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.

.. image:: /_static/sourceports/concept.jpeg
  :align: center
|

We recommended mounting sources in this way whenever possible. However certain restrictions can make this approach unsuitable:

1. The source must be short enough to sit behind the closed gate valve when the linear drive is fully retracted
2. 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)
3. 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 :sub:`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 (:download:`PrepSec <_static/prepsec/PortLayout.pdf>` , :download:`PrepMain <_static/prepmain/PortLayout.pdf>` )

L :sub:`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 :sub:`GV`).

The pumping Ts are 51mm flange-to-flange (L :sub:`PumpT`).

Linear translators ('LTMs') available for loan at the beamline are:

=======   ==========   ==================================   ====================================
Brand     Travel(mm)   Length extended (L :sub:`LTM MAX`)   Length compressed (L :sub:`LTM MIN`)
=======   ==========   ==================================   ====================================
VacGen    50           92                                   42
VacGen    100          163                                  63
PreVac    150          230                                  80
=======   ==========   ==================================   ====================================

In general:

Maximum source length = L :sub:`PumpT` + L :sub:`LTM MAX`

Source-sample distance = (L :sub:`o`  + L :sub:`GV` + L :sub:`PumpT` + L :sub:`LTM MIN`) - L :sub:`Source`

Where L :sub:`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 :sub:`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 :sub:`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.


:download:`Here <_static/sourceports/source length.xlsx>` is a spreadsheet that might help with these calculations.