Penning traps provide a mechanism for confining charged particles using an electrostatic field and a homogeneous magnetic field. The time-independence of the Penning trap's electric and magnetic fields is significant because: (1) the time-independent Hamiltonian mandates conservation of energy; thus, there is no heating mechanism for Penning-trapped particles; (2) Penning-trapped particles are not subjected to the high-energy micromotion induced by the Paul trap's time-varying electric field. As a result of these two properties, Penning-trapped particles can be cooled to an extent that renders second-order Doppler shifts negligible.
The aforementioned attributes of the Penning trap provide ample motivation
for Penning trap particle confinement. To begin with, the magnetic field enables measurement
of magnetic-field-dependent quantities such as the electron magneton
moment. Secondly, the lack of a heating mechanism allows for study of
a large number of interacting particles at constant energy,
which in turn yields insight into behavior of one-component plasmas.
Thirdly, one can, in the absence of micromotion,
reduce kinetic energy more easily in a Penning trap than in a Paul trap.