Laser-driven multi-MeV high-purity proton acceleration via anisotropic ambipolar expansion of micron-scale hydrogen clusters

Abstract

Multi-MeV high-purity proton acceleration by using a hydrogen cluster target irradiated with repetitive, relativistic intensity laser pulses has been demonstrated. Statistical analysis of hundreds of data sets highlights the existence of markedly high energy protons produced from the laser-irradiated clusters with micron-scale diameters. The spatial distribution of the accelerated protons is found to be anisotropic, where the higher energy protons are preferentially accelerated along the laser propagation direction due to the relativistic effect. These features are supported by three-dimensional (3D) particle-in-cell (PIC) simulations, which show that directional, higher energy protons are generated via the anisotropic ambipolar expansion of the micron-scale clusters. The number of protons accelerating along the laser propagation direction is found to be as high as 1.6 $$\pm \,{0.3}$$ ± 0.3 $$\times$$ × 10$$^9$$ 9 /MeV/sr/shot with an energy of 2.8 $$\pm \,{1.9}$$ ± 1.9 MeV, indicating that laser-driven proton acceleration using the micron-scale hydrogen clusters is promising as a compact, repetitive, multi-MeV high-purity proton source for various applications.

The Role of Collision Ionization of K-Shell Ions in Nonequilibrium Plasmas Produced by the Action of Super Strong, Ultrashort PW-Class Laser Pulses on Micron-Scale Argon Clusters with Intensity up to 5 × 1021 W/cm2

“…Total time of the gas injection was 40-45 µs (FWHM). The system allows to produce submicron-sized CO2 and micron-size hydrogen clusters, which was experimentally demonstrated by the Mie scattering method [17][18][19]. Similar measurements were performed for argon as a working gas injected into a vacuum at a pressure of 6 MPa with a nozzle temperature of 140 K. The resulting size distributions of argon clusters are shown in Figure 1a.…”

Cryogenic solid deuterium target formation to realize highly pure deuteron acceleration by high-intensity laser

“…High-purity proton acceleration with cryogenic hydrogen targets has also been reported by other groups. [23][24][25][26] This technique can be applied to deuteron acceleration with higher purity. The triple point of D 2 is 18.7 K at 17.1 kPa, and thus there are two key points for the target formation: extremely low temperature and pressure control.…”

Measurement method for laser-accelerated multi-hundred-MeV protons utilizing multiple Coulomb scattering in an emulsion cloud chamber

“…1,2) Recently, laser-accelerated protons with energies exceeding several tens of MeV have been experimentally demonstrated with improvements in laser and target fabrication technology. [3][4][5] While many types of highenergy proton acceleration schemes have been proposed, such as radiation pressure acceleration (RPA), [6][7][8][9] collisionless shockwave acceleration (CSA), [10][11][12] and magnetic vortex acceleration (MVA), [13][14][15][16] it has been recently reported, based on numerical studies, that 0.3 GeV-class quasimonoenergetic protons could be accelerated from the interaction between a petawatt (PW) laser pulse and a micronsized hydrogen cluster [17][18][19][20] via the Converging Shockinduced Blow-off Acceleration (CSBA) model. 21) Such 0.3 GeV-class protons correspond to the energy region used for proton cancer therapy, which is a common target for the application of laser-plasma acceleration.…”

“…21) More specifically, to increase energy resolution, a pinhole with a diameter of several hundred micrometers is typically equipped to collimate protons before entering the magnetic and electric field. 19) Thus, it's impractical for TPS to enlarge the detection area and to understand the spatial profile of accelerated protons. In addition, the size of the measurement system can be several meters for hundred-MeV protons.…”