Two-Pulse Ionization Injection into Quasilinear Laser Wakefields

Abstract

We describe a scheme for controlling electron injection into the quasilinear wakefield driven by a guided drive pulse via ionization of a dopant species by a collinear injection laser pulse with a short Rayleigh range. The scheme is analyzed by particle-in-cell simulations which show controlled injection and acceleration of electrons to an energy of 370 MeV, a relative energy spread of 2%, and a normalized transverse emittance of 2.0 μm.

Two-Color Laser-Ionization Injection

“…This tworegion gas structure allows control of the injection number and energy spread by changing the gas composition, concentration, and length of the mixed gas region [14]. The ionization injection region is also determined by the Rayleigh range of the injection pulse Z R,1 = πw 2 1 /λ 1 , and the Rayleigh range may be used to control (limit) the effective length of the ionization injection region [15]. The electron density (after ionization by the pump laser) is fixed to n 0 = n e + 8n Kr = 2 × 10 17 cm −3 , where n e electron density produced by ionization of the low-Z gas (e.g., H gas), and the pump laser ionizes the Kr gas to Kr 8+ .…”

“…The length of the Kr gas region may also be increased for generation of additional trapped charge, however, ionization decreases rapidly due to the laser diffraction after a Rayleigh length of the ionization pulse (Z R,1 = 0.2 mm for the example considered). The Rayleigh length of the injection pulse may also be used to control the ionization injection region [15].…”

“…In order to improve the quality and stability of laserplasma-accelerated electron beams, controlled injection methods are actively being pursued, including colliding pulse injection [6,7], plasma density transitions [8,9], and ionization injection [10][11][12][13][14][15]. Ionization injection, compared to self-trapping, allows electron beam generation at lower plasma densities and, hence, higher beam energies can be achieved.…”

Optical plasma torch electron bunch generation in plasma wakefield accelerators

“…That said, the method can also have applicability to LWFA if using higher laser intensities for the torch laser when compared to the drive laser similar as in [30]. Finally, the proposed method does open up a path to higher repetition rates and higher efficiency when compared to hydrodynamic solutions.…”

“…In both cases, injection of electron beams into the proper phase of the plasma wave is of paramount importance to obtain high-quality witness bunches from the plasma. A multitude of injection methods has been conceived, among those hydrodynamics-based plasma density transition [14][15][16][17][18][19][20], injection by additional ionization [21][22][23][24][25][26][27][28][29][30] and Trojan Horse-type methods [31][32][33][34][35][36][37][38].…”