arXiv subjects

C. Amoedo

Publications and source records attributed to C. Amoedo.

4 recordsLinked to original sources

arXiv2026

Demonstration of a 10-metre-long discharge plasma source for plasma wakefield acceleration

The AWAKE experiment at CERN uses high-energy proton bunches to drive plasma wakefields capable of accelerating electron bunches up to hundreds of GeV in a single plasma. Realising this potential requires a plasma source that can extend to tens of metres while maintaining high longitudinal uniformity and reproducibility. Towards this goal, we report on the first experimental characterisation and beam-based validation of a 10-metre-long pulsed-DC discharge plasma source (DPS) used as an alternative to the laser-ionised rubidium vapour plasma source (VPS). The DPS reliably delivered plasma densities in three noble gases (He, Ar, Xe) at electron densities between 10$^{14}$ and 10$^{15}$ cm$^{-3}$. Proton bunch self-modulation was observed with all three gases, and the resulting modulation frequency was used as a beam-based diagnostic of the plasma density, showing good agreement with laboratory interferometry measurements. The event-to-event modulation frequency was demonstrated to be reproducible to within 0.63%, comparable to that of the VPS. These results establish the DPS as a valid alternative plasma source for beam-driven wakefield experiments, and support its further development towards longer plasma lengths. The present design is tailored to AWAKE requirements, but the underlying discharge concept provides a route to long, reproducible plasma sources with straightforward density control through discharge-beam timing for other beam-plasma experiments.

physics.plasm-ph↗

arXiv2024

Measurement of the emittance of accelerated electron bunches at the AWAKE experiment

The vertical plane transverse emittance of accelerated electron bunches at the AWAKE experiment at CERN has been determined, using three different methods of data analysis. This is a proof-of-principle measurement using the existing AWAKE electron spectrometer to validate the measurement technique. Large values of the geometric emittance, compared to that of the injection beam, are observed ($\sim \SI{0.5}{\milli\metre\milli\radian}$ compared with $\sim \SI{0.08}{\milli\metre\milli\radian}$), which is in line with expectations of emittance growth arising from plasma density ramps and large injection beam bunch size. Future iterations of AWAKE are anticipated to operate in conditions where emittance growth is better controlled, and the effects of the imaging systems of the existing and future spectrometer designs on the ability to measure the emittance are discussed. Good performance of the instrument down to geometric emittances of approximately $\SI{1e-4}{\milli\metre\milli\radian}$ is required, which may be possible with improved electron optics and imaging.

physics.acc-ph↗

arXiv2024

Experimental Observation of Motion of Ions in a Resonantly Driven Plasma Wakefield Accelerator

We show experimentally that an effect of motion of ions, observed in a plasma-based accelerator, depends inversely on the plasma ion mass. The effect appears within a single wakefield event and manifests itself as a bunch tail, occurring only when sufficient motion of ions suppresses wakefields. Wakefields are driven resonantly by multiple bunches, and simulation results indicate that the ponderomotive force causes the motion of ions. In this case, the effect is also expected to depend on the amplitude of the wakefields, experimentally confirmed through variations in the drive bunch charge.

physics.plasm-ph↗

arXiv2023

Filamentation of a Relativistic Proton Bunch in Plasma

We show in experiments that a long, underdense, relativistic proton bunch propagating in plasma undergoes the oblique instability, that we observe as filamentation. We determine a threshold value for the ratio between the bunch transverse size and plasma skin depth for the instability to occur. At the threshold, the outcome of the experiment alternates between filamentation and self-modulation instability (evidenced by longitudinal modulation into microbunches). Time-resolved images of the bunch density distribution reveal that filamentation grows to an observable level late along the bunch, confirming the spatio-temporal nature of the instability. We calculate the amplitude of the magnetic field generated in the plasma by the instability and show that the associated magnetic energy increases with plasma density.

physics.plasm-ph↗