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

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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)

Shin-Etsu N Grade B-H Curves

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What “H” vs “V” Means (Temnykh)

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H (bad) V (good)

“Load Lines” – Geometry Matters

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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

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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

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From Temnykh

N42SH-R Thermal Behaviour

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Phantom Reference via EEC

January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 15