The Bennett Pinch

Plate 79 speaks for itself: “Current that strangles itself.”

The Physics

A current along a plasma column makes a magnetic field that squeezes it inward. In equilibrium the magnetic pressure balances the plasma's thermal pressure.

μ₀ I² = 8π N k_B (T_e + T_i)

• μ₀: vacuum permeability, N A⁻²
• I: current, A
• N: particles per unit length, m⁻¹
• k_B: Boltzmann constant, J K⁻¹
• T_e, T_i: electron and ion temperatures, K

Its own magnetic field squeezes the plasma. Bennett, 1934.

Sources

• W. H. Bennett, Phys. Rev. 45, 890 (1934).

On the poster

Plate 079, “The Bennett Pinch”: the pixel-art plate with its slogan “Current that strangles itself.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.