Characterization of laser-driven single and double electron bunches with a permanent magnet quadrupole triplet and pepper-pot mask

Abstract

Electron beams from laser-plasma wakefield accelerators have low transverse emittance, comparable to those from conventional radio frequency accelerators, which highlights their potential for applications, many of which will require the use of quadrupole magnets for optimal electron beam transport. We report on characterizing electron bunches where double bunches are observed under certain conditions. In particular, we present pepper-pot measurements of the transverse emittance of 120-200 MeV laser wakefield electron bunches after propagation through a triplet of permanent quadrupole magnets. It is shown that the normalized emittance at source can be as low as 1 π mm mrad (resolution limited), growing by about five times after propagation through the quadrupoles due to beam energy spread. The inherent energy-dependence of the magnets also enables detection of double electron bunches that could otherwise remain unresolved, providing insight into the self-injection of multiple bunches. The combination of quadrupoles and pepper-pot, in addition, acts as a diagnostic for the alignment of the magnetic triplet.

Design of a double dipole electron spectrometer

“…Knowing both the energy and angle is also of interest for high precision emittance measurements. 28,29 Given the geometry of the experimental chamber, the following constraints are taken into account in the simulations: the source-dipole entrance distance D SD is 100 mm and the source-screen distance D SS is 1350 mm. Subsequently the parameters chosen for the simulations are a magnetic field close to 1 T and an electron beam source of energy ranging from 50 to 1450 MeV with a divergence up to 5 mrad.…”

“…By measuring the electron beam energy and output angle of the bunch, the emittance can be measured employing the pepper pot technique, 28,29 at a selected energy and even at high energies 33,34 using the well-known relation for the RMS emittance rms : rms = √ < x 2 >< x 2 > − < xx > 2 , where < x 2 > is the averaged square position, < x 2 > is the averaged square divergence and < xx > the cross product. This scheme allows to increase the energy resolution and lower the error on the energy determination.…”

Optical control of electron phase space in plasma accelerators with incoherently stacked laser pulsesa)

“…On the other hand, polychromatic, modulated, fs-length electron beams, associated with multiple injections into the first bucket, [70][71][72] or into consecutive buckets of the laser wake, 73 have been frequently observed. By exerting control over the dynamics responsible for multiple injection, these polychromatic (or "comb-like") beams may be deliberately produced, 19,20 optimized, and exploited for unique applications.…”

Optically controlled laser–plasma electron accelerator for compact gamma-ray sources

“…femtosecond) e-beams [25]. Besides, polychromatic (or 'comb-like') beams from an LPA, with the current modulated on a femtosecond scale, have been observed in experiments [26][27][28][29]. Simulations indicate that such beams readily lend themselves to all-optical manipulation, promising generation of spectrally controlled quasi-monochromatic, femtosecond γ-ray pulses, or trains of pulses with a femtosecond synchronization [9][10][11].LPAs, however, face a number of challenges, one of which is preservation of beam quality, that is, elimination of a high-charge, low-energy tail, which develops when acceleration is continued through electron dephasing [30][31][32][33][34].…”

“…femtosecond) e-beams [25]. Besides, polychromatic (or 'comb-like') beams from an LPA, with the current modulated on a femtosecond scale, have been observed in experiments [26][27][28][29]. Simulations indicate that such beams readily lend themselves to all-optical manipulation, promising generation of spectrally controlled quasi-monochromatic, femtosecond γ-ray pulses, or trains of pulses with a femtosecond synchronization [9][10][11].…”