``TIM``: The Transmission Intensity Monitor
===========================================

The transmission intensity monitor (TIM) is used to detect the
intensity after the sample. It is used either for normalization or to
measure x-ray absorption scans.

The TIM detects primarily the x-ray fluorescence coming out a CVD
diamond film or a YAG crystal that is used as active instrument beam
stop. For low intensities, the fluorescence detection could change
into photoelectron detection.  Furthermore, for particular experiments
with very intense beams when the IBS would be damaged by each shot
resulting in a non-linear fluorescence intensity measurement, a gas
will be used as source of fluorescence or photoelectron. The measuring
principle is displayed in :numref:`tim_scheme` below. The x-ray beam
with sizes varying between the blue and green patterns impinges in the
diamond film at 45° and ejects both electrons and fluorescence photons
that can be detected with the MCP.

.. _tim_scheme:
.. figure:: scheme.svg

   TIM measurement scheme using a diamond film or YAG mounted at 45°.


The detection system is a MCP and its charge is integrated, amplified,
digitized and measured with a micro-TCA. The possibility of detecting
both fluorescence and electrons can be realized by means of the
potentials to apply to the MCP and anode. Alternativly a grid can be
put in front of the MCP to repel charged particles in the fluorescence
detection mode. This allows using always the same MCP electric
configuration.

Several MCPs can be installed in the chamber, as well as imagers to
detect the beam on the diamond or YAG screen. The MCPs and imagers
look at the screen at different angles, as shown in
:numref:`tim_chamber`.

.. _tim_chamber:
.. figure:: chamber.svg

   A 3D drawing of the vacuum chamber.

The CVD and the YAG are mounted on a translation stage that allows to
move them in and out and change from one to the other.  At the exit
port of the chamber, a B\ :sub:`4`\ C beam stop is installed.

.. toctree::
   :maxdepth: 2

   MPOD-MCPs.rst

Interlocks
----------

The roughing vacuum is shared with the FCCD, so we better do not open
the roughing vacuum while they are pumping down.


.. conditions loop9 SCS_BLD_TIM/VALVE/SRV3 SCS_BLD_TIM/DCTRL/SRV3

== =========================================== == =====
No Property                                    Op Value
== =========================================== == =====
c1 SCS_CDIDET_FCCD2M/GAUGE/P9.Value            GT 1e-2
c2 SCS_CDIDET_FCCD2M/VALVE/SRV2.state.IsClosed EQ FALSE
c3 SCS_BLD_TIM/TPUMP/TP1.state.RPM80           EQ FALSE
== =========================================== == =====

.. actions loop9 SCS_BLD_TIM/VALVE/SRV3

== ================= ======
No Logic             Action
== ================= ======
a1 c1 or (c2 and c3) CClose
== ================= ======

.. actions loop9 SCS_BLD_TIM/DCTRL/SRV3

== ================= ======
No Logic             Action
== ================= ======
a1 c1 or (c2 and c3) COff
== ================= ======

Like always, if the turbo pumps fail, their gate valve should close.
Unless, well, the vacuum is really bad and the pump is not running
then we probably want to pump down, as described for the DPS.

.. conditions loop9 SCS_BLD_TIM/VALVE/GV1

== ================================= == ===== ==== =======
No Property                          Op Value Hyst Timeout
== ================================= == ===== ==== =======
c1 SCS_BLD_TIM/TPUMP/TP1.state.RPM80 EQ FALSE
c2 SCS_BLD_TIM/GAUGE/PCC22           LT 1e-4  1    100000
== ================================= == ===== ==== =======

.. actions loop9 SCS_BLD_TIM/VALVE/GV1

== ========= ======
No Logic     Action
== ========= ======
a1 c1 and c2 CClose
== ========= ======