Electron Stimulated Desorption of OFE Copper - PowerPoint Presentation

Slide1

Electron Stimulated Desorption of OFE Copper

Chiara Pasquino, Politecnico di Milano

9th March 2011, RF Structure MeetingSlide2

Dynamic Vacuum: an issue for CLIC accelerating structures

9th March 2011, RF Structure Meeting

Static Vacuum: 10

-9 mbar [G.Rumolo, C.Garion

]Dynamic Vacuum: CO2

, H2 < 10

-9

mbar

2

Technical Note, EDMS 1095288

http://ilcagenda.linearcollider.orgSlide3

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

Slide4

Dynamic Vacuum studies : Breakdowns

9th March 2011, RF Structure Meeting

4

2*10

2

H

2

or CO molecules released [

exp. Data DC “spark test” reported in PRST-AB12, 092001 (2009)

];

Uniform pressure along the structure after ~ 3ms;

Background pressure recovered after 20 ms, no dynamic vacuum problems.

[C.Garion]

Slide5

Dynamic Vacuum studies : ESD

9th March 2011, RF Structure Meeting

5

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 2006 - 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!Slide6

Dynamic Vacuum studies: theoretical models

9th March 2011, RF Structure Meeting

6

Gortel Fully Quantum Mechanical Model

MGR Model

e-

Antoniewicz

e-Slide7

Desorption Yield

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Steady State ConditionSlide8

Sample Campaign

9th March 2011, RF Structure Meeting

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3 Cleaning Procedures : w/o etching,

passivation

& SLAC etching

Several Thermal Treatment : Vacuum, Argon, H

2

atmosphere @ 1040 or 820 °CSlide9

H2 Diffusion

Profiles :SLAC bonding9th March 2011, RF Structure Meeting

9

H2

H2

Cu – H is an endothermic system!

equal C

s

at both surfacesSlide10

H2 Diffusion

Profiles: SLAC bonding9th March 2011, RF Structure Meeting

10

THE ANNEALING TIME CAN BE DECREASED !!!Slide11

ESD Experimental Set-Up

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11Slide12

ESD Experimental Set-Up

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12

A

A

V

V

+15 V

2-3 A

35 KVSlide13

Measurement Scheme

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~ 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.Slide14

Experimental Data @ 10 KeV

: Cu spare samples9th March 2011, RF Structure Meeting

14Slide15

Experimental Data @ 10 KeV

: 19_PCV082C9th March 2011, RF Structure Meeting

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Experimental Error Analysis Slide16

Energy Correlation: Stopping Powers

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16Slide17

Energy Correlation: Experimental Data

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Increase up to 2.5

KeV

, then a small decrease; From 5 to 15

KeV

, no dependence!

Something to be studied in the future! Slide18

Conclusions

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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. Slide19

9th March 2011, RF Structure Meeting

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THANKS FOR THE ATTENTION!!!!

Many thanks to: Sergio, Mauro, Walter, Rocio, Helga, Jan, Markus, Ivo, Donat, Pawel, Luigi, Paul,

Wil

, Holger!!!