Beam

Initial probe beam

With the experience gained during the LHC injection test we need to slightly modify the LHC PROBE beam definition.  For this beam it is required to have the intensity lower than the LHCPILOT at around 2x10^9.  Tests with this lower intensity were done during the injection test using longitudinal shaving, but a proper setup throughout the injector chain is to be preferred.

The Probe beam (with the low emittance or 1mm) and very low intensity will be used for initial threading of the beam around the LHC – since we discovered that 3.6x10^9 can provoke a quench if fired directly into the dipoles.  

Single bunch. Start with low emittance of around e_n ~ 1.0 µm.rad which gives a beam size of around 0.6 mm at b = 180 m. at 450 GeV versus 1.1 mm with nominal emittance. This reduction is useful in two ways: firstly the mechanical aperture increases in terms of s and the margin for orbit and optics corrections can be relaxed; secondly the dynamic aperture constraints are relaxed, smaller particle amplitudes means less sampling of the non-linear fields at high amplitudes and more linear motion. Might worry about the increased energy density. Longitudinal emittance around 0.5 eV.s.

Pilot

450 GeV: Pilot should be only be sufficient to quench a magnet if it is lost locally within 1- 5 m. Damage limit ~2 x 10^11

The pilot intensity is 5E9 - 3.5 µm.rad

Relaxed demands on key beam parameters

Tune

Nominal at injection

Stability Island  ΔQ = +/- 0.01

• 2 x 10^-3 for amplitude detuning
• 2 x 10^-3 for chromatic-geometric detuning
• 2 x 10^-3 fpr linear part of chromatic tune modulation
• 1 x 1-^-3 for non-linear part of chromtic tune modulation

Leave 7 x 10^-3 or  ΔQ = +/- 3 x 10 ^-3

Commissioning

In Stephane's spec he quotes that the working tunes chosen are in the centre of a stability island of +-0.01. I would therefore assume that the tune initially have to be controlled at least to this level - true? In his resume table he also quotes a required resolution of 3e-3 for commissioning. The resolution is quoted as being 1/4 of the tolerance for tunes, implying a tolerance of ~0.012.

I've modified my figures accordingly:

Tune tolerance for commissioning now ~0.01
Requested resolution 0.003
Correction rate required 0.1

Coupling at Injection

beam dynamics - mod[C-] < 0.01

diagnostics and feedback mod[c-] < 0.003

Momentum

0.8 x 10^-4 gives 110 micron closed orbit shift in arcs

10^-4 b1 gives  delta Q -0.0086/0.082  delta Q'  -0.7/0.7

Linear Chromaticity

- sngle bunch up to 10^10 : Q' > 150
- Nominal beam structure, 10% nominal current Q' > -15
- Nominal beam Q' > 0    Q' +/- 1  for Q' = 2

First 3 months

• Start with probe beam - establish circulating beam etc.
• Move to pilot - nominal emittance
• Move to single bunch 3 e10 for initial measurement program at 450 GeV [BPM resolution etc.]
• First ramp attempts with probe/pilot, increase intensity to 3-4 e10 as confidence grows.
• Repeat with 2 beam operation
• First colliding beams with 2* 3-4 e10, single bunch, unsqueezed.
• Move to multi-bunch operation: various tests, measurements at 450 GeV
• Single beam multi-bunch up the ramp
• Moving towards 43 on 43 with ~pilot intensities.
• Establish multi-bunch physics with 43 on 43 moving towards 3-4 e10 per bunch.
• Squeeze as confidence grows, backing off to lower number of bunches/intensity for initial runs at lower beta*.

Initial commissioning: Ending with Pilot physics: 43 on 43 with 3 - 4 x e10
 

Year 1

Year one[+] operation:
Lower beam intensity/luminosity:

• Event pileup
• Electron cloud
• Phase 1 collimator impedance etc.
• Equipment restrictions

Therefore, relaxed squeeze, lower intensities, 75 ns. bunch spacing with a maximum bunch intensity of 3 - 4 x e10, moving to 25 ns with experience.