Chapter 6: XTOD Vacuum

Introduction. This document provides procedures for operating the xtod vacuum sub-systems. There are three regions:

• The Instrument region => which includes the Fixed-Mask/Xray-Slits, K-Monochromator, Total Energy Monitor, and Direct Imager instruments
• The Gas Attenuator region => which includes the Gas Attenuator and the two Gas Detectors, as well as the Solid Attenuators. (Only gas-flow and vacuum operations are covered here; for attenuation operations see Chapter 8; for Gas Detector daq operations see Chapter 7)
• The Offset Mirror region => which includes the two soft x-ray lines and the hard x-ray line

 Normal operations should in general use the Sequential Engines (‘Finite-State Machines’, ‘Sequencers’) that are provided for all sub-systems that epics controls. Tier 3 and 4 device level controls should be used only for diagnosing and repairing faults. The Sequencer basic controls that are common to all Regions are:

• Mode => in STEP mode, each micro-step requires a momentary click on MOVE to advance; in GO mode, the Sequencer advances continuously to the Goal
• Goal => (some Sequencers have additional Goals)
  • STOP => causes the Sequencer to stop advancing, i.e,, it stays in the current state (even if not at a Goal)
  • PUMP => causes the Sequencer to advance to the VACUUM state
  • VENT => causes the Sequencer to advance to the VENTED state
• ABORT => causes the Sequencer to try and synchronize with the actual state, for cases where the hardware has spontaneously changed state, or someone has use manual epics controls. The Sequencer momentarily advances to a state SYNC; then selecting a Goal usually will allow it to synchronize accurately with external conditions

I. Instrument Region

Basic Components. The Instrument Region has four sections:

• Fixed-Mask/Xray-Slits section => which must be roughed and vented manually using a temporary Roughing cart
• Diagnostic sections (K-Monochromator, Total Energy Monitor, and Direct Imager) => which have fully automated sequences for roughing and venting; they are also independent, being fitted with isolation valves

 The components are:

• Vent valve => VAT Series 28
• Isolation valve => VAT Series 48
• Ion pumps  => Gamma MPC-2-100 used for maintenance of High Vacuum (hv) steady-state
• Gauge pair with Controller => MKS-937A controller with MKS-317 Convection Pirani and MKS-422 Cold Cathode
• Roughing valve => VAT Series 10
• Turbo-molecular pumps => Varian V-81 used for roughing sufficiently to enable stable operation of the Ion Pumps
• Foreline pump with automatic foreline valve => Varian SH-110

Constraints. The plc directly controls the pumps, valves, and gauges. epics can command the plcs. (It may be useful to look at the xtod gui; it has a Legend screen which explains all the symbols and their colors.)

 The constraints that are enforced by the plc are:

• An Ion pump can only turned on (high-voltage ENA) when the associated Cold Cathode gauge signals a low enough pressure
• For the diagnostic sections only:
  • When roughing the whole system down from high pressure,  READY will show as soon as the foreline pressure is adequate
  • Turbo pumps are READY when the Turbo pump vent valves are CLOSED and the foreline valves are OPEN
  • In order to prepare for gas flow, the bypass feature will have to be enabled, which will show READY as TRUE will for 30 seconds (see Operations)
• When the associated roughing valves are OPEN and the associated apertures are IN, the READY indication for each of the flow-control valves will be TRUE. If any associated roughing valve is CLOSED or any associated aperture is OUT, its READY indication will turn FALSE and the flow-control valve will close
• When the all eight roughing valves are CLOSED, the READY indication for the vent valve will be TRUE. If any associated roughing valve is OPEN, vent valve READY indication will turn FALSE and the vent valve will close

Sequential Engines. Three are provided, one for each of the active instruments. (The Fixed-Mask/Xray-Slits vacuum sub-system is limited; epics can only ENABLE and DISABLE the Ion Pumps) In general, these Sequencers should be used for most normal operations, such as pumping to hv from high pressure; or venting the system. Each has a few basic controls on the Instrument Vacuum screen, and a more detailed screen that shows the paths between states, the conditions needed to advance, and some adjustable parameters (which you should only change if you are an expert):

• Ion Pump Turn-on Maximum Retries => the number of time to attempt the turn on (high-voltage ENA) when the pump (possibly slightly dirty) shuts itself down
• Dwell Time After Turbo-pump Turned On => How long to wait after the Turbo-pump is ON before attempting to turn ON Ion Pump
• Dwell Time After Ion-pump Turned On => How long to wait after the Ion-pump is ON before turning OFF the Turbo-pump (sometimes the Ion-pump needs awhile to stabilize)
• Dwell Time Before Opening Turbo-pump Vent => How long to wait after the Turbo -pump is OFF before trying to OPEN the Turbo-pump vent valve
• Dwell Time After Opening Turbo-pump Vent => How long to wait after the Turbo -pump vent valve is CLOSED before turning OFF the Foreline-pump (effectively giving Turbo-pump adequate time to be braked to a halt by the N₂ gas)
• Dwell Time Before Opening Vent => How long to wait after the Ion–pump is OFF before setting the chamber vent valve OPEN

Operations. You can perform these operational procedures manually and the plc will prevent any damage, however, you may find that you do not achieve your goal, so it is recommended to simply invoke the automatic sequencers. You can follow the dynamic sequence by calling up the sequence gui from within the TOP box at the upper middle of the gui; it shows the current state and the pre-conditions for advancing to the next state. The sequences generally skip any steps that  you have performed manually.

 The automatic sequences are:

• Pump down from high pressure by clicking PUMP from within the box at the upper part of the gui for the instrument These steps will be performed:
  • CLOSE the chamber vent valve
  • CLOSE the Turbo-pump vent valve; the Foreline-pump should show READY
  • START the Foreline-pump; the Roughing valve should show READY
  • OPEN the Roughing valve; the Turbo-pump should show READY
  • START the Turbo-pump; it should show LOW-SPEED
  • When the Turbo-pump shows RUN, and the Cold-cathode gauge shows sufficient vacuum, the Ion–pump should show READY
  • ENABLE the Ion-pump; it should show ON; if it DISABLEs itself, again ENABLE it
  • After a suitable dwell time with the Ion-pump showing ON, CLOSE the Roughing valve
  • STOP the Turbo-pump
  • After a short dwell time, OPEN the Turbo-pump vent valve
  • After a suitable dwell time, STOP the Foreline-pump
• Vent up to high pressure by clicking VENT from within the box at the upper part of the gui for the instrument These steps will be performed:
  • The Ion-pump hv is DISABLED
  • After a delay, the chamber vent valve OPENED

II. Gas-Flow Region

Basic Components. The Gas-Flow region has 11 sections; it is independent of both the Instrument and Offset-Mirror regions, being fitted with isolation valves:

• Regulated Detector Pressure sections (2) => which are kept at the pressure required to achieve the optimum florescence signal
• Regulated Attenuator Pressure section => which is kept at the pressure required to achieve the desired attenuation ratio
• Differential sections (4) => the tandem outer sections that isolate the relatively high pressure in the Regulated Pressure section of the Gas Detector sections from the beam-line. They are fitted with turbo-molecular pumps
• Differential sections (2) => the two inner sections that buffer of the Regulated Detector Pressure sections from the Regulated Attenuator Pressure section. They are fitted with Turbo-molecular pumps
• Pumping sections (2) => the two inner sections that exhaust the heavy gas flow from the Regulated Attenuator Pressure section; they are also used for initial pump-down of the entire sub-system from atmospheric levels. They are fitted with twin-screw pumps pumps

 The components are:

• Vent valve => VAT Series 28
• Isolation valve => VAT Series 48
• Twin-screw pumps (2) => Kashiyama MU-100 high through mechanical pumps; they have two functions:
  • Rough down the entire Gas Flow system
  • Maintain adequate differential pumping pressure by exhausting the N₂ flow of the Gas Attenuator
  • Backed by Tri-Scroll foreline pumps and automatic foreline valves
• Roughing Valve  (2) => VAT Series 10 valves that isolate the Twin-screw pumps:
  • when they are off
  • when they are running, but the differential section has a lower pressure (<20 mT) then the back-streaming pump presssure
• Roughing Valves (6) => VAT Series 10 valves that isolate the Turbo-molecular pumps when they are off
• Turbo-molecular pumps (6) => Varian V-301, V-701, and V1001
  • Pump down the entire Gas Flow system to HV
  • Maintain adequate differential pumping pressure by exhausting the N₂ flow of the Gas Detectors
• Foreline pumps (6) => Varian 600DS with automatic foreline valves
  • Pump down the entire Gas Flow system to HV
  • Maintain adequate differential pumping pressure by exhausting the N₂ flow of the Gas Detectors
• Apertures => VAT 48 series valves with a 4 mm hole that create differential sections on either side of the regulated pressure sections
• Pressure Regulator => MKS-PR4000 controller that drives an MKS-649 proportional flow valve to maintain the pressure of the Regulated Attenuator Pressure section at the desired set-point
• Pressure Regulator (2) => MKS-146C controller that drives an MKS-649 proportional flow valve to maintain the pressure of the Regulated Detector Pressure sections at the desired set-point
• Baratron => MKS-PRD2000 with MKS-626 manometer that provides an independent reading of the actual N₂ pressure in Regulated Attenuator Pressure section. (Installation is in progress.)
• Flow cut-off valve (3) => ensures no N₂ flows from the fee supply to the Pressure Regulators

Constraints. The plc directly controls the pumps, valves, and gauges. epics can command the plc, and epics alone controls the Pressure Regulators. (It may be useful to look at the xtod gui; it has a Legend screen which explains all the symbols and their colors.)

 The constraints that are enforced by the plc are:

• The Twin-screw pumps may be turned on at any time. They have READY indication to do so (which should always be true)
• The Twin-screw roughing valves may only be opened when the pumps are running and have achieved a reasonable foreline pressure, then their READY indication will be TRUE. There are three scenarios:
  • When roughing the whole system down from high pressure, READY will show as soon as the foreline pressure is adequate
  • When low pressure has been achieved in the differential systems (which are effectively pumped from the turbo-molecular pumps in adjacent sections), after 30 seconds the roughing valve READY indication will turn FALSE and it will close
  • In order to prepare for gas flow, the bypass feature will have to be enabled, which will show READY as TRUE will for 30 seconds (see Operations)
• When the associated roughing valves are OPEN and the associated apertures are IN, the READY indication for each of the flow-control valves will be TRUE. If any associated roughing valve is CLOSED or any associated aperture is OUT, its READY indication will turn FALSE and the flow-control valve will close
• When the all eight roughing valves are CLOSED, the READY indication for the vent valve will be TRUE. If any associated roughing valve is OPEN, vent valve READY indication will turn FALSE and the vent valve will close

Sequential Engines. 11 are provided: six for each of the turbo-pumped differential sections; 2 for each of the attenuator banks; two for each of the screw-pump/roughing sections; and one master (Top) engine that controls the other 10. In general, the Top Sequencer should be use for most normal operations, such as pumping to hv from high pressure; starting and stopping gas flow in either Gas Detector or in the Gas Attenuator; venting the system; and opening or closing all of the Apertures. Each has a few basic controls on the Gas-Flow Vacuum screen, and a more detailed screen that shows the paths between states, the conditions needed to advance, and some adjustable parameters:

• When the all eight roughing valves are CLOSED, the READY indication for the vent valve will be TRUE. If any associated roughing valve is OPEN, vent valve READY indication will turn

Operations. You can perform these operational procedures manually and the plc will prevent any damage, however, you may find that you do not achieve your goal, so it is recommended to simply invoke the automatic sequencers. You can follow the dynamic sequence by calling up the sequence gui from within the TOP box at the upper middle of the gui; it shows the current state and the pre-conditions for advancing to the next state. The sequences generally skip any steps that  you have performed manually.

 The automatic sequences are:

• Pump down from high pressure by clicking PUMP from within the TOP box at the upper middle of the gui. These steps will be performed:
  • All of the Apertures will be moved IN; (future) optionally, rough down with Apertures OUT
  • The twin-screw pumps will be set to RUN
  • When the twin-screw pump foreline pressures are low enough, there are two paths:
    • If the their roughing valves’ READY is already set to TRUE , assume the Section pressures are already low, so set them to OPEN
    • Otherwise, assume pressures are high; when the twin-screw pumps indicate LOW_SPEED_READY, set LOW_SPEED (to reduce initial load); then when their roughing valves’ READY becomes TRUE, set them to OPEN; after 10 seconds, set NORMAL_SPEED
  • The turbo-molecular pumps will be set to RUN and will show STARTING status.
  • When the turbo-molecular pump foreline pressures are low enough and the pumps have achieved RUN status and the Detector differential section pressures are low enough, their roughing valve READY will be set to TRUE and they will OPEN
  • When low pressure has been achieved in the Attenuator differential sections, after 30 seconds the roughing valve READY indications will turn FALSE and they will close
  • The twin-screw pumps will be set to STOP
• Start gas flow for the Attenuator or either Detector by clicking FLOW from within the TOP box at the upper middle of the gui. This is only allowed when the TOP system is in the VACUUM mode or the GASFLOW mode (and the buttons are hidden otherwise). When the sequence is complete and stable, you may SET the set-point to your operational value (see Chapter 8). These steps will be performed, in parallel, for both of the Attenuator differential sections:
  • When the twin-screw pump is READY, set it to RUN; if the tank pressure is high—indicated by foreline valve not READY, set the pump to LOW_SPEED
  • When the foreline pressure is low enough, if the READY on the roughing valve is not TRUE, engage the BYPASS
  • When the roughing valve is READY, set it to OPEN
  • When the roughing valve is OPEN, SET the pressure regulator set-point to 0.0
  • When the cut-off valve is READY, set it to OPEN
  • ENABLE the pressure regulator
  • OPEN the pressure regulator valve
  • SET the pressure regulator set-point to 1.0
  •  
• Stop gas flow by clicking OFF from within the TOP box at the upper middle of the gui. This is only allowed when the TOP system is in the the GASFLOW mode. These steps will be performed:
  • SET the pressure regulator set-point to 0.0
  • DISABLE the pressure regulator
  • CLOSE the pressure regulator valve
  • CLOSE the cut-off valve
  • When the foreline pressure is low enough (<20 mT), CLOSE the roughing valve (or wait for the plc to do so)
  • STOP the twin-screw pump
• Vent from low pressure to high pressure by clicking VENT from within the TOP box at the upper middle of the gui. This is permitted only when the TOP is in the VACUUM mode; if it is in the GASFLOW mode then use the OFF button(s) to achieve it. These steps will be performed:
  • The turbo-molecular pump roughing valves will be set to CLOSE
  • The turbo-molecular pumps will be set to STOP
  • (future)If the BLEED option is TRUE, the vent valve will be set to OPEN; when 760 T pressure has been achieved, the vent valve will be set to CLOSE

II. Offset Mirror Region

Basic Components. The Instrument Region has 3 sections, all of which must be roughed and vented manually using a temporary roughing cart; epics can only ENABLE and DISABLE the Ion Pumps:

• Soft X-ray section 1 => which goes to amo experiment in neh Hutch 1
• Soft X-ray section 2 => which goes to sxr experiment in neh Hutch 2
• Hard X-ray section => which goes to xpp experiment in neh Hutch 3 and then to X-ray Tunnel and feh Hutches 4, 5, 6

 The components are:

• Ion pumps  => Gamma MPC-2-100 used for maintenance of High Vacuum (hv) steady-state
• Gauge pair with Controller => MKS-937A controller with MKS-317 Convection Pirani and MKS-422 Cold Cathode

Environment. You must use the bash shell. Add or modify the file .bashrc in your home directory to contain (as one line):

alias epics='export EPICS_HOST_ARCH=linux-x86; 
. /usr/local/lcls/epics/setup/3.14.9/epicsSetup.bash'

Glossary.

• .TBD

Notation. Words shown in italic are defined in Glossary; labeled buttons are shown like Home; command-line text and screen inputs and outputs are shown like edm or STOP, respectively.

List of Figures.