Electrothermal instability mitigation by using thick dielectric coatings on magnetically imploded conductors.

Area of Science:

• Plasma Physics
• Materials Science
• High-Energy-Density Physics

Background:

• Magneto-Rayleigh-Taylor (MRT) instabilities are a key challenge in magnetically driven implosions.
• Surface roughness from target fabrication has been considered a primary driver of MRT instability growth.
• Electrothermal instabilities (ETIs) arising from Joule heating have been hypothesized as an alternative instability source.

Purpose of the Study:

• To investigate the role of electrothermal instabilities in seeding magneto-Rayleigh-Taylor instabilities.
• To evaluate the effectiveness of dielectric coatings in mitigating instability growth.
• To explore new techniques for enhancing the stability of magnetically driven implosions.

Main Methods:

• Experiments were conducted on Sandia's Z facility using solid metallic rods.
• Thick dielectric coatings were applied to the metallic rods.
• Instability growth was measured and compared between coated and uncoated rods.
• Simulations were used to predict and confirm experimental observations.

Main Results:

• Experiments confirmed simulation predictions of dramatically reduced instability growth with thick dielectric coatings.
• Dielectric coatings effectively mitigated density perturbations caused by electrothermal instabilities.
• Results indicate that electrothermal instabilities, not surface roughness, are the dominant instability seed in smooth-surfaced liners.

Conclusions:

• Electrothermal instabilities are the primary drivers of magneto-Rayleigh-Taylor instability growth in smooth-surfaced liners.
• Thick dielectric coatings offer a viable method to suppress electrothermal instabilities and reduce overall instability growth.
• This technique has significant implications for improving the stability and performance of inertial confinement fusion and dynamic material experiments.