yong wang, bo zhan, gjie wang national synchrotron radiation laboratory university of science and...

YONG WANG, BO ZHAN, GJIE WANG

National Synchrotron Radiation Laboratory University of Science and Technology of China

2015-9-11

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


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


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


LHC insulation vacuum--Description

Size and volume: 50 km and 15’000 m3

-2-3 weeks pumping required - mobile turbomolecular pumps

10-1 Pa enough to allow for the cool down- Cryopumping by cold surfaces maintains a static vacuum in the 10-5 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- 178 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.


For SPPC, the circumference is 54.7 Km. It will be a huge challenge for SPPC insulation vacuum.

ASEVA

, 18

Novem

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– M

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ES)

J.M

. Jim

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CER

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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 10-10 Pa after cool down @ 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;


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


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 capacity

@ 4.5 K


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.


Cold beam vacuum at 4.5 K --2

Cryosorbers to pump H2

• Installed onto the back of the beam screen• Provide pumping capacity for H2

• 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


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


BTC

IP1

IP3

e+ e-

e+ e- Linac

LTB

CEPC Collider

Ring

CEPC Booster

BTCSppC ME Booster

SppC LE Booster

IP4

IP2

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 10-9 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


LHC beam vacuum--NEG coatings: Production procedureA

SEVA

, 18

Novem

ber

– M

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ES)

J.M

. Jim

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CER

N V

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G

roup L

ead

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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 (<1015 H2.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 10-6 Torr.l/s

A day of beam operation for He leak rate of 10-5 Torr.l/s

THANKS

yong wang, bo zhan, gjie wang national synchrotron radiation laboratory university of science and...

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