450 GeV Collisions during full beam commissioning

Will be provided for a limited period (2 - 4 shifts, possible over a weekend or at night) during the commissioning for 3.5 TeV

Common view of the experiments: such a run is useful, but should not make a significant impact on ongoing commissioning. A short period with such beam conditions is interesting (up to a few shifts, i.e. in the noise of the commissioning schedule), provided these beam conditions are safe (no compromise on machine & experiment protection) and stable beam conditions are declared.

If the experiments want their solenoids on at this stage, we would need to perform appropriate coupling measurement and correction at 450 GeV as described in phase A12.  CMS's solenoid would be turned off again for the commissioning of the ramp (making the assumption that Atlas and Alice coupling contribution is negligible.)

Would imagine colliding beams at 450 GeV early on in the commissioning sequence. This would probably be with low intensity, few bunches given the probably state of machine protection system commissioning i.e. the first three columns in the table below are realistic. Safe beam at 450 GeV is 1 e12. A squeeze at this stage is ruled out.

No of bunches
1
4
12
43 43 156 156
Particles/bunch 10^10
4
4
4
2 4 4 10
Beam Intensity
4 10^10
16 10^10
4.8 10^11
8.6 10^11 1.7 10^12 6.2 10^12 1.6 10^13
fraction of nominal beam intensity
0.0001
0.0005
0.0015
0.003 0.005 0.02 0.05
beta* [m]
11
11
11
11 11 11 11
Luminosity [cm^-2 s^-1]
1.7 10^27
6.6 10^27
2 10^28
1.8 10^28 7.2 10^28 2.6 10^29 1.6 10^30
Integrated Lumi 24 hours [nb^-1]*
0.06
0.24
0.7
0.64 2.6 8.9 57
Beam size at IP [microns]
293
293
293
293 293 293 293
inelastic event rate [kHz]**
0.07
0.27
0.8
0.7 2.9 10.4 65

* Two eight hour fills in 24 hours, 8 hour turn around, 100% efficiency
** Assuming 450 GeV inelastic cross section 40 mb

Bunch Length

RMS bunch length with longitudinal emittance of 1 eVs  and 8 MV approx 11.24 cm (1 sigma) as per design report (exact value depends on beam from SPS) for nominal intensity.

Actual value measured in November 2009 - near 8 cm - with very low intensity.

Note: RF voltage will remain at 8 MV at injection in 2009.

 

IF the we were to raise the voltage after injecion to 16 MV for the store at 450 GeV. This could improve the beam lifetime. The associated increase in dp/p is from (2sigma) 0.88E-3 to ~1.1E-3 (if we have the 1 eVs emittance; it might be lower), which shouldn't be a problem generally. (Trevor Linnecar).

In the latter case the bunch length is ~10.5 cm - again the exact value will depend on the beam from the SPS.

 

Mike Lamont - last update August 09