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| Book/Dissertation / PhD Thesis | PUBDB-2018-02673 |
; ;
2018
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2018-02673
Report No.: DESY-THESIS-2018-027
Abstract: This thesis explores laser-driven plasma-wakefield acceleration using two different high-power,ultrashort titanium-doped sapphire lasers. The first experiment was performed at the CentralLaser Facility in the Rutherford Appleton Laboratory using the petawatt class Astra GEMINIlaser, focused by an F/40 focusing optic, and a two-stage, variable-length (< 42mm) gas targetfilled with a gas mixture to generate electron beams with charge greater 100 pC and accelerateto above 1 GeV. In this work, two-dimensional (2D) hydrodynamic simulations were performed, using the opensource fluid code OpenFOAM, to simulate the plasma-density distribution and study possiblesources of instability and unwanted effects occuring during the electron injection and acceleration,which might be adjusted in future by improvement of the plasma target design. Experimentaldata describing the properties of the electron bunch obtained with the variable-length target,have been analysed with respect to the properties of the target, including aperture diameter andinlet pressure. Plasma density modulations along the laser propagation axis lead to plasma-waketransverse oscillations and are expected to negatively impact stability.The other experiment was performed in the BOND laboratory at DESY, utilising the new 25 TW, 25 fs, Ti:Sa laser, which is focused by an F/14 off-axis parabolic mirror (OAP), onto a gastarget, reaching a peak intensity of 10$^{19}$W/cm$^{2}(a_{0}\simeq$ 2:2). Using either a gas capillary target ora supersonic gas jet, electrons were accelerated up to energies exceeding 100 MeV. These beamsexhibit a wide range of different charges. A cavity-based charge diagnostic, named DaMon,which has much better sensitivity than commercially available integrated current transformers,was tested.Simultaneous use of the DaMon together with a scintillating screen allowed estimates ofbunch charge, and showed that the sensitivity of the DaMon to beam position was negligible.Results from experiments with a 10 mm gas cell demonstrated detection of 25 $\pm$ 9 fC electronbunches, which is the lowest charge reported at the exit of a plasma wakefield accelerator. Acomparison of the electron-beam charge measured by the DaMon and the electron spectrometerdemonstrated that the DaMon has a significant advantage in acceptance angle compared to thatof the electron spectrometer, which is of crucial importance for a total charge measurement.
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