1. Low SEY Engineered Surface for Electron Cloud Mitigation
Sihui Wang
PhD student of Loughborough University
University Supervisor: Mike D. Cropper
ASTeC supervisor: Oleg B. Malyshev
Reza Valizadeh

2. Outline Background Objective My PhD contents
Examples of SEY Measurements on laser treated samples
Summary 2

3. Background
Electron cloud caused by beam-induced multipacting is a critical problem for high intensity particle accelerators.
First electrons originate from ionised residual gas molecules, photoelectron emission and secondary electron emission from the vacuum chamber walls
Negative impact of E-cloud: causes beam instability, beam losses, emittance growth and heat loads on cryogenic vacuum chamber, reduces a beam lifetime
Electron multipacting is also a problem in RF wave guides and space related high power RF hardware.
Reducing PEY and SEY in other instruments and devices is an important task! 3

4. My PhD project objective
Reduce the Secondary Electron Yield:
By Changing surface Chemistry (deposition of lower SEY material)
By Engineering the surface roughness
Mixture of the above
By active means:
Weak solenoid field along the vacuum chamber
Biased electrodes
Charged particle beam parameters
Bunch charge and sizes
Distance between bunches
By passive means:
Low SEY material
Low SEY coating
Grooved surface
Special shape of vacuum chamber
An antechamber allows reducing PEY 4

5. My PhD contents
Bulk samples (Cu, Al alloys, Stainless steel, Ti, Zr, V and Hf)
Coatings (Ti, Zr, V, Hf, Ti-Zr-V and Ti-Zr-V-Hf) on different substrates (Stainless steel, Si and Blacken samples)
New technology
Laser treated blackening samples (Cu, Al alloys and Stainless steel)
Studying SEY from
In my presentations, I will focus only on our recent discovery.

6. SEY Measurements Analysis chamber with XPS,
Flood e-gun,
Sample heater,
Ar ion beam.
IP is the primary beam current.
IF is the secondary electron current including elastic and inelastic processes, measured on the Faraday cup
IS is the currents on the sample 6

7. Laser treatments Nd:YVO4 Laser
Pulse length =12 ns at Repetition Rate = 30 kHz
For Aluminium
Max Average Power = 20 W at  =1064 nm
For Copper
Max Average Power = 10 W at  = 532 nm
Argon or air atmosphere
Beam Raster scanned in both horizontal and vertical direction
With an average laser energy fluence of just above the ablation threshold of the metal.
(a) Untreated Cu (b) laser treated Cu
Aluminium
Stainless Steel

8. SEY of Cu as a function of incident electron energy
Untreated
Laser treated 8

9. SEY of SS and Al as a function of incident electron energy9

10. δmax as a function of electron dose for Al, 306L SS and Cu
Sample
Initial
After conditioning to Qmax
δmax
Emax (eV)
Qmax (Cmm-2)
Black Cu
1.12
600
0.78
3.510-3
Black SS
900
0.76
1.710-2
Black Al
1.45
2.010-2 Cu
1.90
300
1.25
200
1.010-2 SS
2.25
1.22 Al
2.55
1.34
1.510-2 10

11. XPS analysis of 60 µm Cu in Ar
900
800
700
600
500
400
300
200
100
Binding Energy (eV)
x 10 3 2 4 6 8 10 12 14
CPS
Cu2p1/2
Cu2p3/2
Cu LMM
O1s
Cu3p
Cu3s
C1s
As-received
After electron conditioning
CuO reduced Cu increased

12. Laser surface treatments with different microstructure distances
(a) 50 µm (b) 60 µm (c) 80 µm 12

13. Latest result with laser treated Copper in air: 0.58    0.8013

14. XPS analysis of 50 µm Cu in Air
900
800
700
600
500
400
300
200
100
Binding Energy (eV) 5 10 15 20 25 30 35 40
CPS
Cu2p3/2
Cu2p1/2
O1s
Cu3s
Cu3p
Cu LMM
As-received 50 µm Cu
103
After heating
at 250C for 2 h 14

15. Summary
Laser treatment of the metal surface is a very viable solution for reducing the SEY < 1.
(a) low cost (process is carried out in an inert gas environment at atmospheric pressure)
(b) no new material introduced (this is a surface re-shaping process)
(c) the surface is highly reproducible
(d) the surface is robust and is immune to any surface delamination (unlike thin film coating). 15

16. Acknowledgements People who support me with my PhD Reza Valizadeh
Oleg B. Malyshev
Neil Pashley
Elaine A. Seddon
Adrian Hannah
Svetlana. A. Zotlovskaya
W. Allan Guillespy
Amin Abdolvand
Mike D. Cropper

17. Thank for your attention!