YONG WANG, BO ZHAN, GJIE WANG National Synchrotron Radiation Laboratory University of Science and Technology of China Key vacuum technologies and challenges for SPPC

Outline  Introduction  Vacuum in the accelerators  Insulation vacuum  Cold beam vacuum  Beam screen Vacuum  Vacuum for cryogenics  LSS beam vacuum  Challenges

Introduction  LHC with a circumference of 26.7 km  SPPC with a circumference of 54.3 km  The basic vacuum requirements - Depend more on beam performance than on size - Dynamic effects dominate when increasing beam energy and intensity  Higher beam energy means larger size - Requires a trade-off between performance and cost - Higher demand on integration and logistics ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Vacuum in the accelerators-1 Vacuum aims to reduce beam-gas interaction which is responsible for:  Machine performance limitations - Reduction of beam lifetime (nuclear scattering) - Reduction of machine luminosity (multiple coulomb scattering) - Intensity limitation by pressure instabilities (ionization) - Electron (ionization) induced instabilities (beam blow up ) - Magnet quench i.e. transition from the superconducting to the normal state - Heavy gases are the most dangerous  Background to the experiments - Non-captured particles which interact with the detectors - Nuclear cascade generated by the lost particles upstream the detectors ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Vacuum in the accelerators-2 Beam vacuum pipes are designed to:  Minimize beam impedance and HOM generation  Optimize beam aperture  Intercept heat loads (cryogenic machines ， for LHC) - Synchrotron radiation (0.2 W.m-1 per beam) SPPC-58 W/m/beam - Energy loss by nuclear scattering (30 mW.m-1 per beam) - Image currents (0.2 W.m-1 per beam) - Energy dissipated during the development of electron clouds ★ Intercept most of the heat load, 1 W at 1.9 K requires 1 kW of electricity ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Insulation vacuum--Cryodipole cross section  Insulation vacuum is a high vacuum between: - Cryomagnet and its cryostat - Inner cold cryogenic lines and the outer envelope of the liquid helium transfer lines Both are wrapped with super insulation layers ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

LHC insulation vacuum--Description  Size and volume: 50 km and 15’000 m weeks pumping required - mobile turbomolecular pumps  Pa enough to allow for the cool down - Cryopumping by cold surfaces maintains a static vacuum in the Pa range - Low helium cryo-pumping - Leak tightness is a key issue - 250’000 welds, 90’000 made in-situ, 100 km integrated length - 18’000 elastomer joints, 22 km integrated length turbo-molecular pumps to remove small helium leaks  9 million square metres of multi-layer thermal insulation - Huge outgassing after venting to atmosphere  - Huge amount of water partly trapped by these multi-layers. ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader For SPPC, the circumference is 54.7 Km. It will be a huge challenge for SPPC insulation vacuum.

ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Cold beam vacuum-1  2 independent beam pipes (cold bore) per arc - 8 arcs Some standalone cryomagnets in the long straight sections  1.9 K operating temperature 4.5 K on standalone cryomagnets, except triplets  Non-baked beam vacuum 2-3 weeks pumping time (10 -4 Pa) before cool down Pressure lower than Pa after cool 1.9 K Temperature dependant  Innovating conceptual design with a “beam screen” Beam screen inserted inside cryomagnet cold bore Operated between 5 and 20 K for SPPC operated 50K ?

Cold beam vacuum-2 1. Most of the heat load is intercepted; 2. Cryopumping ensures the beam lifetime; 3. Desorbed molecules transferred to the magnet cold bore; 4. HOM trapping is reduced; ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Beam Screens-1 High intensity, density proton accelerator - Impedance Bunched beam HOM, RF couplings Electron clouds, ion instability High energy particles - Synchrotron radiation induced radiation Heat loads extraction (cryogenic machine) Magnet quench Intercept the heat loads - Synchrotron light Energy loss by nuclear scattering Image currents Electron clouds Insure vacuum stability - Low photo-electron reflection Avoid HOM trapping Optimise the beam aperture Racetrack cross section - Allows integrating the two helium cooling capillaries Various shapes to adapt to the different magnet apertures Orientation adjusted to optimise the beam aperture Quasi-randomised pattern of the pumping slots to minimise HOM couplings ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Beam Screens-2 Manufacturing process Co-lamination of a low permeability 1 mm thick austenitic stainless steel strip with a 75 μm high purity copper sheet Rolling of the saw-tooth structure Partial annealing treatment to restore SSS mechanical properties and to increase RRR of the copper layer Punching of the pumping slots Rolling to the final shape and longitudinal laser welding Spot welding of the cooling capillaries Centering of the beam screen in the cold bore obtained by sliding rings with a bronze layer welded every 750 mm onto the beam screen Straightness is an issure Copper beryllium shields “clipped” onto the cooling capillaries to intercept the electrons escaping through the pumping slots Provide a support for the carbon fibre cryosorber material required to increase the hydrogen pumping 4.5 K ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Cold beam vacuum at 4.5 K --1  He adsorption isotherms on stainless steel  For SPPC, need more data about the gases adsorption properties  We will talk about this issue next time. ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Cold beam vacuum at 4.5 K --2  Cryosorbers to pump H 2 Installed onto the back of the beam screen Provide pumping capacity for H 2 Not required at 1.9 K for SPPC 50K ？  Cryosorbers regeneration Not foreseen during normal operation Regeneration planed during annual shutdowns Beam is OFF while regenerating External pumping is required Temperature to be increased above 80 K Cold bore at more than 20 K by emptying cold mass ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

LSS beam vacuum-1  6 km of RT beam vacuum in the long straight sections - Except in standalone cryomagnets  303 sector valves as vacuum protection - Prevents saturation of the NEG coating during warming up  Extensive use of NEG coatings - All beam pipes are NEG coated Baked-out allows the activation of NEG coatings  780 ion pumps to avoid ion instability - Provide pressure indications In complement to the 1084 Pirani and Penning gauges and 170 Bayard-Alpert Are used as sector valve interlocks ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader BTC IP1 IP 3 e+e- e+ e- Linac LTB CEPC Collider Ring CEPC Booster BTC SppC ME Booster SppC LE Booster IP 4 IP 2 SppC Collider Ring Proton Linac SppC HE Booster

LSS beam vacuum-2  Pre-testing as baseline More than 2300 assemblies tested before installation  Bake-out of beam vacuum 230°C for NEG coated chambers / 250°C non coated parts 320°C for vacuum instrumentation: ports, gauges and RGAs  Pressure lower than Pa after activation Pressure reading limited by outgassing of the gauge port And by the gauge resolution  Beam requirements Impedance, use of thick copper HOM, soft transitions ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

LHC beam vacuum--NEG coatings: Production procedure ASEVA, 18 November – Madrid (ES) J.M. Jimenez, CERN Vacuum Group Leader

Detectors beam vacuum-1  Integration: Vacuum installation follows detector closure “Bad surprises” are not acceptable Temporary supports and protections required at each stage of the installation  Reliability Leak detection and bake-out testing compulsory at each step of the installation Vacuum pipes get encapsulated in the detector  Availability Detector installation imposes the “speed” and sequence of the installation  Performances Vacuum (<10 15 H 2.m -3 ), HOM, impedance and alignment requirements Must be fulfilled

Detectors beam vacuum-2  Engineering - Beryllium and aluminum material used since “transparent” to the particles escaping from the collision point - Innovative bake-out solutions to fit with the limited space available between vacuum pipes and the detector

Challenges  In the insulation vacuum, by: Helium leaks  - In the beam vacuum, by: The expected dynamic effects at high intensities The staging of the collimators The pressure rise induced by the collimator halos The helium leaks  Helium leak rate above 5*10 -7 Torr. l/s shall be detected to avoid the risk of a quench !  Larger leak rate will provoke a magnet quench within : 30 to 100 days beam operation for He leak rate of Torr.l/s  A day of beam operation for He leak rate of Torr.l/s

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