  The Neutralized Drift Compression Experiment-II (NDCX-II) is an induction
linac that generates intense pulses of 1.2 MeV helium ions for heating matter
to extreme conditions. Here, we present recent results on optimizing beam
transport. The NDCX-II beamline includes a 1-meter-long drift section
downstream of the last transport solenoid, which is filled with
charge-neutralizing plasma that enables rapid longitudinal compression of an
intense ion beam against space-charge forces. The transport section on NDCX-II
consists of 28 solenoids. Finding optimal field settings for a group of
solenoids requires knowledge of the envelope parameters of the beam. Imaging
the beam on scintillator gives the radius of the beam, but the envelope angle
dr/dz is not measured directly. We demonstrate how the parameters of the beam
envelope (r, dr/dz, and emittance) can be reconstructed from a series of images
taken at varying B-field strengths of a solenoid upstream of the scintillator.
We use this technique to evaluate emittance at several points in the NDCX-II
beamline and for optimizing the trajectory of the beam at the entry of the
plasma-filled drift section.
