2021 Fiscal Year Research-status Report
Study of electron longitudinal phase space in laser wakefield acceleration via electro-optic streaking technique
| Project/Area Number |
21K17998
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| Research Institution | National Institutes for Quantum Science and Technology |
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Principal Investigator |
黄 開 国立研究開発法人量子科学技術研究開発機構, 関西光科学研究所 光量子科学研究部, 主任研究員 (30866166)
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| Project Period (FY) |
2021-04-01 – 2023-03-31
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| Keywords | high power laser / electro-optic sampling / longitudinal phase space |
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| Outline of Annual Research Achievements |
We proposed a brand new electro-optic streaking technique for the single-shot measurement of the electron longitudinal phase space in laser wakefield acceleration. Major research achievements are:
(1) For the experimental aspect: The experimental set-up was designed carefully. The electron bunches have been optimized with energy of 300 ~ 400 MeV and narrow energy spread. New EO crystals were purchased and aluminum EO mount was manufactured.
(2) For the theoretical aspect: The EO spatial decoding process was investigated with details. The calculations contain Coulomb field propagation in EO crystal considering absorption and dispersion, the smearing between probe laser and the Coulomb field considering the relative angle and speed difference, the broadening of the probe laser, etc.
Major publication highlights: A paper "Kai Huang et al., Applied Physics Express 15, 036001 (2022)" on the single-shot electron timing measurement was published and selected as "Spotlights 2022" of the journal. An invited talk "Temporal characterization of laser driven ultrafast electron bunches via electro-optic sampling" was made in the 30th International Toki Conference on Plasma and Fusion Research (2021). An invited talk "Advanced beam diagnostics with electro-optic effect and its application to laser plasma acceleration" was given in the JPS 2022 Annual Meeting.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
This research is progressing rather smoothly. To achieving the goals of the research, the proposed plan of the first fiscal year is: design of the experimental set-up, purchase items necessary of the experiment and develop EO data processing algorithm. In the first year, we have:
(1) Designed the experimental set-up. Based on the achievable electron bunch energy range in our experiment, the EO spatial decoding geometry has been designed. The electron was designed to bend in a direction orthogonal to the EO spatial decoding direction. The magnet is being designed.
(2) The necessary items for EO sampling were purchased: including EO crystals, crystal mount, relevant optics, vacuum motorized stage components.
(3) The EO spatial decoding algorithm was developed in details. In particular, a new geometric response function was derived for the smearing process between the probe laser and Coulomb field inside the EO crystal. The exact three dimensional (3D) field structure resulted from the original electron 3D profile was calculated. A 2-dimensional EO signal deconvolution algorithm is being investigated.
A paper was published and several invited talks were given on the electron temporal diagnostics using the single-shot EO spatial decoding technique.
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| Strategy for Future Research Activity |
The development of the EO streaking technique is challenging. Although we have already introduced the EO spatial decoding technique to LWFA and achieved some results, several experimental and theoretical issues need to be figured out. To achieve the goal of this proposal, I plan to proceed the study in following aspects:
(1) The electron energy spread from LWFA is not satisfactory yet. With a large energy spread, the propagation time gap in the magnet of electrons with lowest and highest energies might be at picosecond (ps) level, which introduce errors in the LPS reconstruction.
(2) Since the electron energy in LWFA is not well controlled yet, to bend the electrons to the desired detection point at the EO crystal, it is necessary to make a variable strength permanent magnet for fine adjustment. The design of such a magnet is in process.
(3) Since the Coulomb field of the electrons has an opening angle. Even after bending, the fields from nearby electrons overlap on the EO crystal. To reconstruct the LPS of the electron bunch, it's necessary to use special deconvolution algorithms. Several well-recognized 2D deconvolution algorithms could be candidates. The noise of such deconvolution process needs to be assessed.
(4) To enhance the resolution of the detection, a sub-10 femtosecond (ps) probe laser needs to be constructed. Such techniques have already been established in Kansai Photon Science Institute.
(5) To enhance the resolution ultimately, new species of EO crystal needs to be tested. A crystal with broader frequency response range and smaller phase mismatch is desired.
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| Causes of Carryover |
The residual amount, 332 yen, is just a fraction after all the necessary items purchased in FY2021. This amount will be used with FY2022 budget to design and manufacture a variable strength permanent magnet in the next fiscal year.
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