This thesis experimentally investigates laser-driven proton acceleration in the regime of target normal sheath acceleration (TNSA) using ultrashort (pulse duration τL = 30 fs), high power (∼100TW) laser pulses. The work focuses on how the temporal intensity profile of the ultrashort laser pulse influences the plasma formation during the laser-target interaction and the subsequent acceleration process. The corresponding experiments are performed at the Draco laser facility at the Helmholtz-Zentrum Dresden – Rossendorf. The main result of the thesis is the experimental observation of transverse spatial modulations in the laser-driven proton distribution. The onset of the modulations occurs above a target-dependent laser energy threshold and is found to correlate with parasitic laser emission preceding the ultrashort laser pulse. The analysis of the underlying plasma dynamics by using numerical simulations indicates that plasma instabilities lead to the filamentation of the laser-accelerated electron distribution. The resulting spatial pattern in the electron distribution is then transferred to the proton distribution during the acceleration process. The plasma instabilities, which the electron current is subjected to, are a surface-ripple-seeded Rayleigh-Taylor or a Weibel instability. Regarding their occurrence, both instabilities show a strong dependence on the initial plasma conditions at the target. This supports the experimentally observed connection between the temporal intensity profile of the laser pulse and the development of spatial modulations in the proton distribution. The study is considered the first observation of (regular) proton beam modulations for TNSA in the regime of ultrashort laser pulses and micrometer thick target foils. The experiments emphasize the requirement for TNSA laser power scaling studies under the consideration of realistic laser-plasma interaction conditions. In that way, the potential of the upcoming generation of Petawatt power lasers for laser-driven proton acceleration can be assessed and fully exploited. In the second part of the thesis, experimental pump-probe techniques are investigated. With an imaging method termed high depth-of-field time-resolved microscopy in a reflective probing setup, micrometer-size local features of the near-critical density plasma as well as the global topography of the plasma can be resolved. The spatio-temporal resolution of the target ionization and heating dynamics is achieved by probing the target reflectivity, whereas the angular distribution of the reflected probe beam carries signatures of the plasma expansion. The presented probing technique avails to correlate the temporal intensity profile of a laser pulse with the spatio-temporal plasma evolution triggered upon laser-target interaction.

A helicon plasma source is a device that can efficiently ionize a gas to create high density, low temperature plasma. There is growing interest in utilizing a helicon plasma source in propulsive applications, but it is not yet known if the helicon plasma source is able to function as both an ion source and ion accelerator, or whether an additional ion acceleration stage is required. In order to evaluate the capability of the helicon source to accelerate ions, the acceleration and ionization processes must be decoupled and examined individually. To accomplish this, a case study of two helicon thruster configurations is conducted. The first is an electrodeless design that consists of the helicon plasma source alone, and the second is a helicon ion engine that combines the helicon plasma source with electrostatic grids used in ion engines. The gridded configuration separates the ionization and ion acceleration mechanisms and allows for individual evaluation not only of ion acceleration, but also of the components of total power expenditure and the ion production cost. In this study, both thruster configurations are fabricated and experimentally characterized. The metrics used to evaluate ion acceleration are ion energy, ion beam current, and the plume divergence half-angle, as these capture the magnitude of ion acceleration and the bulk trajectory of the accelerated ions. The electrode-less thruster is further studied by measuring the plasma potential, ion number density, and electron temperature inside the discharge chamber and in the plume up to 60 cm downstream and 45 cm radially outward. The two configurations are tested across several operating parameter ranges: 343-600 W RF power, 50-450 G magnetic field strength, 1.0-4.5 mg/s argon flow rate, and the gridded configuration is tested over a 100-600 V discharge voltage range. Both configurations have thrust and efficiency below that of contemporary thrusters of similar power, but are distinct in terms of ion acceleration capability. The gridded configuration produces a 65-120 mA ion beam with energies in the hundreds of volts that is relatively collimated. The operating conditions also demonstrate clear control over the performance metrics. In contrast, the electrodeless configuration generally produces a beam current less than 20 mA at energies between 20-40 V in a very divergent plume. The ion energy is set by the change in plasma potential from inside the device to the plume. The divergence ion trajectories are caused by regions of high plasma potential that create radial electric fields.. Furthermore, the operating conditions have limited control of the resulting performance metrics. The estimated ion production cost of the helicon ranged between 132-212 eV/ion for argon, the lower bound of which is comparable to the 157 eV/ion in contemporary DC discharges. The primary power expenditures are due to ion loss to the walls and high electron temperature leading to energy loss at the plasma sheaths. The conclusion from this work is that the helicon plasma source is unsuitable as a single-stage thruster system. However, it is an efficient ion source and, if paired with an additional ion acceleration stage, can be integrated into an effective propulsion system.

The final thesis was created in cooperation with the Institute of Physics of the Czech Academy of Sciences and European Laser Centre ELI Beamlines. It focuses on design of monitoring device for laser target observation in a high-performance laser particle accelerator. Details of scanning and positioning system designated for operation in UHV environment are presented in this thesis. Design changes were performed in scanning system in order to achieve more effective scanning. Positioning system, consisting of precise linear and rotary motors, is newly designed device with high precision positioning under 1 µm in direction of each axis. The purpose of monitoring device is to improve overall scanning precision, shorten targeting process, and increase user comfort.

No description available.

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No description available.

This thesis experimentally investigates laser-driven proton acceleration in the regime of target normal sheath acceleration (TNSA) using ultrashort (pulse duration τL = 30 fs), high power (∼100TW) laser pulses. The work focuses on how the temporal intensity profile of the ultrashort laser pulse influences the plasma formation during the laser-target interaction and the subsequent acceleration process. The corresponding experiments are performed at the Draco laser facility at the Helmholtz-Zentrum Dresden – Rossendorf. The main result of the thesis is the experimental observation of transverse spatial modulations in the laser-driven proton distribution. The onset of the modulations occurs above a target-dependent laser energy threshold and is found to correlate with parasitic laser emission preceding the ultrashort laser pulse. The analysis of the underlying plasma dynamics by using numerical simulations indicates that plasma instabilities lead to the filamentation of the laser-accelerated electron distribution. The resulting spatial pattern in the electron distribution is then transferred to the proton distribution during the acceleration process. The plasma instabilities, which the electron current is subjected to, are a surface-ripple-seeded Rayleigh-Taylor or a Weibel instability. Regarding their occurrence, both instabilities show a strong dependence on the initial plasma conditions at the target. This supports the experimentally observed connection between the temporal intensity profile of the laser pulse and the development of spatial modulations in the proton distribution. The study is considered the first observation of (regular) proton beam modulations for TNSA in the regime of ultrashort laser pulses and micrometer thick target foils. The experiments emphasize the requirement for TNSA laser power scaling studies under the consideration of realistic laser-plasma interaction conditions. In that way, the potential of the upcoming generation of Petawatt power lasers for laser-driven proton acceleration can be assessed and fully exploited. In the second part of the thesis, experimental pump-probe techniques are investigated. With an imaging method termed high depth-of-field time-resolved microscopy in a reflective probing setup, micrometer-size local features of the near-critical density plasma as well as the global topography of the plasma can be resolved. The spatio-temporal resolution of the target ionization and heating dynamics is achieved by probing the target reflectivity, whereas the angular distribution of the reflected probe beam carries signatures of the plasma expansion. The presented probing technique avails to correlate the temporal intensity profile of a laser pulse with the spatio-temporal plasma evolution triggered upon laser-target interaction.

No description available.