Electron Stimulated Desorption of OFE Copper Chiara Pasquino, Politecnico di Milano 9th March 2011, RF Structure Meeting

Dynamic Vacuum: an issue for CLIC accelerating structures 9th March 2011, RF Structure Meeting  Static Vacuum: mbar [G.Rumolo, C.Garion]  Dynamic Vacuum: CO 2, H 2 < mbar 2 Technical Note, EDMS

Dynamic vacuum sources due to the High Gradient 9th March 2011, RF Structure Meeting  Breakdowns: during the discharge a gas burst is always detected;  Dark Currents: FE currents that don’t lead to a breakdown impinge on the Copper surface causing the ESD Effect. 3 FAST ION – BEAM INSTABILITIES

Dynamic Vacuum studies : Breakdowns 9th March 2011, RF Structure Meeting4  2*10 2 H 2 or CO molecules released [ exp. Data DC “spark test” reported in PRST-AB12, (2009) ];  Uniform pressure along the structure after ~ 3ms;  Background pressure recovered after 20 ms, no dynamic vacuum problems. [C.Garion]

Dynamic Vacuum studies : ESD 9th March 2011, RF Structure Meeting5 e - on faraday cup e - are uniformly distributed inside the cell e - on faraday cup S. Calatroni Faraday Cup measurement - T18_VG24_Disk_2 – KEK [T. Higo] ESD measurement on unbaked Copper [ N. Hilleret, CAS Vacuum School G. Vorlaufer CERN-Thesis (2002)]  H 2 PP = 1.12E-8 mbar 10 times higher  CO 2 PP = 3.37E-9 mbar 3 times higher NEW ESD EXPERIMENTAL DATA ON UNBAKED OFE COPPER AT HIGH ELECTRON ENERGY NEEDED!

Dynamic Vacuum studies: theoretical models 9th March 2011, RF Structure Meeting6 Gortel Fully Quantum Mechanical Model MGR Model e- Antoniewicz e-

Desorption Yield 9th March 2011, RF Structure Meeting7 Steady State Condition

Sample Campaign 9th March 2011, RF Structure Meeting8 3 Cleaning Procedures : w/o etching, passivation & SLAC etching Several Thermal Treatment : Vacuum, Argon, H or 820 °C

H 2 Diffusion Profiles :SLAC bonding 9th March 2011, RF Structure Meeting9 H2 Cu – H is an endothermic system! equal C s at both surfaces

H 2 Diffusion Profiles: SLAC bonding 9th March 2011, RF Structure Meeting10 THE ANNEALING TIME CAN BE DECREASED !!!

ESD Experimental Set-Up 9th March 2011, RF Structure Meeting11

ESD Experimental Set-Up 9th March 2011, RF Structure Meeting12 A A V V +15 V 2-3 A 35 KV

Measurement Scheme 9th March 2011, RF Structure Meeting13  ~ 20 s of desorption pulse;  precise check of the background pressure;  train of measurement continuous check of the pressure through the dual gauge read by Labview [thanks Rocio!!];  steady state condition useful experimental data.

Experimental 10 KeV: Cu spare samples 9th March 2011, RF Structure Meeting14

Experimental 10 KeV: 19_PCV082C 9th March 2011, RF Structure Meeting15 Experimental Error Analysis

Energy Correlation: Stopping Powers 9th March 2011, RF Structure Meeting16

Energy Correlation: Experimental Data 9th March 2011, RF Structure Meeting17  Increase up to 2.5 KeV, then a small decrease;  From 5 to 15 KeV, no dependence!  Something to be studied in the future!

Conclusions 9th March 2011, RF Structure Meeting18  A new experimental set – up has been built in order to provide ESD experimental data for unbaked copper at higher electron energy, as required;  The experimental set – up has been improved and it’s correctly working;  Further investigations about SLAC procedure are needed;  Further investigations on the energy correlation are required as well.

9th March 2011, RF Structure Meeting19 Many thanks to: Sergio, Mauro, Walter, Rocio, Helga, Jan, Markus, Ivo, Donat, Pawel, Luigi, Paul, Wil, Holger!!!