Update of the impedance of new LHC experimental beam pipes M. Galilee, N. Mounet, B. Salvant, G. Schneider, V. Vaccaro

Current layout (for 50 mm diameter): Context The vacuum group is looking at the opportunity to replace the current LHC experimental beam pipes by composites: titanium (or Aluminum) + carbon-carbon NEG coating of 3 micron would still be put on the inside Reason: Beryllium (as now installed in the inner chamber) would be by far the best material (very high Young’s modulus and low atomic number). However cost (150,000 CHF/m!!!) and more importantly toxicity are calling for other options. Proposed layout 1 Vacuum /NEG(3μm) /Ti (0.3 mm or Al (0.4 mm)) /CC(1% diam 0.5mm) /vacuum Current layout (for 50 mm diameter): Vacuum(25mm) /NEG (3μm) /Cu(0.2mm) /SS(1mm) /vacuum Proposed layout 1 Vacuum /NEG(3μm) /CC(1% diam0.5mm) /Ti (0.3 mm or Al (0.4 mm)) /vacuum

Preliminary conclusions The solution with carbon-carbon composite on the inner part of the beam pipe would increase the total longitudinal and transverse impedances of the machine by 5% (if all 160m are at 25mm radius) The large power losses (10 to 30 W/m) may require cooling. The 3 micron NEG coating does not affect the power loss but increases significantly the real tune shifts (both longitudinal and transverse).

Material parameters used for the resistive wall impedance • Beryllium: – Resistivity: 4.24 10-8 Ω.m (from specifications) – Permittivity: 1 • Carbon-carbon composite: – Resistivity: 16 10-6 Ω.m (from specifications) • NEG: – Resistivity: 2.5 10-5 Ω.m (David Seebacher, F. Caspers, NEG properties in the microwave range, SPSU Meeting, 17th February, CERN) – Permittivity: 10 • Titanium: – Resistivity: 0.42 10-6 Ω.m (from specifications) • Aluminum: – Resistivity: 2.8 10-8 Ω.m (from specifications)

Effect of Al coating on the impedance of a carbon pipe (25 mm) layers materials Im(Ztrans) in kohm/m (for 160m) Im(Zlong) in mOhm (for 160 m) Power loss in W dissipated in a 1m length 1 Carbon 113 4 12.9 2 Al (1 mic)+ Carbon 14 0.15 2.6 Al (3 mic)+ Carbon 6.3 0.17 0.99 Al (5 mic)+ Carbon 5.1 0.21 0.66 Al (7 mic)+ Carbon 4.9 0.23 0.57 Al (9 mic)+ Carbon 4.83 0.55 Al (11 mic)+ Carbon 4.82 0.54 Al 4.8 3 NEG(3mic)+Al(5 mic)+CC 8.8 0.48 0.67 NEG(3mic)+Al(5 mic)+CC(500 mic)+Ti

Impedances as percentage of total LHC for 160 m Longitudinal impedance (% of total LHC impedance) transverse impedance (% of total LHC impedance) Already 1 micron Aluminum coating seems sufficient to reach less than 1% of the LHC impedance

Power loss 5 micron Aluminum coating seems sufficient to reach less than 1W/m

Effect of NEG+Al coating on the impedance of a carbon pipe (25 mm) layers materials Im(Ztrans) in kohm/m (for 160m) Im(Zlong) in mOhm (for 160 m) Power loss in W dissipated in a 1m length 2 NEG(3 mic)+Carbon 115 4.1 12.9 3 NEG(3mic)+Al (1 mic)+Carbon 18 0.42 2.62 NEG(3mic)+Al (3 mic)+ Carbon 10 0.44 0.99 NEG(3mic)+Al (5 mic)+ Carbon 8.8 0.48 0.67 NEG(3mic)+Al (7 mic)+ Carbon 8.6 0.5 0.57 NEG(3mic)+Al (9 mic)+ Carbon 8.5 0.55 NEG(3mic)+Al (11 mic)+ Carbon 0.54 1 NEG(3mic)+Al 4 NEG(3mic)+Al(5 mic)+CC(500 mic)+Ti

Effect of NEG Longitudinal impedance transverse impedance (% of total LHC impedance) transverse impedance (% of total LHC impedance) Already 1 micron Aluminum coating seems sufficient to reach less than 1% of the LHC impedance Power loss doe not change with NEG

Recommendations to be discussed Al coating helps a lot reducing the impedance and power loss of the carbon inside option For power loss reasons, at least 5 micron Al coating would be desirable

Varying the Al coating thickness

Varying the NEG coating thickness