Description

The dual beam tube can be used to determine
the specific charge e/m from the diameter of the
path followed by electrons fired into the tube
from a perpendicularly mounted gun with a
vertically aligned magnetic field and observation
of the spiral path followed by electrons fired
axially into a coaxial magnetic field. The dual
beam tube is a partly evacuated electron tube,
filled with helium at low pressure and equipped
with both axial and perpendicular electron
guns. The electron beams are perpendicular
to one another and a common deflector plate
is provided for both guns. The electron beam
source is an oxide cathode heated indirectly via a
heating coil. The electron paths show up as a fine,
slightly greenish beam due to impact excitation
of the helium atoms. Requires a 300V or 500V d.c.
power supply.