Superconducting magnets for SR generation in Budker INP: the status of works

1. Superconducting magnets for SR generation in Budker INP: the status of works N.A. Mezentsev Budker INP, Novosibirsk, Russia RUPAC-2006, Novosibirsk

2. INTRODUCTION • In Budker INP of Siberian Branch of Russian Academy of Science already more than 25 years there is an activity on creation of superconducting special magnets for generation synchrotron radiation, such as superconducting 3-pole magnets – «shifters», superconducting multipole magnets – «wiggler» and bending superconducting magnets – «superbends». • Spectral characteristics of Synchrotron Radiation (SR) from bending magnet are determined by two parameters:electron energy E and magnetic field B,с~E2B. • There are two ways how to make a spectrum harder : • to increase electron energy • to increase magnetic field in radiation point. • The first way of increase of hardness has many advantages, but demands big material and manpower resources, while the second way is cheap enough and rather simple at use of insertion devices like • superconducting wave length shifters • superconducting wigglers • superconducting high field bending magnets (superbends). RUPAC-2006, Novosibirsk

3. Superconducting Wave Length Shifters (WLS) Shifter represents 3-pole magnet with zero first and second field integrals along a trajectory. The central pole of the magnet has strong magnetic field and is used for generation of hard X-raySR, while side poles are used for orbit correction. List of Superconducting Wave Length Shifters at Budker INP RUPAC-2006, Novosibirsk

4. Beam orbit inside a standard (three-pole) wiggler has a bump so, that a point of radiation from Field maximum of of central pole is not on wiggler axis and During field change it moves in horizontal direction perpendicular to beam movement. 10 Tesla WLS on Spring-8 RUPAC-2006, Novosibirsk

5. 7 Tesla WLS for BESSY-2 SCWLS Side view Superconducting magnets e- Normal conducting Corrector-magnets • Wave Length Shifter with fixed radiation point, where the superconducting part of magnet has non-zero first field integral and requirements of zero field integrals are performed by normally conducting correcting magnets which are outside of shifter cryostat. • This variant of shifter allows to compensate for the first and second field integrals over each ½ shifter parts so that in the central pole the radiation point will be always on an straight section axis at any field level of the shifter. Correctors Top view RUPAC-2006, Novosibirsk

6. 9 Tesla superbend prototype for BESSY-2 (2003) All mentioned above devices are intended to be installed into straight sections of storage rings. For storage rings with energy up to 2 GeV the spectrum from bending magnet is limited to energy of photons up to 25 keV and it strongly limits possibilities of realization of experiments. Superbend is a rather cheap approach allowing to considerably expand possibilities for experiments of already existing and expensive experimental stations, needing expanded spectrum in its hard end. A disadvantage of the Superbend is that in comparison with a superconducting high-field insertion devices it is a basic element of the storage ring and all its systems should be not less reliable than conventional magnetic elements forming the storage ring. RUPAC-2006, Novosibirsk

7. Superbend cross -section in median plan External housing Room temperature vacuum chamber Beam orbit 20K shield Iron yoke Liquid helium vessel 60K shield coils RUPAC-2006, Novosibirsk

8. Following the idea to change normal conducting magnet by superbends, Budker INP in collaboration with BESSY-2 designed, fabricated and tested in 2003 a prototype superconducting bending magnet with the magnetic field above 9 Tesla using combined Nb-Ti and Nb-Sn superconducting wire. Cold part of Superbend for BESSY-2 Normal conducting bending magnets Superconducting bending magnets (superbends) Assembled BESSY-2 Superbend. (Quench at 9.6 Tesla) Proposal of compact SR source with energy E=1.2 GeV, Bsc=8.5 Tesla RUPAC-2006, Novosibirsk

9. 13 Tesla supercoducting solenoids for VEPP-2000 13T SC solenoids Scheme of coils distribution in superconducting solenoid General view of VEPP-2000 collider Measured magnetic field distribution along the solenoid axis. Assembled solenoid Cryostat of the solenoid in axial section. RUPAC-2006, Novosibirsk

10. Superconducting Wigglers (SCW) Superconducting вигглеры represent sign-variable magnetic Chain манитов with equal to zero in the first and second integral of a field. Inside Such system movement of a bunch occurs on a trajectory close to Sine wave, with small enough fluctuation of a horizontal corner, That leads to concentration of all radiation inside of this corner. RUPAC-2006, Novosibirsk

11. Optimization of wigglerparameters • Optimization of wiggler period includes: • Maximal photon flux in defined spectral region, • Maximal length of straight section • Maximal radiated power from wiggler (photon absorber limitation) • Minimal vertical beam aperture • Superconducting wire properties Photon flux with energy range 1-4 keV versus wiggler period for CAMD LSU (magnet length – 2m, vertical aperture 15 mm, electron energy- 1.3 GeV) 2-D map of photon flux (a.u.) in axis: x- period length, y- photon energy (Electron energy -3 GeV, magnet length 2 m, Vertical beam aperture – 8 mm, maximum radiated power 20 kWatt for Beam current 0.4 A (CELLS project) Photon flux with energy range 10-40 keV versus wiggler period for CELLS (magnet length – 2m, vertical aperture 8 mm, electron energy- 3 GeV) RUPAC-2006, Novosibirsk

12. Superconducting coils of ELETTRA wiggler Sketch of ½ pole of magnet Photo of ½ pole of the magnet SC Wire characteristics Two halves of magnet before assembling RUPAC-2006, Novosibirsk

13. Superconducting 63 pole 2 Tesla wiggler for CLS (2005) SPECTRAL CHARACTERISTICS OF the WIGGLER RADIATION • Multipole wigglers represent sign-alternating magnetic structure with many poles with high magnetic field. Electron beam passing through multipole wiggler concentrates SR from all poles into the same horizontal angle and increase photon flux. • In an ideal case for infinitely long periodic wiggler and for zero energy spread in electron beam the spectrum of radiation is line spectrum with energy maximum values defined by expression: • where n is the harmonic number,  is the relativistic factor, 0 is the undulator period, B0 is the magnetic field amplitude in median plane, is the undulator parameter defined below: • The maximum of radiation from wiggler falls corresponds to harmonic number: • For CLS wiggler the above parameters are: K~6.3, Nmax 95 and photon energy of the basic harmonic is equal 0.11 keV. In real situation, the spectrum of radiation is continuous due to final number of the wiggler periods, existence of energy and angular spread in electron beam. Presented wiggler has rather complicated spectral structure with transition from spectra of undulator radiation to spectra of set of sign alternating bending magnets (wiggler) depending on energy of photons. XAFS experiments require smoothness of spectrum in range 5-40 keV. Effects of electron beam energy spread and final number of wiggler poles are not enough for spectrum smoothness in photon energy area 5-10 keV. To provide of required spectrum smoothness in low energy range it was required to bring in casual disorder in period length of the wiggler. RUPAC-2006, Novosibirsk

14. CLS WIGGLER MAGNETIC SYSTEM Wire and coils parameters • The strong magnetic field on the wiggler axis median plane is created by 122 central and 4 side coils wound over the ARMCO-iron cores. • The shape of the central pole is racetrack type with dimensions of 88 mm x16.6 mm2 and height of 23.85 mm. • All coils consist of one section with total turns number of 105. • Central coils (122 ps) are energized by two independent power supplies with maximum current 400 A each where currents are summarized. • The Additional 4 side coils are energized by 1 power supply giving a possibility to adjust first field integral to zero. . Sketch of the magnet coils. Photos of the magnet coils. Critical magnetic field value vs the SC wire current at the temperature 4.2 K RUPAC-2006, Novosibirsk

15. Main parameters of superconducting wiggler for DLS ½ pole of the wiggler Longitudinal SC wiggler magnetic field distribution at 3.5 Tesla RUPAC-2006, Novosibirsk

16. Quench history of superconducting wiggler for DLS Remanent magnetic field after setting zero currents in the coils Remanent magnetic field after quench RUPAC-2006, Novosibirsk

17. WIGGLER CRYOGENIC SYSTEM • Used equipment: • Cooling of shield screens is made by means of 2 stage cryocoolers (Leybold, Sumitomo) with temperatures 20К and 60К • 2 stage cryocoolers with temperatures 4K and 50K (recondensors) are used for heat inleak reduction into liquid helium • and recondensation ofthe evaporated helium (Leybold, Sumitomo) • HTSC current leads are used to reduce heat inleakinto liquid helium 20K Copper liner is used In superconducting multipole wigglers to remove all heat created by electron beam Some cryostat concepts in which cryocoolers for refrigerating of evaporated He were used for WLS and wigglers. Cryocooler heat exchangers were placed inside liquid helium vessel. The cooler performance is low in such cheme low liquid helium consumption was about 0.5 liter per hour. More effective cryostat concept is a cryostatwhere cryocoolers are used for interception of heat inleak into liquid helium vessel. This concept of cryostat gives zero liquid helium consumption for normal cryocooler operation. Cryocooler efficiency of work degrades with time and liquid helium consumption became not zero. Average liquid helium consumption during an year is estimated as 0.05 litres per hour under condition of annual technical service of the coolers. RUPAC-2006, Novosibirsk

18. WIGGLER CRYOGENIC SYSTEM 49 pole SC wiggler For Diamond Light Source under Site Acceptance Test RUPAC-2006, Novosibirsk

19. WIGGLER CRYOGENIC SYSTEM Current lead block Main temperature probes values versus time at different field level of the wiggler. • Current leads feeding the magnet with current 400А are the main source of heat in-leak into liquid helium vessel due to both heat conductivity and joule heat. Each current lead consists of two parts: normal conducting brass cylinder and high-temperature superconducting ceramics. • One pair of current leads assembled into one block together with 2 stage cooler 4.2GM which is placed in insulating vacuum of the cryostat. • The junctions of normally conducting and superconducting parts of current leads are supported at temperature 50-65K by first stage of coolers. • The lower part of a superconducting part of the current lead is connected with superconducting Nb-Ti cable and supported at temperature below 4.2K with the help of the second stage of the coolers. • Power of 2-nd stage of the coolers is approximately twice more than heat in-leak power at lower end of superconducting current leads and the rest cooler power is used for cooling liquid helium vessel. Coolpower 4.2GM Brass current lead 60K stage HTSC current lead 4K stage Vacuum-LHe feedthrough RUPAC-2006, Novosibirsk

20. Vacuum chamber and copper liner Insulating vacuum is separated from UH vacuum of a storage ring and keep at vacuum level 10-6 – 10-7Torrby 300l/s ion pump Liquid helium vessel with vacuum chamber fittings Beam vacuum chamber system Copper liner LHe vessel RUPAC-2006, Novosibirsk

21. Wiggler Control system RUPAC-2006, Novosibirsk

22. Thank you RUPAC-2006, Novosibirsk