Self-generated surface magnetic fields inhibit laser-driven sheath acceleration of high-energy protons

Area of Science:

• Plasma Physics
• Laser-Matter Interaction
• Particle Acceleration

Background:

• High-intensity lasers interacting with solid targets generate relativistic electrons and strong sheath electric fields.
• These fields accelerate proton beams with applications in radiography and material science.
• Achieving proton energies over 100 MeV is a key challenge for multidisciplinary applications.

Purpose of the Study:

• To investigate the fundamental limits of sheath-driven ion acceleration at high laser intensities.
• To explore the role of self-generated magnetostatic fields in limiting proton energy gain.

Main Methods:

• Experimental investigation of laser-solid interactions at high intensities.
• Numerical simulations to model self-generated magnetostatic fields and their effect on particle acceleration.

Main Results:

• Self-generated magnetostatic fields on the target surface were observed to increase with laser intensity.
• These fields can reach strengths of approximately 10^5 Tesla at laser intensities of 10^21 W/cm^2.
• The magnetostatic fields were shown to magnetize sheath electrons and deflect protons, limiting their acceleration.

Conclusions:

• Self-generated magnetostatic fields pose a fundamental limit to sheath-driven proton acceleration at high laser intensities.
• This limitation may prevent achieving proton energies exceeding 100 MeV through simple increases in laser intensity.
• Understanding and mitigating these magnetic fields is crucial for advancing applications requiring high-energy proton beams.