fp7 high luminosity large hadron collider design study ...broggi, f (infn) et al 27 may 2014 the...

CERN-ACC-2014-0064

HiLumi LHCFP7 High Luminosity Large Hadron Collider Design Study

Deliverable Report

Preliminary Report on EnergyDeposition Calculations for the Cold

Powering System

Broggi, F (INFN) et al

27 May 2014

The HiLumi LHC Design Study is included in the High Luminosity LHC project and ispartly funded by the European Commission within the Framework Programme 7

Capacities Specific Programme, Grant Agreement 284404.

This work is part of HiLumi LHC Work Package 6: Cold powering.

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

<http://cds.cern.ch/search?p=CERN-ACC-2014-0064>

CERN-ACC-2014-0064

http://hilumilhc.web.cern.ch

http://cds.cern.ch/search?p=CERN-ACC-2014-0064

Grant Agreement No: 284404

HILUMI LHC FP7 High Luminosity Large Hadron Collider Design Study

Seventh Framework Programme, Capac i t ies Spec i f ic Programme, Research In f ras t ructu res, Col laborat i ve Pro ject , Des ign Study

DELIVERABLE REPORT

PRELIMINARY REPORT ON ENERGY DEPOSITION CALCULATIONS FOR THE

COLD POWERING SYSTEM

DELIVERABLE: D6.3

Document identifier: HILUMILHC-Del-D6-3-v1.0

Due date of deliverable: End of Month 30 (April 2014)

Report release date: 06/06/2014

Work package: WP6: Cold Powering

Lead beneficiary: INFN

Document status: Final

Abstract:

This document reports the results of the preliminary studies of energy deposition in order to evaluate the potential radiation damage from the High Luminosity LHC debris in the Superconducting (SC) Links of the cold powering systems for the High Luminosity upgrades. The evaluation of the particle fluencies, energy deposition, and displacements per atom (DPA) has been carried out in a very conservative configuration, putting the MgB2 cable, with its

Grant Agreement 284404 PUBLIC 1 / 13



Doc. Identifier: HILUMILHC-Del-D6-3-v1.0

Date: 06/06/2014

accurate composition, aside Q1 quadrupoles. The analysis shows a small amount of absorbed dose and DPA (about 30 kGy for the dose and 10-6 DPA, scaled at 3000 fb-1). Such values will not have serious impact on the performance of the superconducting links. Neither the neutron induced transmutation of 10B is a concern. The fluencies of the debris from the 7+7TeV p-p interaction have been evaluated in a probable layout of the superconducting links. Future work will be dedicated to more precise evaluation of the effect of the debris, by refining the geometry and installation layout. Copyright notice: Copyright © HiLumi LHC Consortium, 2012. For more information on HiLumi LHC, its partners and contributors please see www.cern.ch/HiLumiLHC The HiLumi LHC Design Study is included in the High Luminosity LHC project and is partly funded by the European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404. HiLumi LHC began in November 2011 and will run for 4 years. The information herein only reflects the views of its authors and not those of the European Commission and no warranty expressed or implied is made with regard to such information or its use.

Delivery Slip

Name Partner Date

Authored by F. Broggi, A. Bignami, C. Santini INFN 09/05/2014

Edited by F. Broggi INFN 19/05/2014

Reviewed by L. Rossi [Project coordinator] A. Ballarino [WP coordinator]

CERN 23/05/2014

Approved by Steering Committee 27/05/2014


http://www.cern.ch/HiLumiLHC




Date: 06/06/2014

TABLE OF CONTENTS

1. INTRODUCTION ........................................................................................................................................ 4

2. CABLE LAYOUT AND COMPOSITION ................................................................................................ 4

3. PARTICLE DEBRIS.................................................................................................................................... 6

4. ENERGY DEPOSITION AND DPA CALCULATION ........................................................................... 6 4.1 MgB2 cable aside Q1 (Near case) ...................................................................................................... 7 4.2 MgB2 cable at 1m from Q1 (far case) ................................................................................................. 8

5. MAGNESIUM DIBORIDE AND THERMAL NEUTRONS ................................................................... 9

6. TOWARDS THE FINAL GEOMETRY .................................................................................................. 10 6.1 Inner Triplet powering scheme and geometry implementation in FLUKA ....................................... 10 6.2 Particle fluencies in air at the location of the SC links .................................................................... 11

7. FUTURE PLANS / CONCLUSION.......................................................................................................... 13

8. REFERENCES ........................................................................................................................................... 13





Date: 06/06/2014

Executive summary This document summarizes the results of the studies so far performed for evaluating the effects of the particle debris from the 7+7 TeV p-p interaction in the High Luminosity configuration on the MgB2 superconducting (SC) links. Accurate material definition, according to the cable layout has been done. The particle fluence, at different locations of the SC links in the upgraded geometry is presented. Fluence, energy deposition and dose aside the first low beta quadrupole are presented too. The energy deposition and the induced DPA should not be a concern on the functioning of the SC links. Thermal neutrons have negligible effect on Boron.

1. INTRODUCTION Cold Powering of the LHC magnets foresees the removal of the power converters and distribution feedboxes on surface [1]. The connecting lines will be made of Magnesium Diboride (MgB2). The lines in the tunnel will be exposed to the debris from 7+7 TeV p-p interaction. The debris in the High Luminosity configuration and its effect on the MgB2 SC links in a possible configuration are evaluated. The effects of neutrons on the Boron consumption by thermal neutrons are evaluated and, being less than 1%, it is not a concern. The implementation of the layout of the SC links in the FLUKA [2],[3] code is well in progress.

2. CABLE LAYOUT AND COMPOSITION The link cold mass contains superconducting cables which are connected at one end, in the tunnel, to the Nb-Ti magnet bus-bar operated in liquid helium and the other end, at the surface (P1 and P5) or in a service tunnel (P7), to the bottom end of the current leads (CL). This CL end is maintained at a maximum temperature (TCL) of about 20 K - if MgB2 were to be used - or 30 K – if YBCO or Bi-2223 were to be used - in helium gas environment, see Figure 1 [4].

Figure 1 Cooling scheme of cold powering system





Date: 06/06/2014

The cable for the links [1] is shown in Fig. 2. The MgB2 wires (0.85 mm diameter) are shown in green color, while the stabilizing copper is in red. The stainless steel inner tubes are in grey, kapton insulation is in orange, while in white is the space for the helium gas cooling flow. The total diameter of the cable is about 65 mm.

Figure 2 SC link cable layout. Green MgB2, red Cu, orange kapton, grey stainless steel, white He gas.

According to this layout the material for the cable composition in the Monte Carlo simulation has been defined. The composition is shown in Tab. 1

Tab. 1 Material composition of the cable for the Monte Carlo simulations

MATERIAL

ATOM CONTENT

PARTIAL DENSITIES (g/cm3)

MAGNESIUM 0.1225 0.2192 BORON 0.24501 0.195

COPPER 0.48231 2.2563

HYDROGEN 2.03E-02 1.51E-03

CARBON 4.88E-02 4.31E-02

NITROGEN 4.07E-03 4.19E-03

OXYGEN 1.02E-02 1.20E-02

HELIUM 8.89E-03 2.62E-03

IRON 4.05E-02 0.16655

NICKEL 5.55E-03 2.40E-02

CHROMIUM 1.19E-02 4.55E-02

The resulting density of the cable is 2.97 g/cm3, with a radiation length of 4.846 cm.





Date: 06/06/2014

3. PARTICLE DEBRIS The particle debris coming out from the insertion quadrupoles has been determined in a 140 mm quadrupole aperture configuration. This will not be the final design one of 150 mm aperture, but at the time of the beginning the study was the only one available. We think that the larger aperture will not affect the results shown here. Anyway the 150 mm configuration will be examined as well. In Fig. 3 the distribution of the particles escaping from the first quadrupole is shown together

with the kinetic energy carried by the particles (from 1000 7+7 TeV p-p interaction).

Figure 3Number of particles laterally escaping from Q1 (left) and Total kinetic energy carried by each particle type (right).

As we can see the 68% of the kinetic energy is carried by neutrons, 17% by pions, 6% by protons and the 5% by photons. This fluence is in the 2π angle, all along the length of the Q1magnet, and only a small fraction of them will impinge the MgB2 cable. The slow neutron nuclear reaction cross section on the constituents of the cable is about some barns and this will not represent any problem. The only reaction of concern is the one on Boron-10 that has a cross section of some kbarns. The possible negative effects of this reaction will be examined in the following.

4. ENERGY DEPOSITION AND DPA CALCULATION The definitive layout will be frozen in the future, so, at the moment, we simulated the energy deposition in cables running parallel to Q1 (as a conservative hypothesis) located at different positions: - in contact with Q1 (near case) at 0°, 90°, 180° and 270° - at 1 m distance from the magnet (far case), at the same angular position.

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1000 7+7TeV p-p events1819624 particles16.8 TeV Kinetic Energy1.5E3 TeV Total Energy

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Date: 06/06/2014

Q1 is 8 m long starting at 23 m from the Interaction Point (IP), the MgB2 cable is 10 m long starting at 22 m from IP. The total dose in the MgB2 cable and the corresponding mean DPA value (averaged over the bin volume of 0.65x0.65x33.3 mm3) is shown in Table 2, for the two cases. The data are scaled to 3000 fb-1.

Tab. 2 Total dose and average DPA for the examined cases (data normalized at 3000 fb-1)

Near Far Cable Dose (kGy) ±

err% DPA±err% Dose (kGy) ±

err% DPA±err%

1 (θ=0°) 32.8 ± 0.5 2.3E-06 ± 0.4 7.1 ± 1.2 4.8E-07 ± 0.8

2 (θ=90°) 38.7 ± 0.3 2.5E-06 ± 0.3 7.6 ± 2.1 5.0E-07 ± 0.7

3 (θ=180°) 35.3 ± 0.6 2.4E-06 ± 0.4 6.5 ± 1.8 4.8E-07 ± 1.0

4 (θ=270°) 34.2 ± 0.5 2.3E-06 ± 0.2 7.4 ± 1.3 4.9E-07 ± 0.6 As we can see the values of dose and DPA are relatively small and should not endanger the functionality cables. Let’s remind that this configuration is a conservative one, being aside the first quadrupole. In section 6.2 the fluences after the separation dipole (D1) will be shown. In section 4.1 and 4.2 the energy deposition maps are shown.

4.1 MgB2 cable aside Q1 (Near case) In Figure 4 the energy deposition maps of the cables, averaged along z, are shown. The values are in GeV per cm3 per p-p event, and the scale is the same for all the plots.





Date: 06/06/2014

Figure 4 Energy deposition (GeV/cm3-event) maps in the cables (averaged over z). Top left cable

1,θ=0°; top right cable 2 θ=90°; bottom left cable 3 θ=180°; bottom right cable 4 θ=270°. (Bin dimension = 0.65x0.65x33.3 mm3). The scale are the same for the four plots.

The energy in cable 2 is slightly higher because of the vertical crossing angle of the primary protons.

4.2 MgB2 cable at 1m from Q1 (far case) In Figure 5 the energy deposition maps of the cables, averaged along z, are shown. The units are the same as in Figure 4.





Date: 06/06/2014

Figure 5 Energy deposition maps in the cables (averaged over z). Top left cable 1, θ=0°; top right cable 2, θ =90°; bottom left cable 3 θ =180°; bottom right cable 4 θ =270°. (Bin dimension = 0.65x0.65x33.3 mm3

The energy deposed in this configuration is, of course, less than in the previous case, being the cable far away from the magnet.

5. MAGNESIUM DIBORIDE AND THERMAL NEUTRONS The natural isotopic composition of Boron is about 80% of 11B and 20% of 10B. The 10B has a very high slow neutron cross section for the reaction α+→+ LinB 7

3105 , being about 4×103 barn

at room temperature (En=0.025 eV) and 1.5×104 barn at 20 K (En=0.0017 eV) as shown in Figure 6.

Figure 6 Cross section for 10B(n,α) reaction at room temperature.

A concern may arise on the consumption of Boron and its changing into Lithium during the exposition to the neutron debris during the LHC life. We assume the SC links as a pure bulk of boron running aside the first quadrupole, working at 20K (σ=1.5 1.5×104 barn), with an integrated (on 3000 fb-1) neutron integrated fluence of





Date: 06/06/2014

Nn=1021. The neutrons impinge perpendicularly to the axis of the cable cylinder, the relative boron consumption is: Where:

- intN is the number of α+→+ LinB 73

105 interactions

- ettBN

argis the number or Boron atoms in the SC links

- nN is the number of incident neutrons

- σ is the reaction cross section - Bn and

Bn10 are the atomic density of the natural B and 10B atoms

- d and l are the diameter and length of the SC links cable

In this calculation, we have done two other important conservative approximations: - We considered a neutron fluence of 1021 neutrons, but this is the whole neutron amount

escaping from the magnet iron yoke towards the external air, actually the number of neutron impinging on the SC links will be much lower.

- All the neutrons are considered thermal (the mean kinetic energy of the neutron debris, in this configuration is of the order of 8 MeV)

- The cable is considered as a bulk of pure boron. But from the actual cable composition as from Table 1 the 10B content is only about 5% of the cable. So the actual consumption is about 0.003 %.

For these reasons the boron transmutation will not be a problem at all for the whole operation of the life of LHC.

6. TOWARDS THE FINAL GEOMETRY The definitive evaluation of the energy deposition and DPA in the SC links depends on the LHC geometry and on the layout of the powering for the triplet.

6.1 Inner Triplet powering scheme and geometry implementation in FLUKA The baseline powering scheme is shown in Figure 7 [5].

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Date: 06/06/2014

Figure 7 Powering scheme for the inner triplet [5].

In the present layout configuration, the SC links will arrive in the tunnel from the surface and will be connected to the Nb-Ti bus bar at about 80 m from the interaction point (IP), after the separating dipole D1, at the location indicated with SM (Shuffling Module) in Figure 8 [6].

Figure 8 Layout of the Hi-luminosity insertion [6]. An evaluation of the particle fluencies in the region around 80 m from the IP has been carried out, implementing in the official CERN FLUKA geometry the “subregion” aside the beam line where the SC links will be located. In addition the new layout for the inner triplet has been implemented in the FLUKA geometry, i.e. - quadrupole aperture of 150 mm - new dimensions of the tungsten absorbers (thicker under Q1) - octagonal beam screen.

6.2 Particle fluencies in air at the location of the SC links The debris in the possible location of the SC links is mostly composed by photons and low energy neutrons, because of the shielding effect of the triplet magnets.





Date: 06/06/2014

In Figure 9 the fluencies of the particles (neutrons, protons, pions, and photons respectively) in the air surrounding the location of the SC links are shown. The central white hole is the beam pipe. The cross section is taken at the location indicated with SM in Figure 4 (integrated over z at 80-84 m from IP).

Figure 9 Particle fluencies after the separation dipole D (integrated over z) at 80-84 m from IP. Top left

neutrons, top right protons, middle left π+ middle right π-, bottom photons.





Date: 06/06/2014

7. FUTURE PLANS / CONCLUSION The energy/dose deposition and the DPA in the MgB2 cables, in conservative hypothesis (just aside Q1) are not a concern over the whole lifetime of the SC links (3000 fb-1). We can state that the Boron consumption by the slow neutron is negligible. The geometry implementation on the official FLUKA LHC layout is well in progress and will continue as the parameter and layout will be defined. Preliminary simulations of the debris at the probable location of the SC links have been performed.

8. REFERENCES [1] A. Ballarino, Development of Superconducting Links for the LHC Machine, EEE/CSC & ESAS SUPERCONDUCTIVITY NEWS FORUM (global edition), October 2013. [2] A. Fasso, A. Ferrari, J. Ranft, and P.R. Sala, "FLUKA: a multi-particle transport code", CERN-2005-10 (2005), INFN/TC_05/11, SLAC-R-773. [3] G. Battistoni, S. Muraro, P.R. Sala, F. Cerutti, A. Ferrari, S. Roesler, A. Fasso`, J. Ranft, "The FLUKA code: Description and benchmarking", Proceedings of the Hadronic Shower Simulation Workshop 2006,Fermilab 6-8 September 2006, M. Albrow, R. Raja eds., AIP Conference Proceeding 896, 31-49, (2007). [4] A. Ballarino, Preliminary report on cooling options for the cold powering system, June 2013, http://cds.cern.ch/record/1557215/files/CERN-ACC-2013-010.pdf [5] A. Ballarino, Presentation at 4th LHC Parameters and Layout Committee, 26th March 2013, https://indico.cern.ch/conferenceDisplay.py?confId=239311 [6] E. Todesco, presentation at L-LHC-PLC, March 2013, https://indico.cern.ch/conferenceDisplay.py?confId=239311


http://cds.cern.ch/record/1557215/files/CERN-ACC-2013-010.pdf

https://indico.cern.ch/conferenceDisplay.py?confId=239311

https://indico.cern.ch/conferenceDisplay.py?confId=239311

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