1. Mezentsev Nikolay Budker Institute of Nuclear Physics
Relevant experience with superconducting wigglers at BINP and plans for supercconducting undulators
Mezentsev Nikolay
Budker Institute of Nuclear Physics
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

2. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Content
Introduction
Three groups of SC wigglers
High field wigglers
Medium field wigglers
Short period wigglers
Comparison of horizontal and vertical racetrack coils
Horizontal racetrack type magnetic structure for undulator application
Wiggler cryogenic systems
Magnetic measurements systems for SC magnets
Resume and future plans
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

3. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Introduction
The history of manufacturing and application of superconducting multipole magnetic systems in Budker INP has been started in 1979 – the year of creation of the first superconducting multipole wiggler (“snake”) ( B=3.5T and period of 9 cm) and its installation on the VEPP-3 storage ring as a powerful x-ray source.
Pole number 20
Pole gap, mm 15
Period, mm 90
Magnetic field amplitude, T
3.5
Vertical beam aperture, mm
7.8
The magnet system of the first superconducting 20-pole wiggler (“snake”) (1979)
The first superconducting 20-pole wiggler (“snake”), assembled with cryostat, before installation on the ring (1979)
Undulator radiation from the first superconducting 20-pole wiggler (“snake”), (1979)
For the period more than 30 years Budker INP has stored the wide experience on creation of superconducting multipole magnetic systems – superconducting wigglers and shifters, used as generators of synchrotron radiation (SR) in many international centres of synchrotron radiations.
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

4. List of SC multipole wigglers, fabricated by Budker INP
Year
Magnetic field, (BMax*) normal
Poles number (main + side)
Pole gap, mm
Period mm
Vertical aperture, mm
7 T wiggler BESSY-II, Germany
2002
(7.67) 7.0
13 + 4 19
148 13
3.5 T wiggler ELETTRA, Italy
(3.7) 3.5
45 + 4
16.5 64 11
2 T wiggler CLS, Canada
2005
(2.2) 2.0
61 + 2
13.5 34
9.5
3.5 T wiggler DLS, England
2006
(3.75) 3.5 60
7.5 T wiggler SIBERIA-2, Russia
2007
(7.7) 7.5
19 + 2
164 14
4.2 T wiggler CLS, Canada
(4.34) 4.2
25 + 2
14.5 48 10
4.2 T wiggler DLS, England
2009
(4.25) 4.2
13.8
4.1 T wiggler LNLS, Brazil
(4.19) 4.1
31 + 4
18.4
2.1T wiggler ALBA-CELLS, Spain
(2.27)2.1
12.6 30
8.5
4.2 T wiggler ASHo, Australia
2012
(4.5) 4.2
59+4
15.2
50.5
7.5 T wiggler CAMD LSU, USA
2013
(7.75) 7.5
11+4
25.2
193.4 15
2.5 T wiggler KIT, Germany
(2.85) 2.5
36+4
46.88
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

5. 3 groups of SC multipole wiggler
The superconducting wigglers may be divided into three groups according to their use.
High field (7-7.5 T) and long period ( mm) wigglers. This type of the wigglers are installing on SR sources with relative low electron energy on purpose to expand a photon energy range to more hard X-ray. As a rule one wiggler may give a SR beam for 3 or more independent beamlines. This kind of the wiggler to be installed on a storage ring with electron energy of 6-8 GeV can give the chance to development of new researches, including possibility of creation of bright sources of positrons and neutrons. (On SR sources with electron energy 1-2 GeV it also can be used as a source of terahertz undulator radiations).
Half of the long period SC multipole wiggler for the CAMD LSU (USA). B0 =7.5 Tesla, 0~200 mm)
After installation of the wiggler on the CAMD ring (The wiggler behind group). (May, 2013)
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

6. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Long period, high field SC multipole wigglers
(B0 =7-7.5 Tesla, 0~ mm)
Moscow, Siberia-2, 2007
21-pole SC wiggler
Field 7.5 T
Pole gap mm
Period 164 mm
BESSY, Germany
2002
2013 cryostat upgrade
17-pole, SC wiggle
Field 7T
Pole gap 19 mm
Period 148 mm
CAMD LSU, USA 2013
15pole SC wiggler
Field 7.5 T
Pole gap mm
Period 193 mm
Low photon energy spectrum of 7.5 T wiggler at CAMD 1.35 GeV (K=148)
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

7. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Medium period and medium field SC multipole wigglers
(B0 = Tesla, 0~48-60 mm)
It makes sense to use two section windings for wigglers with a period more than 48 mm thus it is possible to receive increase in a field at 15%, feeding different sections with different currents according to the behaviour of the SC wire critical curve.
Magnetic pole of superconducting wiggler magnet
T=3.2K
B=4.2T
B=4 T
T=4.2K
Cross section of two sections pole
Load lines of pole sections and critical curves
of SC wire for different temperatures
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

8. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Medium period and medium field SC multipole wigglers
(B0 = Tesla, 0~48-60 mm)
DLS, England, 2006
49-pole SC wiggler
Field 3.5Т
Pole gap 16 mm
Period mm
DLS, England, 2008
49-pole SC wiggler
Field 4.2Т
Pole gap 14.4 mm
Period 47 mm
CLS, Canada, 2007
27- pole SC wiggler
Field 4.2 Т
Pole gap mm
Period 48 mm
LNLS, Brasil, 2009
35-pole SC wiggler
Field 4.2Т
Pole gap 18.4 mm
Period 60 mm
ASHo, Australia 2013
63-pole SC wiggler
Field 4..2 Т
Pole gap 15.2 mm
Period mm
ELETTRA, Italy, 2002
2013 cryostat upgrade
49-pole SC wiggler
Field 3.5 T
Pole gap 16.5 mm
Period 64 mm
KIT, Germany, 2014
40-pole SC wiggler
Field 2.5 T
Pole gap 19 mm
Period 47 mm
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

9. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Short period SC multipole wigglers
(B0 =2-2.2 Tesla, 0~30-35 mm)
CLS, Canada,
2004
63-pole SC wiggler
Field 2.2 T
Pole gap 13.5 mm
Average period 35 mm
SC wire parameters
Wire diameter with/without insulation, mm
0.91/0.85
Ratio of NbTi : Cu
1.4
Number of filaments
312
Critical current (Amp)
(at 7 Tesla)
Assembly of ½ of the wiggler. In order to destroy periodicity between poles special spacers were installed in random order to destroy undulator spectrum in photon energy range 6-10 keV
In spite of the small bending radius of the SC wire (3 mm) the current-carrying property of the wire was not lost.
Calculated spectrum without random spacers
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

10. 2.1 Tesla 119-pole superconducting wiggler ALBA-CELLS (Spain)
Materials Science and Powder Diffraction (MSPD) beamline
ALBA, Spain, 2010
119-pole SC wiggler
Field 2.2 Т
Pole gap 12.4 mm
Period 30 mm
Pole number (main + side)
117+2
Vertical beam aperture, mm
Horizontal beam aperture, mm 10 60
Pole gap, mm
12.6
Period, mm
30.
Maximal field, Tesla
Nominal field, Tesla
2.28
2.1
One section windings,
SC wire–Nb-Ti/Cu , diameter 0.5 mm
Current in section at 2.1 Tesla, A
440
Stored energy, kJ 36
Liquid helium consumption, liter/ hour
<0.03
Total weight, ton
2.5
The wiggler installed on ALBA ring
Assembled superconducting multipole wiggler for ALBA ring
X-ray beam from the wiggler
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

11. 2.1 Tesla 119-pole superconducting wiggler ALBA-CELLS (Spain)
Sketch of the main pole of the wiggler
½ of the SC magnet
Main magnetic element of the magnet
Spectrum photon flux through 1x1 mm^2 at 30m
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

12. 2.1 Tesla 119-pole superconducting wiggler ALBA-CELLS (Spain)
First field integral (angle) behavior at 2.1 T
Longitudinal field distribution at set field 2.1 T
Spatial spectrum of the magnetic field distribution at 2.1 T
Second field integral (coordinate) behavior at 2.1 T
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

13. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Interpolation formula for the fabricated planar, horizontal racetrack SC wigglers
Figure shows the dependance of maximum magnetic field versus gap/λ by the interpolating curve and experimental data of different SC wigglers listed in the table above.
The region which we have a plan to master in the nearest future
First SC multipole wiggler 1979
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

14. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Comparison of horizontal and vertical racetrack coils
Horizontal racetrack
Vertical racetrack
Short SC wire is required
Long SC wire is required
Large number of splices for large number of poles.
Less number of splices.
Total SC wire length is minimal
Total SC wire length is 3-4 time more.
There is a possibility to make multi sections coils
There is no possibility to make multi section coils
The coils are stressed by bronze rods to compensate magnetic pressure in coils.
There is no possibility to stress coils by external compression
Minimal stored magnetic energy and inductance
Stored energy and inductance is larger by at least 3 times
The coils have good thermo contacts with iron yoke after cooling down due to external compression
The thermo contacts became worth after cooling down. This is important disadvantage for indirect cooling magnets
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

15. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Horizontal racetrack type magnetic structure for undulator application
Horizontal racetrack coils assembly allows :
to pre-stress all coils together for compensation of magnetic pressure
to use 2 or more sections coils, which gives a possibility to obtain higher field for the same SC wire.
There is no limitation of pole number
Minimal period of an undulator is about 12 mm with use SC wire diameter of 0.5 mm
Large number of splices does not increase heat in-leak if to use cold welding method of wire connections
Magnet array of horizontal racetrack type poles (example of 30 mm period SC 2.1T wiggler)
Cold welding method of wires connection gives resistance of the connection Ohm
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

16. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Superconducting multipole magnet system with indirect cooling
Electrical and heat sink commutation
Assembling of the poles on the iron yoke
Main pole with heat sink
Assembled magnet before vacuum chamber installing
Assembled magnet
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

17. Wiggler cryogenic system
The primary goal of the cryostat design is to create reliable safe systems with the possibility of long term independent work with close to zero liquid helium consumption. Stages with temperature ~50К of all cryocoolers are used for cooling the external shield screen intercepting of heat coming through the electron vacuum chamber, radiation from the warm walls of the housing and heat coming from normal conducting current leads due to their heat conductivity and Joule heat.
Horizontal bath cryostat for a wiggler magnet
In order to provide zero liquid He consumption four 2-stage cryocoolers are used symmetrically situated relatively of the wiggler ends. The basic cryostat is to prevent of any heat to penetrate into the liquid He tank intercepting it by heat sinks connected to the cryocoolers stages. Two cryocoolers with stages of 4К and 50К (type 1) and two cryocoolers with stages of 10К and 50К (type 2) are used for this aim.
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

18. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Cryostat for SC magnet with indirect cooling
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

19. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Current leads block
The cryocoolers with 4K stage are assembled together with the current leads block, consisting of a normal conducting part and high-temperature superconductors (HTSC)
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

20. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Vacuum chamber and copper liner
The second stages of the cryocoolers with 20K stage are used for cooling down of 20К shield screen and for interception of released heat in the copper liner when the electron beam is passing through the liner.
Cross section of cold vacuum chamber with copper liner inside (bath cryostat version)
Copper liner assembled with vacuum chamber
Copper liner with ULTEM support
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

21. Cryostat parameters during operation
The temperature of HTSC current leads is in a range of 40-50К at different operating modes with or without currents in the wiggler coils. Protection of the HTSC current leads against overheat and combustion is based on temperature sensors located in junctions of normal conducting current leads with HTSC current leads.
Screen of control system shows the cryostat parameters: vacuum, LHe level, currents, magnetic field, pressure and temperature distribution in the cryostat during normal operation mode.
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

22. Cryostat parameters during operation
Top ends of HTSC current leads temperature behavior during stability test
The 4K stages of cryocoolers are equipped with copper heat exchangers which are situated in gas helium inside liquid helium tank. These heat exchangers liquefy helium gas effectively reducing the magnet temperature and the pressure in the helium tank. The equilibrium temperature can be decreased down to K and, accordingly, the pressure in a tank can decrease down to bar.
The insulating vacuum at steady state of the cryostat corresponds to 10-7–10-8Torr.
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

23. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Magnetic measurements systems for SC magnets:
Hall probes measurement system in bath cryostat
Stretched wire measurement in own cryostat
Hall probe measurement in own cryostat
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

24. Hall probe array on rotatable disk Bath cryostat for magnet test
The bath cryostat has a parameters:
Height – 4.5 m
Diameter – 700 mm.
On the top flange contains special scanning system for magnetic measurements.
Five LakeShore Hall probes array is used for measurements inside liquid helium at 4.2K.
The Hall probes are mounted on the rotatable disk with 90 degree rotating angle for relative calibration and for magnetic field mapping.
2 meters
scanner
Top flange of the cryostat
Hall probe array on rotatable disk
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Bath cryostat for magnet test

25. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Relative calibration of Hall probes
at 4.1 Tesla
Longitudinal magnetic field distribution at field level 4.1 Tesla (overlapping of all 5 Hall probes turned 90 degrees using relative calibration data)
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

26. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Each pole has taps connected to fast multichannel voltmeter which accumulate measured data in memory.
Quench signal stops voltmeter and the signal data analysis gives a possibility to know the pole number
in which this quench was occurred.
Voltage behavior in time during quench in different poles. quench was happened in pole 13.
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

27. Field integrals measurements with stretched wire method
Main purposes:
To make a table of currents (main and correctors) to provide field ramping up and down without orbit distortion
To minimize field ramping time
To estimate field multipole integrals at any field level
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

28. Motivation of the method
- beam orbit in magnetic field B(s)
- beam rigidity
- bending of stretched wire with current in magnetic field B(s)
- Rigidity of stretched wire with current
First term of equation may be neglected for thin wire
The equations for beam and for wire are identical for
Beam orbit and curved wire are described by formulas (L-magnet field length)
if initial angle and coordinate are equal to 0 at –L/2:
angle deviation of beam orbit or wire at s-position
X-coordinate of beam orbit or wire at s-position
Angle and coordinate at L/2
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

29. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Scheme of measurements and calculations
Total angle deviation
L=L1=L2
Orbit distortion at condition
Parameters:
L1=L2~2 m
I~0.5-2 A
WPM accuracy – 1-5 mkm
Tension force - ~ 10 N
1-st Field integral accuracy - ~4*10-5 T*m
2-nd field integral accuracy- ~ 10-4 T*m2
Wire position monitor
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

30. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Main and corrector currents behavior during field ramping up for zero field integrals
The currents in the windings versus magnetic field for zero first field integral
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

31. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Second field integral during field ramping up and down
First field integral during field ramping up and down
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

32. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
End of cryostat with antechamber tube (photo)
Antechamber tube
Tube translator
Tube tension system
Cryostat flange
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

33. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Site Acceptance Test with Hall probe measurement system
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

34. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Hall probes measurements setup
Stretched line
For Hall probe
measurements
Step motor
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

35. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Field distribution at zero currents (after normal operation)
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

36. Longitudinal field distribution at B=4.2 Tesla
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

37. Resume and future plans
The technology of fabrication of horizontal racetrack coils for multipole magnetic systems with the period from 30 mm and above is debugged. About 20 superconducting multipole magnetic systems are successfully working in the various SR centers as SR generators.
Use of horizontal racetrack coils in multipole magnetic systems have shown the reliability and simplicity in manufacturing. Almost all defects of some coils caused by defect of a wire or errors at winding are finding at room temperature. If a defective pole is found during low temperatures tests in bath cryostat it is replaced easily.
Large number of splices also does not represent any problem due to very small contact resistance.
The magnetic system with horizontal racetrack coils has no any length limitation.
Bath cryostat with liquid helium and cryocoolers has proved as a reliable cryogenic system able during years to work independently in the conditions of limited access
Based on the experience of the fabricated short period wigglers it is possible to assert that the minimum period of magnetic system with horizontal racetrack coils can be limited by 12 mm.
The magnetic system with horizontal racetrack coils with indirect cooling was developed and created
Cryostat for magnet with indirect cooling was developed and created.
Superconducting undulator with horizontal racetrack coils ,with the period of mm and with indirect cooling system is planned to be fabricated in the nearest future.
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

38. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014
Thanks for attention
Superconducting Undulator Workshop, RAL,UK April 28-29, 2014