1. 1 AFSWG Mtg 15 Aug 2003 Elwyn Baynham RAL Safety Overview Work done by RAL Group Contributors Elwyn Baynham Tom Bradshaw Iouri Ivaniouchenkov

2. 2 AFSWG Mtg 15 Aug 2003 Elwyn Baynham RAL Safety Overview l Contents »Basic model –Model from Columbia mtg with separated magnet and absorber »Safety Criterion –To prevent the condensation and freezing of O2 on any surface which could come into contact with a hydrogen leak »Analysis without 3 rd window or Ar Jacket –Similar to Mike Green assessment – we have now thought through the stages at RAL »What is added by 3 rd window / Ar jacket ?

3. 3 AFSWG Mtg 15 Aug 2003 Elwyn Baynham RAL MICE Focus Absorber Module Magnet Vacuum Absorber vacuum He feed/return Absorber vacuum pipe external General MICE vacuum

4. 4 AFSWG Mtg 15 Aug 2003 Elwyn Baynham RAL Assumptions l Focus Coil / Absorber general vacuum space is common with RF and detector vacuum l Absorber vacuum vessel and secondary windows are at a temperature which is high enough to prevent O2 freezing on windows or vessel l H2 feed pipe to absorber is jacketed with vacuum inside the cryostat l He absorber pipes are not jacketed at present

5. 5 AFSWG Mtg 15 Aug 2003 Elwyn Baynham RAL Observations (1) l Magnet Cryostat is independent - leaks into magnet vessel are not a problem l Leaks between the absorber vacuum and the general MICE vacuum will be negligible due to the differential pressures l The only place where O2 can be cryopumped is on the He feed or return pipes – these should/can be jacketed l If the He pipes are jacketed then leaks into the RF or detector vacuum can be detected and an alarm sounded above a certain level – there is no storage method for O2

6. 6 AFSWG Mtg 15 Aug 2003 Elwyn Baynham RAL Observations (2) l The biggest risk comes from a leak into the absorber vacuum space »This will bring O2 directly to freeze on the H2 window »The greatest risk for a leak is on the vacuum pipe to the absorber when it is outside the focus absorber cryostat ; pumping and dump vacuum vessel »These areas should be jacketed by Ar rather than vacuum l The H2 feed to the absorber will be at +ve pressure so there should be no access for O2 into the H2 space »The vacuum screening of the H2 pipe should end as close to the outer vessel as possible – any screening outside the vessel should be Ar jacketed

7. 7 AFSWG Mtg 15 Aug 2003 Elwyn Baynham RAL Observations (3) l If all the above criteria are met then it is difficult to see what additional safety features the 3 rd window or the Ar jacket will bring - but »We need a good solution for the external part of the absorber vacuum »We need to jacket the He feed/return pipes »We need a robust design for the temperature control of the absorber vacuum vessel – thermal analysis + mechanical design –What are the operating temperature margins l Too low gives O2 freezing l Too high gives too much heat load on the H2 window and vessel –What is the response of this system under other failures – vacuum ;refrigeration etc l Will discuss this with RAL safety in the next week or two

8. 8 AFSWG Mtg 15 Aug 2003 Elwyn Baynham RAL Welded vs non welded l The RAL safety preference is for welded l However there is no fixed statement that non welded is not allowed l Both systems must pass through a rigorous qualification process and have well established procedures for production ; installation and commissioning