The x-ray emission in laser-plasma accelerators can be a powerful tool to understand the physics of relativistic laser-plasma interaction. It is shown here that the mapping of betatron x-ray ...radiation can be obtained from the x-ray beam profile when an aperture mask is positioned just beyond the end of the emission region. The influence of the plasma density on the position and the longitudinal profile of the x-ray emission is investigated and compared to particle-in-cell simulations. The measurement of the x-ray emission position and length provides insight on the dynamics of the interaction, including the electron self-injection region, possible multiple injection, and the role of the electron beam driven wakefield.
Betatron x-ray emission in laser plasma accelerators is a promising compact source that may be an alternative to conventional x-ray sources, based on large scale machines. In addition to its ...potential as a source, precise measurements of betatron emission can reveal crucial information about relativistic laser-plasma interaction. We show that the emission length and the position of the x-ray emission can be obtained by placing an aperture mask close to the source, and by measuring the beam profile of the betatron x-ray radiation far from the aperture mask. The position of the x-ray emission gives information on plasma wave breaking and hence on the laser non-linear propagation. Moreover, the measurement of the longitudinal extension helps one to determine whether the acceleration is limited by pump depletion or dephasing effects. In the case of multiple injections, it is used to retrieve unambiguously the position in the plasma of each injection. This technique is also used to study how, in a capillary discharge, the variations of the delay between the discharge and the laser pulse affect the interaction. The study reveals that, for a delay appropriate for laser guiding, the x-ray emission only occurs in the second half of the capillary: no electrons are injected and accelerated in the first half.
Summary form only given. X-pinch plasma is a point-like source of radiation emitting in a wide spectral range. X-pinches are known to achieve very high density (n > 10 21 cm) and temperature (>1 keV) ...at the same time resulting in energy density, much higher than 105 J/cm 3 . X-pinch radiation source has been proven to be useful for backlighting diagnostic in the keV range as well. A very compact LC generator (40kV, 200 kA) has been used for driving X-pinches made of 18-25 mum diameter Cu, Mo and W wires with a current rise time of 200 ns. A series of XRD and silicon p-i-n detectors with various filters was used to study their x-ray spectra in the range 20 eV - 10 keV. Complementary information on the multicharged ions dominating in the hot spot was provided by time integrated spectra recorded using flat and curved crystals. Time resolved spectral analysis allows us to characterize some stages of the X-pinch process : (a) The preliminary stage is relatively quiet, with an emission mainly in the spectral region below 200 eV. Its radiating power rises up to ~10s W with a time scale of 100 ns. (b) The tail stage is composed of a few bursts with some background radiation. Its spectrum lies mainly below 400 eV and the total power varies in the interval (1-4) x 108 W with time width of the bursts 2-20 ns, during about 100 ns. (c) In between, at the time of the main peak, the total power yield reaches 1.5 GW with about 35% in the energy range above 1 keV. The extreme ultraviolet part of the spectrum can be fitted by a Plankian function with a temperature 65 -75 eV. The spectral part above 1 keV can be approached by an exponential plot with effective temperature ~ 1100 eV for Mo and ~ 500 eV for Cu. The time duration of the peak bursts depends on the spectral range: from 0.4-0.7 ns above 1 keV up to 2-2.5 ns when the 200-450 eV region is recorded. The total radiated energy is estimated to be between 10 and 30 J.
Betatron x-ray emission in laser-plasma accelerators is a promising compact source that may be an alternative to conventional x-ray sources, based on large scale machines. In addition to its ...potential as a source, precise measurements of betatron emission can reveal crucial information about relativistic laser-plasma interaction. We show that the emission length and the position of the x-ray emission can be obtained by placing an aperture mask close to the source, and by measuring the beam profile of the betatron x-ray radiation far from the aperture mask. The position of the x-ray emission gives information on plasma wave breaking and hence on the laser non-linear propagation. Moreover, the measurement of the longitudinal extension helps one to determine whether the acceleration is limited by pump depletion or dephasing effects. In the case of multiple injections, it is used to retrieve unambiguously the position in the plasma of each injection. This technique is also used to study how, in a capillary discharge, the variations of the delay between the discharge and the laser pulse affect the interaction. The study reveals that, for a delay appropriate for laser guiding, the x-ray emission only occurs in the second half of the capillary: no electrons are injected and accelerated in the first half.
The x-ray emission in laser-plasma accelerators can be a powerful tool to understand the physics of relativistic laser-plasma interaction. It is shown here that the mapping of betatron x-ray ...radiation can be obtained from the x-ray beam profile when an aperture mask is positioned just beyond the end of the emission region. The influence of the plasma density on the position and the longitudinal profile of the x-ray emission is investigated and compared to particle-in-cell simulations. The measurement of the x-ray emission position and length provides insight on the dynamics of the interaction, including the electron self-injection region, possible multiple injection, and the role of the electron beam driven wakefield.
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