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Home/Biophysics, Fluids & Geoscience/Quadrupole / Penning-Style Trap

Quadrupole / Penning-Style Trap

A static electric quadrupole Φ ∝ x²−y² creates a saddle potential; combined with a uniform axial magnetic field, Lorentz forces can confine charged particle orbits in the plane. Three test charges with different initial conditions illustrate bounded epicyclic motion — a qualitative cousin of Penning traps, not a radio-frequency Paul trap.

Who it's for: Students linking E×B dynamics to mass spectrometry hardware.

Key terms

  • Penning trap
  • Quadrupole potential
  • Lorentz force
  • Magnetron motion

Trap fields

0.22
1.4
0.85

Idealized 2D motion: E = −∇Φ with Φ = A(x²−y²) (hyperbolic quadrupole) and Lorentz acceleration (q/m)(E + v×B) with B along ẑ. Three non-interacting test charges illustrate bounded “magnetron-like” orbits — not a full RF Paul trap with time-varying fields.

Measured values

Particles3

How it works

Classical charged-particle dynamics in a static electric saddle plus uniform magnetic field: a qualitative cousin of Penning/Paul traps used in mass spectrometry.

Frequently asked questions

Why no RF drive?
Paul traps require time-varying fields for a ponderomotive pseudopotential; this page keeps Φ static for transparent classical trajectories.