LHC Beampipes Ray Veness ATVAC FP 420 6

LHC Beampipes Ray Veness / AT-VAC FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Contents o General requirements for LHC room temperature o beam vacuum Vacuum equipment relevant to FP 420 o Bellows modules o Instrumentation assemblies o Beam position monitors o TOTEM roman pots (from a vacuum perspective) o Summary FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Key Vacuum Requirements Relevant to FP 420 o Physical Aperture o Beam screens on both sides have 34. 3 mm vertical and 44 mm horizontal section o Electrical requirements at low and high frequency o Low frequency o The requirement is a function of geometry (diameter, thickness) and material – see spec. o Standard LSS vacuum chambers are 80 mm diameter, 2 mm thick copper o High frequency o Limits on sharp internal profile transitions (15° is standard) o Cavities such as bellows and pumping ports have RF shields (see slide on bellows) o Vacuum / surface requirements o All standard LHC chambers are NEG coated o Materials with high SEY (eg, aluminium, beryllium) must have NEG coating o Some short stainless steel or copper sections do not have NEG coating o All standard sections are baked to 250 C to activate NEG o Some short lengths are only baked to ~150 C to de-gas water o Designs and Materials o All designs and materials used forming part of the LHC beam vacuum system must be approved by AT-VAC, and acceptance tested before installation o This includes ‘standard’ materials such as stainless steels FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Warm Vacuum Functional Specification This specification is being revised, but contains more information on many of the main requirements for the LSS vacuum system FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Room temperature Bellows modules o Bellows Concept: o Designed to be modular, composed of o o o body with flanges and bellows Removable copper inserts with Cu-Be RF contacts 100+ variants for the ~1600 installed in the LHC machine o Design o Standard LSS bellows are all RF screened o Some exceptions, agreed with Accelerator Physics group, with special designs for LHC experiments (see next slide) o Bakeable to 250°C o Standard bellows units are not NEG coated FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Non-standard bellows for LHC Experiments o Justifications to date o Special request from the experiment for o o minimisation of material close to the interaction point o Examples in all 4 large experiments Limited transverse space, leaving no room for implementation of RF contacts o Inside the ATLAS calorimeter There are ~25 such bellows around the 4 large LHC experiments o Procedure o Derogation to install given by the o Accelerator Physics group leader Design a bellows according to vacuum group guidelines to minimise impact on the machine FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Vacuum Instrumentation Functional Requirements o Separate the cold and warm vacuum sectors o o o Type 47 VAT RF-screened all-metal valve o Different diameters exist in the LHC Interlock the valve between warm and cold sectors o low and high pressure gauges on both sides of valve Allow initial pump-out of vacuum chambers o At least one roughing valve per sector Pump non-getterable gasses in the warm sector o Ion pumps on the warm side of the valve Diagnostics for vacuum status o Low pressure gauges and gas analysers installed where required o Mechanical flexibility o Lateral offsets for alignment of objects o Axial compression during bakeout of warm sector (7 m o o chamber) Bellows on both sides of valve o Safety o Over-pressure rupture disc Detection of beam obstacles o Reflectometers installed in some places FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Beam Position Monitors o General o Fulfill all vacuum requirements PLUS beam instrumentation o Solid stainless steel body o Bakeable, but not NEG coated o 4 button electrodes o A number of variants for the LHC warm sectors o Mounted on rigid, alignable structures with survey targets FP 420 - 6 XII 08 Beam Vacuum- R. Veness

TOTEM Roman Pots were designed in close collaboration with the vacuum group FP 420 - 6 XII 08 Beam Vacuum- R. Veness

FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Roman Pot Bakeout FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Summary o Requirements o The LHC beam vacuum has many inter-linked requirements with accelerator o physics, beam instrumentation, cryogenics, magnets etc There is close control on anything that may impact on the LHC performance or reliability o LHC Vacuum components o There are many variants of ‘standard’ vacuum components in the LHC o They have all been designed, produced and tested according to the same strict criteria o Non-standard components o A number of non-standard components are installed, mainly related to the LHC experiments, but: o Make sure first there is not something that has already been developed and tested that can do o the job Be prepared to defend the justification for installation, and the impact on the machine FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Additional Material FP 420 - 6 XII 08 Beam Vacuum- R. Veness

Vacuum Schematic eg LHCLSVI_0014 FP 420 - 6 XII 08 Drawing STDVTGS_0001 explains symbols Beam Vacuum- R. Veness