the variation of the secondary electron emission …cern.ch/conf-ecloud02/talks/hilleret.pdf ·...

NH – 2STREAMS/02 1

THE VARIATION OF THE SECONDARY ELECTRON

EM ISSION WITH SURFACE M ODIF ICATIONS

B. Henrist, N. Hilleret, M. Jimenez, C. Scheuerlein, M. Taborelli, G. Vorlaufer

CERN - LHC/VAC

EST-SM


TOPICS:

S E CONDARY ELECTRON YIE LD BEFO RE AND AFTER ELE CTRO N B OMB ARDMENT

THE ”SIMULAT OR” TOOL K IT

VA RIA TION OF GA S FL UX DUR ING CONDIT IONING

CONDE NSED GA SES

SURFA CE MODIFIC ATIONS DUR ING CONDIT IONING


E

Rz

SECONDARY

REFLECTED

SIM ULATOR TOOL KIT

MODEL FOR S ECONDARY ELECTRON EMIS S ION

ASSUMPTIONS : FOR SECONDARIESPRIMARY ELECTRON: CONSTANT ENERGY LOSS :

∂∂E

z

E

R=

ESCAPE PROBABILITY

P A z= × −( )exp /λ

NORMALISATION TO δm, Em TO ELIMINATE PHYSICAL CONSTANTS ( e.g. λ )

(D.C. Joy Journal of microscopy 147,1,51-64, 1987)

SIMPLIFIED BY M. FURMANδ δs MAX

p

MAX

p

MAX

s

sE

E

sE

E

=×

− +

( )

1


CU AS RECEIVED

0.0

0.5

1.0

1.5

2.0

2.5

0 100 200 300 400 500

ENERGY (eV)

SE

CO

ND

AR

Y E

LE

CT

RO

N Y

IEL

D

EXPERIMENTAL

DATA

FIT FURMAN

REFLECTED

FIT + REFLECTED

SIM ULATOR TOOL KIT

MODEL FOR S ECONDARY ELECTRON EMIS S ION

NUMERICAL VALUE TO FIT OUR EXPERIMENTAL DATA:

SAMPLE STATE AS RECEIVED FULLYCONDITIONED

dM A X 2.03 1.13

EM A X 262 318

s 1.39 1.35

PRECEDING APPROXIMATION TO FIT HIGHENERGY PART

IF LOW ENERGY ELECTRONS HAVE TO BECONSIDERED:

REFLECTED NOT NEGLIGIBLE :


ENERGY DISTRIBUTION OF SECONDARY ELECTRON EMITTED BY COPPER

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

900.00

1000.00

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

NORMALISED ENERGY

NO

RM

AL

ISE

D I

NT

EN

SIT

Y Ep=30 eV

REFLECTED

SECONDARIES

OTHER CONTRIBUTIONS

E

Rz

SECONDARY

REFLECTED

SIM ULATOR TOOL KIT

δ δ δt S R= +

FOR Ep> 300 eVREFLECTED CONTRIBUTION NEGLIGIBLE

S ECONDARY / REFLECTED PROCES S ES COMPLETELY DIFFERENT


SIM ULATOR TOOL KIT

REFLECTED CONTRIBUTION

δ δ δt S R= + => δ δ δ δ δR t t S tf f= × ⇒ = + ×δ δt s f

= ×−( )1

1

FRACTION OF REFLECTED ELECTRONS (f) : NR / NT OT

CAN BE MEASURED FROM PRECEDING CURVES

AND APPROXIMATED BY THE FOLLOWING RELATION:

1(J.J. Scholtz, D. Dijkkamp, R.W.A. Schmitz, Philips J. Res. 50, 375-389, 1996).

USING: A0 = 20.699890, A1= -7.07605, A2= 0.483547, A3= 0, E0=56.914686

ln( ) (ln( )) (ln( )) (ln( ))f A A E E A E E A E Ep p p= + × + + × + + × +0 1 0 2 02

3 03


ENERGY DISTRIBUTION OF SECONDARY ELECTRON EMITTED BY COPPER

0

100

200

300

400

500

600

700

800

900

1000

0.0 0.2 0.4 0.6 0.8 1.0

NORMALISED ENERGY

NO

RM

AL

ISE

D I

NT

EN

SIT

Y

Ep= 10 eVEp=30 eV

Ep= 100 eVEp=300 eVEp=550 eV


RATIO REFLECTED/TOTAL

1%

10%

100%

0 50 100 150 200 250 300

PRIMARY ELECTRON ENERGY

RA

TIO

RE

FL

EC

TE

D/T

OT

AL

REF/TOT

FIT II

FIT II LOW ENERGY

EXP FIT


CU AS RECEIVED

0.0

0.5

1.0

1.5

2.0

2.5

0 200 400 600 800 1000

ENERGY (eV)

SEC

ON

DA

RY

EL

EC

TR

ON

YIE

LD

EXPERIMENTAL DATA (AVERAGE ON 25

SAMPLES)FIT FURMAN

REFLECTED

FIT + REFLECTED

EXP FIT + REFLECTED


CU AS RECEIVED

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 20 40 60 80 100

ENERGY (eV)

SEC

ON

DA

RY

EL

EC

TR

ON

YIE

LD

EXPERIMENTAL DATA (AVERAGE

ON 25 SAMPLES)FIT FURMAN

REFLECTED

FIT + REFLECTED

FIT + REFLECTED (EXP)


RELATIVE CONTRIBUTIONS IN THE SECONDARY ELECTRON ENERGY DISTRIBUTIONS

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

10 30 100 300 550INCIDENT ELECTRON ENERGY (eV)

FR

AC

TIO

NTRUE SECONDARIES < 20 eV

FRACT > 20 eV (reflected included)

REFLECTED

INTERMEDIATE ENERGY


SIM ULATOR TOOL KIT

TRUE S ECONDARY ENERGY DIS TRIBUTION

ENERGY DISTRIBUTION FITTED USING THE EXPRESSION:

D E C

E

Es

s

( ) exp

ln

= × −

0

2

22τ

(J.J. S cho ltz, D. Dijkkamp, R.W.A. S chmitz, Philips J. Res . 50, 375-389, 1996).

PRIMARYENERGY

(eV)

C E0 τ UPPERENERGYBOUND

(eV)10 0.277 1.57 0.985 530 0.136 1.9 0.99 22100 .126 1.58 1.16 22300 .155 2.1 0.85 21550 0.2 1.48 0.909 26


. S IMULATOR TOOL KIT

TRUE S ECONDARY ENERGY DIS TRIBUTION

TRUE SECONDARY PEAK

0

0.05

0.1

0.15

0.00 5.00 10.00 15.00 20.00 25.00 30.00

30 eV EXPERIMENT

FIT II

TRUE SECONDARY PEAK

0.00

0.05

0.10

0.15

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00

100 eV EXPERIMENT

FIT II


CONDITIONING

VARIATION OF THE MAXIMUM SECONDARY ELECTRON YIELD WITH THE ELECTRON DOSE

1.00

1.20

1.40

1.60

1.80

2.00

2.20

2.40

2.60

1.00E-08 1.00E-07 1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02

DOSE (C/mm2)

SEC

ON

DA

RY

EL

EC

TR

ON

YIE

LD

DELTA MAX 23-03

DELTA MAX 31-01

ELECTRON GUN measured at 500 eV

DELTA MAX EPA 99V


CONDITIONING

DES ORPTION AND S ECONDARY ELECTRON EMIS S ION

PRIMARYPARTICLE

ENERGY LOSS

ENERGYTRANSMISSION

DESORPTIONELECTRONEMISSION

INCIDENT PARTICLE

STIMULATION OFDIFFUSION,

CREATION OFDEFECTS


VARIATION OF THE ELECTRON INDUCED DESORPTION WITH THE ELECTRON DOSE (AS RECEIVED COPPER)

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1E+13 1E+14 1E+15 1E+16 1E+17 1E+18 1E+19 1E+20

ELECTRON DOSE ( cm-2 )

DE

SOR

PT

ION

YIE

LD

RA

TIO

H2

CO

CO2

CH4

C2H6


VARIATION OF THE ELECTRON INDUCED DESORPTION WITH THE BEAM DOSE(AS RECEIVED COPPER)

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1E+12 1E+13 1E+14 1E+15 1E+16 1E+17 1E+18 1E+19 1E+20

ELECTRON DOSE (cm-2)

NO

RM

AL

ISE

D

DE

SOR

PT

ION

YIE

LD

0.1

1

NO

RM

AL

ISE

D

SEC

ON

DA

RY

E

LE

CT

RO

N Y

IEL

D

H2

CH4

CO

C2H6

CO2

DELTA MAX 31-01

DELTA MAX 23-03


CONDITIONING


RELATIONS BETWEEN DESORPTION AND CONDITIONING

EASY OBSERVABLE IN ACCELERATOR : GAS FLUX (I.E. PRESSURE)

RELATION BETWEEN CONDITIONING AND GAS FLUX??

VARIATION OF THE SECONDARY ELECTRON YIELD WITH THE DESORPTION YIELD

1.00

1.20

1.40

1.60

1.80

2.00

2.20

2.40

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

DESORPTION YIELD (MOL. PER EL.)

SEC

ON

DA

RY

EL

EC

TR

ON

YIE

LD

δδδδ = 10.4 x ηηηη + 1.09

δδδδ = 0.822 x ηηηη + 1.836

DOSE: ~ 1016 e- / cm2


CONDITIONING


RELATIONS BETWEEN SecElectronEmission, FLUX AND CONDITIONING

Q gas flux: Q I I k Q k= × ≈ × ⇒ ≈ × ×η δ η δ,

DOSE VARIATION VERSUS TIME:

D I t I k D D k D t= × ≈ × ( ) ⇒ = × ( ) ×δ δ

OVERSIMPLIFIED TO START,

POSSIBLE INFLUENCE OF PRESSURE ON e CLOUD CURRENT

=>FASTER PROCESSING AS DESORPTION DECREASES ALSO WITH THE DOSE


CONDITIONING


VARIATION OF THE DESORPTION AND ELECTRON EMISSION WITH THE ELECTRON DOSE

DELTA = 64.234 DOSE -0.0961

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+15 1.00E+16 1.00E+17 1.00E+18 1.00E+19

ELECTRON DOSE ( e - / cm 2 )

DE

SOR

PT

ION

YIE

LD

(

mol

/ e

- )

0.00

0.50

1.00

1.50

2.00

2.50

SEC

ON

DA

RY

EL

EC

TR

ON

Y

IEL

D

ETA = 15.84 DOSE - 0.5167


CONDITIONING


ACCUMULATED DOSE

1.E+15

1.E+16

1.E+17

1.E+18

1.E+19

0 2000 4000 6000 8000 10000 12000

TIME (arb. units)

AC

CU

MU

LA

TE

D D

OSE

(e

-/cm

2)

1.00

1.20

1.40

1.60

1.80

2.00

2.20

2.40

seco

ndar

y el

ectr

on y

ield

DELTA

CONSTANT

DELTA

VARIABLE CURRENT

DOSE

CONSTANT CURRENT DOSE VARIABLE

CURRENT


CONDITIONING


VARIATION OF SURFACES PROPERTIES WITH CONDITIONNING

1.E-02

1.E-01

1.E+00

1 10 100 1000 10000

TIME ( arb. units)

RA

TIO

TO

IN

ITIA

L V

AL

UE

1.00E-01

1.00E+00

NORMALISED

SEY

NORMALISED

DESORPTION

NORMALISED

DESORBED FLUX


VARIATION OF SURFACES PROPERTRIES WITH CONDITIONNING

ETA = FLUX0.8299

1.E-02

1.E-01

1.E+00

1.E-03 1.E-02 1.E-01 1.E+00

GAS FLUX REDUCTION

SPS 2000

SPS 2001

DELTA = FLUX0.1701

TARGET LHC

CONDITINNING


GAS FLUX PRESSURE IN ACCLERATORS

VARIATION OF FLUX ALLOW TO DEDUCE VARIATION OF ETA AND DELTA

ALLOW TO EXTRAPOLATE FROMSPS TOWARDS LHC

RELATION BETWEEN EL. CLOUD INTENSITY AND DELTA/ETA TO BE REFINED


Maximum SEY from

ondensed Gases on Copper

0

5

10

15

20

25

30

35

0 50 100 150 200 250 30

Gas Coverage ( 1E19 molecules / m2)

Maximum SEY

Ar/Cu(4K)

O2/Cu(77K)

2/Cu(3K)

CO ND ENS ED GA SE S

NO INFLUENCE FOR PRACTICALCOVERAGES

FOR NOBLE GASES

INSULATING

LARGE INCREASE


SURFACE M ODIFICATIONS DURING CONDITIONING

SHIFT IN THE POSITION OF C-KLL PEAK =>

MODIFICATION OF THE CARBON CHEMICAL BOND NO SHIFT FOR OXYGEN

200 220 240 260 280 300

kinetic energy (eV)

N(E

)

2 E-6 C/mm2

2 E-2 C/mm2



0

500

1000

1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

Electron dose (C/mm2)

Aug

er p

eak

area

(a.

u.)

C-KLL

Cu-L3M45M45

O-KLL

1E15 1E16 1E17 1E18 1E19

e-/cm2



INITIAL DECREASE OF OXYGEN AND CARBON ON THE SURFACE (101 7 e-/cm2)

SMALLER DECREASE FOR OXYGEN:

DESORPTION COMPENSATED BY MORE SIGNAL FROM OXIDE

MAXIMUM COPPER PEAK FOR A DOSE ~ 101 7 e-/cm2

DESORPTION MEASUREMENTS =>6x101 5 mol/cm2 RELEASED FOR THIS DOSE

FOR HIGHER DOSES CARBON PEAK INCREASES

EXPERIMENTS AT VARIABLE PARTIAL PRESSURES OF CO, CH4

=> NO INFLUENCE ON THE DOSE DEPENDENCE

ORIGIN OF THE CARBON??? STILL A QUESTION

CONDITIONING:=> INITIAL CLEANING FOLLOWED BY CARBON LAYER BUILD UP


CONCLUSIONS

IMPORTANCE OF THE CORRECTION FOR REFLECTED ELECTRONS WHEN VERY LOW

INCIDENT ENERGY IMPORTANT IN SIMULATIONS

FORMULAE GIVEN FOR : YIELD AND ENERGY DISTRIBUTION

USUAL CONDENSED GASES HAVE LITTLE EFFECT ON THE SECONDARY ELECTRON

YIELD EXCEPTION : NOBLE GASES AT THICK COVERAGES

DESORPTION AND CONDITIONING PARALLEL PHENOMENA:

GAS FLUX VARIATION IS A GOOD INDICATOR OF THE CONDITIONING PROCESS

SUBTLE CHANGES IN THE SURFACE COMPOSITION PARALLEL (AT THE ORIGIN OF}

CONDITIONING

FORMULA AVAILABLE FOR SIMULATIONS :


RECONDITIONING AFTER AIR EXPOSURE IS

the variation of the secondary electron emission …cern.ch/conf-ecloud02/talks/hilleret.pdf ·...

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