From LWFA bunch durations to bunch profile and micro-structure: Longitudinal electron bunch diagnostics for LWFA based on broadband, spectral CTR measurements at single-shot


From LWFA bunch durations to bunch profile and micro-structure: Longitudinal electron bunch diagnostics for LWFA based on broadband, spectral CTR measurements at single-shot

Debus, A.; Zarini, O.; Laberge, M.; Couperus Cabadağ, J. P.; Koehler, A.; Kurz, T.; Schoebel, S.; Kraemer, J.; Hannasch, A.; Zgadzaj, R.; Bussmann, M.; Downer, M.; Schramm, U.; Irman, A.

Laser-wakefield accelerators (LWFA) feature electron bunch durations on a scale of a few fs. Precise knowledge of the longitudinal profile of such ultra-short electron bunches is essential for the design of future table-top X-ray light sources. The resolution limit, as well as the limited reproducibility of electron bunches, pose big challenges for LWFA beam diagnostics.

Spectral measurements of broadband transition radiation from LWFA electron bunches passing through a metal foil are especially promising for analyzing ultrashort longitudinal bunch characteristics ranging from of tens of fs down to sub-fs.

Our broadband, single-shot spectrometer combines the TR spectrum in UV/VIS (200-1000nm), NIR (0.9-1.7μm) and mid-IR (1.6-12μm). A complete characterization and calibration of the spectrometer has been done with regard to wavelengths, relative spectral sensitivities and absolute photometric sensitivity. Our spectrometer is able to characterize electron bunches with charges as low as 1 pC and resolve time-scales from 0.7 to 40 fs.

We present results from recent measurement campaign by analyzing transition radiation spectra produced by nC class LWFA electron bunches using ionization-injection, while complementary data on the transverse bunch profile is provided by simultaneously imaging the CTR in the far- and near-field.

We discuss the data analysis from detection to profile reconstruction with error analysis and show electron bunch profiles as determined from experimental density scan measurements.

Keywords: broadband spectrometer; single-shot bunch length measurement; coherent transition radiation; absolute calibration; electron bunch duration; longitudinal profile; absolute calibration; UV; VIS; NIR; MIR

  • Lecture (Conference)
    Advanced Accelerator Concepts (AAC 2018), 12.-17.8.2018, Breckenridge, Colorado, United States

Permalink: https://www.hzdr.de/publications/Publ-28522
Publ.-Id: 28522