  Reionization of helium is expected to occur at redshifts $z\sim3$ and have
important consequences for quasar populations, galaxy formation, and the
morphology of the intergalactic medium, but there is little known empirically
about the process. Here we show that kinetic Sunyaev-Zeldovich (kSZ)
tomography, based on the combination of CMB measurements and galaxy surveys,
can be used to infer the primordial helium abundance as well as the time and
duration of helium reionization. We find a high-significance detection at
${\sim10\sigma}$ can be expected from Vera Rubin Observatory and CMB-S4 in the
near future. A more robust characterization of helium reionization will require
next-generation experiments like MegaMapper (a proposed successor to DESI) and
CMB-HD.
