A gaussian underdense plasma lens with peak density 5 x 1012
cm-3 and a full width half maximum (FWHM) length of 2.2 cm has been
used to focus a relativistic electron beam. This plasma lens has a focusing
strength equivalent to a quadrupole magnet with a 150 T/m field gradient. The
lens focused a 15 MeV, 16 nC electron beam with initial dimensions σx,y ≅ 650 µm and σz
≅ 6.5 mm onto an optical transition
radiation (OTR) screen ~2 cm downstream of the lens. The average transverse
area of the plasma focused electron beam was typically demagnified by a factor
of 22. The evolution of the beam envelope in the area near the beam waist was
measured for both round beams and asymmetric beams with x:y aspect ratios as
large as 1:5. The light from the OTR screen in the round beam case was also
imaged into a streak camera in order to directly measure the correlation
between z and σr within the
beam.