LBDS and collimation validation tests. Asynchronous dump

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

Asynch. dump tests that muts typically be made:

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.   

or any other configuration depending on the machine setup.

Procedure for measurement:

  • Beam: 1 bunch in bucket 1 of about 8e10 at 450 GeV. At 6.5 TeV lower the bunch intensity to < 4E10 ! (Use vertical excitation blowup, NOT horizontal)
  • Check that the BRSA is working and logging (use the application).
  • Check orbit corrected well by OFB.
  • Set SBF is SETUP.
  • Switch OFB, QFB OFF
  • MASK BIC channels:
    1. RF interlocks (2 channels per beam).
    2. IR6 excursion interlock in BIC (2 channels per beam).
    3. IR6 BLMs.

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 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.

  • 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), at 6.5TeV wait for ~50sec until beam spreads across the AG - see example bellow. 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 < ~3e10 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!

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

When to trigger the dump at 6.5 TeV (shape also valid at injection) ?

After switching off the RF, please wait until the beam reaches the left side of the plot (white/light background, this corresponds to the rising edge of the dump - the part that generates the trouble).


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