KAGRA VIS Operations Manual - Type B Pumpdown and Venting Procedure
Pumpdown of the vacuum chambers causes large mechanical stresses which tilt the IPs and cause them to drift. Also, loss of buoyancy from the air on the suspended masses causes the GAS filters to sag. Similar changes happen in reverse on venting. Therefore it is necessary to monitor the suspensions during pumpdown and venting to correct any alignment issues before they lead to problems. See detailed procedures below.
- Allocate each of the four desktop workspaces of a control room workstation to a different suspension, e.g., BS=1, SR2=2, SR3=3 and SRM=4.
- On the first workspace, bring up:
- The sitemap.
- The VIS_ALL screen. Open all four TOP screens and drag them to the appropriate workspaces.
A terminal window. In the terminal window, log into k1script. Start the drivers for BS_IP, SR2_IP, SR3_IP, SRM_IP with commands like step_start BS_IP. Check that you get the Testing connection: ...ok message for each.
- The STEP_MASTER screen. Open the screens for the BS_IP, SR2_IP, SR3_IP, SRM_IP steppers and drag them to the appropriate workspaces.
- For each suspension, on its allocated workspace, bring up the following screens:
- The OVERVIEW screen.
- The Guardian screen.
A StripTool set to display the three IP LVDT coil outputs on a scale of ±5000: K1:VIS-BS_IP_COILOUTF_H1_OUTPUT, K1:VIS-BS_IP_COILOUTF_H2_OUTPUT, K1:VIS-BS_IP_COILOUTF_H3_OUTPUT or the like.
Optionally also display the three GAS LVDT outputs: K1:VIS-BS_F0_COILOUTF_GAS_OUTMON, K1:VIS-BS_F1_COILOUTF_GAS_OUTMON, K1:VIS-BS_BF_COILOUTF_GAS_OUTMON or the like.
Record Initial State
For each suspension:
- Check that the WDs and DACKILL are not tripped, and reset them if necessary.
Check that the Guardian is in a state with at least IP and GAS control on, e.g., GAS_CONTROL_ENGAGED or IM_DAMP_ENGAGED. If the OL is properly adjusted, consider TM_DAMP_ENGAGED, OL_CONTROL_ENGAGED or ALIGNED. (If there are any OPTICALIGN offsets applied, then assume that the suspension has been deliberately misaligned and do not engage the OL control, manually or via the Guardian.)
- Check and record the IP SET output and whether it is sensible. L/T should be near zero for all suspensions. Y should be 0 for BS, 4020 for SR2, -4091 for SR3 and -3600 for SRM.
- Check and record whether the IP control is managing to bring the IP to the set point.
- Record the IP H1/H2/H3 coil output values. If they are large (e.g., more than 5000) consider doing a round of offloading to the IP FRs before pumpdown/venting begins (see below for instructions).
- Check and record the GAS coil outputs. If the suspension is trimmed for vacuum but is still in air, then some may be large and negative (to press down against the buoyancy of the air). Note that the coil drivers trip at around 25000 counts. If any outputs are very large (e.g., more than 15000) consider making a temporary adjustment to the SET setpoints (e.g., a 500 µm change in the F0 setpoint is good for around 10000 counts of output on BS). Make a note to remember to undo this later!
- Check and record the