Dissipation of electron-beam-driven plasma wakes.

Area of Science:

• Plasma physics
• Accelerator science
• Laser-driven acceleration

Background:

• Metre-scale plasma wakefield accelerators achieve high energy gain (near 10 GeV) for electron bunches.
• Efficient energy dissipation from the wake is critical for achieving high average currents in these accelerators.
• The mechanisms of wake energy dissipation into the surrounding plasma are not well understood.

Purpose of the Study:

• To investigate the mechanisms of energy dissipation in plasma wakes.
• To understand the role of ion channels in wake energy loss.
• To provide insights into the thermodynamics of multi-gigaelectronvolt plasma accelerators.

Main Methods:

• Picosecond-time-resolved optical shadowgraphy of ion channels.
• Large-scale particle-in-cell simulations.
• Experiments using electron bunches from the SLAC linac in lithium plasma.

Main Results:

• Observed ion channels expanding radially at 1 million meters per second for over a nanosecond.
• Simulations confirmed that outward-propagating ions and electrons, carrying 90% of wake energy, drive this expansion.
• Identified impact ionization of neutral lithium as the primary expansion mechanism.

Conclusions:

• The expansion of ion channels is a key mechanism for dissipating energy from plasma wakes.
• Understanding this process is vital for optimizing plasma accelerators for high average beam currents.
• These findings contribute to the fundamental understanding of multi-GeV plasma accelerator thermodynamics and applications.