CNGS HORN

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CNGS HORN

Mini-review induced by the break
of the insulating glass disk
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Summary

• Design evolution of the horn from WANF to CNGS
  (concerns only insulation and vapor tightness)
• Present design with a 19 mm thick glass disk and
  its apparent problems
• Preliminary proposal(s) for a new design
• Preliminary conclusions

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Design evolution of the hornWANF horn

• Generalities
• No vapor tightness asked
• The atmosphere inside the horn was directly in
  contact with ambient atmosphere of the cavern.
• Approximated section of the circular aperture
  130 cm2
• Overall dimensions smaller than CNGS horn
  dimensions (reflector diam /- equivalent to the
  diam of the CNGS horn)
• Horn was about 5 times less transparent to the
  beam than CNGS horn (bolted flanges, deflectors)
• Voltage 300 V maxi

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Design evolution of the hornWANF horn
Beam axis
Water outlet
Schematic view (principle)
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Design evolution of the hornWANF horn CNGS
horn
CNGS HORN
WANF HORN
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Design evolution of the hornCNGS horns

• Reminder
• CNRS/Orsay was in charge of the complete
  development of the horns. Cern agreement
  necessary before manufacture.
• 1st horn delivered was not in conformity with the
  technical specifications (MoU)
• Vapor tightness strongly asked (reference to the
  WANF)
• Only mineral material allowed for insulation.
• Inner diameter of the outer conductor
• Horn 700 mm
• Reflector 1100 mm
• Voltage 500 V maxi

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Design evolution of the hornCNGS horns (CNRS
solution for the glass disk assembly)
Sliver
8 insulator rings (ARCLEX) mm
100 mm
Sliver
R370 mm
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Design evolution of the hornCNGS horns (CERN
solution for the glass disk assembly)

• Main changes done on the design of the glass disc
  assembly to be in conformity with technical
  specifications (vapor tightness)
• Cross section larger and thickness increased from
  15 mm to 19 mm
• 12 bolts instead of 8, placed on a diameter close
  the C-shaped seals
• Exchange of the standard bolts by high grade
  bolts M16 (A4 quality)
• The glass disc is now drilled with 20 holes (12
  used to press the Tin/Ag seals 8 for the
  clamping rods used to maintain the electrical
  connection plates)
• New high quality machining on the both polarity
  plates to accept the new dimensions of the glass
  disc

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Design evolution of the hornCNGS horns CERN
design of the glass disk
Viewable cracks
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Design evolution of the hornCNGS horns
(Comparison between CNRS and CERN glass disk
assembly)
CNRS Assembly
CERN Assembly
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Design evolution of the hornCNGS horns (CERN
solution for the glass disk assembly)
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Design evolution of the hornCNGS horns (CERN
solution for the glass disk assembly)
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Design evolution of the hornCNGS horns CERN
design of the glass disk- Tightening
calculationExtracted from the note S.R
(04/10/2004)

• Vérification de la force décrasement dun joint
  métallique Garlock/Cefilac 175225
•  
• Caractéristiques du joint
• HN200 tore  6.1 mm
• Di 734
• De 746.2
• Revêtement détanchéïté  étain/Ag
• Revêtement interne  inconel 600
• Ressort  Nimonic 90
• Effort de serrage  Y2 100 N/mm pour e2 0.9
  mm
•  Calcul de la force totale transmise par 12 vis
  M16 A4/80
• Longueur linéaire du joint  dia. moyen 739.5
  soit  2323 mm
• Force nécessaire pour e2 0.9 mm  232.300 N
• Couple de serrage  156 N/m
• Force de serrage correspondante  50.210 daN
• Soit pour 12 vis  602.520 N

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Design evolution of the hornCNGS horns (CERN
solution for the glass disk assembly)
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Design evolution of the hornCNGS horns (ratio
between the horn and the reflector)
1400 mm
1000 mm
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Design evolution of the hornPrevious experience
with a glass disk insulator(CERN horn prototype
for NuFact project)
Glass disk
670 mm
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Design evolution of the hornPrevious experience
with a glass disk insulator(CERN horn prototype
for NuFact project)Detail of the glass disk
Dimensions smaller than for CNGS horn Better
ratio between overall dimensions and
thickness Elastomere O-ring seals The annular
pressure area is very limited Assembly with
damping washers Only one row of drilled
holes Assembly concept quite different (5 kV)
23 mm
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Design evolution of the hornCNGS horns
(Preliminary proposal 1)
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Design evolution of the hornCNGS horns
(Preliminary proposal 1- Cross section)
30 mm
Electrical contact surfaces
Al2O3 sector
60 mm
Coaxial spring (s.steel)
ARCLEX insulators (rings)
Spacer ring
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Design evolution of the hornCNGS horns
(Preliminary proposal 1A)
2.5 mm
R
Contact surface of the seals after clamping
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Design evolution of the hornCNGS horns
Advantages/DisadvantagesComparison with the
present solution (glass disc insulator)

• Concern proposal 1 with the alternative solution
  1A
• Advantages
• Risk to break an element is very low
• Vapor tightness can be considered as correct,
  even without Helicoflexseals
• Mechanical characteristics of Al2O3 are better
  known and pieces can be precisely machined.
• Clamping for electrical contacts and for vapor
  tightness can be treated separately
• Disadvantages
• All electrical connection plates must be
  re-designed
• Water tightness lost (risk of leak if dimensions
  of the water deflectors are not sufficient)
• Additional delay estimation about 4 months
• Cost

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Design evolution of the hornCNGS horns
(Preliminary proposal 2)
15 mm
Solution proposed after an open discussion with
Piet Wertelaers PH/DT2
2 Helicoflex seals (lining silver)
Glass disk insulator
Reminder Slope 5.66
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Design evolution of the hornCNGS horns
(Preliminary proposal 2) Advantages/Disadvantage
sComparison with the present solution (glass
disc insulator)

• Advantages
• The glass disk is clamped between the 2 C-shaped
  seals in opposition, without any other contact
  with the connection plates.
• The flatness of the machined faces is less
  critical than previously, except for the seal
  grooves.
• The torque applied on the screws used for the
  clamping of the electrical contact surfaces can
  be dissociate of the torque applied on the screws
  used for the clamping of the seals.
• Water tightness
• Disadvantages
• Seals must be imperatively resistant to the
  corrosion ( not a great experience in moist and
  high aggressive environment)
• Presently, no solution foreseen to empty the
  lower chicane

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CNGS horns Remarks and preliminary conclusion

• Mainly due to the limited choice of mineral
  material for the insulator, (glass, ceramics,
  mica/glass fiber composite, granite, marble)
  several ways can be explored but not a lot.
• Because time is missing for long tests, the
  retained solution must preferably be already
  experienced (bad choices in high radioactive
  areas have a very high cost at a later stage).
• The ends of the inner conductor cannot be
  modified (monolith component of 6.5 m)
• Modifications on the extremity of the outer
  conductor lead to an extra delay not acceptable
  with the installation schedule.
• Overall dimensions of the horn cannot be
  increased
• Choice of the final solution must integrate the
  compulsory over cost and the additional extra
  delay