NdFeB Radiation Effects and RHIC Tunnel Radiation Levels Summary of some existing papers and Paul...

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)

Shin-Etsu N Grade B-H Curves

January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 5

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

January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 13

From Temnykh

N42SH-R Thermal Behaviour

January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 14

Phantom Reference via EEC

January 12, 2015 Stephen Brooks, eRHIC FFAG meeting 15