Prapaiwan Sunwong - Acceleratoraccelerator.slri.or.th/seminar/documents/ATD_SLRI_140709.pdf · •...
Transcript of Prapaiwan Sunwong - Acceleratoraccelerator.slri.or.th/seminar/documents/ATD_SLRI_140709.pdf · •...
Prapaiwan Sunwong
• General background – characteristics of superconductor
• Material selection and cable structure
• Multipole magnets
• Generation of multipole fields
• Magnet function and coil structure
• Insertion devices
• General design requirements
• Superconducting magnet at SPS
• Concluding remarks
Talk OutlineTalk Outline
IntroductionIntroduction
High bending field is required for
High energy
Compact machine
http://home.web.cern.ch
LHC
[ ]ρBE 3.0=
Superconducting CharacteristicsSuperconducting Characteristics
1. Zero resistanceDiscovered by Onnes in 1911– solid mercury exhibitsvanishing resistance below 4.2 K.
2. Meissner effectExclusion of magnetic flux fromits interior – discovered in 1933by Meissner and Ochsenfeld.
Critical TemperatureCritical Temperature
YBCO
www.ccas-web.org/superconductivity/
Critical Magnetic FieldsCritical Magnetic Fields
Type I
Type II
Nb3Al
Keys, 2002
Critical Current DensityCritical Current Density
Keys, 2002
Nb3Al
Critical Surface Phase DiagramCritical Surface Phase Diagram
Applications of SuperconductivityApplications of Superconductivity
• Superconducting electromagnets (low Tc)
• Medical uses – MRI scanners
• Scientific research – NMR
• Transportations – MAGLEV trains
• Fusion tokamak – ITER
• Particle accelerators
• Josephson junction devices – SQUID
• Low-loss power cables (high Tc)
• Magnet current leads (high Tc)
• Electric motors, generators, fault current limiters
Why Superconducting Magnets?Why Superconducting Magnets?
Type Advantages DisadvantagesPermanent • Compact
• Low cost ( in small low field magnets)• No utilities required• No maintenance• Simple to operate• Can result in very precise fields
• Constant field (mostly)• Limited in field
Resistive • Variable field• No need for complicated cryogenic or vacuum systems• Can be built in house or through existing industrial base• Relatively low capital cost
• Limited in field (up to ~ 2 T)• May require large amounts of electrical power and cooling water• Possible large operating costs for power & water
Superconducting • High and variable field• Lower operating costs• Reliability• Cold beam tubes yield very high vacuums• Can be made compact
• High capital costs• Limited industrial base• Requires complicated ancillary systems – cryogenics, vacuum, quench protection
www.magnet.fsu.edu
Material SelectionMaterial Selection
• Alloy of niobium and titanium extremely ductility
• Tc ≈ 9 K, Bc2 ≈ 15 T (vary with composition, 46.5% Ti optimum)
• Ic is influenced by microstructure (flux pinning)
• Copper stabiliser (RRR ≥ 100)
- mechanical stability
- electrical bypass
- heat sink
• Multifilamentary wire
• Typical filament diameter 5 – 50 μm
• Typical wire diameter 0.3 – 1.0 mm
• Twisted filament/wire reduce coupling between filaments
for ac field or during field sweep
NbTi WiresNbTi Wires
ATLAS strand
LHC MQY duadrupole strand
LHC dipole strand
RutherfordRutherford--type Cablestype Cables
Filaments(6 μm each)
Wire/strand(6,300 filaments)
Rutherford cable (36 strands)
http://lhc-machine-outreach.web.cern.ch
• Transposed cable: every wire changes places with every other wire along the length of the cable, to decouple the wires with respect to their own self field and promote a uniform current distribution.
• Rutherford-type cables can be compacted to a high density (88 – 94 %) and rolled to a good dimensional accuracy.
Rutherford Cables ManufactureRutherford Cables Manufacture
Martin Wilson’s lecture
Multipole MagnetsMultipole Magnets
Dipole
Quadrupole
Resistive magnets Superconducting magnets
Generation of Multipole FieldsGeneration of Multipole Fields
)cos()( 0 φφ mII = , m = order of multipole
)sin(2
),(
)cos(2
),(
100
100
θμθ
θμθθ
mar
aIrB
mar
aIrB
m
r
m
−
−
⎟⎠⎞
⎜⎝⎛−=
⎟⎠⎞
⎜⎝⎛−=
PR
θr
x
y
beam axis
φa
current in z direction
In superconducting magnet, field shape is defined by position of each conductor (that carries current) in the coil.
Current distribution
Magnetic field
θBrB
B
θr
x
y
Current distribution can be created by multiple intersecting circles/ellipses carrying constant current densities (J) in differentdirections.
The field inside the current free region is computed by superimposing the field produced by the conductors.
Circular conductor:
Elliptical conductor:
⇒ Difficult to fabricate⇒ Use of current shells for practical constant-CSA conductors
Generation of Multipole FieldsGeneration of Multipole Fields
)cos()( 0 φφ mII =
21
20
21
10 ,
aaxaJB
aayaJB yx +
=+
−= μμ
2 ,
2 00xJByJB yx μμ =−=
+J-J
y
x
1a2a
Magnet Function and Coil StructureMagnet Function and Coil Structure
Dipole • m = 1
• Uniform field for bending
• Intersecting (overlapping) circles
• Intersecting (overlapping) ellipses 2
0JdBB yμ
−==
21
20 aa
daJBB y +−== μ
B
Quadrupole• m = 2
• Intersecting ellipses
• Gradient field for focusing
Magnet Function and Coil StructureMagnet Function and Coil Structure
xaa
aaJB
yaa
aaJB
y
x
21
210
21
210
)(
)(
+−
=
+−
=
μ
μ
y
a1
a2
Sextupole• m = 3
• Intersecting ellipses
• For chromaticity correction
( ) ...
...222 +−=
+=
yxSB
SxyB
y
x
Liu, 2011
Some novel designs (for pure multipole fields)
Sextupole Octupole
Magnet Function and Coil StructureMagnet Function and Coil Structure
Major ProjectsMajor Projects
USPAS Course on Superconducting Accelerator Magnets, 2003
TevatronTevatron
Bottura, 2011
Major ProjectsMajor Projects
USPAS Course on Superconducting Accelerator Magnets, 2003
LHCLHC
Bottura, 2011
LHC TwinLHC Twin--aperture Dipoleaperture Dipole
cds.cern.ch
Insertion DevicesInsertion Devices
Undulator
K ≤ 1, θ ≤ 1/γ
- many alternating low-field magnetic poles- strong interference effects to increase photon flux
Wiggler
K > 1, θ > 1/ γ
Multipole wiggler- several periods to increase photon flux- less important interference effects
Wavelength shifter- one period with high field center pole (usually 5-6 T)- very short-wavelength radiation
http://pd.chem.ucl.ac.uk/pdnn/inst2/insert.htm
2c E
BK
u
u
λλ
λ
∝
∝Parameter
Critical wavelength
Helical undulator Planar undulator
Superconducting helical undulator for ILC (bifilar helix design)
UndulatorUndulator
YuryIvanyushenkov, ASD Seminar, 2013
Argonne National Laboratory’s planar superconductor undulator
Period length switching for hybrid superconducting undulator/wiggler
UndulatorUndulator
Grau, 2010
BK uλ∝
The iron yoke and poles of a CESR superconducting wiggler magnet for ILC
Multipole wigglerMultipole wiggler
Superconducting wiggler at NSLS
Superconducting wiggler at DLS
Wavelength ShifterWavelength Shifter
Prototype SWLS at NIRS
Total power distribution of SWLSat SPS (1.2 GeV, 200 mA)
YuryIvanyushenkov, ASD Seminar, 2013
Country Organization ActivityTaiwan TLS, TPS SC wigglers, R&D on SCUs
Russia Budker Institute SC helical undulator for HEP;SC wavelength shifters;SC wiggler
France ACO, Orsay SCU
Germany ANKA SCU for Mainz Microtron, R&D on SCUs
ACCEL Two SCUs (for ANKA and for SSLS/NUS, Singapore)
Babcock Noell New SCU for ANKA
UK ASTeC, RAL and DL Helical SCU for ILC
Sweden MAX-Lab SC wiggler
USA Stanford Helical SCU for FEL demonstration
BNL R&D on SCUs
LBNL R&D on SCUs
Cornell SC wiggler
NHFML R&D on SCUs
APS R&D on SCUs
Work on superconducting insertion devices around the world
General Design RequirementsGeneral Design Requirements
• Keep it superconductive with a comfortable margin
• Magnet training
- well protected (when quench)
• Reduce heat load
- minimise contact resistance
- vapour-cooled/hybrid current leads
• Good cryogenic system to handle all heating
• Good support structure to handle large Lorentz force
• Cheap and easy to manufacture
• Field quality (uniformity) – relative field error better than 10-4 is required.
• Not degraded by exposure to the high radiation levels
• Well cooling of the chamber and active interlock system
Iron YokeIron Yoke
heat exchanger
bus-bar
saturation control
Wilson’s and Bottura’s lectures
CryostatCryostat
Wilson’s and Bottura’s lectures
Radiative heat transfer ∝ T4
Thermal PropertiesThermal Properties
Ekin, 2007
Quench and ProtectionQuench and Protection
Quench = conversion of magnet energy (LI2/2) into heat inside the volume of
magnet winding which has transited into the resistive state
E = 7.8 × 106 J for LHC dipole magnet
equivalent to the kinetic energy of 26-tonnes magnet
travelling at 88 km/hr
Cause of quenching
• Low specific heat
• Conductor motion (10μm motion of
NbTi
raise local temperature to 7.5 K)
• Resin cracks
• Jc decreases with increasing temperature
Wilson’s lecture
Quench and ProtectionQuench and Protection
3D simulation of quench propagation for a cos theta type magnet
http://research.kek.jp/people/wake/magqt/
Quench and ProtectionQuench and Protection
LHC dipole GSI001
Wilson’s lecture
Safe hot spot temperature = 100 – 150 (300) K
Quench and ProtectionQuench and Protection
ten Kate 2013
1. Normal zone detected 2. Switch opened3. Heater activated
Bypass diodes for magnets connected in series
Training of Superconducting MagnetsTraining of Superconducting Magnets
Several thermal and electrical cycles need to be applied to a new coil before
the optimal performances are obtained.
Wilson’s lecture
LHC short prototype dipoles
Superconducting Magnet at SPSSuperconducting Magnet at SPS
6.5 T Superconducting Wavelength Shifter (from NSRRC, Taiwan)
• Current operating field = 4.0 T at 170 A (maximum field = 6.5 T at 308 A )
• Critical current of NbTi is 428 A at ∽8 T inside the coils.
• Helium consumption = 1.4 L/hr (published value = 1.3 L/hr)
• Hard x-rays radiation used in
macromolecular crystallography
- energy range = 12.7 keV
- flux = 109 photons/s at 100 mA
www.slri.or.th
www.slri.or.th
6.56.5 T Superconducting Wavelength ShifterT Superconducting Wavelength Shifter
Liquid nitrogen
Liquid helium
Cryogenic SystemCryogenic System
www.slri.or.th
Production capacity : 20 L/hr
• From MAX-Lab, Sweden
• Maximum field = 6.4 T at 250 A
• No liquid nitrogen screening
• 10 out of 1482 windings in side pole
were burnt off and replaced by Cu sheet.
• Helium consumption < 5 L/hr (???)
6.46.4 T Superconducting Wavelength ShifterT Superconducting Wavelength Shifter
Wallen, 2002
Concluding RemarksConcluding Remarks
• Magnet is the most important application of superconductivity.
• Superconducting magnets provide high magnetic fields, which are required for
high-energy and/or compact accelerators. NbTi has been used the most.
• Magnetic field profiles from superconducting magnets are determined by position
of superconducting coils, which can be obtained at high accuracy.
• Advantages of superconducting insertion devices:
- High field increases photon energies
- High flexibility
- Smaller period for the same peak field
- New research possibilities