Fig. 5: Plasma density evolution for the best-performing case.
From: Batch Bayesian optimization of attosecond betatron pulses from laser wakefield acceleration
a Early stage of propagation shortly after the first electron injection. b Propagation through an increasing gradient of the density spike. c A second injection is triggered while the laser pulse propagates through the decreasing gradient. d End of the acceleration and degradation of the bubble structure. The density profiles are shown at the center of the z-axis, z = 25.6 μm, and xmw is the x-coordinate comoving with the simulation window. For better visualization, n/n0 is transformed using a power-law function with exponent 0.35, \({\left((n/{n}_{0})/{(n/{n}_{0})}_{\max }\right)}^{0.35}\), where \({(n/{n}_{0})}_{\max }\) corresponds to the maximum value of the normalized density n/n0. \({E}_{x}^{{{\rm{centre}}}}\) (blue lines) corresponds to the longitudinal electric field at the center of the y and z-axis, y = z = 25.6 μm. The red crosses in the insets show the corresponding pulse position within the density gradient. The times shown above the panels are measured from when the pulse center reaches the simulation box entrance.
