Beam loading by distributed injection of electrons in a plasma wakefield accelerator

Area of Science:

• Plasma physics
• Particle acceleration
• Beam-plasma interactions

Background:

• Relativistic electron bunches are used for particle acceleration.
• Plasma wakefields can support strong accelerating fields.
• Beam loading can significantly impact wakefield dynamics.

Purpose of the Study:

• To investigate the effects of electron bunch propagation on plasma wakefields.
• To quantify the impact of beam loading on the transformer ratio.
• To identify the source of injected electrons and their role in wakefield depletion.

Main Methods:

• Experimental studies of relativistic electron bunch propagation through plasma.
• Supporting simulations to model wakefield dynamics and electron injection.
• Measurement of electron energy gain and loss as a function of beam emittance and loading.

Main Results:

• Distributed electron injection observed, originating from rubidium (Rb II) ionization.
• Significant beam loading effect demonstrated, reducing the transformer ratio (T).
• Peak accelerating field reduced from 43 GV/m (weakly loaded) to 26 GV/m (strongly loaded) due to Rb II electron injection.

Conclusions:

• Ionization of Rb II electrons is a primary source of beam loading in this plasma.
• Beam loading severely depletes the accelerating wakefield, reducing transformer ratio and acceleration efficiency.
• Understanding and mitigating beam loading is crucial for advanced plasma-based accelerators.