| 研究実績の概要 |
I visited the Counterpart Research Institution, the Central Laser Facility (CLF), Rutherford Appleton Lab (RAL), UK, during July-December 2021. We performed the planned joint international experiment with the Astra laser, experiment #19210005. The experiment was rather successful, we dramatically (~100 times) enhanced the BISER x-ray yield, and by this might achieve one of the main Goals of the Root Project, i.e. dramatic BISER enhancement by singularity control. However, most of the collaborators from Japan and UK could not join the experiment due to the COVID pandemic. Thus, the experiment was performed with only ~2 (sometimes 3-4) researchers, while we expected 5-6 persons working all the time. Further, the CLF schedule before the experiment was severely affected and there were restrictions on the work in the Lab, resulting in significant delays and problems in experiment preparation.
Due to the lack of man power and preparation problems, two main optical diagnostics were operated in a limited mode without high temporal resolution. Thus, our experimental knowledge of relativistic plasma dynamics was limited. We are now analyzing the existing data, which were anyway high-quality, and performing simulations to unravel the physics behind the achieved BISER enhancement.
Apart from this, we upgraded our imaging XUV spectrograph to provide 4D information, namely 1D spectrally + 1D spatially + 2D angularly resolved data.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
COVID-19 caused delays and problems.
The goals of the Astra experiment #19210005 were high-resolution imaging of plasma singularities by time-resolved Top View imager and 10 fs Schlieren optical probe. Due to COVID-19, the Central Laser Facility (CLF) schedule was delayed; further, most of the collaborators could not come. Thus, we could not obtain time-resolved Top View, neither we could get 10 fs optical probe. Instead, we used time-integrated Top View and ~50 fs optical probe, which limited our understanding of physics behind the great (>100x) BISER enhancement. Despite the problems, we managed to significantly improve performance of these diagnostics compared to the previous experiments: Top View resolution was enhanced from ~2 um (our previous best) down to sub-um, and the Shadow (used previously) was upgraded to the more-informative Schlieren optical probe.
We are now analyzing these high-quality optical data (although without high temporal resolution), very informative x-ray data, and performing hydrodynamic simulations of the supersonic gas jet flow and PIC simulations of relativistic laser-plasma interaction to understand the BISER enhancement physics.
We developed and tested a new 4D XUV spectrograph: We used a strongly-aperiodic VLS grating to focus the 1st spectral order and get 1D spectral resolution of ~300 and 1D spatial resolution of ~8um, while the defocused 0th order was used for simultaneous 2D angular distribution measurement. This provided new insight into the BISER coherent x-ray source properties from the x-ray diagnostics side.
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| 今後の研究の推進方策 |
The 2021 Astra experiment generated extremely bright BISER and it is very important to understand the physics of this enhancement. We plan to reproduce this with the J-KAREN-P laser in the next joint international experiment in Japan, and to further improve our Top View Imaging and Schlieren Optical Probe for obtaining in-depth information on relativistic plasma singularities. With these, we plan to obtain the Project and Root Project Goals, i.e. achieve the Filamentation and Self-Focusing control for further BISER brightness enhancement.
The 2021 Astra experiment also showed that the BISER angular distribution is wider than acceptance angle of our present x-ray optics. Thus, we need larger-diameter x-ray optics in order to collect the entire coherent x-ray beam. We cannot acquire such large optics as this was not in an initial Project plan. Instead, in 2022 we will estimate the BISER angular distribution and try to select best positions for our small x-ray mirrors. This will not be a real angular distribution measurement (just an estimation), nor the full-beam collection. A real measurement and full collection would cost additionally 1,500-2,000 man yen and could probably result in hundreds of micro-Joules and >10^13 photons of collected coherent soft x-rays, i.e. similar to soft x-ray FEL performance. This remains an outstanding scientific problem and a #1 goal for future Projects.
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