Secondary Electron Yield Measurements of TiN Coating and TiZ(6)

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

(NEG)istorecordthedecreaseofthesurfaceoxygenconcentrationwithXPS.DuringtheNEGactivation,thesurfacegoesfromanoxidizedstatetoapartiallymetallicstate.ThebacksideoftheNEGwasheated,directlyviaaholeintheplateholder,byelectronbombardment.TheminimumtemperatureneededtoactivatethisNEGis180 C

[8][11].Thethermocouplesdisplayedatemperatureof216 Cfor2hours.InordertodeterminethetemperatureoftheNEG,aS/Ssampleholder( 0.31)washeated,withahotplate,tovarioustemperaturewithathermocouplespotweldedtoit,withandwithout7056glassviewportcorrection.MatchingthereadingofthepyrometerofthisexperimentalcalibrationwiththereadingrecordedduringaninsituheatingofthesameS/SsampleholderallowedustodeterminetheactualtemperatureoftheNEG,assumingthesameemissivity,TNEG=232 C.Anin-situtemperaturemeasurementwiththeblackbodycalibratedpyrometergivesforthesameS/Ssurface201 CwhenthethermocouplesontheOmniaxcarrierplateholderread216 C.

TheexperimentalelectroniccircuitisidenticaltotheonepresentedinFig.8[3].Thecomputercontrolledelectronbeamcomingfromthegunisdecoupledfromthetargetmeasurementcircuitry.However,thegroundiscommontoboth.Inshort,thetargetisattachedtoabiasingvoltagesourceandanelectrometerconnectedinseriestothedatagatheringcomputerAnalogDigitalConverter(ADC).

Figure8:Electroniccircuitryusedtomeasurethesecondaryemissionyield

3SEYmeasurementmethodology

Inordertocharacterizeoursystem,wehavemeasuredtheSEYin-situofinertgas-ioncleanedmaterials:carbon,copperandgold.Resultsarenotpresentedherebutagreewithwidelypublishedresultsforionsputtercleanedsampleofthesematerials.Aftercon rmingtheSEYfromthesereferencematerials,weproceededtomeasureaTiN-coated