RADIATION DAMAGE ISSUES RELATED TO NEG COATING AT … · - X-ray fluorescence of the Zirconium of...

1 April 01-04, 2014, NSRRC, Hsinchu, Taiwan

OLAV IV : Fourth Workshop on the Operation of Large Vacuum Systems

C. Herbeaux

RADIATION DAMAGE ISSUES

RELATED TO NEG COATING

AT SOLEIL

Christian HERBEAUX

on behalf of the « radiation working group »:

N. Béchu, L. Cassinari, N. Hubert, S. Hustache, J-F.

Lamarre, P. Lebasque, F. Marteau, A. Nadji, L. Nadolski



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OUTLINE

Equipment damages – Description

– Location

Dose measurement

– Dose spatial distribution

– Absolute measurement

Radiation source

– Synchrotron radiation distribution

– Fluorescence X

– Photon spectrum measurement

Experimental Setup : FluoX

– Material comparison

– Shielding

Conclusion



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Equipment damages due to radiations

Fast aging of some equipment:

– Cables insulators become rigid and brittle

Sextupoles

(downstream/upstream) BPM cables

Temperature

sensor boxes

Cable/insulator replacement with radiation hardened material



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Equipment damages due to radiations

Fast aging of some equipment:

– Radiation aging of the glue that sticks together baking out films kapton foils

Replacement needs to open magnet yokes, remove the vacuum chambers, unstick

the heaters, glue new heaters, re-install the chambers and bake and activate the

NEG.

Time and resources consuming : requires a reliable replacement solution



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DIPOLE 1 DIPOLE 2

Equipment damages locations

• Equipment located elsewhere are in perfect condition:

– In the straight section

– Before the first bending magnet

– Around the dipole vacuum chamber

Damages location:

– In each of the 16 cells of the storage ring

– In the arcs

– In the vicinity of given so called NEG coated aluminium “quadrupole vacuum chamber”

– Downstream a bending magnet AREA WITH

DAMAGES



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Dose Measurement : Spatial Distribution

Films installation:

– On arcs in cells C08 and C10 of the storage ring in the area where the damages are

observed

– Longitudinally: complete length of vacuum chambers has been covered on both sides

(up and down)

– Transversally: most all of the quadrupole and sextupole faces covered (upstream and

downstream)

C08 S4 upstream Inside C08 Q8.2

yokes

C08 BPM5

cables

C08 S1

downstream

Radiation measurement is made with Grafchromic Films which are radiation sensitive.



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Dose Measurement : Spatial Distribution

Exposition:

– 12 mn with 16.4 mA stored in the machine

– equivalent to a 3.2 mA.h integrated current

Transverse plane

Longitudinal plane

Calibration method is described in the following paper:

Radiation Damages and Characterization in the SOLEIL Storage Ring, N. Hubert et al., IBIC 2013 proceedings, 644-647



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Absorption of the radiation emitted in the bending magnet

CROTCH

NEG

coated

Quad. VCs

e- trajectrory

Photon distribution

The photons emitted in the dipole impinge the vacuum chambers on different locations :

– The crotch: first 102 mrad, 7.6 kW at 500 mA

– The longitudinal absorber: next 69 mrad, 5.1 kW

– The downstream quadrupole VC’s: last 25 mrad,1.8 kW

Dph ~ 3,6 1017 ph.mm-1.s-1.mA-1

c = 8,6 keV



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X-ray fluorescence

70

25

16°

5,6

2

Quadrupole

vacuum chamber

profile

Aluminium

transmission factor

Perfect correlation between dose

distribution measured with Gafchromic films

and the calculated aluminium transmission

factor for 15 keV X-rays (as a function of the

crossed aluminium thickness)

Primary photons

X-rays Fluorescence

Aluminum vacuum chamber with 1µm thick

layer of NEG TiZrV( 30-30-40)



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Absolute dose measurements

Absolute dose measurement at the location of equipment

damages:

Equipment

Distance

to VC

(cm)

Measure

d dose

(Gy)

Dose

Rate

(Gy/A.h)

Total Dose

since

commissioning

: 9800 A.h

integrated

current (Gy)

Corrector Cables 20 0.5 156 1.5 106

Sextupole

Insulators 25 0.3 94 0.9 106

BPM Cables 25 0.3 94 0.9 106

Baking out Film contact 100 31250 300 106



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X-rays fluorescence spectrum

Sn ?

Zr

NEG

component

Fe Cu Zn

Aluminium

VC

materials

Kr

Silicon Drift Detector



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FluoX experimental setup

Installed on the D08-1 beamline frontend Different vacuum chambers can be

tested easily :

• Aluminum VC with NEG coating

• Stainless steel VC with NEG coating

• Aluminum VC without NEG coating

Beam stopper

Gate valve Sputter ion pump

Vacuum chamber to be tested

- The photon linear density is similar to that measured on the arc

- No contribution of the environment



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Aluminum + NEG coating vacuum chamber

Radiation distribution X-rays spectrum

Objective : reproduction of the results obtained on the storage ring

Sn ? Zr



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Contribution of a copper shielding

A 0,32 mm thick Copper

layer has been added on

the aluminum surface

except on one area. Reduction by a factor of 5 :

less than expected…

Area without copper



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Zr

Sn ?

Cu

Contribution of a copper shielding

- Same hit rate measured without and with copper shielding for

the two beam currents → factor of 6

- Secondary fluorescence of copper appears

With copper shielding, 120 µA

Without copper shielding, 19 µA



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Stainless steel + NEG coating vacuum chamber

• The measured dose rate is a factor 300 lower than for aluminum

vacuum chamber : 17 mGy/mAh

Distribution transverse Cross-section of the 316LN

stainless steel vacuum chamber

with a 1 µm thick layer of NEG

coating TiZrV (30-30-40)

3 mm thick SS Copper absorber



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Stainless steel vacuum chamber: X-rays distribution and spectrum

• Good correlation between dose

measured on the Grafchromic film

and the transmission distribution

calculated for 15,8 keV photons

Fe

Zr

???

Sn, In



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Conclusions

- X-ray fluorescence of the Zirconium of the NEG coating leads to radiation damages

- Energy of emitted X-rays is too high to be efficiently attenuated by the 3 mm aluminum

thickness of the vacuum chamber

- Low attenuation effect of Aluminum for the Zr (Ka and Kb). NEG coating in combination with

aluminum could be a not so good solution when primary photon density is high

- In case of copper NEG coated vacuum chamber, secondary fluorescence of copper could be of

a problem too if thickness of the vacuum chamber is too small.

- Tests will continue to :

- Understand the origin of tin and indium

- Have quantitative measurements

- This phenomenon has to be considered seriously for the design of future accelerators like

USR:

Extensive use of NEG coating

Circular small and thin vacuum chambers

- Effect could be worse if Hafnium (Hf) is added to the composition of the NEG coating

RADIATION DAMAGE ISSUES RELATED TO NEG COATING AT … · - X-ray fluorescence of the Zirconium of...

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