  In a Low Energy Beam Transport line (LEBT), the emittance growth due to the
beam's space charge is typically suppressed by way of neutralization from
either electrons or ions, which originate from ionization of the background
gas. In cases where the beam is chopped, the neutralization pattern usually
changes throughout the beginning of the pulse, causing the Twiss parameters to
differ significantly from their steady state values, which, in turn, may result
in beam losses downstream. For a modest beam perveance, there is an alternative
solution, in which the beam is kept un-neutralized in the portion of the LEBT
that contains the chopper. The emittance can be nearly preserved if the
transition to the un-neutralized section occurs where the beam exhibits low
transverse tails. This report introduces the rationale for the proposed scheme
and formulates the physical arguments for it as well as its limitations. An
experimental realization of the scheme was carried out at Fermilab's PIP2IT
where low beam emittance dilution was demonstrated for a 5 mA, 30 keV $H^{-}$
beam.
