In the beam pipe of the positron Main Damping Ring (MDR) of the Next Linear Collider (NLC), ionization of residual gases and secondary electron emission give rise to an electron cloud which can cause the loss of the circulating beam. One path to avoid the

5Conclusion

WehavepresentedareportonthestatusoftheSEYexperimentcarriedoutatSLAC.Descriptionofourexperimentalsystemhasbeenpresented.

Firstresultsonas-receivedTiNsampleandonanas-receivedTiZrVgetterhavebeenshown.Inthecaseofthegetter,thein uenceoftheactivationandrecontaminationbyitspumpingactionwereinvestigated.ThemaximumSEYδincreasedfrom～1.3to～1.5afterelevendaysandto～1.6aftertwenty-twodaysofexposuretoavacuumof～3.10 10Torr.OurSEYresultsseemtodisagreewithCERN[8].Firstofall,ourstartingδmaxis1.3compareto1.1[8].Second,wehaveanincreaseinδmaxabovetheCERN-predicted1.35[8].Thismattershouldbeinvestigatedfurtherastheimplicationtoelectronclouddevelopmentisofimportanceforapositivelychargedbeamrunninginanaccelerator.

Valuesofδforenergiesbelow20eVshouldbeusedcarefullyifpluggedintosimulation.ItisplannedtoinvestigatefurtherthispartoftheSEYcurve,ashasbeendoneatCERN

[14].

Additionally,wewillstudythein uenceofvarioustreatments,suchasthein-situbakeoutofTiN,electronconditioningappliedfortheNLCcase,andalsothein uenceofionconditioning.Byconditioningwemeanbombardingthesurfacewithagivenspectruminenergyofelectronsandions.Di erentspeciesofionscanalsobeinvestigated.

Ithastobestressedthatconditioning(dosee ect)isaverye cientwayofloweringtheSEYofanytechnicalsurfacestoalmostthesamevalue(δ=1.2);andthusindependentlyoftheinitialδ[4].However,suchmeasurementsaretimeconsumingandmightnotberelevanttotheoperationofanaccelerator,dependingonthe uxofelectronsassociatedwithpost-commissioningproductionoperation.

6Acknowledgments

WewouldliketothankP.HeandH.C.HseuhatBNLforprovidingtheTiNsamplesandtheESTgroupfromC.BenvenutiatCERNfortheTiZrVsample.Wealsothank

A.WolskiatLBNLforshepherdingtheproductionofsampleplates,andinthenearfuture,forthin lmsamplescomingfromLBNL.MostvaluablewastheworkofG.ColletandE.Garwin,SLAC,forconvertingandbakingtheXPSsystemforuseonSEYmeasurements.

References

[1]M.Pivietal.RecentElectron-CloudSimulationResultsfortheMainDampingRingsoftheNLCandtheTESLALinearColliders.InPAC,Portland,Or,USA,2003.SLAC-PUB-9814.

[2]P.PrietoandR.E.Kirby.X-rayphotoelectronspectroscopystudyofthedifer-encebetweenreactivelyevaporatedanddirectsputter-depositedTiN lmsandtheiroxidationprperties.JournalofVacuumScienceandTechnology,A13(6),1995.