MAX IV R&D Accelerator division seminars Vacuum systems and resources at MAX IV laboratory 18th September 2018, MAX IV, Lund Vacuum systems and resources at MAX IV laboratory, 18th September 2018 1 Marek Grabski Contents • What is vacuum - why do we need it in particle accelerators? • Basics of vacuum technology, • Gas sources, • Pumping technology, • Outlook of MAX IV storage ring vacuum systems, • Introduce vacuum team and services. Vacuum systems and resources at MAX IV laboratory, 18th September 2018 2 Marek Grabski What is vacuum? Vacuum is a space with no matter inside – practically not possible to achieve. Vacuum in engineering and physics is a space in which the pressure is lower than atmospheric pressure and is measured by its absolute pressure. Low pressure High pressure (high vacuum) (low vacuum) Force [N] 2 Pressure is Area [m2] measured in Pascals, 1 [Pa] = 1 N/m Vacuum systems and resources at MAX IV laboratory, 18th September 2018 3 Marek Grabski What is vacuum? The force exerted on the walls of an evacuated vessel surrounded by atmospheric pressure is: 1 kg/cm2 Atmospheric pressure Vacuum Vacuum systems and resources at MAX IV laboratory, 18th September 2018 4 Marek Grabski Pressure units Conversion table: units of pressure In vacuum technology: mbar or Pa Vacuum systems and resources at MAX IV laboratory, 18th September 2018 5 Marek Grabski Vacuum ranges 1 Atm. = 1013 mbar =~ 1 bar Pressure range [mbar] Low Vacuum 103 - 1 Medium Vacuum 1 - 10-3 High Vacuum (HV) 10-3 - 10-9 Ultra High Vacuum (UHV) 10-9 - 10-12 Extreme High Vacuum XHV < 10-12 rings, Storage Beamlines Vacuum systems and resources at MAX IV laboratory, 18th September 2018 6 Marek Grabski Why do we need vacuum in particle accelerator? Less beam-gas interaction: • Increase beam lifetime, • Prevents to increase beam size, • Reduces radiation hazard, • Allows the light reach the sample, • Helps to protect optics… OLAV IV 2014, Matthew Cox Vacuum systems and resources at MAX IV laboratory, 18th September 2018 7 Marek Grabski Why do we need vacuum in particle accelerator? The total beam lifetime in a particle accelerator is given by: The interaction between beam particles and residual gas molecules consist of two main mechanisms: elastic and inelastic scattering which contribute to total beam lifetime. Elastic, inelastic beam lifetime: 1 1 , ~ Z - atomic number of the residual gas (depends on gas specie), ng - residual gas density (pressure). Vacuum systems and resources at MAX IV laboratory, 18th September 2018 8 Marek Grabski Flow regimes - Mean free path [m] = - Diameter of flow channel [m] - Knudsen number [dimensionless] d FLOW REGIME VISCOUS TRANSITIONAL MOLECULAR < 0.01 0.01< < 0.5 > . Mean free path: Low vacuum Medium vacuum High/ultra high vacuum At atm. Pressure = 6.5x10-8 m < 10-3 mbar At 10-9 mbar (storage ring) = 66 km Typically: >1 mbar Vacuum Technology Know how by Pfeiffer Vacuum GmbH Increasing pressure Vacuum systems and resources at MAX IV laboratory, 18th September 2018 9 Marek Grabski Gas flow in molecular regime In molecular flow regime the gas flow (Q) from one point to the other is proportional to the pressure drop: Conductance Gas flow Pressure difference = ( ) Slot of area A [] = Conductance depends on the gas = = molecule velocity thus its molar mass and temperature (not on pressure). 1 = Conductance C at 295 K for nitrogen 4 (N2 - molecular mass 28): - conductance of unit surface area for given gas = = 11.8 A – slot Area [cm2] - the average gas molecules speed [m/s] Vacuum systems and resources at MAX IV laboratory, 18th September 2018 10 Marek Grabski Gas flow in molecular regime Combination of conductances: a). For components in series: b). In parallel: Paolo Chiggiato, Vacuum Technology for Ion Sources, CAS 2012 proceedings Vacuum systems and resources at MAX IV laboratory, 18th September 2018 11 Marek Grabski Gas flow in molecular regime In vacuum technology a pump is an object that permanently removes gas molecules from the gas phase. Pumping speed S of a pump is defined as the ratio between the pump throughput Qp and the pressure P at the entrance to the pump. = Pump From the definition of pumping speed: A – is the area of the pump aperture [cm2] p S = - is the conductance of the unit surface area for given gas [ ] – is the capture probability Paolo Chiggiato, Vacuum Technology for Ion Sources, CAS 2012 proceedings Vacuum systems and resources at MAX IV laboratory, 18th September 2018 12 Marek Grabski Gas flow in molecular regime Introduced limitation between pump and pumped vacuum volume limits the nominal pumping speed of chosen pump. Example: Conductance of 1 m long tube of 3,8 cm inside diameter (standard DN40CF vacuum pipe) for air (mass 28) is: 6,6 [l/s] Connected pump of 100 [l/s] to the tube will result in the effective pumping speed : = + = 0,16 Pump / , / = + = 6,3 l/s Paolo Chiggiato, Vacuum Technology for Ion Sources, CAS 2012 proceedings Vacuum systems and resources at MAX IV laboratory, 18th September 2018 13 Marek Grabski Generic vacuum system P = Processes -> Q P – gas pressure, Q – gas load (outgassing), Seff – Effective pumping speed. Pump Seff Vacuum systems and resources at MAX IV laboratory, 18th September 2018 14 Marek Grabski Sources of gases Sources of static gas loads in vacuum system: Processes -> Q Degassing Vacuum chambers are sources of gas Courtesy of Eshraq Al-Dmour Vacuum systems and resources at MAX IV laboratory, 18th September 2018 15 Marek Grabski What process defines pressure What process defines the pressure over time? Outgassing: Material – Binding energy Surface condition – As delivered – Machined Outgassing ~t -1 – Polished Diffusion ~t -(1/2) – Cleaning – Heat treatment… Difussion: - Material - Heat treatment (Vacuum firing) - Inner surface barrier (Air baking, Film deposition) http://web.utk.edu/~prack/Thin%20films/VACUUM-3.pdf Vacuum systems and resources at MAX IV laboratory, 18th September 2018 16 Marek Grabski Thermal outgassing Thermal outgassing (static outgassing) For metals: • If not baked (not heated) in-situ water • If baked (heated above ~1200C) in- is the dominant gas specie. situ hydrogen H2 is the dominant gas Sources, CAS 2012 Sources, proceedings Outgassing rates q at 200C: uum Technology for Ion Technologyfor uum Austenitic stainless steel not baked, Vac 3x10 10 (main gas: H O) after 10 h pumping 2 Austenitic stainless steel baked in- -12 2x10 (main gas: H ) Chiggiato,Paolo situ for 24 h at 1500C 2 OFS copper baked in-situ for 24 h at ~10-14 (main gas: H ) 2000C 2 Polymers (Viton, PEEK, Kapton) have high water vapour solubility, therefore have much higher outgassing rates than metals. Vacuum systems and resources at MAX IV laboratory, 18th September 2018 17 Marek Grabski Dynamic outgassing In particle accelerators energized particles impinging on vacuum surfaces induce desorption of molecules. Usually such dynamic gas load dominate over thermal outgassing. Photon Stimulated Desorption When charged particles (moving at relativistic speeds) are accelerated they emit synchrotron radiation in a narrow cone. This photon flux Synchrotron impinging on vacuum surfaces produces strong radiation outgassing thus a large dynamic pressure increase. http://photon-science.desy.de/research/studentsteaching/primers/synchrotron_radiation/index_eng.html Courtesy of Eshraq Al-Dmour Vacuum systems and resources at MAX IV laboratory, 18th September 2018 18 Marek Grabski Dynamic outgassing Beam stimulated desorption is characterised by - the desorption yield: = – depends on many parameters: • incident particle: type and energy, The desorption may be • material, stimulated by: • surface roughness, • electrons, • cleanliness of the surface, • ions, • history of the material (dose), • synchrotron radiation (photons). • Particle flux. Vacuum systems and resources at MAX IV laboratory, 18th September 2018 19 Marek Grabski Photon Stimulated Desorption Evaluating Photon Stimulated Desorption (PSD): Measured surface Photon beam ) ph / mol ( PSD yield effect of the dose: ield Y = α is between 0.6 and ~1 Photo Photo desorption ‘Vacuum aspects of synchrotron light sources’, R. Reid, Accumulated Photon Dose (ph/m) Vacuum in Accelerators, CAS 2006 proceedings Vacuum systems and resources at MAX IV laboratory, 18th September 2018 20 Marek Grabski Vacuum scrubbing 3 Gev ring vacuum conditioning: Average pressure normalized to machine current vs accumulated beam dose (or photon dose) Dynamic pressure is proportional to current: ∝ Dynamic pressure rise: Δ /I (mbar/mA) av ed average ed average pressure rise dP Normaliz Dose (Ah) Vacuum systems and resources at MAX IV laboratory, 18th September 2018 21 Marek Grabski Pump clasification Vacuum Pumps (molecular regime) Momentum Capture pumps transfer pumps Example: Turbomolecular Pump Example: Sputter Ion Pump, Getter pump, Cryo pump Principle: Molecules impinge on fast moving Principle: gas molecules are fixed surfaces which direct them towards the pump to a surface inside vacuum (pump outlet where they are evacuated by pumps has no moving parts). operating in viscous flow. The molecules do not transfer energy to each other. Vacuum systems and resources at MAX IV laboratory, 18th September 2018 22 Marek Grabski Turbomolecular Pump (Momentum transfer pump) Inlet Inlet Outlet to primary pump Outlet Blade rotational speed 1000 – 1500 Hz S (pumping speed) does not depend significantly on -1 -10 Pressure range: 10 till 10 mbar, the mass of the molecule. (with