The Magnetic Pump: How Plasma Compression Accelerates Particles ✦

Original: "Nonthermal Particle Acceleration by Magnetic Pumping in Pulsating Plasmas"

· Giuseppe Arrò, Vladimir Zhdankin, Fabio Bacchini

arXiv:2606.05286v1 · 2026-06-03 · CC BY · ⏱ 1 min · High Energy Plasma Physics

A computer model has shown for the first time: cyclic compressions of magnetized gas, like a cosmic pump, accelerate particles to near-light speeds.

Abstract

Imagine a box whose walls rapidly compress and expand: any ball inside would bounce harder and harder. That's roughly how the new 'pulsating box' with plasma works: a pulsing magnetic field accelerates charged particles to enormous energies, like an invisible pump. Scientists not only modeled this process but also found a simple rule linking the shaking energy to the acceleration strength. Could such 'magnetic swings' be powering the most powerful accelerators in the Universe?

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In rarefied cosmic gas—plasma—lonely particles are sometimes found rushing almost at the speed of light. Ordinary accelerators—shock waves or magnetic field reconfiguration—can't explain their energy. Recent computer modeling pointed to an unexpected candidate: the magnetic pump. If plasma is repeatedly compressed and expanded, the energy of these pulsations doesn't dissipate but is injected into individual particles. Like a bicycle pump that heats the air with each stroke, cosmic 'pumping' adds speed with each cycle.

The authors recreated on a supercomputer the pulsations similar to those raging near black holes and neutron stars. It turned out that after just five compressions, some particles were accelerated to near-light speed. Their energy distribution took on a characteristic shape with a long 'tail'—such sprinters are few, but they exist. The secret of efficiency lies in disorder: the plasma boils with small instabilities that transfer energy from large eddies to the fastest particles. Nature simply follows the path to maximum disorder, which was first realized by Ludwig Boltzmann.

Such a 'pump' helps explain the mysterious glow of gas around supernovae, in the Sun's corona, in disks near black holes, and even in the voids between galaxies. Astronomers are preparing to test the model by scrutinizing the radiation from these objects with spectroscopy.

🎯 The idea of 'magnetic pumping' was proposed back in 1958 for heating plasma in fusion reactors, and today it explains the most energetic particles in the Universe.

\frac{dN}{dp} = C p^2 \left(1 + \frac{\epsilon(p)}{\epsilon_b}\right)^{-\alpha-2}

The larger α, the steeper the drop in particle number with increasing energy ε(p). The characteristic energy ε_b separates the thermal core from the nonthermal tail, like a threshold between a calm backwater and a mountain stream.

p_H = \frac{e \langle B \rangle \lambda}{c}

A particle stops accelerating when its gyroradius equals the size λ of the accelerator. It's the moment when it can no longer make the magnetic turn and flies out, like a motorcyclist leaving the race track.

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The Magnetic Pump: How Plasma Compression Accelerates Particles ✦