CNGS horn / reflector in 2005:

1
CNGS horn / reflector in 2005 The story of the
glass ring insulator A brief summary by K.
Elsener, A. Pardons, S. Rangod
2
history April 2004 horn-1 delivered from
LAL to CERN April 2004 horn-1 electrical
tests o.k. May 2004 extensive list of
compulsory modifications (S. Rangod) June 2004
CNGS review horn modifications indorsed July
2004 during dis-assembly of horn, glass ring
splinters discovered -gt mistake in LAL
design -gt additional modifications
necessary March 2005 horn modifications
completed ready for electrical tests April 2005
horn electrical tests o.k. Mai 2005 horn
installed on new support frame transport from
BA7 to 887 June 2005 two cracks in horn glass
ring discovered July 2005 (7th-11th) NBI
workshop at Fermilab - discussions July 2005
(18th) CERN mini-review on glass-ring
enigma Aug 2005 L. Bartoszek visit to CERN
discussions decision on new glass rings
(with grafoil seals) Sept 2005 new glass rings
/ grafoil seals ordered Oct 2005 reflector
connection plate / glass ring assembly
complete Nov 2005 reflector electrical tests
o.k. Dec 2005 (5th) reflector installed in
target chamber
3
slide presented by A. Pardons at NBI2005, 9 July
2005
Glass Disk Enigma
Received from LAL
Received from LAL After
modification
Any suggestions?
4
slide presented by S. Rangod at CERN
mini-review, 18 July 2005
(Preliminary proposal 1)
5

• Conclusions of mini-review
• The CERN mini-review did NOT encourage
  solutions with
• pieces of ceramic.
• Separating the functions (i.e. pressure for
  electrical contact and
• sealing against water / vapor leaks) was strongly
  encouraged.
• A solution with an insulating ring other than a
  glass ring would
• have been preferred.
• Conclusion (after more discussions and tests)
• New glass ring (smaller width, no holes)
• Softer seals (GRAFOIL)
• Since work on horn, reflector and spare horn,
  installation in the target
• chamber, stripline installation etc. had to
  proceed almost in
• parallel, it was decided that the first object to
  be equipped with the
• new assembly was to be the reflector.

6
Explanation of final assembly (see the drawing
next page) (from a document written by A.
Pardons) The idea is to only have a limited
force on a fragile glass disk (insulator disk
between two connection plates of different
polarities). Using 6 Belleville washers in a
2-2-2 configuration gives the correct compression
force on disk seal to ensure leak tightness
without risking breaking the disk. The washers
allow us to choose our target force quite
precisely, while giving the assembly a good
elasticity and absorption of shocks.
Specification Belleville Washers M16 P
M16-L-2.4-301 thickness 2.4mm
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20 Sept. 2005 glass-rings cut out of
plate (water/sand jet cutting)
9

• GRAFOIL-rings cut out of plate
• (water/sand jet cutting)
• GRAFOIL details
• - 98 graphite
• - needs only little contact pressure
• (we have applied 5 MPa)
• max. temp. 500o C
• available in 1mx1m pieces
• our rings 3 mm thick
• horn R705-775mm
• reflector R1105-1175m
• (3 pieces of 120o)

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Reflector Sandwich Assembly (1)
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Reflector Sandwich Assembly (2)
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Reflector Sandwich Assembly (3)
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Reflector Sandwich Assembly (4) quality
control
14
Reflector Sandwich Assembly (5)
before placing the second graoil ring and the
second connection plate
after
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Reflector Sandwich Assembly (6)
NOTE final configuration has 6 (not 5)
Belleville washers
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Reflector mounting the sandwich of
connection plates with glass insulating ring
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Reflector short-circuit side before
installation of connection plate
inside the inner conductor
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180 kA double pulse (Dt50 ms)
Reflector on test-bench (18 - 23 Nov. 2005, 20000
double pulses)
21
Reflector transport in access gallery (5 November
2005)
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Reflector in target chamber top passage near
target shielding right installation on base
frame
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CERN horn team (with reflector, in assembly lab)