Post on 26-Dec-2015
NdFeB Radiation Effects and RHIC Tunnel Radiation Levels
Summary of some existing papers and Paul Bergh’s “Special Studies”
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 1
Some Papers People have FoundPaper Materials Radiation type Temperature Machine/labMagnetic flux loss in rare-earth magnets irradiated with 200MeV protons, Yoshifumi Ito et al., NIM-B (2001)
N48, N32Z, (SmCo)R26H
Protons at 200MeV
Room, 22.2±0.3C
W-MAST, Wakasa Wan Energy Research Center (Nagatani, Tsuruga, Japan) http://www.werc.or.jp/
Measurement of NdFeB permanent magnets demagnetization inducedby high energy electron radiation, Alexander B. Temnykh (2008) doi:10.1016/j.nima.2008.01.002
N40, N40SH Electrons at 5GeV
Room, 29-35C Cornell 12GeV Synchrotron
The Effect of Neutron Irradiation on Nd–Fe–B andSm2Co17-Based High-Temperature MagnetsC. H. Chen et al., IEEE TRANSACTIONS ON MAGNETICS, VOL. 41, NO. 10, OCTOBER 2005
NdFeB, SmCo Neutrons at 0.02-10MeV (reactor)
High, ~200C OhioState University Research Reactor
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 2
“SNS” paper turned out to just re-use LANL neutron irradiation data
NB: the Chen paper cites a dozen others that look interesting but I haven’t downloaded yet!
Room Temperature Plots
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 3
Ito et al. (cylinders)Temnykh (blocks)
1kGy = 100krad104Gy = 1000krad
Interpolated Losses at 10kGyStudy Material sample Flux loss at 10kGy
Ito N48 th.=2mm 67%
Ito N48 th.=4mm 49%
Ito N48 th.=7mm 24%
Temnykh N40 H 13%
Temnykh N40 V 1.2%
Ito N32Z th.=2mm 9%
Ito N32Z th.=7mm 0.7%
Temnykh N40SH H 0.4%
Temnykh N40SH V 0.1%
Ito SmCo R26H th.=2mm <<0.7%
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 4
“SH” is high max temperature grade; “Z” is low thermal coefficient gradeeRHIC Shin-Etsu quote used N36SH (~$1/cc) N36Z (~$1.30/cc)
What “H” vs “V” Means (Temnykh)
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 6
H (bad) V (good)
“Load Lines” – Geometry Matters
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 7
From Chen et al.
Irradiation Rate in RHIC Tunnel?
• Paul Bergh sometimes leaves TLD badges in the tunnel for ~2 weeks in “Special Studies”
• Badges record following in rem or mrem:– “Deep photon” gammas– TLD 8814 neutrons (lower energy band)– Optionally CR-39 neutrons (higher energy band)
• Roughly convert to Grays with– Grays = (gamma+(TLD8814+CR39)/5)/100
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 8
Irradiation Rates in RHIC Tunnel
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 9
CR-39 saturated
Total Radiation Dose for eRHIC?
• Maximum measured dose rates of 0.2Gy/day– 50Gy per 250 day operational year– 1kGy over 20 operational years of 250 days
• If using 1kGy can divide values in previously-shown table by 10
• eRHIC magnets will be everywhere around the ring, but TLD studies data is only at a few points, so be cautious!
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 10
Pragmatic Conclusion for eRHIC
• N48 is bad: ~10% flux loss expected• N40 and N32Z are marginal, ~1% loss• N40SH and SmCo both look good, <0.1% loss• This makes one more confident about the
cheaper N36SH grade used in eRHIC costing• Ito’s N32Z result is surprisingly bad• Must check where on B-H curve eRHIC magnet
designs are in terms of permeance=|B/H|
January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 11
Empirical formula/mechanism?
• Domain flipping could be caused by localised heating, or some other triggered “tunnelling” phenomenon
• Should expect degradation rates of the form k1exp(-k2H) where H is “potential barrier”– Temnykh defines it in terms of “de-magnetising
temperature” margin (but why not exp(-kH/T)?)– Could also use H to demagnetisation on the B-H
curveJanuary 12, 2015 Stephen Brooks, eRHIC FFAG meeting 12