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A nonintercepting circulating-beam current monitor that senses the beam's direct-current component through a magnetic core and feedback electronics. It is suitable for total stored intensity and beam lifetime measurements; zero-offset drift and calibration must be controlled. Bunch-resolved signals instead require an appropriate time-dependent pickup or current-transformer bandwidth.

The instantaneous beam lifetime iswhere losses make $dN/dt<0$. If the fractional loss rate is constant, $N(t)=N_0{e}^{-t/\tau }$ and $\tau$ is the time to fall to $1/e$ of the starting population. At fixed revolution frequency, the circulating current has the same exponential decay. Density-dependent loss mechanisms can make the instantaneous lifetime vary, so a single exponential need not fit every fill.

Intra-bunch Coulomb scattering can transfer transverse momentum into longitudinal momentum changes large enough to exceed a storage ring's accepted momentum range. This produces particle losses and a density-dependent contribution to the beam lifetime.