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

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 mBeam 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.

FLOORDump

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 2Beam is NOT bend and beam impacts dump 4 m below surface

FLOORDump

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?