measurement of heavy ion- induced...

GSI Helmholtzzentrum für Schwerionenforschung GmbH

Measurement of Heavy Ion -


Measurement of Heavy Ion -induced Desorption

Markus BENDER (GSI)Sébastien STEYDLI (INSP)

Outline

� Motivation: dynamic vacuum in accelerators

� Investigations on heavy ion-induced desorption

� Theoretic


� Theoretic

� Set up installed at GSI with the results obtained

� Conclusion and outlook

Sébastien STEYDLI Journées RT Vide : « Vide en milieux ionisants »

1973: Intersecting Storage Rings (ISR) @ CERN

First observation of a vacuum instability:- Pressure increase during injection of

protons- Cured by increased pumping, special

cleaning, improved bake out, noblemetal coating


O. Gröbner and R.S. Calder (1973)


1997: Low Energy Antiproton Ring (LEAR)

Pressure increase at continuous injection of Pb ions


Direct limit for beam intensity and lifetime.LEAR achieved: 3 x 10 8 ions, τ ≈ 6.5 sLHC requests: 9 x 10 8 ions, τ = 30 s

J. Bosser et al., Part. Accel. 63, 171 (1999)Courtesy Edgar Mahner

Sébastien STEYDLI

"The LEAR static vacuum was of the orderof 5 x 10-12 Torr, but local pressure bumpsup to 10-9 Torr occurred with continuousinjection of about 108 ions/s."

Journées RT Vide : « Vide en milieux ionisants »

2001: Heavy Ion Synchrotron SIS18 @ GSI

1.00E-09S01

- Pressure rise during high-intensity U28+ run at SIS18 (GSI)

- Triggered by ion injection loss onto vacuum chamber walls and aperture-limiting devices.

A. Krämer et al., Proc. EPAC 2002, 2547


1.00E-12

1.00E-11

1.00E-10

39300 39600 39900 40200 40500 40800 41100

time [seconds]

pres

sure

[m

bar]

S01

S12

S11

S02

Uranium U 28+ losses in S01MU1 @ 8.7 MeV/u

48 µA (5x107 ions) over 200 µs each 6.8 s

48 µA (5x107 ions) over 200 µs each 1.8 s

Sébastien STEYDLI

Pressure increase depends on ion intensity (duty cycle)


Consequences

� Also other facilities observed beam-induced pressure instabilities:� (1998): AGS-Booster S.Y. Zhang et al., EPAC 1998, 2149

� (2002): RHIC � e- - cloud W. Fischer et al., EPAC 2002, 1485


� Upcoming accelerators require higher beam intensity:� FAIR: some 1011 U28+ / s� Spiral2: 5 x 1014 intermediate heavy / s� HIAF: 5 x 1011 U and 4 x 1013 p / s


Consequences


Existing facility (blue) serves as injector for the

new FAIR complex (red).GSI/FAIR accelerator facility

Primary beam intensity x 102 – 103

Secondary beam intensity: x 104

Heavy-ion beam energy: x 30

P. Spiller, CARE-HHH Workshop 2008

For FAIR: reach a SIS18 intensity of 1012 U28+/s @ 4Hz

R&D program in collaboration with CERN on

heavy-ion desorption experiments since ≈ 2003.


Stripper

(Q+1)+ Q+ (Q-1)+

F Déchery, A DrouartHigh Energy Ions

with charge Q+

Production of different charge states

Fingers to get rid of non-desired charge states Collider &

detection systems

FISIC in the S3 experimental room @ Spiral2


Low Energy

Ions with

charge q+

Beam Dump FISIC

(5kW max)

High Energy ions

Q+, (Q±1)+

Detection

detection systems


Accelerator Vacuum


V

Tknp

⋅⋅=ionincident

moleculesreleased=η


What is heavy ion-induced desorption?

� „Heavy ion-induced desorption is the release of gas molecules from surfaces by impacting ions“

� Desorption yield η :=released gas molecules

incident ion


Desorption Sputtering

Release of volatile (gas) molecules Release or target atoms

η can be several 1,000 Y < 10, at least for metals

No preferred direction (2 π) cosn - distribution


Investigations on heavy ion-induced desorption

� Measurement of desorption yields

� Correlation to materials properties


� Correlation to materials properties

� Where is the desorbed gas coming from?

� How can desorption yields be reduced


Desorption yield measurements

ion gauge RGA

conductance

collimator

fromaccelerator

IP

10-7 mbar10-8 mbar

currenttransformer

ion gauge


sample holdersector valve

TMP TSP10-10 mbar

TMP

Experiments by: M. Bender, A. Krämer, H. Kollmus (GSI), E. Mahner (CERN)

TkN

Vp

BI ⋅⋅⋅∆=ηdesorption yield out of

pressure increase:

(short single pulse, no pumping)

time dependent:(continuous bombardment) TkN

Sp

TkN

Vp

BI

eff

BI ⋅⋅⋅∆

=⋅⋅

⋅∆=&&

&

η



ECR source

Low energy line(2.5 keV/u)

J. Hansen et al., CERN Report No.

LHC/VAC-TN-2001-07 (2001).

Mahner. et al., EPAC 2002, 2568;

PRST-AB 6, 013201 (2003);

PRST-AB 8, 053201 (2005).Sublimation pump


U

TV camera

BAG

RGA

BPM

SIP

TSP

TMP group

Gasinjectionvalve

Sector valveCollimator

Beam direction

Test chamber

RFQIH Linac

Medium energy line(250 keV/u)

Filter line

4.2 MeV/u

Stripper

Particles: 1.5 × 109 Pb53+ or 1010 Pb27+ @ 4.2 MeVu

Repetition time: 1.2 s

Impact angles studied: θ = 89.2°, 84.8°, 0° (perpend.)

BPM

Test chamber

Pumping group

Courtesy Edgar Mahner


Desorption yield measurements (in ring)

Projectiles: Au79+ (9 GeV/u), Cu29+ (10 GeV/u), p+ (23 GeV)

Avg. bunch intensities (Au; Cu; p): 7 × 108; 5 × 109; 2 × 1011RHIC @ BNL:


W. Fischer, BNL W. Fischer et al., in Proc. ECLOUD’07 (2007)

Sébastien STEYDLI

Avg. bunch intensities (Au; Cu; p): 7 × 108; 5 × 109; 2 × 1011

Static pressures (Au; Cu; p): 5 × 10-11; 2 × 10-11; 1 × 10-9

Impact angles studied: perpendicular

Target type/material: vacuum valves/stainless steel



SPS T8-H4October 2003


Accelerator: SPS North Area (T4-H8)

Ions: In49+ @ 158 GeV/u

Intensities: 1.5 × 106 ions/spill; spill length: 6.2 s

Impact angles studied: θ = 35 mrad

Targets: graphite, Cu/graphite, TiZrV/graphite, stainless steel (316 LN)

E. Mahner et al., PRST-AB 7, 103202 (2004)

Limit pressure after bake out: 6 × 10-12 Torr

Rotatable setup with 4 different samples, each

mounted on a motorized manipulator.

Aligned Cu/graphite

collimator in its parking

position 18.5 mm below

the beam axis.

Experiment by:

E.Mahner, J. Hansen, E. Page,

I. Efthymiopoulos, H. Vincke

Sébastien STEYDLI

Courtesy E. Mahner


Measurement: pressure

beam scrubbing

Continuous bombardment

1Hz, 9⋅1010 ions/pulse

1.4 MeV/u C2+ ⇒Al, perpendicular incidenceto

tal p

ress

ure

incr

ease

[mba

r]


Single shot

9⋅1010 ions/pulse

time [min]

tota

l pre

ssur

e in

crea

se [m

bar]

Sébastien STEYDLI

η = ∆p⋅VNI ⋅kB ⋅T


Some example numbers

Perpendicular Incident Grazing Incident

GSI Helmholtzzentrum für Schwerionenforschung GmbH Sébastien STEYDLI

Adapted from E. Mahner, PRST-AB 11, 104801 (2008)


Results depend on surface treatment or coating:CERN LINAC3 experiment with 4.2 MeV/u Pb ions

12

14

16

18

20

22

Vac

uum

cha

mbe

r

316 LN (50 µm electropolished)316 LN (LEAR type, not polished)

316 LN (He-O2 glow discharged)Al CuMo (127 µm foil)

316 LN (Ar-O2 glow discharged)Si (0.4 µm evaporated)

316 LN (Ar-O2 glow discharged)

316 LN (150 µm electropolished)E#2

E#1

A

G

O

N

H

D

F#2

B

η = 200 2,000 20,000


0

2

4

6

8

10

12

1E-10 1E-9 1E-8 1E-7

Vac

uum

cha

mbe

r

∆P [Torr]

TiZrV (1.5 µm sputtered)

TiZrV (1.5 µm sputtered)Pd (0.6 µm sputtered)St707 (getter strips)

304 LAu (30 µm galv. coating)Ag (2 µm galv. coating)

316 LN (150 µm electropolished)

316 LN (50 µm electropolished)316 LN (50 µm chem. polished)#316 LN (50 µm chem. polished, getter purif.)

#316 LN (vented after scrubbing)

C#2

K

L

C#1

M

E#3

I#3

J

I#2

I#1

F#1

E#2

E. Mahner, PRST-AB 11, 104801 (2008)

Sébastien STEYDLI

TV camera

BAG

RGA

BPM TMP group

Gasinjectionvalve

Test chamber


Grazing incident


Scattering:- At grazing incidence ions can get

scattered in forward direction.- E.g., 11.4 MeV/u U � stainless steel (1°)

- 15% scattering as calculated with TRIM (J. F. Ziegler, J. P. Biersack, U. Littmark „the stopping and range of ions in solis“, Pergamon Press, New York (1996))

- Increasing with smaller angle

� Undefined multiple desorption


Example results of high melting metals

GSI, Projectile: 1.4MeV/u Zn4+, 5e10 / s, perpendicular incidence

E. Mahner, H. Kollmus, M. Bender, A. Krämer, unpublished

GSI Helmholtzzentrum für Schwerionenforschung GmbH Journées RT Vide : « Vide en milieux ionisants »

Materials analysis

Sample CharacterizationImpossible d'afficher l'image. Votre ordinateur manque peut-être de mémoire pour ouvrir l'image ou l'image est endommagée. Redémarrez l'ordinateur, puis ouvrez à nouveau le fichier. Si le x

rouge est toujours affiché, vous devrez peut-être supprimer l'image avant de la réinsérer.

RGA

Impossible d'afficher l'image. Votre ordinateur manque peut-être de mémoire pour ouvrir l'image ou l'image est endommagée. Redémarrez l'ordinateur, puis ouvrez à nouveau le fichier. Si le x rouge est toujours affiché, vous devrez peut-être supprimer l'image avant de la réinsérer.

Feed Through


element-specific depth profiling up to ~ 1µm resolution few nm� How are the target properties correlated to the desorption?(surface property, bulk purity, oxidation...)

Desorption Yield Measurement

ionincident

moleculesdesorbed=η


Detector


Xe SputterSource

Impossible d'afficher l'image. Votre ordinateur manque peut-être de mémoire pour ouvrir l'image ou l'image est endommagée. Redémarrez l'ordinateur, puis ouvrez à nouveau le fichier. Si le x rouge est toujours affiché, vous devrez

peut-être supprimer l'image avant de la réinsérer.

Beam �Impossible d'afficher l'image. Votre ordinateur manque peut-être de mémoire pour ouvrir l'image ou l'image est endommagée. Redémarrez l'ordinateur, puis ouvrez à nouveau le fichier. Si le x rouge est toujours affiché, vous devrez peut-être supprimer l'image avant de la réinsérer.

Faraday Cup


∆E - Erest Spectrum

Mo / Xe (proj.)

NiFeCr


SPSiAl

ONC


Element Energy Profile

GSI Helmholtzzentrum für Schwerionenforschung GmbH Sébastien STEYDLI Journées RT Vide : « Vide en milieux ionisants »

Depth Profile

O

KONZERD-codeA. Bergmaier, G. Dollinger and C. M. Frey, "Quantitative Elastic Recoil Detection", Nucl. Instr. Meth. B 99, 488 (1995)

GSI Helmholtzzentrum für Schwerionenforschung GmbH Sébastien STEYDLI Journées RT Vide : « Vide en milieux ionisants »

Materials analysis

O

0 nm 180 nm1.4 MeV/u Xe � stainless steel


A. Bergmaier et al., Nucl. Instr. Meth. B 99, 488 (1995)


Finding: desorbed gas is not sputtered oxide layer

fluence [particles/cm2]

oxi

de laye

r


deso

rption

6.5E14 mol/cm2 ~ 1ML

H. Kollmus, M. Bender, W. Assmann, et al., Vacuum 82 (2008)


Finding: material dependenceco

nce

ntr

ation [

%] copper oxide metallic copper

+ acid treatment


Cu2O � insulator: poor el. & th. conductivityη~1530 (Proj: 1.4MeV/u Xe)

mainly CO, H2, CO2 for both samples

Cu � conductor: free electrons moderate energy loadη~350 (Proj: 1.4MeV/u Xe) mainly H2

conce

ntr

ation [

%]

depth [nm] depth [nm]

M. Bender, H. Kollmus, W. Assmann, NIM B 256 (2007)Sébastien STEYDLI Journées RT Vide : « Vide en milieux ionisants »

Gold coating: preserve conductive metallic surface

Gold coating; thickness of the gold-layer: 197nm (RBS: 1.4MeV/u C)

� Diffusion blocking layer needed

as insalled 2h @ 250°C


� Diffusion blocking layer needed

Still under investigation: Cr, Ni, Ag

M. Bender, H. Kollmus, W. Assmann, et al., GSI Scientific Report 2006

Sébastien STEYDLI

100 h @ 300°C12h @ 300°C


Conditioning: how to reduce the desorption yield?

η 0

η∞

= 0.75 η0

η0 ≅ 50,000 Au-coated Cu, irradiated with 4.8 MeV/u Ca


η(t)

/ η

η∞

= 0.29 η0

η∞

= 0.26 η0

η∞

= 0.16 η0

η∞

= 0.04 η0


Summary of the Experimental Results

� Desorbed gas is not the sputtered impurities of the material

� Desorbed gas is always CO, CO2 and H2

� Also the contents of the residual gas

� Link to the substrate� Insulators (Cu2O) desorb more than conductors

� Higher temperature bakeout of loss regions reduces


� Higher temperature bakeout of loss regions reduces desorption� At 350°C highest CO desorption (not shown)

� Thermal moderated surface process with link to the substrate� Desorption is the release of weakly bound surface adsorbats

� Transient overheated spot drives the release

� (dE/dx)2-scaling


Mitigation: how to handle the dynamic vacuum ?

� Reduce base pressure & pumping: apply NEG coating� At GSI, 2/3 of SIS18 are NEG-coated since 2011

� Dipole chambers, quadrupole chambers, injection septum

� Beam cleaning: reduce outgassing by beam scrubbing� Not feasible in an accelerator (month of conditioning beam time)


� Not feasible in an accelerator (month of conditioning beam time)� Problem of activated gas

� Conditioning of critical components� Patent pending, can’t talk about here!

� Dump lost beam ions in a controlled manner� The concept of beam loss-collimators


Beam loss collimators

collector

ion beam

charge exchanged Ionse.g.: U28+� U29+

dipole


- Dump charge-exchanged ions (e.g., for low charge state q+1 � position defined)

- Dump perpendicular

- Increase pumping in collimator region

- Use low-desorbing materials


Beam loss collimators


- Installed in SIS18 and LEIR: both meet intensity requirements now- Planned for SIS100. More complex (cryogenic)


Outlook: cryogenic surfaces

� cold copper tube with thermal screening� cryogenic temperatures constant

� η = 6*104 @ 300K� at 77K and at 15K significantly lower� Monte Carlo simulations needed � Experiments with adsorbed gas planned


E. Mahner, M. Bender, H. Kollmus, AIP CP773 (2005)Sébastien STEYDLI Journées RT Vide : « Vide en milieux ionisants »

Outlook: cryogenic surfaces

- Desorption yield increases with increasing number of CO layers

- Saturation at 100 monolayers- Reproduction of adsorption

isotherme?- Measurement pending

- However, the increase of more


- However, the increase of more than one order of magnitude within the first 25 monolayers is of importance for cryogenic accelerator structures: keep surface coverage low!

Sébastien STEYDLI

E. Mahner et al.,Phys. Rev ST Accel. Beams 14 (2011) 050102


Outlook: new UHV setup for comparingdesorption of various stimuli

Vaccum diagnostic

Flange or window

Cooled apperture

Sample �

Cooling /Heating

Electron-gun

keV-sputter-gun

CRYRING


Turbo pump

UHV-PumpIZ, TSP

Bypass-valve


Conclusion

� Ion-induced desorption still hot topic in research and for development of high intensity accelerators

� Concepts to reduce desorption prior to application under development

� Desorption from cryo surfaces under investigation.


� Desorption from cryo surfaces under investigation. � Different behavior from room temperature desorption observed � Interesting finding: dependence of charge state, attests energy-loss

scaling� Upcoming experiment: desorption of frozen CO rather sputtering of

larger ice-clusters? (beam time granted in 2018)

� Upcoming experiment: energy-loss scaling� Complete parameter variation in one single experiment �

CRYRING at GSI (beam time granted in 2018)


Thanks for your kind attention

This talk was given on behalf of the collaborators and co-workers:

- E. Mahner (CERN)

- H. Kollmus, A. Krämer, C. Bellachioma (GSI vacuum group)

- C. Trautmann, D. Severin, M. Bender, V. Velthaus, A. Warth, B. Tietz (GSI materials research)


- F. Völklein (Hochschule RheinMain, university of applied sciences)

- W. Assmann (LMU Munich)

- M. Toulemonde, C. Stodel, R. Levallois (GANIL, France)

- S. Steydli, E. Lamour, A. Lévy, C. Prigent, M. Trassinelli, D. Vernhet (INSP, France)

- M. Authier, O. Cloue, A. Drouard (IRFU/CEA, France)

- A. Wucher, L. Breuer (Uni Duisburg Essen, Germany)


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