1. E.B. Holzer BLM Meeting: Q & A March 20, 2004 1 Questions and Answers

2. E.B. Holzer BLM Meeting: Q & A March 20, 2004 2 Comparison to SPS chambers Two types? The “new” ones (1982??) filled with N2, paper: The old ones (ISR type), info from xxx –filled with dry air –cleaned according to ISR vacuum standards –He leak test –no baking.

3. E.B. Holzer BLM Meeting: Q & A March 20, 2004 3 Steady proton loss rates and quench levels location450 GeV Nominal life time (Quench level) 7 TeV Nominal life time (Quench level) collimation10 11 (10 13 ) p/s<3 10 9 (8 10 10 ) p/s arc quadrupole30-50% of arc dipoles arc dipole10 7 (10 9 ) p/m/s/<3 10 5 (8 10 6 ) p/m/s LLS quadrupole (4.5K) Triplet (1.9K) Same as arc dipoles? (Mokhov)

4. E.B. Holzer BLM Meeting: Q & A March 20, 2004 4 LHC Project Note 124 Energy deposit along s in coil with (left scale) and without magnetic field (right scale) “ The presence of the magnetic field about doubles the energy deposit. In addition the maximum is reached at a smaller value of s. Both effects stem from the fact that charged particles from the shower which enter the vacuum region of the beam pipe are drawn back into the material by the field.” Simulation of Point Beam Losses in LHC Superconducting Magnets, T. Spickermann, K. Wittenburg (1997)

5. E.B. Holzer BLM Meeting: Q & A March 20, 2004 5 LHC Project Note 124

6. E.B. Holzer BLM Meeting: Q & A March 20, 2004 6 LHC Project Note 124 Energy deposit per cm3 of copper along different x- and y-positions close to the beam pipe (see white lines in figure 6) left: Energy deposit in a copper disc behind the quadrupole cold- mass right: Close-up view around the right beam pipe

7. E.B. Holzer BLM Meeting: Q & A March 20, 2004 7 LHC Project Note 124 Energy deposit in a 1 cm3 copper block positioned along different x- and y-positions - Comparison between GEANT and FLUKA

8. E.B. Holzer BLM Meeting: Q & A March 20, 2004 8 LHC Project Note 124 left: Longitudinal Distribution of MIPs outside the vacuum vessel right: Angular Distribution of MIPS. The angle is measured here from the center of the

9. E.B. Holzer BLM Meeting: Q & A March 20, 2004 9 LHC Project Note 124 left: Longitudinal distribution of MIPs outside the vacuum vessel for impact of proton on the right side of the beam screen and on the left side (i.e. pointing towards center of the magnet) right: Angular Distribution of MIPS for impact on right side and left side

10. E.B. Holzer BLM Meeting: Q & A March 20, 2004 10 LHC Project Note 124 left: Longitudinal distribution of ionization energy loss in a 5 cm thick gas layer (air at standard pressure) for impact of proton on the right side of the beam screen and on the left side (i.e. pointing towards center of the magnet) right: Angular Distribution of ionization energy loss for impact on right and left side “The maxima of the angular distribution in the two cases are at roughly the same angle, which comes from the fact that at 0 (or = 0 if measured from the center of the magnet) particles ‘see’ the least amount of material.”

11. E.B. Holzer BLM Meeting: Q & A March 20, 2004 11 LHC Project Note 124 Angular distribution of MIPs for losses in a dipole. The `cross talk', i.e. the signal on the side of the vessel opposite to the beam pipe where the loss occurred, stems from charged particles that are attracted to the opposite side by the magnetic dipole field

12. E.B. Holzer BLM Meeting: Q & A March 20, 2004 12 LHC Project Note 213 (A. Aurauzo, C. Bovet, 2000) 2-D field map in main magnets. Left: MQ, right: MD. The field data are used up to 60 mm. “Tracks of particles in the MD are spread horizontally …. If the field is set to zero, the azimutal spreading is uniform. In the quadrupoles … this azimutal asymmetry in the tracking is not observed.” “The field in the MD increases the intensity by a factor 2 for an outer loss, by a factor 4 for a top loss and a factor 10 in the case of an inner loss.” “In the MQ, the magnetic field may produce an intensifying of the interactions, but the secondaries are spread out homogeneously over the azimutal angle, and no different signal is detected outside the cryostat.”

13. E.B. Holzer BLM Meeting: Q & A March 20, 2004 13 Ana: uses magnetic field from beam pipe center up to 60 mm (~ outside radius of the coils). Edda: uses more fields. Thomas: ?? Ana: energy cuts: 0.3MeV for electron and positrons and 3 MeV for charged hadrons and muons. Thomas: xxxx. Edda: no? MIP electron: ~ 1 MeV (extrapolated from hadron data), 0.5 cm of Al stops it. Stopping power of electron 1-10 MeV: ~1MeV cm 2 /g Fe density: 7.87 g/cm 3 => 8 MeV/cm energy loss

14. E.B. Holzer BLM Meeting: Q & A March 20, 2004 14 History ISR and SPS BLM chambers SPS, 1 st patch of 350 chambers from 1977. Norbert Aguilar (SC/RP) supervised production and tests. –Tested vacuum with helium at 10^-10 Torr l./s (?) (760 Torr = 760 mm Hg = 1 atm) –Filled with N 2 99,9% pure at 760 mm Hg (1 atm) –Welding (soudures): Without external material (sans metal d’apport) Under argon With 100% penetration SPS 2 nd patch of 100 chambers from 1981, numbers of chambers: 400-500. –Equipped with “vulkollan” joint –Vacuum tested with helium –N2 filled

15. E.B. Holzer BLM Meeting: Q & A March 20, 2004 15 Dose in Gray: –1 Gray (in SiO 2 ) = 7*10 8 protons/cm 2, the proton energy is around 60 MeV (1-100 MeV) Doses at the SPS BLM monitors (estimate from Franco and TIS) J.B. Jeanneret’s IP5 and xxx? References BLM’s (SPS old) Geant calibrations? Sources of errors (energy dependence not linear) Longer chambers? (space available) – long. Losses reproducible? Long losses – compare to quench levels

16. E.B. Holzer BLM Meeting: Q & A March 20, 2004 16

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18. E.B. Holzer BLM Meeting: Q & A March 20, 2004 18 Signal shape/speed: SPS type (Edda) –The ratio of signal which arrives in 89  s compared to 300  s is 80-85%. Ways to double the signal –Double chamber length –Double number of chambers –Use Ar instead of N 2 (factor 2.3) –Double the pressure Pulse length for ions –Calculated 69  s ion drift in chamber –Measured > 400  s ion pulse signal. –Impurities (water, O 2 ) increase drift by about a factor 2. Signal from neutrons in different gases? –Smaller for heavy gases and clean chambers Ar + 10% CO2: electron are 6.3 times faster, ions ~ same speed compared to N2.

19. E.B. Holzer BLM Meeting: Q & A March 20, 2004 19 Signal calculation for parallel plate (SPS type) and coaxial chambers