K. Tsuji

Model experiment of cosmic ray acceleration due to an incoherent wakefield induced by an intense laser pulse

The first report on a model experiment of cosmic ray acceleration by using intense laser pulses is presented. Large amplitude light waves are considered to be excited in the upstream regions of relativistic astrophysical shocks and the wakefield acceleration of cosmic rays can take place. By substituting an intense laser pulse for the large amplitude light waves, such shock environments were modeled in a laboratory plasma. A plasma tube, which is created by imploding a hollow polystyrene cylinder, was irradiated by an intense laser pulse. Nonthermal electrons were generated by the wakefield acceleration and the energy distribution functions of the electrons have a power-law component with an index of ∼2. The maximum attainable energy of the electrons in the experiment is discussed by a simple analytic model. In the incoherent wakefield the maximum energy can be much larger than one in the coherent field due to the momentum space diffusion or the energy diffusion of electrons.

Autoinjection of electrons into a wake field using a capillary with attached cone

By using a cone attached to a capillary, electrons generated through a laser interaction were autoinjected and accelerated in a low-density wake field. The cone attached to the entrance of the capillary serves as an electron supplier. It increases the number of electrons from below the detection limit to 1.1 pC and the energy from 4 to 30 MeV. A two-dimensional particle-in-cell simulation reveals that a significant number of energetic electrons are extracted from the surface of the cone and are subsequently trapped in the wake field and accelerated in the capillary.

Absolute calibration of imaging plate for electron spectrometer measuring GeV-class electrons

An electron spectrometer (ESM) using imaging plate (IP) is designed and tested to measure relativistic electrons which are generated from laser-plasma interactions. The measurable energy range extends to 1 GeV or even higher. The absolute sensitivity of IP for 1 GeV electrons was calibrated using electrons from Linac in SPring-8. An IP has enough sensitivity for 1-GeV electrons. The electron spectrometer, which is measurable to ~ 1 GeV, has been developed using IP detector.

High energy electron acceleration with PW‐class laser system

We performed electron acceleration experiment with PW‐class laser and a plasma tube, which was created by imploding a hollow polystyrene cylinder. In this experiment, electron energies in excess of 600 MeV have been observed. Moreover, the spectra of a comparatively high‐density plasma ∼1019 cm−3 had a bump around 10 MeV. Additionally, we performed the absolute sensitivity calibration of imaging plate for 1 GeV electrons from the injector Linac of Spring‐8 in order to evaluate absolute number of GeV‐class electrons in the laser acceleration experiment.

Electron acceleration in imploded hollow cylinder

Energetic electrons were generated using a 3-mm-long plasma tube created by imploding a hollow polystyrene cylinder. The spectra of a comparatively high-density plasma ~1019cm−3 had a bump around 10 MeV. Moreover, electron energies in excess of 600 MeV have been observed. The results of numerical calculations indicate that the bump around 10 MeV is produced by multi-dephasing of accelerated electrons in the electron plasma wave.