union of compact accelerator-driven neutron sources (ucans ... › download › pdf ›...

Physics Procedia 26 ( 2012 ) 196 – 204

1875-3892 © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of UCANS

doi: 10.1016/j.phpro.2012.03.025

Union of Compact Accelerator-Driven Neutron Sources (UCANS) I & II

Neutron applications laboratory for ESS-Bilbao

S. Terrona,b, M. Magana,b, F. Sordoa,b, A. Ghiglinoa,b, F. Martıneza,b, F.J. Bermejoa, J.M. Perladob,

aESS-Bilbao Consortium, Bizkaia Technology Park, Laida Bidea, Building 207 B Ground Floor, 48160 Derio (Spain)bInstituto de Fusion Nuclear, ETS Ingenieros Industriales, Jose Gutierrez Abascal, 2 28006 Madrid (Spain)

Abstract

The ESS-Bilbao Accelerator Center site at Lejoa UPV/EHU campus will be provided with a proton accelerator

up to 300-400 MeV. In the first construction phase, a beam extraction will be set at the end of the DTL, which will

produce a 50 MeV proton beam with an average current of 2.25 mA and 1.5 ms pulses at a frequency of 20 Hz.

These beam characteristics allow to configure a low intensity neutron source based on Be (p, n) reactions, which

enables experimentation with cold neutrons similar to that of LENS. The total beam power will be 112 kW, so the

configuration of the neutron production target will be based on a rotating disk of beryllium slabs facing the beam on

one side and a cryogenic methane moderator on the other, with the target-moderator system surrounded by a beryllium

reflector. In this paper, first estimates will be presented for thermomechanical conditions of the target cooling scheme,

neutron source intensities, and cold neutron pulses.

c© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of UCANS.

Keywords: Beryllium, Neutron source, Target, ESS-BILBAO

1. Introduction

The strategy of building a MW-range, accelerator-based spallation neutron source as the next generation neutron

facility for Europe is at present under scrutiny on the basis of experience gained during commissioning of the SNS[1]

in the US and the JPARC[2] facility in Japan as well as from current operational experience achieved by high through-

put installations such as the ISIS source at the U.K. The underlying technology has however advanced since the time

when previous generation facilities reached final design stages, and therefore, time is now ripe to learn from ongoing

experience and define the development areas which would allow the European Spallation Source (ESS)[3] to benefit

from recent advances in technology while maintaining a reliable, low risk, design.

Within the current European context, ESS-Bilbao (ESS-B) has entered a new endeavor within which while being a

partner of the ESS project aims to develop significant in-house capabilities needed to support the country participation

in a good number of accelerator projects worldwide (IFMIF/EVEDA, LINAC4, FAIR, XFEL, ESRF upgrades, ISIS-

FETS etc.). On such grounds ESS-B has started the construction of a modular, multipurpose research accelerator

which should serve as a benchmark for components and subsystems relevant for the ESS project as well as to provide

the Spanish science and technology network with hands-on experience on power accelerators science and technology,

a task long overdue.

The present document reports on the development of ongoing projects which basically comprise the construction

of the room temperature accelerating structures plus some prototyping of a first demonstration cryomodule comprising

Available online at www.sciencedirect.com

© 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of UCANSOpen access under CC BY-NC-ND license.

Open access under CC BY-NC-ND license.

http://creativecommons.org/licenses/by-nc-nd/3.0/

http://creativecommons.org/licenses/by-nc-nd/3.0/

S. Terrón et al. / Physics Procedia 26 ( 2012 ) 196 – 204 197

two superconducting spoke resonators, as well as some foreseen applications of the generated proton and neutron

beams. The current design parameter values are to be considered as a basis for a feasibility assessment of the ESS linac

components and consist of 75 mA of proton current, 20 Hz repetition rate using 1.5 ms proton pulses and two 352/704

MHz bunch frequencies with a single frequency jump (Table 1). The accelerator structures either planned or under

development at present are meant to satisfy such stringent demands. A number of applications of proton and neutron

beams have already been envisaged. Here we report on the state of our conceptual design for the Neutron Applications

Laboratory which consists of a rotating beryllium target, a multimaterial reflector (lead, water or beryllium), two low

energy neutrons lines and one hight energy neutron line.

Proton Energy 50 − 60MeVPeak Current 75mA

Frequency 20 − 50HzPulse Length 0.3 − 1.5ms

Average Current 2.25mANeutron source 9.25 · 1014n/s

Table 1: Number of neutrons produced per target proton over beryllium

2. Source term definition

Neutron source term is probably the main parameter to design ESS-B Neutron Applications Laboratory. Table

2 shows different evaluations of total neutron production for Be9(p, n) reaction (evaluated with MCNPX code [4])

compared to the experimental results of I. Tilquin [5]. The best evaluation below 55 MeV is achieved with ENDEF

cross section library [6]. However a bug in cross section data generates an error for 43.3 MeV protons-beryllium

collision, and due to it, it is not possible to apply it. In order to study this reaction by means of nuclear models, Isabel

[7] and INCL-ABLA [8] have been analyzed. Isabel model produces a good agreement with experimental results for

55 MeV, so, an adequate evaluation is expected for 50 MeV.

Energy I. Tilquin Isabel INCL ENDEF45MeV 0.056 0.062 0.066 0.064

55MeV 0.078 0.080 0.089 0.077

65MeV 0.104 0.103 0.116 0.059

Table 2: Neutron source for proton over beryllium

Considering Isabel model as a reference, several target materials have been compared on Table 3. The highest

neutron production will be achieved on beryllium, so it will be the best option. Nevertheless, lithium targets will

produce less neutrons but with a higher energy so it could have some interest in high energy neutron applications

(section 5.1).

Material N/p Av. Energy (MeV)Carbon 7.54 · 10−3 8.04

Lithium 4.27 · 10−2 13.15

Beryllium 6.49 · 10−2 7.76

Table 3: Target material selection

The neutron source is one of the main parameters but not the only one. In order to analyze angular distribution of

neutrons, a 50 MeV proton beam over a beryllium cylinder has been simulated. Figure 1 shows neutron flux at 1 m

198 S. Terrón et al. / Physics Procedia 26 ( 2012 ) 196 – 204

for different angles. High energy neutrons are mainly emitted in a forward direction, so in order to reduce fast neutron

background, thermal and cold neutrons experiments should not be placed in that direction. On the other hand, high

energy experiments should be placed on forward direction in order to maximize high energy neutrons spectra.

0

1e-08

2e-08

3e-08

4e-08

5e-08

6e-08

7e-08

8e-08

9e-08

0 10 20 30 40 50

[n/cm2-MeV-proton]

Energy (MeV)

0.0o

22.5o

45.0o

67.5o

90.0o

Figure 1: Angular distribution.

3. Thermomechanical design

The 50MeV@[email protected] proton beam will produce a heat deposition of 110 kW over the beryllium target.

This energy deposition will produce a sharp increase of temperature and stress that could be difficult to withstand for

the beryllium target. In order to spread heat deposition over a larger volume a rotating target is proposed (Figure 2).

Concerning cooling system, an individual water loop is proposed pressurized up to 5 bars in order to cool beryllium

sheet surface. This engineering solution allows the thermomechanical requirements to be relaxed in exchange for

introducing a much more complicated layout.

Figure 2: Rotating target elements with water cooling channel.

Figure 3 shows maximum temperature over the beryllium sheet (1 cm thickness). A 2σ = 5cm Gaussian profile

has been considered for the proton flux distribution which impacts the sheet with a 45o angle. The beam frequency


viewed by beryllium sheets could be adjusted depending on rotation speed and number of elements which compose

the target. Thermal and mechanical results show acceptable temperature and stress profiles for 1 Hz frequency, so 20

elements will be required. Considering 20 elements, the rotating target dimensions will be 1.7 m diameter and will

have a total weight below 200 kg, so engineering problems associated with layout are not expected.

In order to conclude a target overview, a CFD evaluation of cooling channels has been performed. A pressure

drop of 5000 Pa will ensure enough velocity to remove heat deposited on beryllium sheet (Figure 3). So, refrigeration

conditions are not very severe.

Figure 3: Maximum Temperature for a 45o incidence beam.

4. Hydrogen implantation and lifespan

The last parameter that will be analyzed in this document is hydrogen implantation. Only a small fraction of

protons from the beam will suffer nuclear interactions, and due to it, a large amount of free protons will be introduced

in the target material. These free protons will gain an electron and will become hydrogen. Hydrogen inside a metallic

matrix will produce swelling and finally the mechanical failure as in LENS case [9]. In order to analyze this issue, a

large MCNPX simulation has been performed. The last position of protons has been saved and based on that, the gas

accumulation has been inferred (Figure 4). All the protons are assumed to be stopped inside the material in order to

have a meaningful comparison with LENS first targets. Since the proton energy is higher than in LENS, the dispersion

is greater, and therefore the gas concentration per proton is lower.

Table 4 shows gas implantation estimation for LENS conditions vs ESS-B conditions. The lifespan of each

beryllium sheet on ESS-B beam conditions has been inferred assuming a linear dependency of the proton damage,

roughly estimated as dependent on the proton current and the implanted atoms per cubic centimeter and per incident

proton. Taking the observed lifespan of the LENS target and its irradiation conditions as a reference, and taking into

account that the ESS-B target will have 20 elements, more than 3400 full power operation hours can be expected.

Since ESS-B accelerator facility is being designed to operate 3000 hour per year, the target lifespan time will be

enough for one operation year.


H implantation ( atms/cm2-proton )

-45 -42.5 -40 -37.5 -35

Y (cm)

0

0.475

0.95

1.425

1.9

Z (cm)

0.00

0.00

0.01

0.1

1

10

Figure 4: Hydrogen implantation for 50 MeV protons on beryllium

LENS ESS-B ESS-B 20Intensity (mA) 0, 62 2, 25

Operation (h) 156 171 3420

Imp. (atms/cm3 − p) 18 4, 5

Table 4: Life time estimation regarding gas implantation

5. Applications

Taking into account the source term analysis, a multipurpose experimental facility is proposed with three experi-

mental lines, two of them for low energy neutrons and one for high energy neutrons. Figure 5 shows relative positions

of experimental lines. The high energy neutron line is oriented forward in order to maximize high energy neutron flux.

The low energy neutron lines are oriented at 45o and 65o from beam direction to reduce fast neutrons background.

In order to produce low energy neutrons, a solid methane moderator in slab configuration will be implemented sur-

rounded by a reflector. The moderator will be removable, so, if it is removed, the high energy line can be operated,

and if not, the low energy lines will be available.

5.1. High energy neutrons & Irradiation facilityHigh energy applications for ESS-B are divided in Time Of Flight experiments (TOF) and irradiation. The TOF

application line is focused on measuring high energy cross sections and test instruments and detectors in this energy

range. Due to that, a neutron line with direct view of the target is needed in order to maximize high energy neutron

flux.

Regarding the irradiation capabilities, it is possible in this line to introduce samples close to the neutron source in

order to obtain high neutron fluxes. Figure 6 shows neutron and photon fluxes at difference distance from the target

surface. The maximum neutron flux at 8 cm from the target surface will be around 6 · 1012[n/cm2 − s].

The second possibility of materials irradiation is to irradiate samples far from the target surface. The Chipir

instrument at ISIS is one line dedicated to the irradiation of electronic components for aerospace applications. Table

5 shows fast neutron flux > 10MeV produced on this instrument. ESS-B will be able to produce similar fluxes if

samples are located 3 to 5 m away from target surface as it is shown on Table 6.


Figure 5: Target-moderator-reflector system

106

108

1010

1012

1014

1016

1018

1020

10-810

-710

-610

-510

-410

-310

-210

-110

010

110

2

[n/cm2/MeV-s]

Energy (MeV)

8 cm 17 cm 25 cm 34 cm

106

107

108

109

1010

1011

1012

1013

10-2

10-1

100

101

102

[p/cm2/MeV-s]

Energy (MeV)

8 cm 17 cm 25 cm 34 cm

Figure 6: Fig (a): Neutron Spectra. Fig (b):Photons Spectra

In order to be able to contribute in this area, ESS-B is planning an irradiation test area placed at 6 m from ESS-B

target in the TOF line that could produce a neutron flux similar to ISIS-Chipir. The main difference will be that ESS-B

average neutron energy will be lower (7-8 MeV compared with 9-10 MeV).


Instrument Mode Flux [n/cm2 − s] Max Energy (MeV)ISIS-Chipir Pencil Beam 4 · 107 800

ISIS-Chipir Flood Beam 3 · 105 800

Table 5: Neutron flux between 20 and 800 MeV in ISIS-CHIPIR instrument

Distance to Target (cm) Flux > 10MeV[n/cm2 − s]

300 6.0 · 108

500 2, 1 · 108

700 1, 1 · 108

Table 6: Neutrons flux between 20-50 MeV in the TOF line

5.2. Cold Energy neutrons

In order to produce cold neutrons a methane moderator at 20 K will be introduced in the target area. This methane

moderator will have a view surface of 10x10 cm and 4 cm of thickness, similar to LENS configuration (slab box

type of 12x12x1) [10], but with an increased thickness to accommodate the higher source neutrons energy. Figure

7 shows the neutron distribution of < 5 meV neutrons on moderator surface for long proton pulses using different

reflecting materials. Beryllium reflector will produce the highest integrated cold neutron flux. Nevertheless, lead

reflector will produce a lower tail distribution so both of them could be interesting for experimental applications.

These neutron fluxes are around 4 orders of magnitude below ESS neutron flux, nevertheless they will be useful to test

components such as neutron guides, moderators and instrument for ESS, in the same way as LENS is doing significant

contributions to bigger devices such as SNS and LANL neutron sources. [11].

0

5e+13

1e+14

1.5e+14

2e+14

2.5e+14

0 750 1500 2250 3000

[n/cm2-eV-s-sr-MW]

Time (μS)

Beryllium Water Lead

Figure 7: Long pulse for 5 meV neutrons


6. The neutron Laboratory

Figure 8 shows a tentative layout of the ESS-B Neutron Applications Laboratory. It will have a heavily shielded

central room for the target in order to reduce radiation level around this area, and three experimental lines. A hot cell

will be placed close to the target in order to have enough space for maintenance operations on target components and

to manipulate irradiated moderators.

Figure 8: ESS BILBAO Neutrons Laboratory

7. Conclusion

As conclusions for the studies carried out related to ESS-B Neutron Applications Laboratory, the following high-

lights can be summarized:

1. A multi-purpose facility for high and low energy neutrons is being designed for ESS-Bilbao accelerator research

center.

2. Cold neutrons produced with a water reflector and a methane moderator con reproduce pulse shape of ESS

scaled by a factor 10.000. This neutron brightness should be enough to test ESS components.

3. High energy neutron flux will be useful for TOF experiments and materials science.

Acknowledgments

This work has been possible thanks to the support of the computing infrastructure of the i2BASQUE academic

network

References

[1] T. McManamy, A. Crabtree, D. Lousteau, J. DeVore, L. Jacobs, M. Rennich, Overview of the sns target system testing and initial beam oper-

ation experience, Journal of Nuclear Materials 377 (1) (2008) 1–11, spallation Materials Technology, Proceedings of the Eighth International

Workshop on Spallation Materials Technology. doi:10.1016/j.jnucmat.2008.02.024.

URL http://www.sciencedirect.com/science/article/pii/S0022311508001086


[2] M. Futakawa, K. Haga, T. Wakui, H. Kogawa, T. Naoe, Development of the hg target in the j-parc neutron source, Nuclear Instruments

and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 600 (1) (2009) 18–21.

doi:10.1016/j.nima.2008.11.103.

URL http://www.sciencedirect.com/science/article/pii/S016890020801646X

[3] G. Bauer, The ess project, Tech. rep., The ESS Council (2002).

[4] G. McKinney, Mcnpx user’s manual. version 2.6.0.

[5] I. Tilquin, Experimental measurements of neutron fluxes produced by proton beams (23-80 mev) on be and pb targets, Nuclear Instruments

and Methods in Physics Research,Section A 545 (1-2) (2005) 339–343.

[6] M. Chadwick, P. ObloÅinsk, M. Herman, N. Greene, R. McKnight, D. Smith, P. Young, R. MacFarlane, G. Hale, S. Frankle, A. Kahler,

T. Kawano, R. Little, D. Madland, P. Moller, R. Mosteller, P. Page, P. Talou, H. Trellue, M. White, W. Wilson, R. Arcilla, C. Dunford,

S. Mughabghab, B. Pritychenko, D. Rochman, A. Sonzogni, C. Lubitz, T. Trumbull, J. Weinman, D. Brown, D. Cullen, D. Heinrichs,

D. McNabb, H. Derrien, M. Dunn, N. Larson, L. Leal, A. Carlson, R. Block, J. Briggs, E. Cheng, H. Huria, M. Zerkle, K. Kozier, A. Courcelle,

V. Pronyaev, S. van der Marck, Endf/b-vii.0: Next generation evaluated nuclear data library for nuclear science and technology, Nuclear Data

Sheets 107 (12) (2006) 2931 – 3060, evaluated Nuclear Data File ENDF/B-VII.0. doi:10.1016/j.nds.2006.11.001.


[7] Y. Yariv, Z. Fraenkel, Intranuclear cascade calculation of high-energy heavy-ion interactions, Phys. Rev. C 20 (6) (1979) 2227–2243.

doi:10.1103/PhysRevC.20.2227.

[8] C. Volant, S. Vuillier, J. Cugnon, Improved intranuclear cascade model for nucleon-nucleus interactions, Nuclear Physics A.

[9] T. Rinckel, P. E. Sokol, Target Failure Report, internal report LENS (2006).

[10] C. Lavelle, D. Baxter, A. Bogdanov, V. Derenchuk, H. Kaiser, M. Leuschner, M. Lone, W. Lozowski, H. Nann, B. Przewoski, N. Remmes,

T. Rinckel, Y. Shin, W. Snow, P. Sokol, Neutronic design and measured performance of the low energy neutron source (lens) target moderator

reflector assembly, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated

Equipment 587 (2-3) (2008) 324 – 341. doi:10.1016/j.nima.2007.12.044.


[11] P. Pherguson, Sns neutron source development at the low energy neutron source, in: UCANS-II, Union of Compact Accelerator-Driven

Neutron Sources.

union of compact accelerator-driven neutron sources (ucans ... › download › pdf ›...

Documents