Hello everybody.
We have started up the ABS tonight after a long and thorough
alignment procedure. The main components were the alignmentr
of all components except for the nozzle to a vertical line that
is centered on the target flange. Then we aligned the nozzle
to the skimmer through a theodolite from below. In addition
we welded pushers to the top flange to be able to adjust the
nozzle repeatably with a high precision. finally we started
to map the nozzle position in 1/32 in steps and looked at the
pressure increase in the target chamber for RFpower on and off.
The results show a small signal of maxuimum 1.5e-8 torr but
we have indication that we operate close to the edge of the
skimmer. The expected pressure difference is in the order
2e-7 torr to 3e-7 torr. The following numbers were measured
for an ABS flow of 30sccm and 200W power:
1 center position 1.5e-8
2 center + downstream 1/32in 1.2e-8
3 center + upstream 1/32 in 0.3e-8
4 center + beam left 1/32 in 0.04e-8
5 bcenter + beam right 1/23 in 1.0e-8
and follow the pattern
4
3 1 2 downstream ->
5
We will continue with more positions in the morning to get
a consitent picture.
In general we find much better vacuum conditions for the ABS
after activating the NECS all in parallel for the first time.
The pressure in the sixpole chamber dropped by a factor of
5 to 7 during operation and the top flange with the new
adjustment enables us for the first time to control the
position of the nozzle with good precision. We did not observe
a movement of the flange while pumping down (precision
ca 0.2mm through optical plummet). These improvements are
already a great step forward in the operation of the ABS.
Hauke
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Hauke Kolster MIT * Bldg 26-551 * Cambridge, MA 02139
hauke@lns.mit.edu Tel (617) 253-2693 Fax (617) 253-9599
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