Overview of the pumping system
Default setup of the pumping system
MEC's pumping system is comprised of 2 multi-stage dry vacuum pumps (Ebara A70) located on the mezzanine above the hutch, and 2 turbo pumps (Varian TV-2KG) backed with a scroll pump (Edwards xds35i). The following sketch shows the vacuum system as displayed in the controls window.
The dark grey rectangle in the center symbolizes the target chamber and displays the readout values of different vacuum gauges measuring the in-chamber pressure (top: cold-cathode, bottom-left: pirani, right: capacitance). Let's note that the capacitance gauge is out of order and displays incorrect values.
The top right side of the window details the primary pump subsystem. The ends of this branch lead to the 2 Ebara pumps. Controllable gate-valves are positioned at the target chamber entrance to isolate the primary pump subsystem, at the inlet of each independent Ebara pump, and along the line to allow for venting of the subsystem. Pirani gauges are also used to monitor the pressure along the subsystem pumping line and at the inlet of both Ebara pumps.
The bottom side of the window details the secondary pump subsystem. It comprises 3 branches: 2 of them are identical and symmetric on the sketch, and 1 of them (left-most), the shortest one with only 3 symbols in a straight one, is obsolete. The 2 indentical branches each contain a Varian turbo pump and a scroll pump. The chamber is isolated from these subsystems by a gate-valve, a second gate-valve is used to isolate the turbo from the scroll when the system is shut down. A pirani gauge monitors the quality of the backup pressure provided by the scroll pump.
Finally, the top left side of the windows helps control the venting valves. There are 2 independent venting valves: one supplies compressed dry air (CDA) to initiate the venting procedure, the second one simply opens the chamber to the ambiant atmospheric air (Atm).
Current modifications in the pumping system
MEC has recently experienced a turbo pump failure. As a consequence, we are operating the pumping system with the following structural modifications. The primary vacuum subsystem and the venting valves are unchanged. The modifications are at the bottom side of the window with the failed turbo pump in a "Disabled" status and a backup turbo pump (Maglev) positioned in the formerly obsolete left-most branch.
The target chamber is in a secondary vacuum state on this sketch. The primary subsystem is vented and the maglev (gate-valve TC1-VGC-01 open/green) is pumping the chamber which reached 2.10-4 torr on the cold-cathode gauge (the pirani gauge reached its lower readout limit). The Varian turbo branch (gate-valve TC1-VGC-02 closed/red) is not activated yet, but the turbo is accelerating after startup as shown by the yellow circle.
The procedure presented on this page will explain how to operate the primary vacuum subsystem and a branch of the secondary vacuum subsystem when running with a Varian turbo pump. The Maglev pump is a temporary solution for experiments needing high-quality vacuum, most of our beamtimes run with only one Varian.
Nomenclature of the vacuum system components
| Component | Description | Component | Description | Component | Description |
|---|---|---|---|---|---|
| Multi-stage dry pump (pre-pump) RUN and STP buttons are used |
| Gate-valve state: closed, not allowed to open |
| Pressure gauge state: reading |
| Scroll pump |
| Gate-valve state: closed, allowed to open |
| Pressure gauge state: out of range |
| Turbo pump state: off |
| Gate-valve state: open, allowed to open |
| Pressure interlock display red: condition not met |
| Turbo pump state: accelerating |
| Cold-cathode status display circle: status display |
Tools necessary for operation
It is necessary to open a couple of windows to be ready to operate the vacuum system. You must be operating from one of the hutch computer (mec-daq, mec-monitor, mec-console, mec-laser, mec-hutch01, mec-laptop08), or you can ssh to these computers.
~> mechome in a terminal to open the above window. In the top left diagram, press the "Vacuum" button to unfold a menu and select MEC Vacuum. The following window will open.
The above window will be used to operate the pumping system components: pumps, gate-valves, etc
~> tc_vacuum in a terminal when logged as mecopr. It opens the above window, called "striptool graph" with 4 curves. You can reshape the window and change the time axis range to monitor pressure values over a long time span (~ 1 hour). The curves correspond to the following gauges:
MEC:TC1:GPI:01:PMON → target chamber Pirani gauge
MEC:TC1:GCC:01:PMON → target chamber Cold-cathode gauge
MEC:SEW:GPI:03:PMON → scroll pump Pirani gauge (Maglev roughing)
MEC:SEW:GPI:04:PMON → scroll pump Pirani gauge (Varian turbo roughing)