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Mocko, Michal

Publications and source records attributed to Mocko, Michal.

12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Laser-plasmas in the relativistic-transparency regime: science and applications

Laser-plasma interactions in the novel regime of relativistically induced transparency (RIT) have been harnessed to generate intense ion beams efficiently with average energies exceeding 10 MeV/nucleon (>100 MeV for protons) at “table-top” scales in experiments at the LANL Trident Laser. By further optimization of the laser and target, the RIT regime has been extended into a self-organized plasma mode. This mode yields an ion beam with much narrower energy spread while maintaining high ion energy and conversion efficiency. This mode involves self-generation of persistent high magnetic fields (~10 4 T, according to particle-in-cell simulations of the experiments) at the rear-side of the plasma. These magnetic fields trap the laser-heated multi-MeV electrons, which generate a high localized electrostatic field (~0.1 TV/m). After the laser exits the plasma, this electric field acts on a highly structured ion-beam distribution in phase space to reduce the energy spread, thus separating acceleration and energy-spread reduction. Thus, ion beams with narrow energy peaks at up to 18 MeV/nucleon are generated reproducibly with high efficiency (≈5%). The experimental demonstration has been done with 0.12 PW, high-contrast, 0.6 ps Gaussian 1.053 μm laser pulses irradiating planar foils up to 250 nm thick at 2–8 × 10 20 W/cm 2 . These ion beams with co-propagating electrons have been used on Trident for uniform volumetric isochoric heating to generate and study warm-dense matter at high densities. These beam plasmas have been directed also at a thick Ta disk to generate a directed, intense point-like Bremsstrahlung source of photons peaked at ~2 MeV and used it for point projection radiography of thick high density objects. In addition, prior work on the intense neutron beam driven by an intense deuterium beam generated in the RIT regime has been extended. Neutron spectral control by means of a flexible converter-disk design has been demonstrated, and the neutron beam has been used for point-projection imaging of thick objects. Finally, we discuss the plans and prospects for further improvements and applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Progress on FP13 Total Cross Section Measurements Capability

An accurate knowledge of the neutron capture cross section is important for many applications. Experimental measurements are important since theoretical calculations of capture have been notoriously difficult, with the ratio of measured to calculated cross sections often a factor of 2 or more in the 10 keV to 1 MeV region. However, a direct measurement of capture cannot be made on many interesting radioactive nuclides because of their short half-life or backgrounds caused by their nuclear decay. On the other hand, neutron transmission measurements of the total cross section are feasible for a wide range of radioactive nuclides since the detectors are far from the sample, and often are less sensitive to decay radiation. The parameters extracted from a total cross section measurement, which include the average resonance spacing, the neutron strength function, and the average total radiation width, (Γ γ ), provide tight constraints on the calculation of the capture cross section, and when applied produce much more accurate results. These measurements can be made using the intense epithermal neutron flux at the Lujan Center on relatively small quantities of target material. It was the purpose of this project to investigate and develop the capability to make these measurements. A great deal of progress was made towards establishing this capability during 2016, including setting up the flight path and obtaining preliminary results, but more work remains to be done.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Redesign of the Target-Moderator-Reflector-Shield Assembly for Optimization of the Neutron Flux in the 0.001 – 1 MeV at LANSCE

These are the slides for a presentation at the 2016 Postdoc Summer Seminar Series at Los Alamos National Laboratory. The conclusions of the research presented are the following: we can provide a significant gain in intensity in the upper tier; lower and upper tier are coupled: translating the target in the FOV of the upper tier decreases the intensity in the lower tier; it is possible to balance the production between the upper and lower tier if we keep some of the material between the tiers.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Overview of the Neutron experimental facilities at LANSCE

This presentation gives an overview of the neutron experimental facilities at LANSCE. The layout is mentioned in detail, with a map of the south-side experimental facilities, information on Target-4 and the Lujan Center. Then it goes into detail about neutron sources, specifically continuous versus pulsed. Target 4 is then discussed. In conclusion, we have introduced the south-side experimental facilities in operation at LANSCE. 1L target and Target 4 provide complementary neutron energy spectra. Two spallation neutron sources taken together cover more than 11 orders of magnitude in neutron energy.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

Demonstration of a Single-Crystal Reflector-Filter for Enhancing Slow Neutron Beams

The cold polycrystalline beryllium reflector-filter concept has been used to enhance the cold neutron emission of cryogenic hydrogen moderators, while suppressing the intermediate wavelength and fast neutron emission at the same time. While suppressing the fast neutron emission is often desired, the suppression of intermediate wavelength neutrons is often unwelcome. It has been hypothesized that replacing the polycrystalline reflector-filter concept with a single-crystal reflector-filter concept would overcome the suppression of intermediate wavelength neutrons and thereby extend the usability of the reflector-filter concept to shorter but still important wavelengths. In this paper we present the first experimental data on a single-crystal reflector-filter and compare experimental results with hypothesized performance. We find that a single-crystal reflector-filter retains the long-wavelength benefit of the polycrystalline reflector-filter, without suffering the same loss of important intermediate wavelength neutrons. Ultimately, this finding extends the applicability of the reflector-filter concept to intermediate wavelengths, and furthermore indicates that the reflector-filter benefits arise from its interaction with fast (background) neutrons, not with intermediate wavelength neutrons of potential interest in many types of neutron scattering.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Beam line shielding calculations for an Electron Accelerator Mo-99 production facility

The purpose of this study is to evaluate the photon and neutron fields in and around the latest beam line design for the Mo-99 production facility. The radiation dose to the beam line components (quadrupoles, dipoles, beam stops and the linear accelerator) are calculated in the present report. The beam line design assumes placement of two cameras: infra red (IR) and optical transition radiation (OTR) for continuous monitoring of the beam spot on target during irradiation. The cameras will be placed off the beam axis offset in vertical direction. We explored typical shielding arrangements for the cameras and report the resulting neutron and photon dose fields.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Mo100 to Mo99 Target Cooling Enhancements Report

Target design requirements changed significantly over the past year to a much higher beam current on larger diameter disks, and with a beam impingement on both ends of the target. Scaling from the previous design, that required significantly more mass flow rate of helium coolant, and also thinner disks. A new Aerzen GM12.4 blower was selected that can deliver up to 400 g/s at 400 psi, compared to about 100 g/s possible with the Tuthill blower previously selected.Further, to accommodate the 42 MeV, 2.7 mA beam on each side of the target, the disk thickness and the coolant gaps were halved to create the current baseline design: 0.5 mm disk thickness (at 29 mm diameter) and 0.25 mm coolant gap. Thermal-hydraulic analysis of this target, presented below for reference, gave very good results, suggesting that the target could be improved with fewer, thicker disks and with disk thickness increasing toward the target center. The total thickness of Mo100 in the target remaining the same, that reduces the number of coolant gaps. This allows for the gap width to be increased, increasing the mass flow in each gap and consequently increasing heat transfer. A preliminary geometry was selected and analyzed with variable disk thickness and wider coolant gaps. The result of analysis of this target shows that disk thickness increase near the window was too aggressive and further resizing of the disks is necessary, but it does illustrate the potential improvements that are possible. Experimental and analytical study of diffusers on the target exit has been done. This shows modest improvement in requcing pressure drop, as will be summarized below. However, the benefit is not significant, and implementation becomes problematic when disk thickness is varying. A bull nose at the entrance does offer significant benefit and is relatively easy to incorporate. A bull nose on both ends is now a feature of the baseline design, and will be a feature of any redesign or enhanced designs that follow.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Practical in-situ determination of ortho-para hydrogen ratios via fiber-optic based Raman spectroscopy

An experiment was designed and developed to prototype a fiber-optic-based laser system, which measures the ratio of ortho-hydrogen to para-hydrogen in an operating neutron moderator system at the Los Alamos Neutron Science Center (LANSCE) spallation neutron source. Preliminary measurements resulted in an ortho to para ratio of 3.06:1, which is within acceptable agreement with the previously published ratio. As a result, the successful demonstration of Raman Spectroscopy for this measurement is expected to lead to a practical method that can be applied for similar in-situ measurements at operating neutron spallation sources.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Design of the Fifth-Generation Target-Moderator-Reflector-Shield Assembly

The facilities at the Los Alamos Neutron Science Center are described first. The target is being redesigned so that the Flight Paths (FP) in the upper tier provide a higher intensity in the epithermal and medium energy range. It is found that a 3-piece design looks promising: intensity in epithermal and medium energy range in upper tier is an order of magnitude higher than current Mark III, and intensity in the thermal energy range is higher in the lower tier than current Mark III. Time emission spectra show a bump due to the scattering of fast neutrons. Other investigations such as the addition of wings around the upper target will be conducted.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Facility target insert shielding assessment

Main objective of this report is to assess the basic shielding requirements for the vertical target insert and retrieval port. We used the baseline design for the vertical target insert in our calculations. The insert sits in the 12”-diameter cylindrical shaft extending from the service alley in the top floor of the facility all the way down to the target location. The target retrieval mechanism is a long rod with the target assembly attached and running the entire length of the vertical shaft. The insert also houses the helium cooling supply and return lines each with 2” diameter. In the present study we focused on calculating the neutron and photon dose rate fields on top of the target insert/retrieval mechanism in the service alley. Additionally, we studied a few prototypical configurations of the shielding layers in the vertical insert as well as on the top.

Accelerator Design, Technology, and Operations↗