Monochromated X-Ray Source with XR5 Electron Gun
Issue 5
Monochromator and XR5 (HA600054)
21
5.3 Anode
Maintenance
The anode has an active length of 25mm, but the electron gun spot on the anode is of
the order of 1mm in diameter or less. Over a time, the period of which depends upon
the power density impinging upon the anode, the X-Ray signal obtained will decrease
in amplitude due to degradation of the coating. When the signal has dropped to
unacceptable levels the anode can be moved to a fresh area by turning the knurled
knob on the
“Z”
drive on which the anode is mounted. This is best achieved by
monitoring the signal using the ratemeter so the improvement can be ascertained in
combination with viewing the spots on a suitable phosphor sample. In general a
movement of 1mm or less should be sufficient, which corresponds to a little less than
one turn of the drive. This will give a total of 25 fresh areas on the anode.
Figure 5-2: Location of the Anode Shift Drive
Follow the procedure below to replace the monochromator anode surface:
1. Set up the ESCALAB 250 system so that you can observe the intensity of the
monochromator source, either by observing the spot on a phosphor sample or
an XPS signal, such as Ag3d
5/2
from a standard silver sample.
2. Locate the anode linear motion drive with reference to Figure 5-2.
3. Rotate the linear motion drive to move the anode by less than 1 turn (< 0.8
mm) in either direction, or until the signal level or spot brightness are restored
to their normal level and further movement has no effect.
4. If observing the spot on a phosphor, burn marks will be visible as dark patches.
Move the anode until these are not visible in the beam spot diameter that is
required. It is wise to start at one end of a new anode and then to
systematically move the anode in the same direction to obtain each fresh
surface. In this way it is possible to judge what fraction of the anode has been
used at any time and to plan to replace the anode as part of a routine
maintenance schedule.
Monochromated X-Ray Source with XR5 Electron Gun
Monochromator and XR5 (HA600054)
Issue 5
22
5.4 Replacing
Anodes
In general, the anode will need replacing only when all the aluminium coating has been
degraded sufficiently to attenuate the X-Ray flux below acceptable levels along its
entire length.
If the anode condition requires its replacement, the vacuum system will have to be fully
shut down and vented to dry nitrogen.
Figure 5-3: XR5 Anode Assembly
Refer to
Figure 5-3: XR5 Anode Assembly
.
1.
Unplug the cables from the XR5.
2.
Expose the anode terminations by withdrawing the anode safety shield. This is
identical to the shield covering the Twin Anode gun, and requires the loosening
of the M4 x 8 cap head clamp screws and then a twist to disengage from the
locking pins mounted in the side of the 70mm flange of the anode assembly.
3.
The PTFE tube covering the external end of the anode can now be unscrewed
from its mating PTFE collar. This exposes the end of the anode with the HT
connector and 2 cooling pipes attached.
4.
Unplug the HT connector
5.
Unplug the 2 cooling line connectors from the anode cap. This may require the
use of a tool such as a flat blade screwdriver to lever the connectors away from
the anode cap. There will be a slight spillage of cooling water at this stage. Bear
in mind that the anode will also contain a few cc of water when removed - watch
out for your clothes!
6.
Loosen the locking screw from the end ferrule of the cooling/HT steel conduit
and withdraw the conduit from the anode-shield-support assembly.
7.
Unscrew the 4-off M4 x 12 cap head screws from the steel collar retainer for the
PTFE collar. Remove these items and the PTFE tube from the anode assembly.
8.
Retract the Linear Motion Drive fully.
9.
Remove the 6-off M4 x 12 cap head screws from the FC19 mini-flange of the
anode.
10. Carefully withdraw the anode from the gun assembly. It should withdraw
smoothly. If any resistance is felt inspect the end of the copper tube after
withdrawal for signs of gouging. If gouging is apparent the anode-locating-cap
will need its bore to be cleaned.
11.
If the anode was extracted smoothly with no signs of gouging a new anode can
be fitted, with a new FC19 copper gasket. This should fit smoothly into place
without need of force.
12.
When fitting the anode note the orientation of the anode-flat relative to the gun
axis - reference the Figure 5-4 showing XR5 Anode Orientation.
