LBDS and collimation validation tests. Asynchronous dump

Principle: validate the TCDQ and collimator setup by dumping a debunched low intensity beam.

Asynch. dump tests to make:

1.  450 GeV with injection protection IN

2.  450 GeV with injection protection OUT

3.  6.5 TeV, end of ramp.

4.  6.5 TeV end of squeeze.

5.  6.5 Tev collisions.   

3,4,5 based on the run1 procedure, to be confirmed

Procedure for measurement:

  • Beam: 1 bunch in bucket 1 of about 8e10 at 450 GeV / 4 TeV.
  • Check that the BRSA is working and logging (use the application).
  • Check orbit corrected to high intensity reference.
  • Check explicitly with collimator settings display application that the TCSG and TCDQ are both in to the settings (around 9/10 sigma respectively, so jaws should be around 7-8 mm from the beam axis at 4 TeV, and around 16 mm at 450 GeV), and check that TCTs are all in their correct positions.
  • Check Relaxed SBF is TRUE.
  • Switch OFB, TFB OFF
  • MASK BIC channels:
    1. RF interlocks (2 channels per beam).
    2. IR6 excursion interlock in BIC (2 channels per beam).
    3. IR6 BLMs.
  • MASK SIS channels:
    • RF_VOLTAGE_MIN_FT_B1 and RF_VOLTAGE_MIN_FT_B2

In YASP: go to menu Machine-specials, option Interlocks, item Asynch, Dump Test Bumps. Select the bump amplitudes and the beam (by default use B1+B2). The amplitude of the bump should correspond to the interlock limit in SIS, presently 2 mm at injection, 1.5 mm at 1.38 TeV and 1.2 mm at 6.5 TeV – use a positive value. Click on calculate to prepare the bump (see figures below, the bump is NEGATIVE for B1 [automatic by YASP] and POSITIVE for B2). The bump sign is important – the bump must move the beam away from the TCDQ jaw, which means it must be – for B1 and + for B2. In case of doubt on the amplitude, in the console manager go to 'LHC Machine Interlocks' -> 'Beam-TCDQ Interlock Monitor'. Start the acquitision, wait a bit until all values have been acquired/retrieved. You can then read off the limit and bump amplitude from the red tolerance lines (in the present example - see below - ~0.9 mm).

 

  • Send the bump(s) in steps of 25-50%.
  • Switch off the RF at the low level as usual, for both beams at the same time
  • Wait for 90 s (for 450 GeV).For 6.5TeV wait for 50sec,  nominal bunch placed in bucket #1 so that it goes to the abort gap faster.Before doing the asynch. dump reduced the bunch intensity with the ADT to about half. The injection has to be done with 1 nominal for the orbit.
  • Watch the gap fill up on the BRSA – objective is peak intensity at the TCDQ (left) side of the gap.
  • Check that the abort gap population is <1e10 to avoid any risk of damage at the TCTs!
  • Dump using the operator switch (PM data needed).
  • Check if Q4 L/R6 has quenched.

Bump shape for B1 (at -1 mm amplitude). Negative at TCDQ!

Bumps shape for B2 (at 1mm amplitude). Positive at TCDQ!

 

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