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CNGS horn / reflector in 2005: The story of the glass ring insulator “A brief summary”

CNGS horn / reflector in 2005: The story of the glass ring insulator “A brief summary” by K. Elsener, A. Pardons, S. Rangod. “history” April 2004: horn-1 delivered from LAL to CERN April 2004: horn-1 electrical tests o.k.

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CNGS horn / reflector in 2005: The story of the glass ring insulator “A brief summary”

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  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 -> mistake in LAL design -> 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 Problem Solution Number of screws & distance Glass plate broken Problem = conceptual After modification More cracks present or to be expected? Crack discovered ~weeks after electrical tests Ceramic ring? Pieces instead of ring? 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 12 coaxial springs used during assembly phases Critical angular geometry 12 identical sectors Al2O3 (thickness 30 mm) For centering pins 6 necessary gaps to guarantee the contact on lateral faces (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

  7. 20 Sept. 2005: glass-rings cut out of plate (water/sand jet cutting)

  8. 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 R=705-775mm • reflector R=1105-1175m • (3 pieces of 120o)

  9. Reflector – “Sandwich” Assembly (1)

  10. Reflector – “Sandwich” Assembly (2)

  11. Reflector – “Sandwich” Assembly (3)

  12. Reflector – “Sandwich” Assembly (4): quality control

  13. Reflector – “Sandwich” Assembly (5) before placing the second graoil ring and the second connection plate after

  14. Reflector – “Sandwich” Assembly (6) NOTE: final configuration has 6 (not 5) Belleville washers

  15. Reflector: mounting the “sandwich” of connection plates with glass insulating ring

  16. Reflector: “short-circuit” side before installation of connection plate inside the inner conductor

  17. 180 kA double pulse (Dt=50 ms) Reflector on test-bench (18 - 23 Nov. 2005, 20000 double pulses)

  18. Reflector transport in access gallery (5 November 2005)

  19. Reflector in target chamber top:passage near target shielding right: installation on base frame

  20. CERN horn team (with reflector, in assembly lab)

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