  A novel emittance meter has been developed to measure the four-dimensional,
transverse phase-space distribution of a low-energy ion beam using the
pepper-pot technique. A characteristic feature of this instrument is that the
pepper-pot plate, which has a linear array of holes in the vertical direction,
is scanned horizontally through the ion beam. This has the advantage that the
emittance can also be measured at locations along the beam line where the beam
has a large horizontal divergence. A set of multi-channel plates, scintillation
screen and ccd camera is used as a position-sensitive ion detector allowing a
large range of beam intensities that can be handled. This paper describes the
design, construction and operation of the instrument as well as the data
analysis used to reconstruct the 4D phase-space distribution of an ion beam.
Measurements on a 15 keV He+ beam are used as an example.
