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

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

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

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)2.1 117 + 2 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

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 (150-200 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

Superconducting Undulator Workshop, RAL,UK April 28-29, 2014 Long period, high field SC multipole wigglers (B0 =7-7.5 Tesla, 0~150-200 mm) Moscow, Siberia-2, 2007 21-pole SC wiggler Field 7.5 T Pole gap 20.2 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 25.2 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

Superconducting Undulator Workshop, RAL,UK April 28-29, 2014 Medium period and medium field SC multipole wigglers (B0 =2.5-4.5 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

Superconducting Undulator Workshop, RAL,UK April 28-29, 2014 Medium period and medium field SC multipole wigglers (B0 =2.5-4.5 Tesla, 0~48-60 mm) DLS, England, 2006 49-pole SC wiggler Field 3.5Т Pole gap 16 mm Period 58.5 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 14.5 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 50.5 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

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) 510-550 (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

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

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

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

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

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

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 connection10-10- 10-13 Ohm Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

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

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

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

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

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

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

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 3.0-3.6 K and, accordingly, the pressure in a tank can decrease down to 0.3-0.5 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 15-20 mm and with indirect cooling system is planned to be fabricated in the nearest future. Superconducting Undulator Workshop, RAL,UK April 28-29, 2014

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