X-ray spot motion during 220 ps laser pulses

Technical Report · Wed May 01 00:00:00 EDT 1991

OSTI ID:5693537

Langer, S H

To meet the goals of the Precision NOVA campaign, we need to discover how to accurately and repeatably position all 10 x-ray spots at the desired location. As part of this effort, a series of shots sending all 10 beams onto a gold disk are made. There are 5 beams per side and the individual beams are aimed at 5 equally spaced points around a circle. Each beam has an incidence angle of 50 degrees relative to the disk normal. The laser pulse is a 100 or 200 ps Gaussian and each beam has an energy of roughly 200 J of 3{omega} light. A pinhole camera (PHC) with a 9 {mu}m aluminum filter is used to measure the emitted x-rays. The transmission of the filter and the response of the detector means that most of the signal comes from below the aluminum K-edge at 1.6 keV if only the aluminum filter is present. If the beryllium filter is also used, half of the remaining signal is due to the gold M-band. The sub-critical portions of the ablated gold produce M-band emission, so some of the PHC signal comes from significantly in front of the disk. The direction of the offset is consistent with the hypothesis that the spot has shifted backward along the beam in a fashion similar to the spot motion that has been measured in longer pulse shots. On the other hand, there is no obvious reason why spot motion would leave 4 beams at their intended positions and 6 beams with large repeatable offsets of 100 {mu}m. The goal of this paper is to find out if LASNEX models support the suggestion that the offset between the measured x-ray spot positions and the point at which the laser beams were aimed can be explained by spot motion. Ron Thiessen's modeling in support of indirect drive implosions has shown that the spot motion reaches 100--150 {mu}m at the end of a 1 ns pulse, so the motion should be quite small for the 100 or 200 ps pulses considered here. The models run for this paper show the expected result, they predict roughly 10{mu}m of spot motion for the 200 ps pulse.

• Research Organization: Lawrence Livermore National Lab., CA (USA)
• Sponsoring Organization: USDOE; USDOE, Washington, DC (USA)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5693537
• Report Number(s): UCRL-ID-107120; ON: DE91012111
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
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POSITIONING
COORDINATES
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MATHEMATICAL MODELS
MOTION
NOVA FACILITY
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TIME DEPENDENCE
COMPUTER CODES
ELECTROMAGNETIC RADIATION
IONIZING RADIATIONS
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