LASE Surfaces for electron cloud mitigation Taaj Sian

LASE Surfaces for electron cloud mitigation Taaj Sian Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 1

Why are high SEY materials a problem • High SEY materials are a problem in positively charged accelerators • When a charged particle is accelerated it emits Photons • These photons release electrons in the wall via the photoelectric effect and also ionise residual gas in the chamber Taaj Sian Illustration of electron cloud build up by F. Ruggiero • The next bunch of protons accelerate the electrons into the opposite wall creating more electrons • Causes the build up of an electron cloud Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 2

SEY measurement facility • Taaj Sian Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 3

PIXIE Taaj Sian Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 4

SEY of untreated copper • As received OFHC copper • SEY peak at 1. 9 at 275 e. V Cu Bulk 2 1, 9 1, 8 1, 7 SEY 1, 6 1, 5 1, 4 1, 3 1, 2 1, 1 1 0 Taaj Sian 100 200 300 400 500 Energy (e. V) 600 700 Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 800 900 1000 5

Laser Treated Copper • Surfaces have a micro and nanostructure • Optically black • Various laser parameters can be varied to change the topology • Images (left) are of different scan speeds, 180 mm/s. WP 4 shown meeting, CERN, 9 -10 October Taajand Sian 30 Euro. Cir. Col 2017 6

λ=1064 nm P=5 W τ=70 ns F=100 k. Hz H=5 and 10 μm v=100 and 200 mm/s Varying speed and pitch Produced with Micronanics Optimising speed and pitch 1, 2 1 SEY 0, 8 200 mm/s 10 μm 100 mm/s 10 μm 200 mm/s 5 μm 0, 6 0, 4 400μm 0, 2 0 0 5μm 100 mm/s 5 µm Taaj Sian 5μm 100 mm/s 10 µm 200 400 600 Energy (e. V) 800 1000 Ø Same SEY observed for faster scan speed when matched with a smaller pitch Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 7

SEM of samples at Manchester λ=355 nm P=6. 5 W τ=2 ps F=404 k. Hz H=100, 50 and 25μm v=200, 100, 50 and 25 mm/s Still optimising the parameters of this laser Note the 200 mm/s 200μm sample has a 200 mm/s (top left), 100 mm/s (top right), 50 mm/s spacing of about (bottom left) 25 mm/s (bottom right) 200 μm due to Euro. Cir. Col Taaj Sian problems with the WP 4 meeting, CERN, 9 -10 October 2017 8

SEY of samples at Manchester samples with 100 μm spacing 1, 8 1, 6 1, 4 1, 2 SEY λ=355 nm P=6. 5 W τ=2 ps F=404 k. Hz H=100 μm v=200, 100, 50 and 25 mm/s 1 0, 8 200 mm/s 0, 6 100 mm/s 50 mm/s 0, 4 25 mm/s 0, 2 0 0 200 400 600 800 1000 Energy (e. V) Taaj Sian Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 9

Potential problems of laser treatment • The LASE treatment increases surface resistance • ESD will be studied futher at ASTe. C • PSD will be studied within this collaboration • Dust particulates depending on the chosen micro and nano-structure of the Cu • Outgassing (Presented by Oleg at CERN, preliminary data shows no problems) • All new surfaces should be fully tested before application Taaj Sian Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 10

Cryogenic Design Bellows Bottom flange of Sample at 4 -80 K test chamber at 60 -80 K Test chamber 1 st stage Conductor from 2 nd stage to heat shield 2 nd stage Insulation vacuum Taaj Sian Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 11

Summary • Laser treated samples can achieve SEY<1 with different wavelengths and pulse length lasers but laser parameters need to be adjusted • All parts of the cryogenic system should arrive by end of Febuary so commissioning of the new system can begin Taaj Sian Euro. Cir. Col WP 4 meeting, CERN, 9 -10 October 2017 12

Future Work • Finish ordering the parts for the Cryogenic facility • Measure SEY as a function of temperature and cryosorbed gas on SEY • Measure relation of SEY on other laser parameters and create samples that have less dust on the surface while maintaining low SEY • Write my Ph. D thesis 13

Merry Christmas! Questions? 14