Report
2005-05-12
Ekaterini.Tsoulou@cern.ch
Estimate of the radiation levels at the Wire Scanner position in IR4 and
draft shielding scenarios.
K. Tsoulou, AB-ATB
Summary
The Wire Scanner in IR4 is planned to be installed at the dogleg bends in IR4. Taking into
account the high radiation levels found by a previous study, a few shielding scenarios are
studied. This is a quick study and the results shown are indicative for further action to be
taken.
1.
Introduction
Following the studies for the radiation levels and shielding in IR4 for the BDI
optics, there was a necessity to calculate the dose levels at the position of the Wire Scanner
(WS). This device monitors the beam profile and is going to be installed at the dogleg bend
between the magnets D3 and D4, around 4 m after the end of the enlarged beam pipe. From
the simulation results presented in [1] (see also Figure 1) the doses expected at the position
of interest are a few kGy/year.
Some rough shielding solutions are presented in the following paragraph, but it
seems that a more detailed study is necessary to be done in order to reduce the radiation
levels at acceptable values, i.e. 10-20 Gy/year [2]. The scenarios shown herein are draft
shielding studies indicative of the situation in the region of interest.
2.
Simulation Conditions
For the current study the FLUKA Monte Carlo simulation code was used [3],[4].
The conditions are described in more details in reference [1]. For this study and in order to
speed up the calculations only the residual gas interactions in the beam pipes were taken
into account. Then the results were scaled in order to estimate the total radiation levels
expected according to a previous finding that the beam lines contributes to the 62% of the
total radiation created in IR4 [5]. Energy deposition (dose in Gy) of all particles was scored
in a mesh covering the geometry of interest. Scorings were made in air.
Figure 1
3.
Dose rate in Gy/y around the shielding proposed for the BDI telescope. This
vertical cut is at 22cm from the centre of the two beam lines and a mean of the
values 0-50cm from the centre of the beam line. The dose level in the BSRT tube
is estimated to be a few Gy/y.
Shielding Studies
As a first approach to the problem the following scenarios were studied in order to
reduce the radiation levels at the position of the Wire Scanner. The first one takes into
account two shielding walls on both sides of the device (towards D3 and D4) while the rest
serve to an attempt to isolate the contribution of the radiation coming only from beam1 or
beam2.
Shielding Scenario1: The Wire Scanner is in between two large shielding blocks of
either 1m (case A) or 2m (case B) thick. A thinner concrete slab of 30cm thick was used on
either inner side of the shielding to collect the lower energy neutrons.
Shielding Scenario2: A 2m thick shielding block was used followed by a 30cm
thick concrete slab only from the side of D3. To further protect the Wire Scanner
electronics a 5cm horizontal iron slab was situated 50cm below the beam line level at the
currently foreseen WS position.
Shielding Scenario3: A 2m (case A) or 4m (case B) thick shielding block was used
followed by a 30cm thick concrete slab only from the side of D4. To further protect the
Wire Scanner electronics a 5m horizontal iron slab was situated 50cm below the beam line
level at the currently WS position.
For the scenarios 2 and 3 extra shielding was used at the end of the enlarged beam
pipes consisting of a lead block covering the conical connector of the two pipes supported
by an iron base.
Figures 2-4 show schematically the different shielding scenarios used, as described
above.
A
B
Figure 2
Shielding Scenario1: Two shielding walls on either side of the Wire Scanner
device consisting of 1m (panel A) and 2m (panel B) iron. Inside the shielding
two 30cm concrete slabs were used to reduce the low energy neutron flux.
Figure 3
Shielding Scenario2: A 2m thick shielding block was used followed by a 30cm
thick concrete slab only from the side of D3. To further protect the Wire Scanner
electronics a 5cm horizontal iron slab was situated 50cm below the beam line
level at the currently foreseen WS position. The extra shielding at the end of the
enlarged beam pipe was also implemented consisting of a lead block covering the
conical connector of the two pipes supported by an iron base.
A
B
Figure 4
4.
Shielding Scenario3: A 2 m (panel A) or 4 m (panel B) thick shielding block was
used followed by a 30 cm thick concrete slab only from the side of D4. To
further protect the Wire Scanner electronics a 5cm horizontal iron slab was
situated 50cm below the beam line level at the currently WS position. The extra
shielding at the end of the enlarged beam pipe was also implemented consisting
of a lead block covering the conical connector of the two pipes supported by an
iron base.
Results
Figures 5-7 show the results obtained for the previous shielding scenarios. As it can
be seen by a fast comparison with Figure 1 the situation has not ameliorated, since the dose
levels have remained at around 1 kGy/year. This is due to the position of the WS, very
close to the beam: especially at the dogleg bends the residual gas interactions create high
energy secondary particles which are hard to shield. In Figure 8 the energy spectra of the
particles scored at the position of the WS are shown. Hadrons reach energies of up to a few
TeV.
A
B
Figure 5
Dose rate in Gy/y for Shielding Scenario1: Two shielding walls on either side of
the Wire Scanner device consisting of 1m (panel A) and 2m (panel B) iron
followed by a 30cm concrete slab. This vertical cut is at 22cm from the centre of
the two beam lines and a mean of the values 0-50cm from the centre of the beam
line. The dose levels at the position of the Wire Scanner (box shown in the
middle of the shielding) reach ~1.3 kGy/y for case A and ~800 Gy/y for case B.
Figure 6
Dose rate in Gy/y for Shielding Scenario2. This vertical cut is at 22cm from the
centre of the two beam lines and a mean of the values 0-50cm from the centre of
the beam line. The dose levels reach ~1 kGy/y at the position of the WS and
~130 Gy/y at the position of the electronics (below the horizontal iron slab).
A
B
Figure 7
5.
Dose rate in Gy/y for Shielding Scenario3: A 2 m (panel A) or 4 m (panel B)
thick shielding block was used followed by a 30 cm thick concrete slab. This
vertical cut is at 22cm from the centre of the two beam lines and a mean of the
values 0-50cm from the centre of the beam line. The dose levels calculated reach
~1.2 kGy/y for the WS and ~50 Gy/y for its electronics, for both cases.
Conclusions
The position of the WS is very close to the beam and it will unavoidably suffer from
high radiation levels. Moreover, its installation at the dogleg bend increases the radiation
levels, since this region is the hottest in IR4, as shown by previous studies [1], [6]. From
the results shown in this report, it is important that an extensive shielding study takes place
in order to ensure the good functionality of the WS and its electronics. Especially for the
latter, the 5cm iron slab placed horizontally below the WS position was not proved to be
enough for appropriate shielding.
It is suggested that a market survey and radiation tests take place so that affordable
radiation hard devices are used. In case shielding is still necessary, an extensive study will
be needed in collaboration with the radiation and the BDI experts in order to (re)design the
WS installation and ensure the radiation tolerance of the device.
E×Φ (cm-2 / year)
Energy (GeV)
Figure 8
6.
Energy spectra of the particles reaching the Wire Scanner. The energy of the
particles is up to a few TeV.
References
[1] K. Tsoulou, V. Vlachoudis, A. Ferrari, Simulation of the radiation levels and
shielding studies at the BDI positions in IR4, LHC Project Note, CERN, May 2005, to be
published.
[2]
J. Koopman, personal communication, March 2005.
[3] A. Fassò, A. Ferrari and P. R. Sala, Electron-photon transport in FLUKA: Status. In
Proceedings of Monte Carlo 2000 Conference Lisbon, October 23-26 2000 (A. Kling, F.
Barao, M. Nakagawa, L. Tavora and P. Vaz, Eds.) pp. 159-164. Springer-Verlag, Berlin,
2001.
[4] A. Fassò, A. Ferrari, J. Ranft, P. R. Sala, FLUKA: Status and Perspectives for hadronic
applications, In Proceedings of the Monte Carlo 2000 Conference, Lisbon, October 23-26
2000, (A. Kling, F. Barao, M. Nakagawa, L. Tavora and P. Vaz, Eds.), pp. 955-960.
Springer-Verlag, Berlin, 2001.
[5] K. Tsoulou, Estimate of radiation levels at BDI positions in Point 4 produced from
beam gas collisions, 70th BDI LHC/SLI/CNGS Technical Board, http://project-bdi-lhc-slicngs-tb.web.cern.ch/project-bdi-lhc-sli-cngstb/Minutes/Minutes_70/BDI_TechnicalBoard.ppt , 13 July 2004.
[6] A. Butterworth, A. Ferrari, K. Tsoulou, V. Vlachoudis, T. Wijnands, Radiation
studies of single event upsets in the low-level electronics of the LHC 400MHz RF system
due to beam-gas collisions, LHC Project Note 342, CERN, March 2004.