Table of contents

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.

MEC vacuum system control diagram

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and symmetric on the sketch, and 1 of them (left-most), the shortest one with only 3 symbols in a straight one, is obsolete.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.

MEC vacuum system control diagram with the current temporary modifications

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 2.0e-04 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

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, type mechome to open the above window. It is the start point of many processes in the MEC system.

MEC Vacuum

In mechome, in the top left part of the window, press the "Vacuum" button to unfold the menu, then select MEC Vacuum to open the above window. It will be used to operate the pumping system components: pumps, gate-valves, etc

tc_vacuum

In a terminal logged as mecopr, type tc_vacuum to open the above window. Often called "striptool", this type of window can display the time evolution of some environmental parameters. Here it shows 4 curves monitoring the pressure value read by 4 different gauges. 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)

Venting

Prerequisites

• If ending operation with the x-ray beamline, make sure that the pulse picker is closed, stopper S6 is inserted, hutch search is broken and glass window inserted.
• Stand next to the chamber during the procedure to be ready to react once the chamber is vented and avoid over-pressurization.

Venting procedure

• Press CLS on all opened gate-valves connecting a vacuum line to the chamber (TC1-VGC-01, TC1-VGC-02, TC1-VGC-03, TC1-VGC-04)
• Press OPN on TC1:VGC:11
  - a new window will open
  
• Press Yes and close the window immediately
  - chamber will start venting
• Optional: Press OPN on on TC1:VGC:12 when allowed
  - after a while, doors can open and you will hear the compressed dry air intake loudly
• Press CLS on TC1:VGC:11, and on on TC1:VGC:12 if necessary
• Open the chamber doors and let some time to ventilate the chamber before breathing inside the chamber

Turbo pump shutdown

It is not mandatory to shutdown the turbo pump during each venting cycle. We usually let it run when venting for a short time during a shift. If venting for a longer time between two shifts, we usually turn off the turbo pump but not its rouging. The following steps describe a full shutdown of the turbo line after venting.

• Press STP next to the turbo pump logo
  - let the turbo spin down for at least 15-20 minutes (the off-status logo on the turbo does not mean the blades have stopped spinning)
  - stop at this step if you will restart the turbo in less than a day, additionally you can set the scroll ballast to level I (it can be set to level 0 or I during operation)
• Press CLS on SEW-VGC-15
  - make sure ballast level is set to 0 before going to the next step
• Open mechome
• Go the tab "User Devices"
• Open the panel "User Sentry PDU"
• Turn Off "Roughing pump PTM 02 (turbo 2)"

List of PVs associated to the vacuum system components

Pumps

Gate-valves

Logical permissions on the gate-valves 

Pressure gauges