Molecular desorption of stainless steel from high energy Au and Cu ...

Molecular desorption of stainless steelfrom high energy Au and Cu ionsunder perpendicular impactW. Fischer, H.C. Hseuh (BNL, US),U. Iriso (CELLS-ALBA, Spain), E. Mustafin (GSI, Germany)ECLOUD’07 – Daegu, Korea9 April 2007

Outline1. Motivation2. Measurement setup3. Desorption measurementsof baked stainless steelwith Au, Cu, (p) ionsWolfram Fischer 2

First pressure rise observation, October 20011 st fill with 110 Au 79+ bunches N=0.50·10 9Beam lossesduring accelerationnext fill N=0.44·10 910 -7 Torr abort limitConsidered• Ion-impact desorptionafter rest gas ionization(like ISR)• Ion-impact desorptionafter beam loss(few η data at the time)• Electron clouds(turned out to be dominant)Wolfram Fischer 3

MotivationIon-impact desorption from beam loss operationallyrelevant for:• GSI SIS18 – 11.4 MeV/n U 28+ (also SIS100/200)• AGS Booster – 0.92 MeV/n Au 32+• CERN LEIR – 72.2 MeV/n Pb 54+• HIF drivers – MeV– GeV (HIF = Heavy Ion Fusion)(All low and medium energies with partially stripped ions.)Relevance for RHIC was not know when dynamic pressurerises were first observed – few desorption coefficientmeasurements at the time, no measurements at RHICion energies.Wolfram Fischer 4

Related papers1. O. Gröbner and R.S. Calder, “Beam induced gas desorption in the CERN IntersectingStorage Rings”, PAC’73 (1973).2. D. Edwards Jr., “Neutral molecule desorption from SS(304) and Al(6061) due to particlebombardments”, PAC’79 (1997).3. J.P. Thomas et al., “Ion-induced desorption by high-energy (600 keV) hydrogen clusters”,PRL 55, 103-106 (1985).4. E. Mahner et al., “Molecular desorption of stainless steel vacuum chambers irradiatedwith 4.2 MeV/u lead ions”, PRST-AB 6, 013201 (2003).5. E. Mahner et al.,”Beam-loss induced pressure rise of Large Hadron Collider collimatormaterials irradiated with 158 GeV/u In 49+ ions at the CERN Super Proton Synchrotron”,PRST-AB, Vol. 6, 103202 (2004).6. P. Thieberger et al., “Estimates for secondary electron emission and desorption yields ingrazing collisions of gold ions with beam pipes in the Relativistic Heavy Ion Collider:proposed mitigation”, PRST-AB 7, 093201 (2004).7. A.W. Molvik et al., “Gas desorption and electron emission from 1 MeV potassium ionbombardment of stainless steel”, PRST-AB 7, 093202 (2004).8. E. Mahner et al., “Ion-stimulated gas desorption yields of electropolished, chemicallyetched, and coated (Au, Ag, Pd, TiZrV) stainless steel vacuum chambers and St707 getterstrips irradiated with 4.2 MeV/u lead ions”, PRST-AB 8, 053201 (2005).9. M. Bender et al., “Understanding of ion induced desorption using the ERDA technique”,EPAC’06 (2006).10. H. Huang et al., “Beam pipe desorption rate in RHIC”, EPAC’06 (2006).11. A.W. Molvik et al., “Heavy ion induced electronic desorption of gas from metals”, PRL98, 064801 (2007).Wolfram Fischer 5

Some reported desorption coefficientsMaterialProjectileIncidentangleDesorptioncoefficient hReferenceSS, bakedPb 53+ , 4.2 MeV/ngrazing2×10 4Mahner, CERNSS, bakedIn 49+ , 158 GeV/ngrazing3.7×10 4Mahner, CERNSS, bakedCr 7+ , 1.4 MeV/nPb 27+ , 1.4 MeV/nperp.perp.3001900Bender, Kollmus,Krämer, GSISS, bakedU 28+ , 8.9 MeV/ngrazing1.1–2.7 ×10 4Mustafin, GSISS, bakedK + , 25 keV/ngrazing9–14 ×10 3Molvik, LBNLSS, baked (NEG)Au 79+ , 8.9 GeV/ngrazing0.3–1.8 ×10 4Huang, Zhang,BNL[RHIC injection energy: Au – 8.9 GeV/n, Cu – 10.3 GeV/n, p – 23.4 GeV]Wolfram Fischer 6

Measurement setupUsed closed vacuum valvesin warm section IR12 astarget (limited amount ofdeliberate beam loss possible).Wolfram Fischer 7

Measurement set-upRHIC warm region (IR12) with• Ion pumps (P1 – P4)• Vacuum gauges (G1– G4)• Vacuum valves (stainless steel, 8 mm, 24 h at 200°C) (V1, V2)• Rest gas analyzer (RGA)• NEG (2 h bake at 250°C)• Beam in both directionsInject beam into closed valves to measure ion-impact desorption⇒ 4 measurements (2 valves, 2 beam directions)Wolfram Fischer 8

Beam and vacuum parametersParameterUnit197 Au 79+ 63 Cu 29+Relativistic γ… 10.52 12.07Kinetic beam energyGeV/n 8.86 10.30Average bunch intensity10 9 0.73 4.8Bunch spacings 4.0 4.0No bunches deposited… 18-28 20-37Inner beam pipe diameterm0.1215Pipe conductance, N 2 m4·s-10.22Pumping speed per pump, N 2 m3·s-10.27Pumping speed of NEG coating, N 2 m3·s-125Static pressureTorr 5×10 -11 2×10 -11Time of measurement… 2004 20051p +25.9423.401865.1561×10 -92005Wolfram Fischer 9

197Au 79+ measurement, E kin = 9 GeV/nWolfram Fischer 10

197Au 79+ measurement, E kin = 9 GeV/nGas load from desorptionbalanced by pumpingWolfram Fischer 11

AnalysisGas load from desorptionis balanced by pumpingη – desorption coefficient∆p – pressure increasedN/dt – incident ion ratek b – Boltzmann constantT – TemperatureWolfram Fischer 12

197Au 79+ analysis, E kin = 9 GeV/nMeasurementV1 + BlueV1 + YellowV2 + YellowV2 + BlueAverageh G2(next to NEG)2300300800054004000h G3(no NEG)110016002603003260Analysis by E. MustafinWolfram Fischer 13

63Cu 29+ measurement, E kin = 10 GeV/nWolfram Fischer 14

63Cu 29+ analysis, E kin = 10 GeV/nMeasurementV1 + YellowV1 + BlueV2 + BlueV2 + YellowAverageh G2(next to NEG)4025010—100h G3(no NEG)12040040170180Analysis by E. MustafinWolfram Fischer 15

1p + measurement attempt• Deliberate beam loss only possible inshielded locations• Higher background pressure for protonmeasurement (H- jet for polarized protons)• No other location available with good vacuumand large allowable beam lossWolfram Fischer 16

1p + measurement attempt∆p < 1×10 -11 Torr• 56 bunches deposited with total intensity of 10 13 protons(both Blue and Yellow)• only very small pressure rise observe• h < 1 (very approximate)Wolfram Fischer 17

CommentsConclusion from recent PRL (Molvik et al.)• η scales with electronic energy loss (dE e /dx) n , n = 1…2• varies little with impact angle θ, less than 1/cos(θ)h-scaling with Z• Electronic energy loss scales with Z 2 (Bethe-Bloch formulae)• Data consistent with η ~ Z 2 , with about factor 2 error in η• RGA shows H 2 as the dominant source of static pressure• RGA showed little change in H 2 pressure with beam lossWolfram Fischer 18

Summary• Measured ion-impact desorption– of stainless steel (baked 24 h at 200°C)– with high energy ions– under perpendicular impact– at static pressure of ≈ 5×10 -11 Torr (5×10 -9 Torr for p)• Measured desorption coefficients are– η ≈ 3500 for 197 Au 79+ with kinetic energy 9 GeV/n– η ≈ 150 for 63 Cu 29+ with kinetic energy 10 GeV/n– η < 1 for 1p + with kinetic energy 23 GeV(error analysis not yet completed, ∆η ~ 100%, η ~ Z 2 for same rigidity?)• Complements measurements at CERN (Mahner), GSI (Bender,Kollmus, Krämer), LBNL (Molvik) mostly at lower ion energiesWolfram Fischer 19