Generation and characterization of millimeter-scale plasmas for the research of laser plasma interactions on Shenguang-III prototype
Zhichao LiJian ZhengYongkun DingQiang YinXiaohua JiangSan-Wei LiLiang GuoDong YangZhebin WangHuan ZhangYonggang LiuXiayu ZhanQi Tang
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Abstract:
In order to produce millimeter-scale plasmas for the research of laser-plasma interactions (LPIs), gasbag target is designed and tested on Shenguang-III prototype laser facility. The x-ray pinhole images show that millimeter-scale plasmas are produced with the gasbag. The electron temperature inferred from the stimulated Raman scattering (SRS) spectrum is about 1.6 keV. The SRS spectrum also indicates that the electron density has a flat region within the duration of 200 ps. The obvious differences between the results of the gasbag and that of the void half hohlraum show the feasibility of the gasbag target in creating millimeter-scale plasmas. The LPIs in these millimeter-scale plasmas may partially mimic those in the ignition condition because the duration of the existence of a flat plasma density is much larger than the growth time of the two main instabilities, i.e., SRS and stimulated Brillouin scattering (SBS). So we make the conclusion that the gasbag target can be used to research the large-scale LPIs.Keywords:
Hohlraum
Thomson scattering
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Recent changes in the manner of performing hohlraum drive experiments have significantly advanced the ability to diagnose, understand and control the x-radiation flux (or drive) inside a laser heated hohlraum. Comparison of modeling and data from a very broad range of hohlraum experiments indicates that radiation hydrodynamics simulation codes reproduce measurements of time dependent x-radiation flux to about ±10%. This, in turn, indicates that x-ray production and capsule coupling in ignition hohlraums will be very close to expectations. This article discusses the changes to experimental procedures and the broad variety of measurements and tests leading to these findings.
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National Ignition Facility
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We describe designs of hohlraums and capsules for both ignition (∼1–10 MJ) and high yield (up to ∼200 MJ) Z-pinch driven indirect-drive ICF concepts. Two potential Z-pinch hohlraum configurations – 1) the “static wall” or “on-axis” hohlraum; and 2) the “imploding liner” or “dynamic” hohlraum – are considered. Both concepts involve cryogenic, DT-filled capsules (∼2–4 mm in diameter) with Be or CH ablators (O, F, and Cu are currently being considered as dopants). Both types of hohlraums involve a Helium and/or CH foam fill. In the static wall hohlraum concept, the ICF capsule is isolated from the x-ray generation region. Advantages in the areas of capsule drive symmetry and diagnostic access might be gained from this arrangement. In the dynamic hohlraum, the ICF capsule has a direct view of the stagnation radiation. The potential advantage would result from the higher x-ray intensity and larger total capsule absorbed energy.
Hohlraum
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A novel ignition hohlraum named three-axis cylindrical hohlraum (TACH) is designed for indirect-drive inertial confinement fusion. TACH is a kind of 6 laser entrance holes (LEHs) hohlraum, which is orthogonally jointed of three cylindrical hohlraums. Laser beams are injected through every entrance hole with the same incident angle.
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National Ignition Facility
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In order to establish the applicability conditions of incoherent laser Thomson scattering (LTS) for plasma diagnostics of electron properties to various kinds of discharge plasmas, a method of approach was discussed, and criteria for applicability were established. These criteria were then applied to three representative discharge plasmas: inductively coupled plasmas (ICP) in Ar/CF4 and Ar/O2 gases, and a microwave-produced plasma in a H2/CH4 gas. Implications of the results are discussed.
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Summary form only given. Recent development of high power Z-pinches (>150 TW) on the Z driver has permitted the study of high-temperature, radiation-driven hohlraums. Three complementary, Z-pinch source-hohlraum-ICF capsule configurations are being developed to harness the X-ray output of these Z-pinch's. These are the dynamic-hohlraum, static-wall hohlraum, and Z-pinch-driven hohlraum concepts. Each has different potential strengths and concerns. In this paper, we report on the first experiments with the Z-pinch-driven hohlraum (ZPDH) concept. A high-yield ICF capsule design for this concept appears feasible, when driven by Z-pinches from a 60 MA-class driver.
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Z-pinch
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In low temperature plasmas, tokamaks and other experimental fusion devices, the electron temperature and densities in the plasma can be measured with high accuracy by detecting the effect of Thomson scattering of light from a high‐intensity laser fired through the device. It has been established as a robust technique to measure these parameters and in particular it can be used to provide detailed profiles right through the plasma.
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X-ray Thomson scattering (XRTS) is a powerful diagnostic for probing warm and hot dense matter. We present the design and results of the first XRTS experiments with hohlraum-driven CH2 targets on the OMEGA laser facility at the Laboratory for Laser Energetics in Rochester, NY. X-rays seen directly from the XRTS x-ray source overshadow the elastic scattering signal from the target capsule but can be controlled in future experiments. From the inelastic scattering signal, an average plasma temperature is inferred that is in reasonable agreement with the temperatures predicted by simulations. Knowledge gained in this experiment shows a promising future for further XRTS measurements on indirectly driven OMEGA targets.
Hohlraum
Thomson scattering
Warm dense matter
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Some of our recent studies on hohlraum physics are presented, mainly including simulation study on hohlraum physics experiments on SGIII prototype, the design of Au + U + Au sandwich hohlraum for ignition target, and an initial design of elliptical hohlraum and pertinent drive laser power in order to generate an ignition radiation profile.
Hohlraum
National Ignition Facility
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This work is a summary of experiments, numerical simulations, and analytic modeling that demonstrate improved radiation confinement when changing from a hohlraum made from gold to one made from a mixture of high Z materials (“cocktail”). First, the results from several previous planar sample experiments are described that demonstrated the potential of cocktail wall materials. Then a series of more recent experiments are described in which the radiation temperatures of hohlraums made from uranium-based cocktails were directly measured and compared with a gold reference hohlraum. Cocktail hohlraums meeting the oxygen specification (<5% atomic fraction oxygen) demonstrated an increase in radiation of up to 7 eV, agreeing well with modeling. When applied to an indirectly driven fusion capsule absorbing ∼160kJ of x-ray energy, these data suggest that a hohlraum made from a suitably chosen uranium-based cocktail would have about 17% less wall losses and require about 10% less laser energy than a gold hohlraum of the same size.
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National Ignition Facility
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