Mark Sherlock | 20-FS-013
Magnetic fields in excess of 1 gigagauss enable various diagnostic and scientific capabilities. To enable these capabilities, we studied the theoretical feasibility of reliably generating laboratory magnetic fields in excess of 1 gigagauss with future short-pulse laser-plasma experiments. Our approach to reach high magnetic fields was to design laser targets with varying material resistivity, such as by inserting a high-compressibility factor (high-Z) material core inside an outer layer of low-Z material. The resistivity gradient introduced in this type of design leads to magnetic field generation at the material boundaries, driven by the target's electromagnetic response to the flood of fast electrons generated by the short-pulse. Prior modeling work on this topic was limited to relatively low-Z materials since it did not include radiation transport.
We developed a new computational model that includes radiation transport and material properties, allowing us to study highly radiating targets. Our simulations suggest that moving into the highly radiative regime enables the generation of much stronger magnetic fields. We obtained 0.3 gigagauss using copper (Z=29) layers and 8 picosecond pulses, with the preliminary simulations indicating that this should exceed 1 gigagauss in more appropriate materials (e.g., gold) and with longer pulses. In addition, we developed a model for describing fast electrons with properties typical of the long-scale-length plasmas present in this experimental regime.
We successfully demonstrated that radiative cooling in high-Z targets is a route to the generation of very strong magnetic fields, around 1 to 2 orders of magnitude greater than previous studies. This finding should enable future applications that require the control of very energetic electrons. For example, a short-pulse gamma-ray source would be useful for radiographing imploding primaries. Synchrotron x-ray sources are used to study material properties and biological samples, and a laser-driven source enabled by this work may be brighter.
Our project supports high-energy-density (HED) science research, including Lawrence Livermore National Laboratory's nuclear weapons science mission research challenge and HED science core competency. For example, weapons science research could benefit from intense sources in the energy range of tens of kiloelectron volts. Our research could also enable other types of future research, such as exploring the use of a short-pulse gamma-ray source for destroying tumors, or studying shocked materials.