by radiation of high electron temperature plasma at the centre field (Te=290.7 eV ± 1.2 eV) and radiation of lower electron temperature plasma at shell region (Te=95.3 eV ± 8.3 eV). Spectral lines reflect the information of high electron temperature plasma at the centre field. According to the calculation by using NLTE model, the electron temperature of such a plasma is in the range of 299–313 eV. The diagnose result by spectral lines is identical with the continuum's results.

Simulation of Z-pinch Al plasma radiation and correction with considering superposition effect

In this article, the X ray special line radiation from Z-pinch Al plasma is calculated by using non-local-thermodynamic-equilibrium model (NLTE) based on digital energy level. The electron density of Z-pinch plasma at centre is obtained. The single plasma state parameter cannot well describe the special line radiation. In the next step, the Z-pinch plasma is divided into two parts: high electron temperature plasma at centre and low electron temperature plasma. The superposition of radiations from two parts is analyzed, and modified calculation result is presented. The calculation results are significantly improved after the superposition of radiations from two parts has been taken into account.

Physical investigation of dynamic process of the gas-puff Z-pinch through particle-in-cell simulation

In this paper the physical model and numerical algorithm of particle-in-cell (PIC) simulation for gas-puff Z-pinch in two-dimensional cylindrical coordinates are briefly introduced. The code is also developed according to the model and algorithm. The rarefied gas-puff Z-pinch driven by a low current is simulated through the code, and some reasonable results are obtained. The results include the spatiotemporal distributions of current, electromagnetic field, particle positions and density, as well as the trailing mass and current. It is found that the simulated current reflects the plasma Z-pinch characteristics, i.e., the plasma current arrives at a minimum when the plasma enters into stagnation, and it begins to increase after the plasma has moved outwards. The simulated magnetic field agrees well with the theoretic value. The electric field force and magnetic field force experienced by electron are almost the same in magnitude, while the force acting on ion is mainly the electric field force. Firstly the electron is accelerated in the z direction and reaches a velocity, then it moves inward the axis in the same time by the Lorentz force. That causes the separation between electron and ion, and a strong electric field is produced. The produced electric field attracts the ion inward the electron. When the electrons arrive at the axis, they move inversely due to the static repellency among them, while the ions continue to move initially inwards, and later enter into stagnation, and finally collapse. The trailing mass is about 20% of the total Z-pinch plasma, and the maximum trailing current is about 7% of the driven current. In the future the code needs to develop further and realize parallel computation in order to simulate the practical Z-pinch processes by PIC simulation.

Radiative signatures of Z-pinch plasmas at UNR: from X-pinches to wire arrays

University-scale Z-pinch generators are able to produce High Energy Density (HED) plasmas in a broad range of plasma parameters under well-controlled and monitored experimental conditions suitable for radiation studies. The implosion of X-pinch and wire array loads at a 1 MA generator yields short (1-20 nsec) x-ray bursts from one or several bright plasma spots near the wire cross point (for X-pinches) or along and near Z-pinch axis (for wire arrays). Such X- and Z-pinch HED plasma with scales from a few µm to several mm in size emits radiation in a broad range of energies from 10 eV to 0.5 MeV and is subject of our studies during the last ten years. In particular, the substantial number of experiments with very different wire loads was performed on the 1 MA Zebra generator and analyzed: X-pinch, cylindrical, nested, and various types of the novel load, Planar Wire Arrays (PWA). Also, the experiments at an enhanced current of 1.5-1.7 MA on Zebra using Load Current Multiplier (LCM) were performed. This paper highlights radiative signatures of X-pinches and Single and Double PWAs which are illustrated using the new results with combined wire loads from two different materials.

Simulation and mitigation of the magneto-Rayleigh-Taylor instabilities in Z-pinch gas discharge extreme ultraviolet plasma radiation sources

The development and use of a single-fluid two-temperature approximated 2-D Magneto-Hydrodynamics code is reported. Z-pinch dynamics and the evolution of Magneto-Rayleigh-Taylor (MRT) instabilities in a gas jet type Extreme Ultraviolet (EUV) source are investigated with this code. The implosion and stagnation processes of the Z-pinch dynamics and the influence of initial perturbations (single mode, multi- mode, and random seeds) on MRT instability are discussed in detail. In the case of single mode seeds, the simulation shows that the growth rates for mm-scale wavelengths up to 4 mm are between 0.05 and 0.065 ns−1. For multi-mode seeds, the mode coupling effect leads to a series of other harmonics, and complicates MRT instability evolution. For perturbation by random seeds, the modes evolve to longer wavelengths and finally converge to a mm-scale wavelength approximately 1 mm. MRT instabilities can also alter the pinch stagnation state and lead to temperature and density fluctuations along the Z axis, which eventually affects the homogeneity of the EUV radiation output. Finally, the simulation results are related to experimental results to discuss the mitigations of MRT instability.

Time-resolved K-shell line spectra measurement of z-pinch plasmas

A Johann-type crystal spectrometer integrated with x-ray PIN diodes has been developed for measuring the time-resolved K-shell line spectra of the imploding Al wire array. In this spectrometer, the PIN diodes are mounted on the Rowland circle of the cylindrical bent crystal with an appointed position to collect the line emissions from z-pinch plasmas. The spectrometer with four typical channels, which are keyed to the Al ion hydrogen-like (Hα, 0.7171nm and Hβ, 0.6052nm) and helium-like (Heα, 0.7757nm and Heβ, 0.6634nm) resonance lines is designed and fabricated. Example data from the experiment on the Yang accelerator are shown and the time-dependent electron temperature is determined from the signal ratios of Al ion Hα line to Heα line using the collisional and radiative model.

Time-resolved grating spectroscopy of a N capillary discharge plasma for a recombination pumped x-ray laser

Capillary discharge plasmas can serve for recombination-pumped x-ray lasers. We present time-resolved x-ray spectra and density measurements of a nitrogen capillary discharge z-pinch plasma. We use a free-standing transmission grating spectrometer and a gated MCP camera. This is the first time both K-shell and L-shell line emission of the nitrogen plasma are recorded simultaneously. Comparison of the spectra with a 4-ion collisional-radiative atomic model, which accounts for opacity effects, shows that the plasma reaches a maximum temperature of kTe=75–85eV during the pinch, and adiabatically cools in less than 4ns. This is slightly less than the newly estimated goal temperature of 110eV. The fast cooling demonstrates the feasibility of a recombination-scheme laser in the nitrogen Hα line at 13.37nm, if higher plasma temperature is achieved.

Observation of emission process in hydrogen-like nitrogen Z-pinch discharge with time integrated soft X-ray spectrum pinhole image

The emission spectra of hydrogen-like nitrogen Balmer at the wavelength of 13.4 nm in capillary Z-pinch discharge plasma are experimentally examined. Ionization to fully strip nitrogen at the pinch maximum, and subsequent rapid expansion cooling are required to establish the population inversion between the principal quantum number of n = 2 and n = 3. The ionization and recombination processes with estimated plasma parameters are evaluated by utilizing a time integrated spectrum pinhole image containing radial spatial information. A cylindrical capillary plasma is pinched by a triangular pulsed current with peak amplitude of 50 kA and pulse width of 50 ns.

Increasing the K-shell yield of line radiation in Z-pinch implosions using alloyed Al/Mg wire-arrays

The variation of the K-shell yield of pure aluminum wire-array Z-pinch implosions with load parameters is discussed. The mechanism and the efficiency of increasing the K-shell yield using alloyed Al/Mg wire-arrays are numerically investigated. It has been shown that the maximum K-shell yield from a pure aluminum wire-array Z-pinch implosion can be obtained at an optimal load mass for a given generator and at a fixed initial wire-array radius. This optimal load mass is determined by the load energy coupling with the generator, the capability of Z-pinch plasmas to emit the K-shell radiation, and the self absorption of K-shell lines. For different generators, the optimal load mass increases as the drive current increases, and the line absorption limits the further increase of K-shell radiation. The coupled energy per ion is likely decreasing with increased mass, so the plasma might not be able to ionize into the K-shell. Also, the ability of the plasma to radiatively cool can increase with mass, thus, making it difficult for the plasma to ionize into and remain in the K-shell during the stagnation phase of the implosion. Alloyed Al/Mg wire-arrays were thus suggested to be used to decrease the opacity of K-shell lines and to increase the overall K-shell yield. In this paper, we show that using alloyed Al/Mg wire-arrays will decrease the opacity and increase the K-shell yield remarkably if the plasma is optically thick. We will also show that the efficiency of increasing the K-shell yield with alloyed Al/Mg wire-arrays cannot increase indefinitely. The ratio of K-shell yield from an alloyed Al/Mg wire-array to that from a pure aluminum wire-array reaches a limit. For example, we show that when the mass share of magnesium is 10% then this limit is 1.2, and for a 50% mass share, the limit is 1.3.

五通道Z箍缩等离子体K壳层线谱成像

五通道Z箍缩等离子体K壳层线谱成像

Guest Editorial Special Issue on Z-Pinch Plasmas

The 24 papers in this special issue focus on Z-pinch plasmas. There are three invited papers and 25 contributed papers.

Electron temperature diagnostics of aluminium plasma in a z-pinch experiment at the “QiangGuang-1" facility

Two curved crystal spectrometers are set up on the “QiangGuang-1" generator to measure the z-pinch plasma spectra emitted from planar aluminum wire array loads. Kodak Biomax-MS film and an IRD AXUVHS5# array are employed to record time-integrated and time-resolved free-bound radiation, respectively. The photon energy recorded by each detector is ascertained by using the L-shell lines of molybdenum plasma. Based on the exponential relation between the continuum power and photon energies, the aluminum plasma electron temperatures are measured. For the time-integrated diagnosis, several “bright spots" indicate electron temperatures between (450 eV ∼ 520 eV) ± 35%. And for the time-resolved ones, the result shows that the electron temperature reaches about 800 eV ± 30% at peak power. The system satisfies the demand of z-pinch plasma electron temperature diagnosis on a ∼ 1 MA facility.

High-Resolution UV Laser Diagnostics on the 1-MA Zebra Generator

Laser diagnostics at the wavelength of 266 nm with a spatial resolution of 5-8 μm were developed for the investigation of dense <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinches at the 1-MA generator. The absorption and refraction in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinch plasma are significantly smaller at the ultraviolet (UV) wavelength of 266 nm compared to the optical range. This allows for observation of the fine internal structure of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinches at the stagnation phase. A UV laser beam penetrates through the trailing plasma around <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinches and shows strong instabilities of the dense pinch inside this plasma column. Kink instability, necks, and areas of disruption are seen in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -pinches at the peak of the X-ray pulse and later in time. UV two-frame side-on and end-on shadowgraphy show plasma dynamics in the pinch at stagnation.

Peculiarities of the spatial structure and dynamics of the plasma of a fast Z-pinch produced in the high-Z medium of a high-current vacuum spark

The spatial structure and dynamics of the plasma of a high-current vacuum spark is investigated using pulsed shadowgraphy. Anisotropy of the plasma outflow from a micropinch region has been revealed. The existence of cavities in the sausage-type instability in the final stage of pinching has been recorded. The formation of a filamentary plasma structure at the discharge periphery is revealed.

Spatially-resolved spectra from a new uniform dispersion crystal spectrometer for characterization of Z-pinch plasmas

Based on self-focusing and uniform dispersion principle, a novel mica uniform dispersion crystal spectrograph (UDCS) was developed, whose linear dispersion was designed to be constant. An aluminum wire-array imploding experiment was performed at “Yang” accelerator and K-shell emission spectra were measured to investigate Z-pinch aluminum plasma characteristics by using the UDCS. The linear dispersion deduced from obtained spectra with linear fitting was in good agreement with the theoretical value. By using the collisional–radiative equilibrium (CRE) model, the intensity ratios of Ly-α/He-α line and Ly-β/He-ε were given as a function of electron temperature. The measured intensity ratios were compared to the computed ones and the electron temperatures were estimated to be 512eV and 489eV. The slope of the free-bound X-ray continuum provides a model-independent diagnostic of the core electron temperature which was around 1215eV for this implosion. Analysis of Z-pinch radial temperature gradient shows that the temperature decreases sharply near the core and slowly to the shell regions. Benefiting from the UDCS providing high spectral resolution (λ/Δλ∼2500), the existence of first-order Langmuir dips were observed and reliably identified in Al Ly-α and Ly-γ resonance line profiles. The relationship between the position from the line center of red Langmuir dips and electron density was studied. The electron densities deduced from these fine spectral features were 5.52×1021cm−3 and 4.57×1021cm−3 respectively, which compared well with those derived from measurements of the line shift. The ion temperature was determined from the Doppler broadening of Al He-α resonance, He-like intercombination and Li-like s, t (n=2) satellite lines.

Novel X-ray uniform dispersion crystal spectrograph for Z-pinch plasmas

Based on self-focusing and uniform dispersion principle, novel uniform dispersion crystal spectrographs (UDCS) are developed for diagnostics of K-shell X-ray emission from wire array Z-pinch plasmas. To demonstrate the feasibility and validity of the developed UDCS, the linear dispersion is estimated to −116.198mm/nm, −115.996nm/mm and −177.802nm/mm for α-quartz, mica in 2nd order and in 3rd order respectively. It shows that the linear dispersion is almost constant for both crystal analyzers. The measured linear dispersions are in well agreement with theoretical values. Experimental results indicate that uniform dispersion can be perfectly realized with properly design.

X-ray absorption spectroscopy of aluminum z-pinch plasma with tungsten backlighter planar wire array source

Absorption features from K-shell aluminum z-pinch plasmas have recently been studied on Zebra, the 1.7 MA pulse power generator at the Nevada Terawatt Facility. In particular, tungsten plasma has been used as a semi-backlighter source in the generation of aluminum K-shell absorption spectra by placing a single Al wire at or near the end of a single planar W array. All spectroscopic experimental results were recorded using a time-integrated, spatially resolved convex potassium hydrogen phthalate (KAP) crystal spectrometer. Other diagnostics used to study these plasmas included x-ray detectors, optical imaging, laser shadowgraphy, and time-gated and time-integrated x-ray pinhole imagers. Through comparisons with previous publications, Al K-shell absorption lines are shown to be from much lower electron temperature (∼10-40 eV) plasmas than emission spectra (∼350-500 eV).

Mapping return currents in laser-generated Z-pinch plasmas using proton deflectometry

Dynamic return currents and electromagnetic field structure in laser-generated Z-pinch plasmas have been measured using proton deflectometry. Experiments were modeled to accurately interpret deflections observed in proton radiographs. Current flow is shown to begin on axis and migrate outwards with the expanding coronal plasma. Magnetic field strengths of ∼1 T are generated by currents that increase from ∼2 kA to ∼7 kA over the course of the laser pulse. Proton deflectometry has been demonstrated to be a practical alternative to other magnetic field diagnostics for these types of plasmas.

Radiation characteristics and implosion dynamics of tungsten wire array Z-pinches on the YANG accelerator

We investigated the radiation characteristics and implosion dynamics of low-wire-number cylindrical tungsten wire array Z-pinches on the YANG accelerator with a peak current 0.8–1.1 MA and a rising time ∼ 90 ns. The arrays are made up of (8–32) × 5 μm wires 6/10 mm in diameter and 15 mm in height. The highest X-ray power obtained in the experiments was about 0.37 TW with the total radiation energy ∼ 13 kJ and the energy conversion efficiency ∼ 9% (24 × 5 μm wires, 6 mm in diameter). Most of the X-ray emissions from tungsten Z-pinch plasmas were distributed in the spectral band of 100–600 eV, peaked at 250 and 375 eV. The dominant wavelengths of the wire ablation and the magneto-Rayleigh—Taylor instability were found and analyzed through measuring the time-gated self-emission and laser interferometric images. Through analyzing the implosion trajectories obtained by an optical streak camera, the run-in velocities of the Z-pinch plasmas at the end of the implosion phase were determined to be about (1.3–2.1) × 107 cm/s.