X-ray Generation in Strongly Nonlinear Plasma Waves

We show that a laser wake field in the “bubble” regime [A. Pukhov and J. Meyer-ter-Vehn Appl. Phys. B 74, 355 (2002)], works as a compact high-brightness source of x-rays. The self-trapped relativistic electrons make betatron oscillations in the transverse fields of the bubble and emit a bright broadband x-ray radiation with a maximum about 50 keV. The emission is confined to a small angle of about 0.1 rad. In addition, we make simulations of x-ray generation by an external 28.5 GeV electron bunch injected into the bubble. $\gamma$ quanta with up to GeV energies are observed in the simulation in good agreement with analytical results. The energy conversion is efficient, leading to a significant stopping of the electron bunch over 5 mm interaction distance.

Figure 1

The evolution of the laser pulse intensity (the colored scale) and the bubble (the electron density is given in the black/white scale) in the strongly nonlinear broken-wave regime. The laser pulse propagates in a plasma layer from left to right. The plasma density and the laser intensity at (a) $ct/\lambda =500$, (b) $ct/\lambda =1000$, (c) $ct/\lambda =2000$, and (d) $ct/\lambda =4000$.

Figure 2

(a) The transversal force acting on the relativistic electrons moving in the $x$ direction at $ct/\lambda =2000$. (b) Temporal variation of the energy spectrum of the electron bunch: (1) $ct/\lambda =1000,$ (2) $ct/\lambda =2000,$ (3) $ct/\lambda =3000,$ (4) $ct/\lambda =4000$.

Figure 3

(a) The synchrotron spectrum from the plasma at $ct/\lambda =1000$, (b) at $ct/\lambda =4500$, (c) the photon flux (the number of photons per second in 0.1% bandwidth), and (d) the spectral brilliance. The dashed line in frames (c) and (d) corresponds to $ct/\lambda =1000$; the solid line corresponds to $ct/\lambda =4500$.

Figure 4

Temporal evolution of the plasma density, laser intensity, and the envelope of the external 28.5 GeV electron bunch (blue): (a) at the beginning of interaction and (b) at $ct/\lambda =1500$.

Figure 5

(a) Synchrotron spectrum from the external 28.5 GeV electron bunch at $ct/\lambda =4500$; (b) energy distribution of the bunch electrons: the solid line corresponds to $ct/\lambda =4500$ while the dashed arrow marks the initial energy of the electron bunch; (c) photon flux and (d) spectral brilliance. The dashed line in frames (c) and (d) corresponds to $ct/\lambda =500$; the solid line corresponds to $ct/\lambda =4500$.