Schematic overview of the controlled laser wakefield accelerator. The Ti:sapphire laser is drawn as one block, indicating that the two laser beams, to drive the plasma wakefield and to generate the electrons in the photogun, originate from the same oscillator. The figure is not on scale; the plasma channel is long, while the total beamline measures .
Beam envelope and bunch length along the beamline for a , bunch (a) and a bunch without space charge (b). Magnetic fields at the injector and the final solenoid are set to minimize beam scalloping and to focus the beam at the entrance of the plasma channel, at , respectively.
Energy spread, , as it develops during propagation of the bunch along the beamline for a bunch without space charge and bunches of 1 and , for beamline settings corresponding to those for the results shown in Fig. 2.
Same as Fig. 2 ( bunch), but for magnetic fields set for an intermediate crossover at the position of the on-axis mirror, and a waist at . Compare to Fig. 2 and note the dramatic increase of the bunch length due to the intermediate crossover, which causes locally high space charge forces and additional beam scalloping.
Current profile in longitudinal position of a , electron bunch at the entrance of the plasma channel.
Map of the final energy in MeV (numbers 40–160) (a), standard deviation of the electron energy as percentage of the average electron energy (b), and accelerated charge in pC (c) as a function of the plasma density and the injection energy of the electron bunches. The injected charge is . The length of the plasma channel is calculated for each value of , according to Eq. (3). The black dot indicates the operational point of this design and of the experiment being built up. In the dark grey areas the entire bunch is lost within a few plasma periods.
Average electron energy of the bunches, , standard deviation of the electron energy relative to the average energy, and charge , inside the plasma channel relative to the injected charge , where includes all electrons that have not yet been ejected out of the channel at the given position. For input parameters, see Table I.
Current profile in time of accelerated electron bunches at the exit of a long plasma channel with a plasma density of . Other conditions are as indicated by the black dots in Fig. 6. The bunch injected into the channel is shown in Fig. 5. The injection energy is . The central bunch has an exit energy of . The arrows indicate the width of the central bunch, FWHM.
Input parameters for the controlled LWA experiment, optimized for maximum output energy and minimum energy spread.
Output parameters according to GPT simulations for acceleration in a plasma channel with a plasma density of and a channel length of . For input parameters see Table I.
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