Engineering topics
Publications and source records attributed to Geissel, Matthias.
We’re happy to report that the full-aperture upgrade project, started in FY18, is now complete and short-pulse target experiments are underway. The table below lists the present performance level of ZPW. Additional laser improvements are in progress to increase the laser energy and pulse contrast along with implementing a correction for achromatic aberrations to reduce the focused spot size and pulse width.
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All experiments involving the Pecos target chamber in calendar year (CY) 2020 were dedicated to Pre-Heat studies in the context of Magnetized Liner Inertial Fusion (MagLIF). Activities at the target area included actual laser shots but also diagnostic and maintenance, and preparatory work for experiments with cryogenically cooled targets. The latter took up a large part of CY2020’s shot availability, and consequently there were fewer shots performed than in previous years. Since the Z-Beamlet and Z-Petawatt lasers support multiple campaigns, we can only anticipate laser and laser-operator time for one out of three shot windows in a day, and typically not on every day of the week. For that reason, many of our non-shot activities need to be traded against shots as well.
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The long-term x-ray diffraction (XRD) detector scheme compatible with Z-containment experiments will involve conversion of the diffracted x-rays to optical light, which will be transported away from the Z-Dynamic Materials Properties (DMP) load and detected on a fast-gated camera. In this so-called DIffraction SCintillator Optic (DISCO) scheme , the scintillator is coupled to a long, coherent imaging fiber bundle using a custom lens system with high numerical aperture. In addition, the DISCO diagnostic incorporates time-gating to allow measurement only during the short time window of the x-ray pulse in which XRD occurs, thereby significantly reducing unwanted background generated by the Z-DMP load. Dynamic compression experiments were performed at the Chama target chamber to evaluate the DISCO diagnostic . Specifically, a Zr sample was laser-shocked with the Chaco laser while the Z-Beamlet (ZBL) laser was used to generate x-rays, which enabled time-gated 6.7-keV XRD patterns from the compressed Zr sample to be obtained.
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Prior to implosion in Magnetized Liner Inertial Fusion (MagLIF), the fuel is heated to temperatures on the order of several hundred eV with a multi-kJ, multi-ns laser pulse. In this paper, we present two laser heated plasma experiments, relevant to the MagLIF preheat stage, performed at Z with beryllium liners filled with deuterium and a trace amount of argon. In one experiment, there is no magnetic field and, in the other, the liner and fuel are magnetized with an 8.5 T axial magnetic field. The recorded time integrated, spatially resolved spectra of the Ar K-shell emission are sensitive to electron temperature T e . Individual analysis of the spatially resolved spectra produces electron temperature distributions T e (z) that are resolved along the axis of laser propagation. In the experiment with magnetic field, the plasma reaches higher temperatures and the heated region extends deeper within the liner than in the unmagnetized case. Radiation magnetohydrodynamics simulations of the experiments are presented and post-processed. A comparison of the results from experimental and simulated data reveals that the simulations underpredict T e in both cases but the differences are larger in the case with magnetic field.
All experiments involving the Pecos target chamber in calendar year (CY) 2019 were dedicated to Pre-Heat studies in the context of Magnetized Liner Inertial Fusion (MagLIF). Activities at the target area included actual laser shots but also diagnostic and maintenance, and preparatory work for experiments with cryogenically cooled targets, which are anticipated for CY 2020. Since the Z-Beamlet and Z-Petawatt lasers support multiple campaigns, we can only anticipate laser and laser-operator time for one out of three shot windows in a day, and typically not on every day of the week. For that reason, many of our non-shot activities need to be traded against shots as well.