Steering @ LHC An LHC OP guide… under construction J. Wenninger 10/17/2019 YASP@LHC

Acquisition Modes - Trajectory First turn acquisition as activated by selecting the ‘Fturn’ option. There are 2 acquisition modes: FIFO (Fist In First Out) is a self triggered mode that is used for threading of for trajectory measurement with an empty ring. It relies on injection of a single bunch. CAPTURE is a triggered mode where the bunches/buckets must be configured via the sequencer or the multi-turn application. This mode only works once all BPMs have been timed in (bunch number). 10/17/2019 YASP@LHC

Acquisition Modes – Closed Orbit Closed orbit acquisition as activated by selecting the ‘Orbit’ option. There are 3 acquisition modes: 1Hz: one orbit (averaged over 224 turns/20 ms) is returned at 1 Hz. Average-1Second: all orbits acquired during one second are averaged. Data is returned at 1 Hz. Average-10Second: all orbits acquired during 10 seconds are averaged. Data is returned at 0.1 Hz. 10/17/2019 YASP@LHC

Corrector Settings The settings of the correctors (CODs) used for steering may be obtained from 2 sources: The LSA DB (settings associated to the selected actual BP). The kicks are only correct if the Orbit FB is OFF, no real time corrections are present in the FGC and when the machine is static (i.e. not in ramp and squeeze). The Orbit Feedback Controller (OFC). The kicks are reconstructed in real time from the MEASURED currents of the CODs. When the Orbit FB is active, only option 2/ will give the correct state of the correctors. No item checked: no settings are acquired (all kicks are 0). ‘Read CODs’ checked (default): settings from LSA DB (1.) Both items checked: settings from OFC (2.) 10/17/2019 YASP@LHC

Threading (1) The first operation after a shutdown is to establish a closed orbit. Because of the size of the LHC and the alignment tolerances, the beam will not circulate immediately, but be lost along the circumference. Threading consists in establishing the first turn step by step by correcting the trajectory with a few orbit corrector in each step. 10/17/2019 YASP@LHC

Threading (2) Threading is best done with the MICADO algorithm, using between 1 and 3 correctors at the time (per plane). In some cases MICADO may return an error with a ‘suspicious’ corrector: in that case one can reduced the number of correctors or disable the corrector manually. Select the beam you are threading to reduce the numerical complexity Matrix Reconditioning will attempt to filter out correctors that may the source of numerical singularities. 10/17/2019 YASP@LHC

From FT to CO (1) Once the first turn(s) has(ve) been established, it may be necessary to perform further correction to obtain a closed orbit. This is best done by averaging the first N good turns (N >= 3, ‘estimate’ for the closed orbit) and then applying a MICADO correction on the resulting average as if it was a closed orbit. >> ‘Machine Specials’ menu, option ‘Multiple Injection Turns’ 10/17/2019 YASP@LHC

From FT to CO (2) Select the N first good turns (N >= 3) and click on ‘Average’. This will build an averaged data set from the selected turns. Then go to the ‘Steering’ menu, select ‘General Steering’, MICADO. Apply MICADO with some correctors (10-20), send in steps (~20-30%) and observe if the new acquisitions improve the situation. Watch the tune !! 10/17/2019 YASP@LHC

Status Control The ‘Status Control’ menu gives access to a variety of tools to enable-disable monitors and correctors. For the LHC special options are available to deselect the BPMs or the CODs of one plane. One option allows to deselect all common (region) correctors that affect both beams at the same time. 10/17/2019 YASP@LHC

Reload of Settings (1) To reload ‘old’ (or just different) corrector settings to the HW. Select a dataset and load it into the display. The reload function will only act on the dataset+settings that are in the display. I recommend to stop any acquisition during this operation. Example: for the 2010 startup one could reuse settings from Nov. 2009 before the MCBX correctors were used. From the ‘File’ menu, select ‘Data Set Catalog’. Choose the entry from 28-Nov-2009 at 17:56, click on ‘Load Entry’. 10/17/2019 YASP@LHC

Reload of Settings (2) From the ‘TRIM’ menu, select ‘Settings Reload’. Select the plane, and click on ‘Prepare settings’. The present LSA DB settings will be retrieved and compared to the data that is in the display. The difference will be calculated and presented as a correction…. 10/17/2019 YASP@LHC

Reload of Settings (3) The corrector settings will be presented as a correction : before (what is in the DB), difference (settings to reload – DB), after (settings to reload). You can now trim like any other correction. You can even send it step by step if you want to be sure… 10/17/2019 YASP@LHC

Aperture limits (1) In the dataviewer there is now a new view (1 per beam) where the BPM data is plotted together with the aperture and the beam envelope. 10/17/2019 YASP@LHC

Aperture limits (2) Zoom into the region of interest to see something... Parameters for the envelope: g, the normalized emittance (mm) and the no. of sigmas that are plotted. 10/17/2019 YASP@LHC

Aperture limits (3) To set the emittance and no. sigmas for the plot, select ‘Emittance Setup’ in the ‘Optics and Model’ menu. 10/17/2019 YASP@LHC