Hadron stop Design Features

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Hadron stop Design Features

• Introduction
• Layout of the WANF design
• and some problems
• Hadron stop for CNGS
• Design features
• Conclusions

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WANF design, a bit of history
At the start of the West Area Neutrino
Facility WANF at 400 Gev in 1976 the mu
background was much to high for BEBC 3 ton
Hydrogen/Neon bubble chamber and was not
acceptable for the counter experiments CDRS and
CHARM. Also an upgrade of the proton beam to
450 Gev was planned. After a year of study it was
planned to install a toriodal magnet of 12Tm Bl
10m long, 6m diameter followed by a 5000 ton
4x4.5x36 m3 iron dump
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WANF design, a bit of history
The problem with the background was due to
the fact that the mu shielding, made from disks
of 2,5m diameter was too small to match the decay
tunnel of 1.2m diameter. This left a large hole
at angles of about 3 mr Additional steel added in
77 made no difference.
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WANF design, a bit of history
The mu background comes from the wrong sign
defocused particles. Mu are from Pi focused by
the horns into the shield (lower plot). The Pi-
are defocused by the toriod. The mu range out
in the Fe shield
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WANF design, a bit of history
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WANF design, a bit of history
The toriodal magnet was 10m long with a
diameter of 6m 12Tm at a current of 5000 amps.
The central core of 1.2m diameter was isolated
from the magnetic field by an air gap of 5cm.
Only the outer part of the magnet was magnetised
as the four coils were offset from the
center.
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WANF design, a bit of history
Cross section of the toridal magnet. The four
coils only magnetise the outer ring. The inner
core is not magnetised and is seperated from the
outer by a 5cm air gap
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WANF design, a bit of history
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WANF, a bit of history
When it was all built we turned on the field and
the background dropped by a factor of 100
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WANF design, a bit of history
During the final set of experiments Nomad and
Chorus we had sufficient CPU and disk to log all
the data at the three mu pits, this showed that
there were problems with the mu flux monitoring.
The silicon detectors were sensitive to e and mu,
the emulsion calibration was only sensitive to mu
Calculation (Fluka) and measurements showed that
there was a strong mu induced elecftron
background coming from the iron shield.
Calculation showed that this electron flux was
only reduced to a reasonable level after 5 m. The
length of the 3 pits was 1.2m and .8m, hence no
useful absolute flux measurement was possible,
better than 7. Both experiments were appearance
of tau neutrinos, so no problem. However some
impact on CNGS design
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Hadron stop for CNGS

• Very bad access - 2km tunnel to move 2000tons Fe
  
• - Difficult access
  to mu pits, safety
• Cavern 24m long, floor 5.2m
• Iron beam stop 4x4x15m3 with 3.x2.4x2.4 graphite
  section in front to spread the heat more evenly.
• The cross section of 4x4m2 was confirmed by
  calculation, matching the simple scaling from WANF

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Hadron stop for CNGS

• The length of the beam stop came from two
  sources the first was the wish to have a SBL
  experiment TOSCA. A feasibility study was made.
  The minimum necessary extra material required to
  ensure no serious mu background was 15m Fe. The
  second reason was that this also matched the
  reuuirements of the heat sink, to make it
  possible to work at the first mu pit.
• The two pits are separated by 67m sandstone,
  equivalent to 25m Fe as in WANF.
• Both pits are 5m long , material in front of the
  pit is similar concrete or sandstone(mollase)
• Detectors will be placed at the rear, to
  minimise e flux

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Hadron stop for CNGS
A SBL experiment was proposed called TOSCA A
feasibility study was made,and a reasonable site
found. However it was abandoned due to cost and
safety factors. If the site is ever required the
mu shielding is adequate to avoid mu
background.
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Access After Installation
Hadron Stop
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View of Hadron Stop
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Different materials
Iron - Graphite - Aluminium
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Energy Deposition
FLUKA Calculations (A. Ferrari et al.)
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Hadron stop for CNGS
A possible stacking procedure around the
graphite using the recuperated iron blocks from
WANF. Most of the iron are 1.6x.8x.8 m3 A
corrected drawing would show a second cooling
system on top of the graphite.
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Hadron stop for CNGS
Cooling system, possible design with twelve
stainless steel tubes embedded in an aluminum
block. For redundancy the tubes must be connected
externally to the cooling system
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Hadron stop for CNGS
There is still some discussion as to whither
the graphite should be contained in an box or
left in contact with the iron. There is some
concern about the mechanical shock of the beam
damaging the structure? The sketch is taken from
the CNGS proposal, could be a neat solutuion
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Assembly Trans
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Recuperation Iron Blocks
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Conclusions

• Civil engineering is well under way.
• The transport of the steel blocks has been
  studied but an assembly model can only be made
  when the actual number and sizes of the blocks
  are known
• We do not yet have a detailed study of the
  cooling system, with enough redundancy to last 20
  years.
• The question of boxing the graphite has to be
  understood
• However everything seems to be under control