SPECS EBE-1, Manual

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Mounting rods and crucibles
(3) Secure the rod or crucible with the titanium screw. Just lightly pinch the rod
with the screw. It need be no tighter than this. Over-tightening should be
avoided to prevent the screw locking in place.
(4) Drive the rod holder forward while checking the alignment and looking for pos-
sible contact between the rod holder, rod or crucible and copper block or fila-
ment.
(5) The crucible should be driven forward to within ~2 mm of the top of the copper
cooling block. This ensures that the filament is situated around the middle of
the crucible. If necessary, bend the filament back a little. It is only necessary to
insert the crucible into the rod holder far enough for the first screw to secure it.
This improves the thermal isolation of the crucible and allows it to sit forward in
the filament.
(6) Rods should be positioned as described below.
3.4 Conditioning the filament
If the filament is being used for the first time, it should be heated slowly and the HV
voltage should be off. Raise the current to say 4 A. Allow it to stay at this current for a
few seconds, then turn the filament current off. Repeat this procedure, increasing the
current by 1 A each time. When 7 A is reached leave the filament on, while a keeping
an eye on the system pressure. If the pressures rises higher than is desirable, reduce the
filament current and wait for the pressure to drop before repeating the procedure.
After several minutes of combined time operating at 7 A the system pressure will cease
to rise and start gradually falling again. At this point the filament is conditioned but
the vacuum will continue to improve with use for some time.
The filament is conditioned in this way to limit the amount of filament drift which can
occur. Filament drift could cause it to move until it touches the rod or crucible in which
case it must be replaced again. Filament drift is reduced my minimising the amount of
adjustment of the filament after the grub screws which retain it have been tightened. If
at any point during the conditioning, the electron emission current is suddenly seen to
rise, even though the HV is set to zero, a short circuit may have occurred.
EBE-1 7