Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam

Area of Science:

• Plasma Physics
• Astrophysics
• Particle Accelerators

Background:

• Matter-antimatter beams are crucial for understanding high-energy astrophysical phenomena.
• Previous models suggested magnetic field generation in such interactions, but experimental evidence was lacking.
• Electron-positron beams are relevant to astrophysical jets and gamma-ray bursts.

Purpose of the Study:

• To experimentally observe and characterize magnetic field generation in a quasineutral matter-antimatter beam.
• To investigate the persistence and strength of these magnetic fields.
• To compare experimental findings with astrophysical models.

Main Methods:

• Utilizing a proton radiography technique to measure magnetic fields.
• Propagating a neutral electron-positron beam through a background electron-ion plasma.
• Employing particle-in-cell simulations and analytical estimates for data interpretation.

Main Results:

• First experimental observation of a current-driven instability in a matter-antimatter beam.
• Measurement of strong magnetic fields (≥1 T) generated by the beam.
• Determination of an equipartition parameter (εB ≈ 10^-3) consistent with gamma-ray burst models.
• Evidence of persistent magnetic fields in the background plasma for thousands of inverse plasma frequencies.

Conclusions:

• The experiment confirms the generation of significant magnetic fields in matter-antimatter plasmas.
• The observed magnetic field strength and persistence align with theoretical predictions for astrophysical systems.
• These findings provide insights into the dynamics of lepton-dominated jets and gamma-ray bursts.