Fast entry source ports
‘Fast entry source ports’ are CF40 ports on the two preparation chambers where a VAT mini gate valve and a short pumping T-piece have been installed. If a source is mounted to this port using a linear translator, it is possible to introduce it into the prep chamber within 6-12 hours, without needing to vent the preparation chamber.
We recommended mounting sources in this way whenever possible. However certain restrictions can make this approach unsuitable:
The source must be short enough to sit behind the closed gate valve when the linear drive is fully retracted
The gate valve, pumping T and compressed linear drive add a distance offset, which can be a problem if you require the source to be close to the sample (<5cm)
If the source has a shutter, it needs to protude far enough into the chamber that the shutter can open
As of August 2019, fast entry source ports are:
Chamber |
Port number |
Focus position |
L o (mm) |
|---|---|---|---|
PrepSec |
3 |
F1 |
200 |
PrepSec |
5 |
F1 |
200 |
PrepSec |
15 |
F2 |
155 |
Prepmain |
22 |
F2 |
270 |
PrepMain |
20 |
F2 |
200 |
Port numbers are indications in the chamber drawings (PrepSec , PrepMain )
L o is the distance from the flange edge to the focus point in the chamber.
Prep Main has one extra valved port intended for a vacuum suitcase, which could be modified for a third source or gas port with some advance notification.
Calculating length requirements
The VAT mini gate valves are 35mm flange-to-flange (L GV).
The pumping Ts are 51mm flange-to-flange (L PumpT).
Linear translators (‘LTMs’) available for loan at the beamline are:
Brand |
Travel(mm) |
Length extended (L LTM MAX) |
Length compressed (L LTM MIN) |
|---|---|---|---|
VacGen |
50 |
92 |
42 |
VacGen |
100 |
163 |
63 |
PreVac |
150 |
230 |
80 |
In general:
Maximum source length = L PumpT + L LTM MAX
Source-sample distance = (L o + L GV + L PumpT + L LTM MIN) - L Source
Where L Source is measured from the CF40 knife-edge to the furthest tip of the source.
If you need the source to be as close as possible to the sample, use the smallest L o port and and longest travel LTM. (It is also possible to gain a few extra centimeters by bringing the sample closer to the port).
Example:
We wish to mount a source on PrepSec port 3 (L o = 200mm), using a 100mm LTM.
Maximum source length = 51 + 163 = 214mm
So if we set the source length to 210mm, the closest it can come to the focus point is: (200 + 35 + 51 + 63) - 200 = 149mm.
Here is a spreadsheet that might help with these calculations.