EUROPEAN LABORATORY FOR PARTICLE PHYSICS

INTERNAL REPORT CERN/TIS–RP/IR/98–10

THE RADIATION ENVIRONMENTAT THE LHC INSERTION POINT 2 (ALICE)

IN BEAM LOSS SITUATIONS

S. Roesler and G. R. Stevenson

Abstract

The radiological safety of the civil engineering for the various shafts at LHC Point 2 (PX24,PM25 and PGC2) in accidental beam loss situations is studied. Radiation fields induced by the lossof a full LHC beam at different locations in the beam pipe are calculated using the Monte-Carlocode FLUKA. The calculations are based on a detailed geometrical treatment of the installations atPoint 2 including the ALICE detector and the inner quadrupole triplet of the low-� insertion. Itis shown that the ambient dose equivalent values around the PX24 and PM25 shafts and, after aslight modification of the present shielding, around the PGC2 shaft can be expected to be belowthe relevant CERN limits.

CERN, Geneva, Switzerland7 April 1998

1 Introduction

At LHC Point 2 there are three shafts situated in the proximity of the collider (see also Figs. 1 and2):

� PX24: The main access shaft, 23 m in diameter, provides a 15 � 15 m2 opening for the in-stallation of magnets and detector units and will accommodate the counting rooms of theALICE experiment. The LHC beam line will pass directly through the bottom part of theshaft.

� PM25: This shaft, 8.4 m in diameter, allows access to the machine bypass area and, viatwo access tunnels on either side of the ALICE detector, also a second access to the mainexperimental cavern.

� PGC2: The PGC2 shaft is located downstream� of the ALICE detector at the junction of themachine bypass tunnel and the beam tunnel and has a diameter of 12 m. The beam line ofthe LHC will pass close to the bottom part of this shaft.

Any accidental loss of the LHC beam causing exceptionally high radiation fields around theaccelerator ring might result in an increased radiation level in underground areas occupied bypersonnel and, via the three shafts, also above ground.

According to the CERN Radiation Safety Manual [1, 2] the counting room area inside thePX24 shaft is classified as Controlled Radiation Area (maximum allowed ambient dose equiva-lent: 50 mSv), the surface areas around the PX24 and PM25 shafts are Supervised Radiation Areas(2.5 mSv) and the surface area around the PGC2 shaft a Non-Designated Radiation Area (0.3 mSv).In order keep the radiation levels below these dose limits detailed studies of beam loss situationsare required and sufficient shielding has to be designed and installed.

Results of earlier calculations of the radiation fields at Point 2 during normal collider operationand in beam loss situations are discussed for the PX24 shaft in Refs. [3] and [4] and for the PGC2shaft in Ref. [5] (see also [6]). No similar studies existed for the PM25 shaft.

Recently the civil engineering of the PGC2 shaft, the upstream beam shield and the down-stream access tunnel between the machine bypass area and the main experimental cavern waschanged, which made an update on the calculations necessary.

Here we report on studies of the radiation environment in the three shafts after accidentallosses of the full LHC beam. These calculations are based on the latest design drawingsy and ona very detailed treatment of the geometry of Point 2, now including also the ALICE detector andthe inner quadrupole triplet (optics version 5).

�In the following we use “upstream” and “downstream” as defined by the clockwise circulating beam, e.g. theALICE forward muon spectrometer points “downstream”.

yOf particular importance for the present studies are: (i) Access between US/UX25, date: 1997-07-24, (ii) upstreambeam shield and blockhouse, date: 1997-09-01.

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2 Details of the calculations

All calculations were carried out using the ‘97 version of the particle interaction and transport codeFLUKA (see [7, 8] and references therein). The FLUKA code has been extensively benchmarkedagainst experimental data over a wide energy range for both hadronic and electromagnetic show-ers [7, 8, 9, 10, 11, 12]. For the present study FLUKA has been used to simulate all componentsof the particle cascades in the inner triplet, detector and shielding components as well as in thecaverns and shafts from TeV-energies to that of thermal neutrons.

In the following we summarize a few aspects of the calculations which are of particular im-portance to the radiation studies discussed in this report.

Geometry: The complex geometry of the caverns, tunnels, shafts, the ALICE detector [13]and the inner quadrupole triplet [14] has been modelled in detail using of the ALIFE geometryeditor [15]. The geometry is described in a right-handed orthogonal system with its origin at theALICE interaction point, x as the vertical axis and y pointing towards the centre of the LHC ring.Hence the z axis coincides with the beam. A horizontal section through the FLUKA geometryat the level of the beam line is shown in Fig. 1. The positions of the three shafts are indicatedby dashed boxes. Vertical sections through the shafts are shown in Fig. 2. All lines representboundaries between different materials as used in the calculations. Particle-backscattering fromconcrete walls of caverns and shafts is taken into account by approximating the walls by a layer ofconcrete (in most cases of a thickness of 30 cm). All regions behind this layer are treated as ”blackholes”, i.e. particles which would penetrate further into the rock are not considered. The innerquadrupole triplets of the low-� insertion are situated at a distance between about 21 m and 55 mon either side of the interaction point. As will be discussed further below, their inclusion into thegeometry is important for an adequate description of beam loss situations. An enlarged sectionthrough the FLUKA geometry of one of the quadrupole magnets is shown in Fig. 3.

Chemical composition of concrete: All concrete shielding components were assumed tohave a density of 2.35 g/cm3 and the following chemical composition (the values in brackets givethe corresponding mass fractions): oxygen (51.1%), silicon (35.8%), calcium (8.6%), aluminium(2.0%), iron (1.2%), hydrogen (0.6%), carbon (0.4%) and sodium (0.3%).

Particle energy thresholds: Lower thresholds for particle transport were set to 10 MeV forhadrons except neutrons which were followed down to thermal energies. In order to keep theCPU-time within reasonable limits and to obtain results of still sufficient statistical significancethe electromagnetic component of the particle cascade which accounts for only up to 30% of thetotal dose equivalent in the shafts [16] was not calculated.

Biasing: In order to enhance the statistical significance of the results in or behind regions ofhigh attenuation and inside the shafts, significant use was made of region-importance biasing.

Ambient dose equivalent: Ambient dose equivalent due to neutrons, protons and pions hasbeen directly derived from their fluences by multiplying the latter by energy dependent conver-sion factors [17].

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3 The radiation environment in the shafts at the ALICE experiment

In the following results on dose levels which can be expected in the three shafts at Point 2 inaccidental beam loss situations are presented. In all cases it has been assumed that one of thecirculating beams of 4:7� 10

14 protons [18] is fully lost by hitting the beam pipe.z

3.1 The main access and counting room shaft PX24

The dose level in the counting room area above the shield plug depends strongly on the positionof the loss point. “Worst case” scenarios can be expected if the beam is lost inside the inner triplet.Here, materials of rather high density are placed very close to the beam pipe and cause thereforea strong particle cascade. The radiation level has been studied for different loss points. In thefollowing we report on the results for two beam loss positions which might lead to the highestdose values in the PX24 shaft.

Beam loss position 1 (z = �2600 cm): In this case the clockwise circulating beam is lostinside the innermost quadrupole Q1 at a distance of 26 m from the interaction point. For thisbeam loss position the cascade develops its lateral maximum about in the centre of the PX24shaft. In Fig. 4 the ambient dose equivalent values normalized per lost proton are shown for avertical longitudinal section containing the beam line. With 4:7 � 10

14 protons per circulatingbeam the dose limit of 50 mSv for the counting room area translates into a constraint of about1 � 10

�4 pSv per lost proton. For the shown section the dose equivalent values above the shieldplug are well below this limit. Furthermore the labyrinth for the ventilation system providessufficient shielding against radiation streaming through the duct. The vertical transverse sectionat z = �25 m (longitudinal position of the cryogenics hole in the shield plug) shown in Fig. 5demonstrates the effect of the cable ducts and the cryogenics hole on the radiation fields abovethe plug. Whereas the design for the cable ducts meets the radiation safety requirements, the doseequivalent values above the cryogenics hole might slightly exceed the limit of 50 mSv (keepingin mind that a 30% contribution from the electromagnetic cascade has to be added to the shownvalues). Finally in Fig. 6 we show dose equivalent values for a horizontal section through the shaftat a level of about 1 m above the main part of the plug. The slightly enhanced values in the centreof the shaft clearly reflect the longitudinal position of the loss point.

Beam loss position 2 (z = �3390 cm): The study of a beam loss position in between the twolift shafts might be of particular interest since in addition to the leakage through the top part of thebeam shield (thickness: 1.6 m) there might be a contribution streaming up the lift shafts. For thisreason we show in Fig. 7 the dose equivalent values for the same vertical longitudinal section asin Fig. 4 but here for a loss point at a distance from the interaction point of 33.9 m. As compared tothe previous loss position the air duct labyrinth is now less efficient since it provides less shieldingagainst particles of higher energies which move predominantly into forward direction. Hence, thedose level on top of the main part of the plug is similar to the one in the previous case but the doselevel above the ventilation duct is slightly higher (but still below the limit of 1�10

�4 pSv/proton).The dose equivalent values inside the lift shafts are shown for a vertical transverse section in Fig. 8.The right-left asymmetry is due to the position of the loss point which was assumed to be at x = 0

zIn the FLUKA calculations the starting point of the particle cascade was assumed to be at a radial distance to thez-axis equal to the average value of the inner and outer radius of the beam pipe at the considered longitudinal (z-)position. The “source”-protons were assumed to move parallel to the z-axis (“worst case”).

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and negative y. Although the figure might suggest that there is a considerable contribution to thedose in the counting rooms from radiation streaming up the lift shafts it should be mentioned thatthe lift shafts will finally be shielded by 40 cm of concrete against the counting room area whichhas not been taken into account in the calculations.

The ambient dose equivalent values averaged over the whole shaft for the above beam losspositions are given in Fig. 9. Here the dose equivalent values are shown for the loss of a fullLHC beam. The two dotted vertical lines indicate the level of the outer surface of the shaft plugand the ground level. The horizontal dash-dotted and dashed lines represent the dose constraintsfor the counting rooms as a Controlled Radiation Area (50 mSv) and for the surface buildings asa Supervised Radiation Area (2.5 mSv), respectively. The figure shows that the dose equivalentvalues which can be expected in accidental beam loss situations are lower by at least a factor of 1.5than the corresponding maximum allowed values. This conclusion even holds for an area abovethe ventilation duct where the radiation level is in general higher than the average (see Fig. 9).

Finally, a loss in the beam pipe of the lightly shielded section around the forward muon spec-trometer must be considered as well since it might also lead to an increased radiation level aroundPX24. Results of calculations for such a loss point are shown in Fig. 10. In order to save CPU-timethe particle transport was strongly negatively biased in regions which were not of interest, as forinstance the L3-magnet. Therefore any values inside this magnet do not reflect the real situation.Comparing the dose equivalent values around PX24 with those obtained in the two situationsdiscussed previously it is interesting to note that although the dose values underneath the shieldplug are higher in the present case there is now a strong absorption in the concrete plug. This canbe attributed to the fact that the radiation reaching the PX24 is directed mainly upstream with onlya very soft component directed upwards. This soft component is able to penetrate the ventilationduct but is strongly absorbed in the plug itself. As can be seen from the figure, the radiation levelin the counting room area is still below the 1�10

�4 pSv/proton limit. The dose equivalent aroundthe ventilation duct however might reach the highest values for this beam loss situation. Never-theless we consider the present shielding design to be sufficient since the dose values do still notexceed the limits and in addition there are no barracks or staircases directly above the duct.

It should be mentioned that the dose equivalent values obtained for the PX24 shaft in thiswork cannot be directly compared to the ones given in [3, 4] since the latter were calculated fora different beam shield thickness as well as simplified assumptions for the geometry of the innerquadrupole triplets, the shield plug and the ventilation duct.

3.2 Attenuation in PM25

Increased radiation levels in the PM25 shaft might be caused if the LHC beam is lost at positionsclose to the entrances of the up- and downstream access tunnels which connect the machine by-pass region with the main experimental cavern (see Fig. 1).

Downstream beam loss: Parts of the forward muon spectrometer, in particular the dipolemagnet and the muon absorber, already provide a certain shielding of the main cavern againstradiation from losses in the beam pipe. The worst case might be reached if the beam is lost inthe lightly shielded section in between the magnet and the absorber. Since this part of the beampipe is not exactly in front of the access tunnel but slightly shifted downstream we assumed thatthe anticlockwise circulating beam is lost right behind the muon absorber at z = 14 m. In Fig. 11the dose equivalent distribution around the loss point, in the access tunnel and in the machine

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bypass area is shown for a horizontal cut containing the beam line. Particles possibly penetratingthrough the rock between UX25 and the bypass area (thickness: approx. 4 � 5 m) have not beenconsidered since their contribution is assumed to be negligible. The dose equivalent values in thePM25 shaft are given in Fig. 12. Here the dose constraint is the 2.5 mSv limit for the building aboveground (Supervised Radiation Area). This limit translates into about 5:3 � 10

�6 pSv/proton withcan directly be applied to the plotted values. The graph given in Fig. 13 showing the average doseequivalent in the shaft as function of the height demonstrates that this constraint is fulfilled withthe present design. The radiation level caused by the hadronic part of the cascade above groundis lower than the dose limit by almost one order of magnitude.

Upstream beam loss: This situation even improves for losses upstream of the detector sincehere the beam pipe is shielded with concrete of 1.6 m thickness and the cross-sectional area ofthe upstream access tunnel is much smaller. However this might be somewhat compensated bya stronger cascade caused by the inner quadrupole triplets. Results are shown for a horizontalsection in Fig. 14. Comparing this figure with the situation shown in Fig. 11 it can be clearly seenthat now the dose equivalent at the PX24 entrance of the access tunnel is already down at valueswhich are in the previous situation only reached inside the bypass area. We have therefore notattempted to obtain better statistics for the dose equivalent in the bypass area.

In summary, a downstream beam loss inside the forward muon spectrometer might causedose equivalent values at the US25 entrance to the UX25-US25 access tunnel which are higher bytwo orders of magnitude than those at the US25 entrance to the PX24-US25 tunnel for upstreamlosses. Radiation leakage through the rock between PX24 and UL24 has not been studied here(see [4] for a discussion on this subject). The rock provides an additional shielding of at least onemetre resulting in dose values inside UL24 which are already much lower than those at the US25entrance in the downstream loss situation.

3.3 Attenuation in PGC2

In case of beam loss in the junction cavern UJ26 between the machine bypass and the beam tunnelthe dose values inside PGC2, which is situated above this junction, might increase considerablydue to two contributing sources:

� particle cascades penetrating the ceiling of UJ26,

� radiation streaming through the access tunnel connecting PGC2 and UJ26.

Whereas the first is similar for any loss position inside the quadrupole magnet Q3, the secondcontribution is most pronounced if the loss position is in front of the entrance to the access tunnel.Therefore we assume in the following that the clockwise circulating beam is lost at z = 46 mclosest to the entrance. The horizontal cut in Fig. 15 shows the average dose equivalent at thelevel of the beam resulting from the loss of one proton.

In the following we denote the civil engineering of the PGC2 shaft and its bottom part datedDec. 1987 by “Layout 0”. Any modifications proposed below are based on results obtained withthis layout. The in course of this study modified layout will be called “Layout 1”.

Initial situation (Layout 0): Results obtained with the initial layout are shown in Fig. 16 fora vertical section through the vertical part of the access tunnel. Both sources mentioned above

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contribute significantly and cause dose equivalent values above ground which exceed the limitfor Non-Designated Radiation Areas (0.3 mSv or 6� 10

�7 pSv/proton) by more than one order ofmagnitude. It follows that the thickness of the concrete shield above UJ26 has to be increased andthat a different solution for the access tunnel has to be found. It is not sufficient to increase theshield thickness only and to leave the tunnel layout unmodified (detailed calculations exist butare not shown here).

Proposed modifications (Layout 1): We propose to increase the top shield up to a levelof 10 m above beam line and to add a further bend to the labyrinth as can be seen from thefollowing figures. Fig. 17 shows (for the same section as in the previous figure) the dose equivalentdistribution in the shaft and above ground after the modifications. The modifications proposedfor the tunnel can be seen in Fig. 18 which shows a vertical, but now longitudinal section throughPGC2 and the access tunnel at y = �6:7 m. Finally, we present in Fig. 19 the dependence ofthe average dose equivalent in the PGC2 shaft on the height for both layouts. The ground leveland the dose equivalent limit to be met above ground are again indicated by dotted vertical anddashed horizontal lines, respectively. With the proposed modifications the dose equivalent aboveground will be lower than the safety limit by at least a factor of 1.5 in any beam loss situation.

4 Summary and conclusions

The present report summarizes a comprehensive study of the radiation levels which have to beexpected in the shafts at Point 2 and at ground level after the loss of a full LHC beam in the beampipe.

Ambient dose equivalent distributions were obtained from hadron fluences calculated for dif-ferent beam loss scenarios with the Monte-Carlo code FLUKA. For the first time the calculationswere based on a very detailed treatment of the geometry of the experimental site including theALICE detector and the inner quadrupole triplets. It has been found that the strength of the radi-ation field resulting from beam losses inside inner quadrupole triplets closely resembles that onewhich would be obtained with an “optimum target” [19]. This underlines the importance of anadequate treatment of the material distribution close to the beam pipe in beam loss studies.

The present design of the beam shield and the shield plug inside PX24 meets the radiationsafety requirements for the counting rooms as Controlled Radiation Areas and the surface build-ing as Supervised Radiation Areas. Likewise, the latter limit is fulfilled for the PM25 shaft.

With the present design of the bottom part of the PGC2 shaft the dose level above groundwould exceed the limit for a Non-Designated Radiation Area by more than an order of magnitude.As shown in this report this can be avoided by increasing the thickness of the shielding betweenUJ26 and PGC2 and by modifying the labyrinth for the UJ26-PGC2 access.

Acknowledgments

We would like to thank G. Chabratova, I. Dawson, L. Leistam, A. Morsch and B. Pastircak formany discussions. We are grateful to A. Fasso and A. Ferrari for providing the FLUKA code and to

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I. Dawson and A. Morsch for providing the FLUKA geometry of the inner triplets and the ALICEdetector.

References

[1] M. Hofert and G. R. Stevenson, Design limits for doses and dose rates for beam operation at theLHC. CERN Internal Report TIS–RP/IR/95–04 (1995).

[2] Radiation Protection Group, Radiation Safety Manual 1996, CERN (1996).

[3] G. Chabratova, W. Klempt, L. Leistam and N. Slavin, The radiation environment of the ALICEexperiment. ALICE Internal Note, ALICE/95-41 (1995).

[4] G. Chabratova and L. Leistam, Estimation of the radiation environment and the shielding aspectsfor the Point 2 area of the LHC. (1997).

[5] E. Wallen and G. R. Stevenson, Shielding properties of the PGC2 shaft at the ALICE experiment.CERN Internal Report TIS–RP/IR/97–13 (1997).

[6] The ALICE Collaboration, Technical proposal for a large ion collider experiment at the CERN LHC.CERN/LHCC/95-71 (1995).

[7] A. Ferrari, T. Rancati and P. R. Sala, FLUKA applications in high energy problems: from LHC toICARUS and atmospheric showers. In Proceedings of The Third Workshop on Simulating Accelera-tor Radiation Environments (SARE-3), KEK, Tsukuba, Japan, 1997, p. 165, 1997.

[8] A. Fasso, A. Ferrari, J. Ranft and P. R. Sala, New developments in FLUKA modelling of hadronicand EM interactions. In Proceedings of The Third Workshop on Simulating Accelerator RadiationEnvironments (SARE-3), KEK, Tsukuba, Japan, 1997, p. 32, 1997.

[9] P. A. Aarnio, A. Fasso, A. Ferrari, H.-J. Mohring, J. Ranft, P. R. Sala, G. R. Stevenson andJ. M. Zazula, FLUKA: hadronic benchmarks and applications. In Proceedings of the InternationalConference on Monte-Carlo Simulation in High Energy and Nuclear Physics, MC’93, Tallahas-see, U.S.A., 1993 (P. Dragovitsch, S. L. Linn and M. Burbank, Eds.), p. 88, World Scientific,Singapore, 1994.

[10] C. Birattari, E. De Ponti, A. Esposito, A. Ferrari, M. Magugliani, M. Pelliccioni, T. Rancatiand M. Silari, Measurements and Simulations in High Energy Neutron Fields. In Proceedings ofthe 2nd Specialists’ Meeting on Shielding Aspects of Accelerators, Targets and Irradiation Facilities,CERN, Geneva, Switzerland, 1995, p. 171, published by OECD Nuclear Energy Agency,1996.

[11] A. Ferrari, P. R. Sala, R. Guaraldi and F. Padoani, An improved multiple scattering model forcharged particle transport. Nucl. Instrum. Meth. B71 (1992) 412.

[12] C. Birattari, E. De Ponti, A. Esposito, A. Ferrari, M. Pelliccioni and M. Silari, Measurementsand characterization of high-energy neutron fields. Nucl. Instrum. Meth. A338 (1994) 534.

[13] A. Morsch, private communication (1998).

[14] I. Dawson, private communication (1998).

[15] A. Morsch, ALIFE: A geometry editor and parser for FLUKA, November 1997.

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[16] H. Nakashima, M. Huhtinen and G. R. Stevenson, Estimations of the shielding wall thicknessfor the LHC-B detector. CERN Internal Report TIS–RP/IR/96–30 (1996).

[17] A. V. Sannikov and E. N. Savitskaya, Ambient dose and ambient dose equivalent conversion fac-tors for high-energy neutrons. CERN Divisional Report TIS–RP/93–14/PP (1993).

[18] M. Hofert, K. Potter and G. R. Stevenson, Summary of design values, dose limits, interaction ratesetc. for use in estimating radiological quantities associated with LHC-operation. CERN InternalReport TIS–RP/IR/95–19.1 (1995).

[19] S. Roesler and G. R. Stevenson, Radiation studies for the design of the main shielding wall of theLHC-B experiment. CERN Internal Report TIS–RP/IR/97–31 (1997).

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Figure 4: Ambient dose equivalent values in the counting room shaft PX24 which are caused bybeam loss interactions at z = �2600 cm. The ground level, 45 m above the beam line, is indicatedby a solid line.

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Figure 5: As in Fig. 4, here shown for a vertical transverse section through the PX24 shaft atz = �2500 cm demonstrating the radiation leakage through the cable ducts and the cryogenicshole.

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Figure 6: Horizontal section through the PX24 shaft at a vertical distance from the beam pipe ofabout 25 m (first floor of the counting room barracks). The beam loss position was assumed to beat z = �2600 cm.

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Figure 7: Ambient dose equivalent values in the counting room shaft PX24 which are caused bybeam loss interactions in between the two lift shafts (loss point: z = �3390 cm).

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Figure 8: Vertical transverse distribution of ambient dose equivalent caused by the loss of oneproton of 7 TeV at z = �3390 cm inside PX24 in between the two lift shafts.

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Figure 9: The dependence of the ambient dose equivalent in the PX24 shaft on the vertical distancefrom the beam pipe is shown for two different beam loss positions. In addition to the valueobtained by averaging over the whole shaft this dependence is also given for the average doseequivalent above the ventilation duct (only for the loss point z = �3390 cm). The level of theouter surface of the shaft plug and the ground level are indicated by dotted lines. The designlimits appropriate to a Supervised Radiation Area (2.5 mSv) and to a Controlled Radiation Area(50 mSv) are indicated by dashed and dash-dotted lines, respectively.

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Figure 10: Ambient dose equivalent in the UX25 cavern and the PX24 shaft after a loss of a 7 TeVproton in the beam pipe between the dipole magnet and the muon absorber (z = 1450 cm). Thedistribution is shown for a longitudinal section containing the beam pipe.

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Figure 11: Distribution of ambient dose equivalent around the beam loss point inside the UX25and US25 caverns and the downstream access tunnel after the loss of one proton of an energy of7 TeV in the beam pipe. The anticlockwise circulating beam was assumed to be lost in the lightlyshielded section of the pipe between the dipole magnet and the muon absorber (z = 1400 cm).The location of the PM25 shaft above the US25 cavern is indicated by a shaded area.

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Figure 12: Average ambient dose equivalent in the PM25 shaft after a beam loss at z = 1400 cm.The ground level, 45 m above the beam line, is indicated by a solid line.

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Figure 13: Average ambient dose equivalent in the PM25 shaft after the loss of one LHC beam of4:7 � 10

14 protons in the beam pipe at z = 1400 cm. Calculated values are shown as function ofthe vertical height in the shaft. The vertical dotted line indicates the ground level. The maximumdose equivalent value allowed for a Supervised Radiation Area (2.5 mSv) is indicated by a dashedline.

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Figure 14: Ambient dose equivalent values caused by secondary hadrons in the UX25 cavern, thePX24 shaft and in the US25-PX24 access tunnel after the loss of one proton of 7 TeV inside theinner triplet at z = �2500 cm.

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Figure 15: Distribution of ambient dose equivalent around the loss point in the UJ26 junction. Theloss point was assumed to be in the beam pipe inside the inner triplet quadrupole which is locatedin front of the opening of the access tunnel (z = 4600 cm).

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1.0E+02 1.0E+01 1.0E+00 1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09

(PGC2 layout 0)

Figure 16: Ambient dose equivalent values around the loss point in the UJ26 junction, insidethe UJ26-PGC2 access tunnel and in the PGC2 shaft after the loss of one 7 TeV proton. The losspoint was assumed to be in front of the opening of the access tunnel at z = 4600 cm. The spatialdose equivalent distribution is shown for a vertical transverse section through the geometry atz = 5140 cm (centre of the vertical part of the access tunnel). The ground level, 45 m above thebeam line, is indicated by a solid line.

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0

1000

2000

3000

4000

5000

-1500 -1000 -500 0 500 1000 1500

1.0E+02 1.0E+01 1.0E+00 1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09

(PGC2 layout 1)

Figure 17: As in Fig. 16, here for the modified layout.

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0

1000

2000

3000

4000

5000

3500 4000 4500 5000 5500 6000 6500

1.0E+02 1.0E+01 1.0E+00 1.0E-01 1.0E-02 1.0E-03 1.0E-04 1.0E-05 1.0E-06 1.0E-07 1.0E-08 1.0E-09

(PGC2 layout 1)

Figure 18: Ambient dose equivalent values are shown for a vertical longitudinal section throughthe modified layout at a distance of 670 cm from the beam line (section through most parts of theaccess tunnel).

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Figure 19: Average ambient dose equivalent in the PGC2 shaft after the loss of one LHC beam of4:7 � 10

14 protons in the beam pipe at z = 4600 cm. Calculated values are shown for the initiallayout (layout 0) and the modified layout (layout 1) of the bottom part of the PGC2 shaft (see text).The vertical dotted line indicates the ground level. The maximum dose equivalent allowed for aNon-Designated Radiation Area (0.3 mSv) is indicated by a dashed line.

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