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The Evolution of Vacuum System Design for

Accelerators over 30 years at Daresbury Lab

Ron ReidGroup Leader, Vacuum Science Group

ASTeCCCLRC Daresbury Laboratory

Warrington WA4 4AD, UK

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Outline

• Our second accelerator (SRS)• System Design

• Pressure calculations• Materials• Pumps• Gauges• Conditioning• Our next accelerator

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The SRS

• NINA• SRS (1980)

• First 2nd Generation Light Source• Medium Energy• 2GeV, 1A (350mA), 100m, 3.88Å• 10-9 Torr; 12 hours

• < 10-9 Torr, >40 hrs @300mA• Two major upgrades

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The SRS

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The SRS

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Simple Vacuum Layout

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Vacuum System Design - Then

• Highly simplified – • Analytical solution of gas flow equations

• No PCs – mainframes with turnround of days

• Simple “finite element” models• Fortran decks

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Vacuum System Design - Now

• PCs ubiquitous• Realistic calculations of complex systems

• Monte Carlo simulations• Angular coefficients

• Quick optimisations of layouts

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Materials

• Stainless steels as now• Aluminium less common• Absorbers

• Copper• Finite element calculations

• Glidcop

• Fabrication Techniques• EB and plasma welding now more generally

available

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Pumps

Then Now

Roughing

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Pumps

Then Now

Roughing Sorption; Diaphragm

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos Oil sealed

Air Bearing

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos Oil lubricated;

Air Bearing

Greased ceramic

Magnetic

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos Oil lubricated;

Air Bearing

Greased ceramic

Magnetic

Ion Pumps

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos Oil sealed

Air Bearing

Greased ceramic

Magnetic

Ion Pumps Diode; Triode; “Noble”

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos Oil sealed

Air Bearing

Greased ceramic

Magnetic

Ion Pumps Diode; Triode; “Noble”

Diode; Triode; DI; Starcell

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos Oil sealed

Air Bearing

Greased ceramic

Magnetic

Ion Pumps Diode; Triode; Noble

Diode; Triode; Noble; Starcell

UHV

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos Oil sealed

Air Bearing

Greased ceramic

Magnetic

Ion Pumps Diode; Triode; Noble

Diode; Triode; Noble; Starcell

UHV TSP

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Pumps

Then Now

Roughing Sorption; Diaphragm

Dry mechanical pumps

Turbos Oil sealed

Air Bearing

Greased ceramic

Magnetic

Ion Pumps Diode; Triode; Noble

Diode; Triode; Noble; Starcell

UHV TSP TSP; Neg

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Pumping schemes

• In SRS about 50% of circumference is dipole magnets vacuum vessels

• Main radiation absorbers are linear (distibuted) in dipole vessels• Main gas load

• Most restricted pumping

• Solution: DIPs

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DIPs

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Pumping schemes

• In SRS the DIPs give almost half the applied pumping speed during beaming

• Losing just one DIP gives a noticeable decrease in lifetime

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Pumping schemes

• Our new machine designs have much smaller apertures, dipoles occupy only a small fraction of the circumference

• DIPs no longer appropriate

• Machines use discrete photon stops

• Current preferred solution• NEG (discrete and film)

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Gauges

• Little change in type of gauge• Except BAG often replaced by IMG

• Main difference is the electronics – now compact, more reliable

• Biggest difference is in control - then home brewed, now uses standard interfaces

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Conditioning

• Then - beam scrubbing effect was known• But limited data and best measured values of

η were ~10-6 mol γ-1

• SRS design needed 10-7

• Cleanup rate not well characterised

• Now much greater range of systematic data and clean up rates predictable as a function of beam dose

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Our next accelerator – 4GLS

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4GLS

• Direct vacuum challenges are few

• Most of the machine needs to be at modest UHV, maybe HV

• But• Photocathode gun is XHV

• Superconducting linacs

• Particulate Cleanliness is a real challenge

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Concluding Ramblings

Thanks for your indulgence!