Several high-field superconducting wigglers (SCW) and wavelength shifters (WLS) are fabricated in the Budker INP for generation of synchrotron radiation. Three-pole WLS with the magnetic field of 7.5 T are installed on LSU‑CAMD and BESSY-II storage rings for shifting the radiation spectrum. WLS with the field of 10.3 T will be used for generation of slow positrons on SPring-8. Creation of a 13-pole 7 T wiggler for the BESSY-II and 45-pole 3.5 T wiggler for ELETTRA now is finished. The main characteristics, design features and synchrotron radiation properties of SCW and WLS created in the Budker INP are presented in this article

Batrakov, A.M.

Bekhtenev, E.A.

Borovikov, V.M.

Djurba, V.K.

Fedurin, M.G.

Karpov, G.V.

Khruschev, S.V.

Kulipanov, G.N.

Kuzin, M.V.

Lev, V.K.

Mezentsev, N.A.

Repkov, V.V.

Shkaruba, V.A.

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

SUPERCONDUCTING HIGH-FIELD WIGGLERS AND WAVE LENGTH SHIFTERS IN BUDKER INPA.M. Batrakov, E.A. Bekhtenev, V.M. Borovikov, V.K. Djurba, M.G. Fedurin, V.V. Repkov, G.V. Karpov, S.V. Khruschev, G.N. Kulipanov, M.V. Kuzin, V.K. Lev, N.A. Mezentsev, V.A. ShkarubaBudker Institute of Nuclear Physics, SB RASLavrentiev Ave.11, 630090 Novosibirsk, Russia e-mail: shkaruba@inp.nsk.suSeveral high-field superconducting wigglers  (SCW) and wavelength shifters (WLS) are fabricated in the Budker INP for generation of synchrotron radiation. Three-pole WLS with the magnetic field of 7.5 T are installed on LSU-CAMD and BESSY-II storage rings for shifting the radiation spectrum. WLS with the field of 10.3 T will be used for generation of slow positrons on SPring-8. Creation of a 13-pole 7 T wiggler for the BESSY-II and 45-pole 3.5 T wiggler for ELETTRA now is finished. The main characteristics, design features and synchrotron radiation properties of SCW and WLS created in the Budker INP are presented in this article.PACS numbers: 41.60.ap, 07.85.Qe1  INTRODUCTIONLast few years in the Budker INP several high-field superconducting  wigglers  (SCW)  and  wavelength shifters (WLS) used as insertion devices (ID) for storage rings  are  developed  and  fabricated  for  generation  of synchrotron radiation (SR).  Such devices are used for shifting  the  photon  critical  energy  to  the  hard  X-ray range due to a high magnetic field and for magnification of  the  photon  flux  with  the  use  of  many poles.  This gives new possibilities for the existing SR sources and allows to conduct new experiments. In addition this ID can be used to control the emittance of the storage ring, to decrease the polarization time of electron or positron beam etc. In the Table 1 the main features of SCW and WLS which are produced by the Budker INP are pre-sented.2  MAGNETIC SYSTEMSuch devices as SCW and WLS are not the main el-ements of the storage ring lattice and do not reduce reli-ability of the machine. The compensation of the wiggler effects on beam dynamics has to be performed. One of the main demands for the wiggler field distribution is the minimization of the field integrals along the ID for closing rbit.  Only the central  pole of  three-pole PLS-WLS [1] has a high-field level of 7.5 T and is used for generation of SR. Two side poles with a low-level field of 1.5 T are needed for closing the beam orbit. The side pole field level is selected as low as possible for spectral separation of SR from the central and the side poles to reduce  contribution  of  the  so-called  “second source”. Some inconvenience of using of three-pole wiggler is the deviation of the equilibrium electron orbit and shift-ing the radiation point at the different field level. There-fore for the next three-pole 7.5 T WLS (CAMD-WLS [2], BESSY-WLS [3] and BESSY-PSF) two additional usual steering magnets were placed at the both ends of the ID straight section for compensation of the orbit de-viation. In this case the geometry of the SR experiments is not changed at any field level since the radiation point is fixed in the center of WLS. The distribution of mag-netic field and electron beam orbit along the BESSY-WLS straight section are presented in Fig. 1.-2000 -1500 -1000 -500 0 500 1000 1500 2000-2-1012345678magnetic fieldorbitcentral poleside polescorrectorsBESSY-II WLSB=7 Tesla  magnetic field, Tesla; orbit, cmlongitudinal coordinate, mmFig. 1. The distribution of the magnetic field and electron beam orbit along the BESSY-WLS straight section.The three-pole wiggler magnetic system (see Fig. 2) consists of two halves of an iron yoke with three super-conducting dipoles which are located above and below of the vacuum chamber. The iron yoke is designed so that a whole magnetic flux is closed inside of the mag-net  and  there  are  no  stray  magnetic  fields  outside  of wiggler. The key element of three-pole wigglers is the high-field superconducting racetrack central  pole with the iron core.  The coils  are reeled up from supercon-ducting Nb-Ti wire with the diameter of 0.85 mm and impregnated with the epoxy compound. The critical cur-rent of the used wire is equal to 360 A at a field of 7 T. Each of the central coils is separated into two sections to optimize the field – current relationship and reach the maximum field. To feed the coils two independent pow-er supplies are used. The inner and outer sections of the central coils and all side coils are powered by the first power  supply  with  a  current  of  ~150 A.  The  second power supply with a current of ~100 A feeds the outer section of the central coils. In this way the currents are summarized at the outer sections and the value of the current is equal to ~250 A. Thus each section is ener-ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3. Серия: Ядерно-физические исследования (38), с. 59-61.59gized by the optimal current and there is a possibility for easy control of the first field integral to zero at any field levels. The magnetic field homogeneity of 10-4  at 7 T is obtained at the central pole as a result of shimming in the aperture of the magnet by special iron plates. For bandaging the superconducting windings inside of the iron yoke we used two pairs of wedges produced from a material with a low heat extension factor (e.g.  invar). Different  thermal  contraction  of  the  used  material makes  it  possible  to  compress  the  superconducting winding during cooling down to the liquid helium tem-perature. Such design makes it enable to achieve a max-imum current of about 90% of the short sample current.Fig. 2. Magnetic system of three-pole BESSY-WLS.The installation of the wiggler with a field of about 10T on the Spring-8 with the electron beam energy of 8 GeV makes it possible to create a slow positron source of  high  brightness  [4].  To  obtain  the  magnetic  field higher than 8 T it is needed to use a Nb3Sn supercon-ducting wire with a higher critical current. The technol-ogy  of  manufacturing  the  high-field  superconducting Nb3Sn windings  of  the  racetrack  type  was  developed and  tested  successfully.  A  rectangular  Nb3Sn  tie 1.45x 0.85 mm2 in size was used for manufacturing the inner section of the central pole for the 10 T wiggler for Spring-8. For protection of a Nb3Sn wire from degrada-tion during the quenching the current distribution inside of the coils is matched so that two outer Nb-Ti sections are closer to the critical condition than the inner Nb3Sn section. In 2000 the wiggler was assembled and tested at the Spring-8 site and the maximum field of 10.3 T was achieved.The photon flux generated by wigglers is proportion-al to the number of the wiggler poles. So the multi-pole wigglers are used for enhancement of the X-ray flux. The multi-pole 7 T wiggler with 13 poles and 3.5 T one with 45 poles are produced now by the Budker INP for BESSY-HMI and ELETTRA, respectively. In 2001 the short  prototypes  of  these  wigglers  with  three  central poles and four side poles used for orbit compensation were successively tested. The maximum fields of 7.6 T on the magnetic gap of  19 mm were obtained for the BESSY-HMI  prototype.  For  ELETTRA  prototype  a maximum field of 3.7 T on the 16.5-mm magnetic gap was achieved.  The  full-size multi-pole wigglers  men-tioned above will be finished and installed on the stor-age rings in 2002.3  CRYOGENIC SYSTEMThe superconducting magnets are inserted into spe-cial  liquid-helium  cryostats.  In  the  first  cryostat  for PLS-WLS with liquid helium consumption of 3 liter per hour there was only one copper thermal screen cooled by liquid nitrogen. A whole series of improvements was carried out for reduction of liquid helium consumption. The view of  another cryostat  for  BESSY-WLS where heat inleakage into the helium vessel from the outside is minimized is shown in Fig. 3.Fig. 3. View of BESSY-WLS on the BESSY-II stor-age ring.The  liquid  helium  vessel  is  surrounded  by  two screens to reduce the heat flux into the helium volume. The outer and inner screens are wrapped by 30 and 10 layers  of  super-insulation,  respectively.  The  screens with the temperature of 60 K and 20 K are cooled by a two-stage cooling machine with a cooling power on the stages of 115 Watt and 15 Watt, respectively. There is the vacuum insulation with the value of 10-7 Torr be-tween the helium vessel and the external warm stainless vessel.This insulating vacuum of the cryostat is indepen-dent and completely separated from the vacuum system of the storage ring. The special cevlar suspensions are used for hanging the helium vessel and the screens to minimize heat inleakage. The ends of the suspensions pass through the external vessel walls and are used for precise alignment of the magnet position. Two pairs of HTSC ceramic current leads which connected with the optimized cooper current leads are used to energize the magnet coils.  The using of ceramic current leads per-mits to  decrease  heat  inleakage 5 times less  compare with optimized cooper current leads. Heat flux coming along  the  current  leads  from the  upper  flange  due  to thermal conductivity is taken off by connecting of coop-er current leads to the cooler stages through the special ceramic contact. After energizing the magnet coils are closed by persistent current superconducting switch and wiggler  goes  into  "freezing  current"  operation  mode. 60Then a  special  system controlled  by  computer  makes mechanical disconnection of cooper current leads from HTSC ones inside of the cryostat. The consumption of the liquid helium at the mode of disconnected current leads is equal to 0.12 liters per hour. It enables to refill liquid helium in the cryostat not often then 1 time per month. To compensate the current decay in the "freez-ing current" mode the magnetic field is stabilized with accuracy of 10-4 at 7 T by feedback system with using of NMR probes and special transformers called magnetic flux pumps [5]. To decrease the current decay a special welding technique was developed for decreasing of con-tact resistance between the superconducting coils.Table 1. Main parameters of SCW and WLS produced in BINPMagnetic field, TMax/normalNumber of polesPole gap, mmMain Pole length, mmMagnetic length, mmVertical aperture, mmRadiation power, kWPLS-WLS(Korea), 19957.68 (7.5)1+2 48 170 800 26 3.6CAMD-WLS(USA), 19987.55(7.0)1+2 51 172 972 32 5.3SPring-8(Japan), 200010.3(10.0)1+2 40 200 1042 20 100BESSY-WLS(Germany),20007.5(7.0)1+2 52 172 972 32 13 BESSY-PSF(Germany),20017.5(7.0)1+2 52 172 972 32 13 BESSY-HMI(Germany),20027.67 (7.0)13+4 19 74 1360 14 60ELETTRA(Italy), 20023.7(3.5)45+4 16.5 32 1680 11 8.84  CONCLUSIONThe installation of the high-field WLS and SCW as insertion devices enables one to improve characteristics of the storage ring for conducting new experiments with hard X-ray. Design of all the high-field wigglers manu-factured by Budker INP has much in common. Howev-er, these wigglers do not repeat each other but have their own  distinctive  features,  defined  by  specific  require-ments of concrete SR users.REFERENCES1. A.V.Grudiev et al., Superconducting 7.5 Tesla wig-gler  for  PLS //  NIM.  1995,  Vol.  A359,  No.  1-2, p. 101-106.2. V.Borovikov et  al.,  Superconducting 7 T wiggler for LSU-CAMD //  Journal of Synchrotron Radia-tion. 1998, v. 5, Part 3, p. 440-442.3. V.M.Borovikov et al. Superconducting 7 T Wave-length Shifter for BESSY-II // NIM. 2001, v. A467, No. 1-2, p.181-184.4. A.Ando et al. Proposal of the high magnetic field superconducting wiggler for slow positron source at SPring-8  //  Journal  of  Synchrotron  Radiation. 1998, v. 5, Part 3, p. 360-362.5. V.M.Borovikov et al.,  Precise NMR measurement and stabilization system of magnetic field of a su-perconducting 7 T wavelength shifter // NIM. 2001, v. A467, No. 1-2, p. 198-201.ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.Серия: Ядерно-физические исследования (38), с. 61-61.61

Superconducting high-field wigglers and wave length shifters in Budker INP

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Superconducting high-field wigglers and wave length shifters in Budker INP

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Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)