Download - Final Focus Magnet Shielding Update
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Final Focus MagnetFinal Focus MagnetShielding UpdateShielding Update
Jeff Latkowski and Wayne Meier
ARIES Meeting
October 2-4, 2002
Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
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JFL—10/02 ARIES
Outline
• Review/update of point design results from last meeting
• Analysis for “off-center” target implosions
• Issues/comments for case without beamline cross jets & plans for FY03
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JFL—10/02 ARIES
General requirements for the finalfocusing magnet shielding design
• Shielding design consistent with target beam requirements (e.g., half-angle of array <24º)
• Magnets don’t quench on a per-shot basis (limits energy deposition to ~100 mJ/cc/shot)
• Recirculating power for magnet cooling doesn’t cause unacceptably large economic hit
• Magnets have reasonable radiation damage lifetime
• Avoid generation of above Class C waste, if possible
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JFL—10/02 ARIES
What limits the radiation lifetimeof the final focusing magnets?
• Total dose to the insulators is limited to 100 MGy (ref. 1); tends to be dominated (90-95%) by contribution from gamma-rays
• “Conservative limit” for the fast neutron fluence (En 0.1 MeV) in Nb3Sn superconductor is 1019 n/cm2 (ref. 1):– Room-temperature anneal required after 3 1018 n/cm2
– 70% recovery assumed
Inorganic insulators that may be usable with high-temperature superconductors (HTS)
offer significantly (~103) greater limits (ref. 2)
HTS appear to have fast neutron fluence limits that are at least as good as that for Nb3Sn (ref. 2)
References:(1) Sawan and Walstrom(2) Bromberg, ARIES meeting (Jan. 2002)
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shielding structure for last magnet set
target injection pathway
cylindrical crossing flibe jets for gross beamline shielding
target location at shot time
vortex tubes for precision beamline shielding
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size of beamat front oflast magnet
1 cm of structure, insulation, and H2O cooling
alternating layers (1 cm each/5 cm total) of W and a proprietary material (good for neutrons)
1 cm of structure, insulation, and LN2 cooling (inside and outside coil)
3 cm thick coil region (40 vol% each of Cu and Nb3Sn + 20 vol% LHe)
2.3 cm of SS304 for banding/shielding
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JFL—10/02 ARIES
Review of point designresults from last meeting
• Results for the final magnet:– Average insulator lifetime (total dose limited): 26 years (18-42)– Average superconductor lifetime (n,fast limited): 33 years– WDRcoil = 14
• Second-to-last magnet:– Insulator lifetime: 300 years– Superconductor lifetime (n,fast limited): 33 years– WDRcoil = 5.6
• Third-to-last magnet:– Insulator lifetime: 120 years– Superconductor lifetime (n,fast limited): 33 years– WDRcoil = 15
1st room-temp anneal needed at ~10 years
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JFL—10/02 ARIES
0
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Centered R+0.5cm Z+0.5cmIns
ula
tor
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e (
full-p
ow
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Case
Insulator lifetime of100 MGy assumed.
Analysis performed for“off-center” targets
• Target position was varied by 0.5 cm in two directions:– Along the axis of
symmetry– Perpendicular to the
axis of symmetry
• The average insulator lifetime is insensitive to the target position at “bang time.”
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JFL—10/02 ARIES
The distribution of magnet lifetimes (notall are equal) is essentially unchanged
• We observe a slight shift in the magnet lifetime distribution
• Effect is probably not real, but statistical
• Error bars are 15-20% (2-4 years at the low end and 5-9 years at the high end)
• Waste disposal results are unaffected 0
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Centered
x+0.5 cm
z+0.5 cm
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Lifetime range (full-power-years)
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JFL—10/02 ARIES
Issues/comments for casewithout beamline cross jets
• Assume that wetted wall protects structural material from x-ray and ion threats
• Removing liquid cross jets increases neutron damage to port plug structure by nearly 5x
• Expect magnet dose to increase by similar factor; Compensate by thickening port plug?
• Port plug is difficult location to tolerate damage given desire for precision shielding; need swelling-tolerant design variable thickness liquid vortices?
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JFL—10/02 ARIES
• Examine damage to vortex structures and flow nozzles
• Address port plug issues in more detail
• Waste disposal needs considerable improvement: WDRcoil = 14 (94Nb) for last magnet; consider high-temperature (low-activation, in some cases) superconductors?
• Look at life-cycle waste volume vs. shielding design (ironically, long life magnets may actually increase overall waste volume and lead to production of high-level waste)
• Work is planned for FY03
Additional work is needed forthe final focus shielding issues