Update for muon studies Helmut Vincke

Additional dump calculations Two options were studied: Option 1: beam is bend by 2 degree towards soil and beam impacts dump 2 m below surface DUMP Option 2: beam is NOT bend and beam impacts dump 4 m below surface

Dump design In contrast to first set of calculations the dump is slightly modified to reduce backscattering of particles. Iron or carbon core (radius 20 cm length 2 m) was set to vacuum Iron dump (radius: 1.5 m, length: 7 m) Concrete part (radius: 5 m, length 9 m)

Beam on dump Muon axis inside and outside CERN Distances: Beam impact point to end of West hall: ~300 m Beam impact point to CERN fence: ~600 m

Option 1 Bending beam by 2 degree, beam impact point in a depth of 2 m below surface In order to get result in reasonable time transformation of situation into cylinder symmetric description is required. FLOOR Dump

Muon dose rate expected for Option 1 CERN FENCE Except for some statistical fluctuations (caused by heavy biasing) both dose rate outside the West Hall and outside the CERN territory fulfill the optimization criteria (10 uSv/year for public and 100 uSv/year for CERN).

In order to get result in reasonable time transformation of situation into cylinder symmetric description is required. Option 2 Beam is NOT bend and beam impacts dump 4 m below surface FLOOR Dump

Muon dose rate expected for Option 2 CERN Fence Conclusion to option 2: Also here statistical fluctuation due to strong biasing  leading to some spikes inside and outside CERN showing a dose rate above optimization limit. No surface morphology considered yet. => beam might reappear in case the height profile downstream the West Area is dropping by 4 m. Range of muons of the maximum energy can travel more than a km in earth.

Conclusion Both options seem to be feasible for continuous operation with an intensity of 3E13 protons per shot at a frequency of 1/30 Hz. Final depth of the beam impact point are expected to be in the range of 2 m for option 1 (bending beam by 2 degree) and at 4 m for option 2. This information should be sufficient for our CDR

Muon dose rate expected for Option 1 (better statistics) CERN FENCE More accurate results for option 1 Dose rate along beam axis (important for option2): at 600 m the dose rate is about 10 uSv/year.  If option 2: height profile of area downstream West hall required!!

Additional comments for option 1 Considering only particles on dump: situation is controllable. However, losses in the beam line on the surface must be kept at a bare minimum otherwise the muon problem reappears. Two reasons: Lost particles do not see our dump!!!!  additional hadron dose Produced pions have much longer flight path for decaying into muons than considered in the beam-on-dump case  much higher muon dose In order to cope with losses (hadrons and muons) we need to shield heavily the beam line at the surface to the forward direction and lateral. From a certain beam loss level (~1E13 per year) the loss situation becomes “unshieldable”!!!!! See slide 19, muons in direction of beam axis (beam impinging on 7m of iron). For a more realistic (but still very heavy) shielding the loss level should be rather in the range of 1E12 protons per year. Question: What is the beam loss level we have to expect? Do we have a chance to have such low levels?