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.

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and symmetric on the sketch, and 1 of them (left-most), the shortest one with only 3 symbols in a straight one, is obsolete.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 2.0e-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 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)

Primary vacuum

Prerequisites

• All chamber doors must be closed.
• All chamber ports must be covered.
• All gate-valves to the chamber must be closed (TC1:VGC:11, TC1:VGC:12, TC1-VGC-01, TC1-VGC-02, TC1-VGC-03, TC1-VGC-04).
• Both Ebara pre-pumps must be off. If faulted, press RESET.
• All gate-valves in the primary vacuum subsystem must be closed (TC1-VGC-04, MEZ:VGC:17, MEZ:VGC:18, MEZ-VIC-19).
• Primary pumping line must be vented with Pirani gauge (MEZ-GPI-02) displaying ~ 6.5e+02 torr. If pressure is lower, use venting valve (MEZ:VGC:18) until situation is restored.
• All gate-valves in the primary vacuum subsystem must be closed and allowed to open (TC1-VGC-04, MEZ:VGC:17, MEZ:VGC:18, MEZ-VIC-19).

Primary vacuum pumping procedure

• Press OPN on TC1-VGC-04 (primary vacuum gate-valve to chamber)
• Press RUN on MEZ-PMF-01 (pre-pump 1)
• Press OPN on MEZ:VGC:17 (pre-pump 1 gate-valve to primary pumping line)
  - wait until allowed to open if MEZ:VGC:17 cannot open
• Press RUN on MEZ-PMF-02 (pre-pump 2)
• Press OPN on MEZ-VIC-19 (pre-pump 2 gate-valve to primary pumping line)
  - wait until allowed to open if MEZ-VIC-19 cannot open

Both Ebara pumps will start running in MAIN mode. On the striptool graph, the target chamber Pirani gauge value should drop rapidly. Once pre-pump Pirani gauges (MEZ-GPI-06 and MEZ-GPI-07) drop below 7.5e+00 torr, the Ebara pumps will start running in BOOSTER mode (typically after 10-15 minutes from startup). The primary vacuum procedure is finished when the target chamber Pirani gauge (MEC:TC1:GPI:01) drops below 5.0e-02 torr (typically after 30-40 minutes from startup).

If something goes off track during this procedure, initiate the venting procedure and check for leaks (flanges, virtual leaks, waterlines, etc).

Secondary vacuum

Turbo pump startup procedure

This procedure can be done anytime as long as the turbo gate-valve to the target chamber is closed. The following steps assume that the turbo pump branch is fully shutdown (scroll off, scroll to turbo gate-valve closed, turbo off, turbo to target chamber gate-valve-closed). If the system is in an intermediate state, you can restart the following procedure from the corresponding step. In this example, we consider only turbo pump #2 associated with gate-valve TC1-VGC-02.

• Open mechome
• Go the tab "User Devices"
• Open the panel "User Sentry PDU"
• Turn On "Roughing pump PTM 02 (turbo 2)"
  - after a while, scroll to turbo gate-valve (SEW-VGC-15) will switch to allowed to open.
• Press OPN on SEW-VGC-15
  - turbo status goes to "OK to Run"
• Press RUN next to the turbo pump logo
  - turbo status will go through "Accelerating" then "Full Speed" mode

The turbo pump subsystem is now ready for operation.

Prerequisites

• Turbo pump subsystem must be up and running as described above.
• Primary vacuum pumping procedure must have been completed.
• Target chamber Pirani gauge (MEC:TC1:GPI:01) must be below 5.0e-02 torr.
• On the striptool graph, the target chamber Pirani gauge curve should look asymptotic, meaning the primary vacuum subsystem has reached saturation.

Secondary vacuum pumping procedure

• Press OPN on TC1-VGC-02
  - primary vacuum gate-valve will automatically close first, before turbo gate-valve opens → do not forget the primary vacuum shutdown procedure below
  - target chamber Pirani gauge value should plummet, until it goes out of range and the target chamber cold-cathode gauge takes turn
• Press STP on both Ebara pumps
• Press CLS on MEZ:VGC:17 and MEZ-VIC-19
• Press OPN on MEZ:VGC:18
  - primary vacuum line will start venting
  - wait until Pirani gauge MEZ-GPI-02 goes above ~ 6.5e+02 torr
• Press CLS on MEZ:VGC:18
  - primary vacuum venting valve should not stay open longer than ~ 5 minutes as it may heat up too much

The target chamber is now fully pumped down, ready to be exposed to the x-ray beamline through the beryllium window system.

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)"