METHODOLOGY FOR THE CERTIFICATION OF RADIATION …cds.cern.ch/record/1417804/files/EuCARD-NOT-2012-001.pdf · 2012-01-20 · Date: Doc. Identifier: EuCARD-M7.2.1 20/10/11 Grant Agreement

EuCARD-NOT-2012-001

European Coordination for Accelerator Research and Development

PUBLICATION

METHODOLOGY FOR THECERTIFICATION OF RADIATION

RESISTANCE OF COIL INSULATIONMATERIAL; MILESTONE: M7.2.1

Polinski, J (Wroclaw University of Technology) et al

20 January 2012

The research leading to these results has received funding from the European Commissionunder the FP7 Research Infrastructures project EuCARD, grant agreement no. 227579.

This work is part of EuCARD Work Package 7: Super-conducting High Field Magnets forhigher luminosities and energies.

The electronic version of this EuCARD Publication is available via the EuCARD web site<http://cern.ch/eucard> or on the CERN Document Server at the following URL :

<http://cdsweb.cern.ch/record/1417804

EuCARD-NOT-2012-001

http://cern.ch/eucard

http://cdsweb.cern.ch/record/1417804

Doc. Identifier: EuCARD-M7.2.1

Date: 20/10/11

Grant Agreement 227579 PUBLIC 1 / 15

Grant Agreement No: 227579

EuCARD European Coordination for Accelerator Research and Development

Seventh Framework Programme, Capac i t ies Spec i f ic Programme, Research In f ras t ruc tu res , Combina t ion o f Co l labora t ive Pro jec t and Coord ina t ion and Suppor t Ac t ion

MILESTONE REPORT

METHODOLOGY FOR THE CERTIFICATION OF RADIATION RESISTANCE OF COIL

INSULATION MATERIAL MILESTONE: M7.2.1

Document identifier: EuCARD-M7.2.1

Due date of deliverable: End of Month 30 (Sep 2011)

Report release date: 20/10/11

Work package: WP7: HFM

Lead beneficiary: PWR

Document status: Final

Abstract:

The goal of the WP 7.2.1 of the EuCARD program is determination of the Nb3Sn based accelerator magnet coil electrical insulation resistance against irradiation, which will occur in future accelerators. The scope of the certification covers determination of mechanical, electrical and thermal properties changes due to irradiation. The report concerns definition of radiation certification methodology with respect of the insulation materials to be certified, radiation type, energy and doses, irradiation method as well as the selected insulation properties to be measured.


Date: 20/10/11


Copyright notice: Copyright © EuCARD Consortium, 2011. For more information on EuCARD, its partners and contributors please see www.cern.ch/EuCARD The European Coordination for Accelerator Research and Development (EuCARD) is a project co-funded by the European Commission in its 7th Framework Programme under the Grant Agreement no 227579. EuCARD began in April 2009 and will run for 4 years. The information contained in this document reflects only the author’s views and the Community is not liable for any use that may be made of the information contained therein.

Delivery Slip

Name Partner Date

Authored by J. Polinski, M. Chorowski PWR 09/10/11

Edited by J. Polinski PWR 09/10/11

Reviewed by G. de Rijk CERN 18/10/11

Approved by 20/10/11


Date: 20/10/11


TABLE OF CONTENTS

1. EXECUTIVE SUMMARY ............................................................................................................................ 4

2. INTRODUCTION .......................................................................................................................................... 4

3. RADIATION SPECTRUM IN FUTURE ACCELERATORS .................................................................. 4

4. SELECTION OF THE INSTITUTE CAPABLE OF THE IRRADIATION .......................................... 6

5. SELECTION OF THE POSSIBLE CANDIDATE FOR MAGNET COIL ELECTRICAL INSULATION ....................................................................................................................................................... 10

6. SELECTION OF CERTIFICATION TEST STANDARD/METHOD ................................................... 11 6.1. THERMAL CERTIFICATION METHOD ......................................................................................................... 11 6.2. ELECTRICAL CERTIFICATION METHOD ..................................................................................................... 11 6.3. MECHANICAL CERTIFICATION METHOD ................................................................................................... 12

7. DEVELOPMENT OF INSULATION IRRADIATION METHOD IN THE CRYOGENIC TEMPERATURE ................................................................................................................................................. 12

8. REFERENCES ............................................................................................................................................. 14


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1. EXECUTIVE SUMMARY The goal of the WP 7.2.1 of the EuCARD program is determination of the Nb3Sn based accelerator magnet coil electrical insulation resistance against irradiation, which will occur in future accelerators. The scope of the certification covers determination of mechanical, electrical and thermal properties change due to irradiation. The report concerns determination of radiation types, doses and energy, selection of the possible candidate for magnet coil electrical insulation, selection of the Institute capable of the irradiation, selection of certification test standard/method, development of insulation irradiation method at the cryogenic temperature

2. INTRODUCTION Magnets in accelerators like the upgraded LHC and neutrino factories will be subjected to very high radiation doses. The electrical insulation employed on the coils needs to be resistant to this radiation. A certification program for the radiation resistance of the insulation material has been launched within the WP7.2.1 of EuCARD program sub-task. At the beginning of the program the Radiation Working Group was established to select insulation material candidates and determine a future accelerator irradiation specification, certification scope and methods as well as certified insulation irradiation method.

3. RADIATION SPECTRUM IN FUTURE ACCELERATORS To determine the radiation type, energy spectrum and doses, which can occur in the future Nb3Sn SC magnet based accelerators, within the WP7.2 Task the Radiation Working Group (RWG) has been established. The RWG decided to perform radiation certification for conditions corresponding to the maximum expected radiation doses in the LHC Upgrade phase II accelerator. Figure 3.1 presents the radiation map for the Interaction Region (IR) Quadrupoles (Q) for the LHC Upgrade I case. This case was available the moment when the study was started and is used as a typical case from which others can be estimated as an extrapolation. It can be seen, that the peak of irradiation will occur in the Q2a, 35m from Collision Point.


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Q1 Q2a Q2b Q3

Peak fluence in 10 years:2.5 x 1017 neutrons/cm2

Distance from collision point (cm) 3.1 Radiation map for the Interaction Region (IR) Quadrupoles [1]

FLUKA simulations allow to define the contents of given radiation type in the Q2a radiation peak point. The simulation information and influence of given radiation type on the SC magnets coil material are collected in the Table 3.1

Table 3.1 Radiation spectrum at Q2a: 35m from Collision Point [1,2]

Radiation type Contents, % Influence on magnet coil materials

Neutrons 4.82 SC and Cu Protons 0.14 SC and Cu

Photons (γ) 88.93 Insulation Electrons 4.31 small effect Positrons 2.23 small effect Pions + 0.19 probably small effect Pions - 0.26 probably small effect

From the Table 3.1 it can be found that photon (γ) radiation has the strongest influence on the SC magnet coil electrical insulation, which is expected to constitute almost 90% of total radiation on the Q2a magnet. Simulations done in the FLUKA code also allow a determination of the energy spectrum for all radiation types listed in table 3.1. Figure 3.2 presents the photons spectrum in the inner coil of Q2a at the peak location.


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e+/e-‐ annihilation peak

Photons

Figure 3.2 Photon spectrum on the inner coil of Q2a at the peak location for 2 different magnet aperture

diameters [2]

It can be found from Figure 3.2 that the higher number of photons colliding with Q2a have an energy from range 0.1 MeV – 1.0 MeV. Also the influence of the higher energy (up to 100 MeV) photons on the insulation properties can’t be neglected. On the other hand, from the science point of view, the influence of the protons with energies in the GeV range are of interest to be determined. In view of that, the RWG has preliminary defined the certification photons energy bands: 0.2 MeV – 1.0 MeV, 20 MeV – 100 MeV, 50 GeV – 100 GeV (marked with light-blue area on Figure 3.2). As the goal certification maximum radiation dose the RWG decided the value 50MGy.

4. SELECTION OF THE INSTITUTE CAPABLE OF THE IRRADIATION

After reviewing the ability and accessibility of the irradiation sources installed over the Europe, the RWG decided to select NCBJ in Poland (former Andrzej Sultan Institute for Nuclear Studies) as irradiation Institute. NCBJ posses an industrial accelerator for irradiation with 4 MeV – 15 MeV photons. Photons are produced in collision of electrons with a 1 mm thick tungsten and a 0.2 mm thick gold target [3]. Available photon spectra from the electron linac for different energies are presented in Figure 4.1


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Figure 4.1 Typical spectrum of brehmstrahlung radiation induced by: 9 MeV electrons (blue), 6 MeV electrons

(red), 4MeV electrons (yellow) and 3 MeV electrons (green).[3]

It can be found from the Figure 4.1 that the flux of photons is between 3 to 7 orders of magnitude lower than the flux of electron colliding with the target. It suggests that to obtain the specified 50 MGy dose a relatively long time would be needed. On the other hand, it is well known that the character of the damage to the insulation material from > 1 MeV electrons is identical as for > 1 MeV photons. Therefore, an electron beam has been selected as the source of the certification radiation. For determination of the best irradiation parameters 3 different accelerator structures, namely 6 MeV, 12 MeV and 15 MeV have been tested between Oct 2010 and Jan 2011 at NCBJ. Figures 4.2 and 4.3 present the experimental results of the electron beam penetration depths in PMMA (Plexiglas) for 12 MeV and 15 MeV structures. The results are obtained for optimized accelerator gun current, gun voltage, solenoid voltage and with a pulse repetition rate of PRR = 5 Hz.


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Figure 4.2 Measured depth-dose curve of “12 MeV” structure - confirmed energy: 7 MeV - 8 MeV.

Figure 4.3 Measured depth-dose curve of “12 MeV” structure - confirmed energy: 10 MeV - 11 MeV.

Based on the PMMA penetration results it was determined that the confirmed 12 MeV structure energy is 7 MeV - 8 MeV, while the confirmed 15 MeV structure energy is 10 MeV - 11 MeV. The energy of the 6 MeV structure has been confirmed in another experiment as 4 MeV Figures 4.4 and 4.5 presents experimental results of the radiation dose with a distance from radiation source for 6 MeV and 15 MeV structures. The PRR was 76,4 Hz and 5 Hz respectively.


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Figure 4.4 Dose rate variation with distance from radiation source for 6 MeV structure, PRR = 76.4 Hz. Accelerator parameters not optimized. [4]

Figure 4.5 Dose rate variation with distance form radiation source for 15 MeV structure, PRR = 5 Hz. Optimized accelerator parameters not.[5]

It should be pointed out that the dose rate variation results presented for the 6 MeV structure in Figure 4.4 have been obtained for not optimized accelerator parameters. The maximum dose for optimized parameters for PRR = 76.4 Hz was measured as 2200 Gy/min [4]. The results for the 12 MeV structure are very similar as for the 15 MeV structure and therefore not presented in the report. To compare and select the best acceleration structure the calculation of the necessary irradiation time for 1 irradiated insulation material sample has been done. For the calculation purpose the following assumption have been made:

- the material samples can be collected in to a package,

0

2

4

6

8

10

12

14

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Distnce form gun, cm

D, G

y/m

in

Distance from gun (cm)


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- the average sample thickness is 0.5 mm (see paragraph 5), - the sample density is about 1.8 g/cm3 (density of G10 material, which is similar to

insulation material – see paragraph 5), - irradiation dose 50 MGy, - PRR 300 Hz (maximum available for NCBJ electron linac).

For the above listed assumptions the penetration depth in the insulation material for a given structure has been determined that allows finding the amount of samples in the irradiation package. The dose rate scaled to PRR = 300 Hz allows the determination of the time necessary to accumulate 50 MGy in the package. Finally, the irradiation time of one sample can be found. The calculation input and results for considered structures are collected in Table 4.1

Table 4.1. Irradiation time for different accelerator structures

Structure 6 MeV 12 MeV 15 MeVConfirmed electron energy MeV 4 8 11Depth of insulation penetration mm 5.6 14.4 21.1Nbrs of samples radiated at once 11.1 28.9 42.2

Max recorded dose rate Gy/min 2200 12 12Repetition frequency Hz 76.4 5 5Expected dose @f=300Hz Gy/min 8638.7 720.0 720.0Irradiation time for 50 MGy Working days 12.1 144.7 144.7Irradiated samples Work. days/sample 1.1 5.0 3.4

From Table 4.1 it can be found that the 6 MeV structure allows irradiation of the one material sample more than 3 times faster than with the 15 MeV structure and almost 5 times faster than with the 12 MeV structure. It was finally decided by the RWG that the irradiation can be conducted in NCBJ Poland, the certification radiation will be electron radiation and a 6 MeV electron accelerator should be used. It should be pointed out that disadvantage of electron beam use is a relatively small beam diameter, measured for the 6 MeV structure as 5 mm - 7 mm. It is possible to increase the beam diameter by a magnetic filed, but it is connecting with a strong beam dose rate decrease. Therefore it is decided to perform the irradiation with the raw beam.

5. SELECTION OF THE POSSIBLE CANDIDATE FOR MAGNET COIL ELECTRICAL INSULATION

Insulation candidates:

- RAL mix 71 – DGEBA epoxy + D400 hardener

- RAL mix 237 – Epoxy TGPAP-DETD(2002)

- LARP insulation; CTD101K + filler ceramic

- Cyanate ester epoxy mix T2 (40% AroCy L10)


Date: 20/10/11


6. SELECTION OF CERTIFICATION TEST STANDARD/METHOD Review of literatures concerning properties of low temperature irradiated epoxy/glass fiber composites [6] done by PWR showed missing development of scientific research, which could be useful for this EuCARD task. The topic of radiation damage in reinforced polymers is complicated and poorly understood. Twenty articles concerning the irradiation effects have been identified and they cover the following materials: pure epoxy (2 articles) and composites (18 articles). Direct comparison of published data was impossible due to differences in radiation dose, materials, tested properties, radiation and testing conditions. Nevertheless the literature review has enabled to identify the tendencies of the radiation influence on mechanical, thermal and electrical properties of the samples. The effect of irradiation temperature (room/cryogenic temperature) is still not fully investigated and in case of irradiation at cryogenic temperatures, the effect of warming-up between the irradiation and the test process on the change of insulators properties is not clarified. Literature review showed that there is not sufficient research taking the temperature aspects into account. Therefore, RWG decided to perform the irradiation and certification tests at a cryogenic temperature without warming up, if technically possible. Due to the technical difficulty the irradiation will be performed in liquid nitrogen (LN2) conditions as well as the electrical and mechanical certification tests. Only the thermal certification test will be done in pressurized superfluid helium HeIIp conditions, but for this case the irradiated test samples need to be warmed-up for installation in the test cryostat. The main purpose of certification tests is the comparison of given material properties before and after irradiation. Therefore, each certification test method will be repeated for unirradiated and for irradiated insulation candidates.

6.1. THERMAL CERTIFICATION METHOD As thermal certification test, the drum method in HeIIp condidtions is selected. This method, described in details in [7], allows simultaneous determination of the thermal conductivity and the Kapitza resistance of tested materials. Experimental data concerning those material properties are essential for HeIIp cooled SC magnet thermal modelling and for magnet design purpose, which is a goal of WP7.2.2 and WP7.3 of the EuCARD program. In the drum method, minimum 2, typically 3 to 5 different material thickness samples need to be tested. The thickness of the samples varies usually from 0.1 mm to 0.6 mm. The sample has a circular shape with a diameter of about 100 mm. The active heat transfer area of the sample is limited by a 80 mm diameter circle. The RWG decided to use 4 different thickness of one tested material specified to be of about 0.1 mm, 0.2 mm, 0.3 mm and 0.4 mm. For one test of one material thickness two 100 mm diameter samples will be used. It means that for 4 insulation candidates, for the thermal certification test 64 samples are needed.

6.2. ELECTRICAL CERTIFICATION METHOD As electrical certification test a EN 60243-1 standard: “Methods of test for electric strength of solid insulating materials. Tests at power frequencies” has been selected and it will be implemented at LN2 conditions.


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In this method two electrodes are placed on the opposite side of the tested material sheet. An increasing voltage difference is applied on the electrodes untill an electrical breakdown in the material occurs. The breakdown can be detected with a current measurement. Before the breakdown the current increase is proportional to the voltage difference, while at the breakdown point the current increases rapidly to a very large value. The EN 60243-1 standard recommends using a close to 0.5 mm thickness sheet and external dimensions of about 100 mm × 100 mm. It can be seen that the tested sample dimensions are very similar to one of the thermal samples. Therefore, to reduce a samples production cost it is decided to produce 0.4 mm thickness samples for the electrical certification purpose. The electric strength test procedure recommends 5 times repetition of the test on a separate material sample. As the final electric strength is an average value from 5 tests.

6.3. MECHANICAL CERTIFICATION METHOD For mechanical test of the laminate material two methods are commonly used: a method based on EN ISO 14130 standard: “Fibre-reinforced plastic composites – Determination of apparent interlaminar shear strength by short-beam method” and a method based on ISO EN 15024” Fibre-reinforced plastic composites — Determination of mode I interlaminar fracture toughness”[8]. Nevertheless, in both methods the tested specimen volume needs to be uniformly irradiated. For this, the sample length should not exceed 5 mm in length and rectangular cross section shape dimensions should inscribe to the 5 mm - 7 mm (beam diameter) circle. Since the EN ISO 14130 standard specified the test specimen as rectangular bars of uniform thickness h, the length of the specimen should be l=10h and its width b=5h. It imposes the maximum specimen dimensions as: (thickness × width × length) 0.5×2.5×5.0 mm×mm×mm. It should be pointed out, that for selected irradiation method only one such specimen can be irradiated at a time. Therefore, and due to fact that the above listed mechanical certification methods require the test of 5 specimens of a given material, irradiation time and costs of mechanical samples can be relatively high. Some compromise between a proper certification test method and relatively low specimens irradiation time and costs brings the implementation of the EN10002-1 standard: “Tensile testing of metallic materials” for laminates. For such a method, the specimens can have relatively small thickness and it will allow simultaneous irradiation of a set of specimens. On the other hand, a maximum capacity test rig for laminates should not exceed 1 kN, while capacity of market available standard facilities start from 10 kN. Therefore, to apply the tensile test certification method for laminate certification a special design test stand needs to be used.

7. DEVELOPMENT OF INSULATION IRRADIATION METHOD IN THE CRYOGENIC TEMPERATURE

A series of preliminary tests performed in NCBJ in Nov 2010 concerning the irradiation absorption ability of different solids and liquids have shown that 15 mm layer liquid nitrogen absorbs almost 100% of electron beam [4]. Therefore, immersing of the insulation samples in the LN2 during irradiation process can not be applied. Nevertheless, the cooling of the samples with a thin film of liquid nitrogen is a satisfactory solution.


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LN2

Accelerator gun

Accelerator gun possitoner

Electron beam

LN2 film

Sample holder

Samples package

LN2

LN2

LN2Heater

LN2 Vapour

LN2 level meter

Figure 7.1. Irradiation cryostat scheme.

Figure 7.1. presents the irradiation cryostat scheme. In the cryostat a horizontal direction electron beam is provided from the accelerator gun to the sample package, through a hole created in the cryostat side. The sample package is placed in the sample holder. The sample holder is connected on its top with the line providing the LN2. Nitrogen flowing down through the samples package and absorbs the heat deposited in the sample package by the electron beam. The remaining LN2 flows down to the cryostat bottom, where it is collected. It is important that level of collected LN2 does’t reach the sample holder. To avoid this, the cryostat is equipped with a LN2 regulation system composed of a LN2 level meter and a heater. When the collected liquid reach the specified level the system triggers the heater located in the liquid. It is considered that nitrogen vapours generated inside the cryostat will be directed to the accelerator gun for cooling of an accelerator window.


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Figure 7.2 a) presents the irradiation cryostat conceptual design while a photo of the manufactured cryostat is presented in Figure 7.2 b).

8. REFERENCES

[1] L. Bottura, R. Flukiger, A. Ballarino, F. Liberati, L. Oberli, I. Pong, G. de Rijk, An R&D program to Address Irradiation Effects in Superconductors for LHC , EuCARD workshop on insulator

irradiation, December 2, 2009 , CERN, Geneva, CH [2] R. Flukiger, Radiation spectra in LHC phase II -‐ Effect on superconducting materials, EuCARD

workshop on insulator irradiation, December 2, 2009 , CERN, Geneva, CH

[3] S. Wronka, The analysis of possible certification scenario based on research accelerators located at Świerk Nuclear Center, NCBJ, June 2010

[4] J. Polinski, M. Chorowski, P. Bogdan, Task 7.2.1 – Radiation certification status report, EuCard-‐WP7-‐HFM Collaboration Meeting , CERN, Geneva 26.11.2010

[5] J. Polinski, M. Chorowski, P. Bogdan, S. Wronka, Task 7.2.1 – Radiation certification status

report, EuCard-‐WP7-‐HFM Collaboration Meeting – CEA Grenoble 22.03.2011 [6] J. Polinski, M. Chorowski , E. Roszak, Review of literatures concern properties of low

temperature irradiated epoxy glass fibre composites, 3th Radiation Working Group Meeting,

12.01.2010, phone conference

a) b)

Figure 7.2 a) Conceptual design of irradiation cryostat, b) cryostat photo


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[7] B. Baudouy, J. Polinski, Thermal conductivity and Kapitza resistance of epoxy resin fiberglass tape at superfluid helium temperature, Cryogenics 49 (2009), p. 138–143

[8] F.Rondeaux: Insulator radiation hardness: Definition of tests and samples, EuCARD workshop on insulator irradiation, December 2, 2009 , CERN, Geneva, CH

Documents

METHODOLOGY FOR THE CERTIFICATION OF RADIATION …cds.cern.ch/record/1417804/files/EuCARD-NOT-2012-001.pdf · 2012-01-20 · Date: Doc. Identifier: EuCARD-M7.2.1 20/10/11 Grant Agreement