Stability of the modulator in a plasma-modulated plasma accelerator

Area of Science:

• Plasma physics
• Accelerator science
• Laser-plasma interactions

Background:

• The plasma-modulated plasma accelerator (P-MoPA) scheme proposes a pathway for high-repetition-rate, GeV-scale accelerators using picosecond laser pulses.
• The initial stage involves a plasma modulator where a drive pulse is spectrally modulated by a plasma wave generated by a seed pulse.
• This spectral modulation, when combined with dispersion, can create a pulse train capable of resonantly driving wakefields in subsequent stages.

Purpose of the Study:

• To explore the operational regime of the modulator stage in the P-MoPA laser-plasma accelerator scheme.
• To develop a 3D analytic theory for the drive pulse evolution within the plasma modulator.
• To identify limitations and potential improvements for high-energy drive pulses in the P-MoPA scheme.

Main Methods:

• Derivation of a 3D analytic theory for the spectral modulation of the drive pulse in the plasma modulator.
• Identification and analysis of a transverse mode instability (TMI) affecting drive pulse energy.
• Comparison of analytic theory predictions with particle-in-cell (PIC) simulations.

Main Results:

• The derived analytic theory shows that spectral modulation is independent of the transverse coordinate, which is advantageous for pulse compression.
• A transverse mode instability (TMI) was identified, imposing limits on the drive pulse energy based on laser-plasma parameters.
• PIC simulations validated the analytic theory and indicated that drive pulses with higher energies than initially proposed can be modulated.

Conclusions:

• The P-MoPA modulator stage exhibits robust spectral modulation suitable for generating pulse trains.
• The identified TMI is a critical factor in determining the operational limits for high-energy drive pulses.
• The study suggests that the P-MoPA scheme can potentially accommodate higher drive pulse energies, enhancing its feasibility for advanced accelerators.