Transcript Magnet?

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 Found
Paper
Materials
Radiation type
Temperature
Machine/lab
Magnetic flux loss in rareearth 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 induced
by 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 and
Sm2Co17-Based HighTemperature Magnets
C. H. Chen et al., IEEE
TRANSACTIONS ON
MAGNETICS, VOL. 41, NO.
10, OCTOBER 2005
NdFeB, SmCo
Neutrons at
0.02-10MeV
(reactor)
High, ~200C
Ohio
State University
Research
Reactor
NB: the Chen paper
cites a dozen others
that look interesting
but I haven’t
downloaded yet!
“SNS” paper turned out to just re-use LANL neutron irradiation data
January 12, 2015
Stephen Brooks, eRHIC FFAG meeting
2
Room Temperature Plots
Temnykh (blocks)
Ito et al. (cylinders)
1kGy = 100krad
104Gy = 1000krad
January 12, 2015
Stephen Brooks, eRHIC FFAG meeting
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Interpolated Losses at 10kGy
Study
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%
“SH” is high max temperature grade; “Z” is low thermal coefficient grade
eRHIC Shin-Etsu quote used N36SH (~$1/cc) N36Z (~$1.30/cc)
January 12, 2015
Stephen Brooks, eRHIC FFAG meeting
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Shin-Etsu N Grade B-H Curves
January 12, 2015
Stephen Brooks, eRHIC FFAG meeting
5
What “H” vs “V” Means (Temnykh)
H (bad)
January 12, 2015
V (good)
Stephen Brooks, eRHIC FFAG meeting
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“Load Lines” – Geometry Matters
From Chen et al.
January 12, 2015
Stephen Brooks, eRHIC FFAG meeting
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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
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Irradiation Rates in RHIC Tunnel
CR-39 saturated
January 12, 2015
Stephen Brooks, eRHIC FFAG meeting
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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 previouslyshown 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
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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
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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 DH to demagnetisation on the B-H
curve
January 12, 2015
Stephen Brooks, eRHIC FFAG meeting
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From Temnykh
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Stephen Brooks, eRHIC FFAG meeting
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N42SH-R Thermal Behaviour
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Phantom Reference via EEC
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