dépôt neg, élaboration, caractérisation et...

Dépôt NEG, élaboration,

caractérisation et application.

Pedro Costa Pinto

Technology Department

Vacuum Surfaces and Coatings group

Vacuum, Surfaces & Coatings Group


1 Introduction

2 Élaboration

3 Caractérisation

4 Application

5 Sommaire

OUTLOOK

2 Rencontres Nationales du Réseau des Technologies du Vide 2016


Technology Department 3 Rencontres Nationales du Réseau des Technologies du Vide 2016

1 Introduction

Getters are materials capable of chemically adsorbing gas molecules (by

chemisorption).

Getter

Limited to 1 monolayer(~5x1014 molecules/cm2)

Getter

Very large capacity!

Reactive gases are pumped:

CO, O2, H2O, N2, H2, CO2

noble gases and methane are not pumped.

Chemisorption

(surface pumping) Diffusion

(bulk pumping)

At room temperature only H2 diffuses

Other reactive gases require higher

temperature

To do so, their surface must be clean.



1 Introduction

The pumping speed of a getter, Sgetter:

𝑆𝑔𝑒𝑡𝑡𝑒𝑟 = 𝐴 ∙𝑘∙𝑇

2∙𝜋∙𝑚 ∙ 𝑠

surface A Molecular

impingement rate

sticking probability

sH2 0.005 ~ 0.05

sN2 0.003 ~ 0.03

sCO, O2 H2O 0.4 ~ 0.9



1 Introduction

The pumping speed of a getter, Sgetter: depends on the amount of gas pumped.

James M. Lafferty, Foundations of Vacuum Science and Technology, ISBN: 978-0-471-17593-3.



1 Introduction

Getters can be classified by the way the clean surface is obtained:

In situ deposition of a fresh getter

film (under vacuum) Evaporable Getters

Ti filaments



1 Introduction


Diffusion of the oxide layer into the

bulk (usually by heating in vacuum

to the activation temperature)

Non Evaporable Getters

(NEG)





1 Introduction


Diffusion of the oxide layer into the

bulk (usually by heating in vacuum

to the activation temperature)

Non Evaporable Getters

(NEG)



Before coating after coating


Technology Department 9

NEG coatings have been produced by Magnetron Sputtering of elements and

alloys from the IV and V group of the periodic table.

high oxygen

Solubility and diffusivity

2 Élaboration

Rencontres Nationales du Réseau des Technologies du Vide 2016

More than 20 materials were investigated by combining 2 or 3 of this elements

in the form of thin films.



NEG coatings have been produced by Magnetron Sputtering of elements and

alloys from the IV and V group of the periodic table.

More than 20 materials were investigated by combining 2 or 3 of this elements

in the form of thin films.

In 2002, Ti-Zr-V was retained for large scale production for the LHC.

Activation: 24 hours at 180oC.

ZrV

Ti

30 40 50 60

TiZrV

Substrate

(degrees)

30 40 50 60

TiZrV Nanocrystalline

grain size 3~5 nm

Well crystallised

grain size ≥ 100 nm

good

bad


2 Élaboration



More than 1300 beampipes, with different shapes and lengths, were coated at

CERN for the LHC.

3mm wires

of Ti, Zr

and V

8 m

ete

r so

len

oid


2 Élaboration



At CERN, many other accelerators and experiments use NEG coatings.


2 Élaboration

LEIR - Low Energy Ion Ring Paverage ~ 10-12 mbar





2 Élaboration

Plates for ALICE





2 Élaboration

ELENA - Extra Low Energy Antiproton Ring



Also in collaboration with other institutes: the MAX IV project, Sweeden.


2 Élaboration

VC2a





2 Élaboration



ESRF (France) SAES getters

(Italy)

LNLS (Brazil)

GSI (Germany)


FMB Berlin (Germany)

Several producers worldwide (industry and research institutes)

2 Élaboration



The users community is still growing:


CERN

ESRF ELECTRA

SOLEIL DESY DIAMOND

MaxLab

BNL

LNLS

KEK

NSRRC

AS

ISA

ALBA

SESAME

ILSF

ANL

2 Élaboration



Evaluate NEG activation by X-ray Photoelectron Spectroscopy (XPS)

3 Caractérisation

0

20000

40000

60000

80000

100000

120000

140000

0 50 100 150 200 250 300 350

Activation temperature (ºC) - 1h heating

O 1

s p

eak a

rea (

a.u

.)

old reference on stst

preseries HCVCD__001-

CR000002

protptype series/Cu

prototype series/ stst

Ti

Zr

V

Good activation if reduction of O 1s

peak area > 66%

Monitoring the evolution of the surface oxygen in

function of the temperature. (in steps of 1 hour)

Rencontres Nationales du Réseau des Technologies

du Vide 2016 19



Measure the pumping speed of a thin film: aperture method

c

P1 P2

RGA

Pumping

group

Getter disk

(flange)

Gas injection

(H2, CO, ..)

𝑆𝑔𝑒𝑡𝑡𝑒𝑟 = 𝑆𝑎 =𝑃1 − 𝑃2

𝑃2𝑐

𝑆𝑎

𝑆𝑔𝑒𝑡𝑡𝑒𝑟 = 𝐴𝑘𝑇

2𝜋𝑚 𝑠

𝑠 =𝑃1 − 𝑃2

𝑃2𝑐

1

𝐴

2𝜋𝑚

𝑘𝑇


Pumping speed dome

3 Caractérisation




c

P1 P2

RGA

Pumping

group

Getter disk

(flange)

Gas injection

(H2, CO, ..)

𝑆𝑎

𝑆𝑔𝑒𝑡𝑡𝑒𝑟 = 𝑆𝑎 =𝑃1 − 𝑃2

𝑃2𝑐

𝑆𝑔𝑒𝑡𝑡𝑒𝑟 = 𝐴𝑘𝑇

2𝜋𝑚 𝑠

𝑠 =𝑃1 − 𝑃2

𝑃2𝑐

1

𝐴

2𝜋𝑚

𝑘𝑇


Pumping speed dome

3 Caractérisation




c

P1 P2

RGA

Pumping

group

Gas injection

(H2, CO, ..)

𝑆𝑎

Getter tube

L/R

L

R

𝑆𝑎 =𝑃1 − 𝑃2

𝑃2𝑐

𝑆𝑎 = 𝐴𝑘𝑇

2𝜋𝑚 𝛼

𝛼 → 𝑐𝑎𝑝𝑡𝑢𝑟𝑒 𝑝𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦

Monte Carlo

simulation


Pumping speed dome

1

5

10 20

50 100 200

500

3 Caractérisation





3 Caractérisation

Smooth (coated at 100oC) Rough (coated at 300oC)



Measure the pumping speed of a thin film:

c

P1 P2

RGA

Pumping

group

Gas injection

(H2, CO, ..)

𝑆𝑎

Getter tube

L/R

L

R P3

=𝑃3

𝑃2 Pressure ratio

Monte Carlo

simulation

If pressure ratio too low:

very high P2 is necessary to get signal in P3

Cool down

with Liquid N2

transmission method


Pre

ssu

re r

atio

If using CO => fast saturation at the entrance

If using H2 => dissociation of H2 in hot filament => methane

3 Caractérisation



Pre

ssu

re r

ati

o

25

Measure the pumping speed of a thin film: transmission method

Example: H2 transmission in NEG coated tube with L/R=95

𝐿

𝑅=

1000

10.5

Pend Pin

H2 injection

Pressure ratio sticking

5x10-3 5.5x10-3

9x10-4 1.5x10-2

Cool with

Liquid N2

to pump CH4

LN2

𝒑𝒓𝒆𝒔𝒔𝒖𝒓𝒆 𝒓𝒂𝒕𝒊𝒐 =𝑷𝒆𝒏𝒅

𝑷𝒊𝒏

LN2

Expected value for a first activation


3 Caractérisation



Measure the pumping speed of a thin film: transmission method


3 Caractérisation

101

102

103

0 10 20 30 40 50 60

10-4

10-3

10-2

H2 p

um

pin

g s

peed [

l s

-1 m

-1]

Number of heating/venting cycles

200°C 250°C 300°C 350°C

200°C

250°C

300°C

48 h48 h

250°C

300°C

Heating duration 24 hours

unless otherwise indicated

beam pipe diameter = 80 mm

H2 s

tickin

g p

robability

TiZrV/St. Steel5 m thick



3 Caractérisation

Evaluate NEG Secondary Electron Yield (SEY)

B. Henrist, N. Hilleret, C. Scheuerlein, M. Taborelli,

App. Surf. Sci. 172 (2001) 95.

SEY after saturation with CO




3 Caractérisation

Evaluate NEG Photon Desorption Yield (PSD)

Yasunori Tanimoto

KEK

Marton Ady

CERN

@ KEK Photon Factory, Japan




3 Caractérisation

Evaluate NEG Photon Desorption Yield (PSD)




4 Application The Large Hadron Collider beam vacuum system

8 Arcs (superconducting bending

dipoles) ~ 45 km of cryopumping

The Large Hadron Collider beam vacuum system

~ 27 km particle accelerator




4 Application

8 Long Straight Sections (LSS)

at Room Temperature (~6 km)

~5 km NEG coated

4 experiments, also with NEG

coated beampipes

After NEG activation, average

pressure in LSS ~ 10-11 mbar

The Large Hadron Collider beam vacuum system




4 Application Accidental air venting in IP6:

vacuum chamber of beam 1 vented

during technical stop.

Compare dynamic vacuum

of activated and non

activated NEG




4 Application Accidental air venting in IP6:

vacuum chamber of beam 1 vented

during technical stop.

Compare dynamic vacuum

of activated and non

activated NEG

Before accidental venting After accidental venting




5 Sommaire

Ti-Zr-V NEG coatings can be produced by sputtering at “industrial-like” scale.

Grain size appears to play a crucial role in the activation process.

The wide range of geometries of the beam pipes to be coated requires constant

development of sputtering sources.

These coatings are used worldwide in particle accelerators and are produced

by several institutes and companies.

XPS can be used to assess the activation of NEG coatings by evaluating the

decrease of the oxygen peak.

Vacuum performance can be evaluated by measuring the pumping speed by

the aperture method or by the sticking coefficient by the transmission method.

In addition to pumping, NEG coatings provide low SEY and PSD.

More than 8 years of use in particle accelerators, NEG coatings proven to be a

reliable technology.


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