irradiation experiments and magnet protection plans at spring-8
DESCRIPTION
Irradiation Experiments and Magnet Protection Plans at SPring-8. T. Bizen Y. Asano, X. –M. Maréchal SPring-8. Outline. Proposal of radiation-induced demagnetization model Experimental methods Experimental results Energy dependence Protection plans. - PowerPoint PPT PresentationTRANSCRIPT
Irradiation Experiments and Magnet Protection Plans at
SPring-8
T. BizenY. Asano, X. –M. Maréchal
SPring-8
OutlineOutline
• Proposal of radiation-induced demagnetization model
• Experimental methods
• Experimental results
• Energy dependence
• Protection plans
High-energy electron causes photonuclear interaction
High-energy electron causes photonuclear interaction
・ (γ , n) (γ , xn) (γ , p)
・ (n , γ ) (n , α)
e- e±
e±
e±
e±
e±
γγ
γγ
γn
・ Electromagnetic shower
Typical radiation-induced demagnetization of Nd2Fe14B magnets
Typical radiation-induced demagnetization of Nd2Fe14B magnets
Sample
Coercivity is the intensity of the applied magnetic field that required to reduce the magnetization to zero after the magnetization of the sample has been driven to saturation.
Coercivity DependenceCoercivity Dependence
Proposal of Radiation-induced Demagnetization
Model
Proposal of Radiation-induced Demagnetization
Model
Magnetic Domain in MagnetsMagnetic Domain in Magnets
Magnetic Domain Domain WallMagnetic Moments
A magnetic domain is a region within a magnet that has uniform magnetization.
Magnetization ReversalMagnetization Reversal
Magnetized Direction
Magnetic Domain
Domain wall
Expansion of Reverse Domain
Reversed Magnetization
Inverse domain nucleate and expand at the defect or the grain boundary where the anisotropy barrier is the lowest.
Inverse domain nucleate and expand at the defect or the grain boundary where the anisotropy barrier is the lowest.
Applied magnetic field
Concept of the modelConcept of the model
The remanence of the irradiated magnets were recovered by remagnetization.
Magnetization reversal is occurred by heat before the crystalline structure is damaged severely.
1. Magnetization reversal caused by thermal fluctuation.2. Magnetization reversal caused by thermal spike like heat
generation.
1. Magnetization reversal caused by thermal fluctuation.2. Magnetization reversal caused by thermal spike like heat
generation.
Heat ProcessHeat Process
Model of radiation-induced demagnetizationModel of radiation-induced demagnetizationModel of radiation-induced demagnetizationModel of radiation-induced demagnetization
Inverse domain nucleate and expand at the defect or the grain boundary where the anisotropy barrier is the lowest.
The coercivity in the grain decreases with temperature rise.
Thermal Fluctuation
Thermal Spike Like Heat GenerationThermal Spike Like Heat Generation
nHigh energy
High energy recoil atoms lose energy predominantly by inelastic interaction (electronic excitation) in a very small volume and produce very high temperature in a very short time.
D. Kanjilal (2001)
Inelastic
Elastic
Model of radiation-induced demagnetizationModel of radiation-induced demagnetizationModel of radiation-induced demagnetizationModel of radiation-induced demagnetization
Thermal Spike Like Heat Generation
Not all inverse domain walls can expand Not all inverse domain walls can expand
Low Coercivity Magnet High Coercivity Magnet
Inverse domain walls expand easily
Inverse domain walls hardly expand and some of them stop
Low coercivity regionLow coercivity region
Inverse domain produced by thermal spike like heat generation
Inverse domain produced by thermal spike like heat generation
Process of radiation-induced demagnetization in the modelProcess of radiation-induced
demagnetization in the model
Thermal Fluctuation
Thermal Spike Like Heat Generation
Magnetic domain (>10μm)
[T>starting temp. of heat demagnetization]
Heat effected region
Spike track (>several nm)
[T>Currie temp.]
Reason of demagnetizationStarting point of magnetization reversal
Lowest point of anisotropy
Spike track
(γ , e )
( n )
Thermal Fluctuation
• Temperature rises in wide area.• Inverse domain nucleates and
expands at the defect or the grain boundary where the anisotropy barrier is the lowest.
• Coercivity decreases in wide area.• Inverse domain wall expand easily in
the low coercivity region.
• Temperature rises in wide area.• Inverse domain nucleates and
expands at the defect or the grain boundary where the anisotropy barrier is the lowest.
• Coercivity decreases in wide area.• Inverse domain wall expand easily in
the low coercivity region.
Thermal Spike Like Heat Generation
• The recoil atom generates heat over the Curie temperature in a very small region and forms core or track.
• The spike occurs both in grain boundary that anisotropy is low and in grain that anisotropy is high.
• The coercivity around the track is kept high because the thermally effected region is very small.
• Not all inverse domain wall expand in the grain that coercivity kept high.
• The recoil atom generates heat over the Curie temperature in a very small region and forms core or track.
• The spike occurs both in grain boundary that anisotropy is low and in grain that anisotropy is high.
• The coercivity around the track is kept high because the thermally effected region is very small.
• Not all inverse domain wall expand in the grain that coercivity kept high.
High coercivity ( or heat resistant) magnetsHigh coercivity ( or heat resistant) magnets Thermal spike like heat generationThermal spike like heat generation
Thermal fluctuation Thermal fluctuation Low coercivity magnetsLow coercivity magnets
Energy Transfer by Neutron Elastic Scattering
Energy Transfer by Neutron Elastic Scattering
EA:KineticenergyofrecoilnucleusA:AtomicmassnumberE0: Kinetic energy of neutron
A EA
at 2 GeV
B (10.8) : 274 MeV
Fe (55.8) : 56 MeV
Co (58.9) : 52.8 MeV
Nd (144.2) : 21.6 MeV
Sm (150.4) : 20.8 MeV
A EA
at 2 GeV
B (10.8) : 274 MeV
Fe (55.8) : 56 MeV
Co (58.9) : 52.8 MeV
Nd (144.2) : 21.6 MeV
Sm (150.4) : 20.8 MeV
Maximum possible energy transfer from a 800 MeV neutron to the recoil nucleus in 2 GeV electron irradiation.Maximum possible energy transfer from a 800 MeV neutron to the recoil nucleus in 2 GeV electron irradiation.
Experimental Methods
Experimental Methods
The experiments of the 2 GeV electron beam irradiation were made at Pohang Accelerator Laboratory.
Accelerator FacilityAccelerator Facility
Irradiation Area( Beam Dump )
Irradiation Area( Beam Dump )
Magnetic Field Measurement MachineMagnetic Field Measurement Machine
LinacLinac
Magnetic Field Measurement Machine( Cryostat )Magnetic Field Measurement Machine( Cryostat )
Collaboration with Dr. H. S. Lee et. al.
Compare the magnetic field before and after irradiation.
Compare the magnetic field before and after irradiation.
Field above the surface of the magnet is measured by the Hall-probe.
The probe moves into the shield cover during irradiation.
Low Temperature IrradiationLow Temperature Irradiation
Cryostat Configuration of Sample Setup
Experimental ResultsExperimental Results
Thermal FluctuationThermal Fluctuation
Estimation of the temperature Estimation of the temperature generated by the thermal fluctuationgenerated by the thermal fluctuation
Estimation of the temperature Estimation of the temperature generated by the thermal fluctuationgenerated by the thermal fluctuation
Heat demagnetization of the Nd2Fe14B magnet (NEOMAX35EH)
Heat demagnetization of the Nd2Fe14B magnet (NEOMAX35EH)
Starting temperature of heat demagnetization
Little demagnetization
Large demagnetizationCurie Temperature : 590 K
1. Estimation by using the permeance coefficient 1. Estimation by using the permeance coefficient
Radiation-induced demagnetization depends on the permeance coefficient.Radiation-induced demagnetization depends on the permeance coefficient.
Permeance coefficient (Pc) is a function of magnet geometry related to demagnetization.
2 GeV electrons irradiation
Starting temperature of heat demagnetization depend on the permeance coefficient
Starting temperature of heat demagnetization depend on the permeance coefficient
Pc=0.74Pc=1.68
Below the starting temp. of demagnetization
Over the starting temp. of demagnetization 410 K
Just before the starting temp. of demagnetization 450 K
Data sheet from NEOMAX Co.,
The difference of demagnetization appears between 410 〜 450 K. The temperature of thermal fluctuation was 410 〜 450 K.
The difference of demagnetization appears between 410 〜 450 K. The temperature of thermal fluctuation was 410 〜 450 K.
Little demagnetization at R.T.
2. Estimation by using coercivity dependence on heat and radiation-induced demagnetization
2. Estimation by using coercivity dependence on heat and radiation-induced demagnetization
Radiation-induced demagnetizationHeat demagnetization
Coercivity and starting temp. of heat demagnetization is proportional on Nd2Fe14B magnet.
Little demagnetization occurs over this coercivity
Little demagnetization occurs over this coercivity
Thermal Fluctuation Temp. : 〜 440KThermal Fluctuation Temp. : 〜 440K
Stabilization to the demagnetization induced by thermal fluctuation
Stabilization to the demagnetization induced by thermal fluctuation
Stabilization technique to heat demagnetizationStabilization technique to heat demagnetization
• The flux of newly magnetized magnets decrease by thermal fluctuation over a long time period.
• The magnets fabricated in high temperature are stabilized before they use to prevent the flux loss by thermal fluctuation. Commonly used stabilization techniques are designed demagnetization by heat or opposite magnetic field.
Stabilization and radiation-induced demagnetization 1
Stabilization and radiation-induced demagnetization 1
Freshly magnetized magnets (NEOMAX35EH) were stabilized thermally ( 24 hrs. exposure ) on different temperature.
Thermal treatment largely increases the radiation resistance. Thermal treatment largely increases the radiation resistance.
The stabilization temperature and the radiation resistanceThe stabilization temperature and the radiation resistance
The radiation-induced demagnetization at the electron number of a 1×1015 Heat Demagnetization
The radiation resistance was enhanced around the stabilized temperature of 410 K 〜 470 K.The radiation resistance was enhanced around the stabilized temperature of 410 K 〜 470 K.
Heat demagnetization does not exceed the stabilized temperature.Heat demagnetization does not exceed the stabilized temperature.
The temperature of thermal fluctuation was 410 K 〜 470 K.The temperature of thermal fluctuation was 410 K 〜 470 K.
NEOMAX35EH
This enhancement of the radiation resistance was observed in another Nd2Fe14B ( NEOMAX-27VH)
magnet.
This enhancement of the radiation resistance was observed in another Nd2Fe14B ( NEOMAX-27VH)
magnet.
Coercivity : 2864 kA/m
Stabilization and radiation-induced demagnetization 2
Stabilization and radiation-induced demagnetization 2
Demagnetization induced by applying opposite magnetic field is also enhanced the radiation resistance.Demagnetization induced by applying opposite magnetic field is also enhanced the radiation resistance.
Thermal fluctuation is one of the reason of the radiation-induced demagnetization.
Summery of thermal fluctuationSummery of thermal fluctuation
• Several estimations of the thermal fluctuation temperature produced by radiation indicate in good agreement (around 450 K).
• The stabilization technique to decrease the thermal fluctuation was also effective to the radiation-induced demagnetization.
Thermal fluctuation is realThermal fluctuation is real
Thermal Spike Like Heat Generation
Thermal Spike Like Heat Generation
Thermal Spike Like Heat GenerationThermal Spike Like Heat Generation
• The recoil atom generates heat over the Curie temperature in a very small region.
• Not all inverse domain wall expand in the grain that coercivity kept high.
• The recoil atom generates heat over the Curie temperature in a very small region.
• Not all inverse domain wall expand in the grain that coercivity kept high.
Radiation-induced demagnetization is also observed in the heat resistant magnets of SmCo5, Sm2Co17.
Radiation-induced demagnetization is also observed in the heat resistant magnets of SmCo5, Sm2Co17.
Starting temperature of heat demagnetization : 520 K 〜Starting temperature of heat demagnetization : 520 K 〜 > Thermal fluctuation temperature
: around 450 KThermal fluctuation temperature : around 450 K
Thermal spike like heat generation can explain this phenomena.
Mobility of the domain wallMobility of the domain wall
Nucleation Type Pinning Type
Inverse domain wall is pinned Inverse domain wall is pinned Inverse domain wall expand easilyInverse domain wall expand easily
SmCo5 , Nd2Fe14B Sm2Co17
Applied magnetic field
obstacles
Nucleation TypeNucleation Type
Hcj
796
Hcj
8361623676
Pinning TypePinning Type
Large DemagnetizationLarge Demagnetization A Little DemagnetizationA Little Demagnetization
Radiation-induced demagnetization depends on the mobility of the domain wall.Radiation-induced demagnetization depends on the mobility of the domain wall.
Mobility of the domain wall and the radiation-induced demagnetization
Mobility of the domain wall and the radiation-induced demagnetization
These two type of magnets show approximately same thermal properties.
Radiation-induced demagnetization under low temperature
Radiation-induced demagnetization under low temperature
The resistance of radiation-induced demagnetization increases with lower the temperature.
The resistance of radiation-induced demagnetization increases with lower the temperature.
Nd2Fe14BNEOMAX50BHWithout thermal treatment
Hcj 3060 kA/m
Hcj 1116 kA/m
Coercivity increases at low temperatureCoercivity increases at low temperature
The coercivity increases with lower the temperature.The coercivity increases with lower the temperature.
The temperature coefficient of the coercivity of Pr2Fe14B ( 53CR) is larger than that of Nd2Fe14B ( 50BH 、 35EH).
The temperature coefficient of the coercivity of Pr2Fe14B ( 53CR) is larger than that of Nd2Fe14B ( 50BH 、 35EH).
T. Hara, T. Tanaka, H. Kitamura, T. Bizen, X. Marechal, T. Seike, T. Kohda, and Y. Matsuura,: “Cryogenic permanent magnet undulators”, Phys. Rev. Spec. Top.: Accel. Beams 7, 050702-1-050702-6 (2004)
The magnets with high coercivity enhanced by the low temperature were more sensitive to the radiation than the one attribute to the Dy additive.
The magnets with high coercivity enhanced by the low temperature were more sensitive to the radiation than the one attribute to the Dy additive.
27VH Hcj 2864 kA/m (Dy)27VH Hcj 2864 kA/m (Dy)
53CR Hcj 5000 kA/m (temperature 90 K)53CR Hcj 5000 kA/m (temperature 90 K)
50BH Hcj 3060 kA/m (temperature 145 K)50BH Hcj 3060 kA/m (temperature 145 K)
35EH Hcj 1989 kA/m (Dy)35EH Hcj 1989 kA/m (Dy)
Two demagnetization mechanisms under low temperature
Two demagnetization mechanisms under low temperature
Thermal FluctuationThermal Fluctuation
Thermal Spike Like Heat GenerationThermal Spike Like Heat Generation
Magnetic Domain
Around Spike Track
Coercivity Temperature
: Coercivity enhanced by low temperature
: Coercivity enhanced by Dy additive
Same DemagnetizationSame Demagnetization
Different DemagnetizationDifferent Demagnetization
ΔT is very high
Thermal spike like heat generation is the main reason for the demagnetization at low temperature.
Thermal spike like heat generation is the main reason for the demagnetization at low temperature.
・ Thermal fluctuation < Starting temperature of heat demagnetization (estimated <290 K) (340 K for 50BH).
・ Different demagnetizations were observed on the magnets with same magnitude of coercivity generated by different mechanism.
・ Thermal fluctuation < Starting temperature of heat demagnetization (estimated <290 K) (340 K for 50BH).
・ Different demagnetizations were observed on the magnets with same magnitude of coercivity generated by different mechanism.
The magnet that coercivity enhanced by low temperature was much influenced than the Dy additive one.
The magnet that have large coercivity coefficient was more sensitive to radiation even if the temperature was very low.
Energy DependenceEnergy Dependence
Experimental Method
The electron beam energies were varied 4-8 GeV
The electron beam energies were varied 4-8 GeV
Synchrotron in SPring-8
Sample setupSample setup
Magnet samples were thermally stabilized to reduce the effects of thermal fluctuation.
Dependence of magnetic field loss on the electron –beam energy
Dependence of magnetic field loss on the electron –beam energy
Magnetic field intensities decrease with the number of electrons
Magnetic field change rate is not proportional to the beam energy
The radiation-induced demagnetization grew keeping its field change profile.
The radiation-induced demagnetization grew keeping its field change profile.
Field change increases with irradiated electron numbers
The profiles normalized by maximum change show same profile.
8 GeVProfile
The profiles of the magnetic field change that demagnetized at a 2 % with a 4 GeV and 8 GeV electron irradiations.The profiles of the magnetic field change that demagnetized at a 2 % with a 4 GeV and 8 GeV electron irradiations.
The profiles were approximately same.
Protection PlansProtection Plans
SPring-8 Storage RingSPring-8 Storage Ring
• High coercivity magnets ( NEOMAX35EH 1989 kA/m)
•Stabilization ( thermal treatment 415 K × 24hrs)
Magnet propertyMagnet property
XFELXFEL
Principle of the diamond detectorPrinciple of the diamond detector
The electron beam halo monitor has been developed for an interlock device.The beam tests carried out at the beam dump of the SPring-8 booster synchrotron.
•High radiation hardness•High insulation resistance•Sufficient heat resistance
Configuration of the test DetectorConfiguration of the test Detector
H. Aoyagi et.al. XFEL : 60 nC/sec 3.7×1011 electrons/secHalo Monitor
Linearity of the Output SignalPeak current100 mAAverage current 200 pA
Peak current 10 μAAverage current 20 f A
preliminary
H. Aoyagi et.al.
The incident electron of 1.5×103/pulse results in the charge signal of about 25 fC.
CryoundulatorCryoundulatorIn-vacuum undulator
200 W@80KCryocooler
Flexiblethermalconductor
Heater
Supporting shaft
T. Tanaka, H. Kitamura
Future Plan Future Plan
TemperatureTemperature
Cryoundulator PrototypeCryoundulator Prototype
Cryocooler
Flexible thermal conductor
Permanent magnet
Cryoundulator PrototypePM Material: NEOMAX50BHu=15mm,L=0.6m
Temperature ControlGM-cycle Cryocooler & Sheath Heater