- Email: [email protected]
A 6.4 T superconducting wavelength shifter for the generation of hard X-rays at the Siam Photon Source
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 582 (2007) 47–50 www.elsevier.com/locate/nima
A 6.4 T superconducting wavelength shifter for the generation of hard X-rays at the Siam Photon Source P. Klysubun, S. Rugmai, C. Kwankasem, W. Klysubun, P. Prawatsri National Synchrotron Research Center, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand Available online 12 August 2007
Abstract The Siam Photon Source plans to provide hard X-rays to synchrotron radiation users specifically those in the fields of macromolecular crystallography and X-ray absorption fine-structure spectroscopy. In order to generate synchrotron radiation in the hard X-ray spectral range from a low-energy (1.2 GeV) electron storage ring, installation of a high-field superconducting insertion device is necessary. A warm-bore superconducting magnet wavelength shifter, which was given to NSRC by MAX-LAB, Sweden, will be inserted into the storage ring in the middle of a straight section. The magnet consists of three pairs of iron-cored superconducting NbTi coils with a nominal peak field of 6.4 T. This report will discuss the characteristics of the WLS, the beam dynamics effects of the wiggler on the SPS storage ring optics and the necessary compensations, as well as radiation properties and radiation masking. r 2007 Elsevier B.V. All rights reserved. PACS: 41.85.Lc; 85.25.j; 07.85.Qe Keywords: Superconducting magnet; Wavelength shifter; Siam Photon Source
1. Introduction The Siam Photon Source is a dedicated 1.2 GeV synchrotron light source located in Nakhon Ratchasima, Thailand. Currently, there are three photon beamlines in operation, all of which utilize radiation in the VUV and low-energy (o8 keV) X-ray spectral regions generated by bending magnet. It had been decided that the light source should also be capable of delivering high-energy (8–20 keV) X-rays to researchers in order to expand research possibilities, specifically in the fields of macromolecular crystallography and X-ray absorption fine-structure spectroscopy involving heavy elements. For this purpose, a superconducting wavelength shifter with a peak field of 6.4 T will be inserted into one of the storage ring straight sections. The magnet was initially built for MAX-LAB, Sweden [1], where it was briefly installed and tested in the 1.5 GeV MAX-II ring [2]. Later, MAX-LAB decided that it had no use for the device and gave it to NSRC in late 2004. Corresponding author.
E-mail address: [email protected] (P. Klysubun). 0168-9002/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2007.08.084
The magnet was transported from Sweden and arrived in Thailand in 2005. 2. 6.4 T superconducting wavelength shifter The WLS magnetic structure is composed of three pairs of racetrack-shaped NbTi superconducting coils wound around iron poles. The central pole produces a nominal peak field of 6.4 T, while the two side poles generate 3.7 T opposing field for restoration of the closed orbit. The WLS utilizes two independent power supplies: a main power supply and a smaller correction power supply which supplies additive trim current to the side poles. This scheme provides the ability to adjust the first field integral (and thus, the total deflection of the beam) to zero at any wiggler field level, which eliminates the need for horizontal steerers. The maximum orbit displacement at the wiggler center and the maximum angular deviation are 7.4 mm and 772 mrad, respectively. Important characteristics of the WLS have been presented in Refs. [1,2]. The critical photon energy ec of synchrotron radiation generated from a dipole is c ðkeVÞ ¼ 0:665E 2 ðGeVÞB ðTÞ,
ARTICLE IN PRESS P. Klysubun et al. / Nuclear Instruments and Methods in Physics Research A 582 (2007) 47–50
48
which in the case of the SPS 1.2 GeV ring, ec will be increased from 1.4 keV with 1.4 T bending magnet radiation to 6.1 keV with the 6.4 T WLS field. Since the magnet had been out of commission for some time, preliminary test of the magnet coils had been carried out. Magnetic field measurements at low applied currents were performed, and the results were compared with the magnetic fields obtained from 2-D magnet simulation using the Poisson/Superfish code. The test shows good agreement between the measurement and the simulation. 3. Beam dynamics effects on the SPS storage ring To perform beam dynamics calculation, we first construct the hard-edge model of the WLS. For the main pole, the period length can be found directly from the field profile, while for the side pole it is found by comparing the field integral of the actual WLS with that of ideal sinusoidal wiggler field. This is done to ensure the same focusing strength between the two. After obtaining the period lengths, the lengths of the magnet in the hard-edge model were calculated following Ref. [3]. The bending radii of the hard-edge model were obtained from peak fields of the three poles. Finally, the bending angles were then derived from the magnet lengths and the bending radii of the hard-edge model. Parameters of the calculated hardedge model are listed in Table 1. Inserted in the SPS storage ring, the WLS distorts the ring optics and introduces +0.08 shift in the vertical Table 1 WLS hard-edge model parameters
Bending radius, rh (mm) Bending angle, yh (rad) Magnet length, 2lh (mm)
Main pole
Side pole
800.87 0.1403 112.36
1380.14 0.0702 96.89
betatron tune, as shown in Fig. 1. Matching calculation was done using the MAD code [4]. The optical functions were matched to the original unperturbed values using three pairs of quadrupole magnets adjacent to the WLS. Subsequently, the betatron tunes are adjusted to the original operating point (vx ¼ 4.749, vy ¼ 2.823) using the rest of the quadrupoles. Design and matched quadrupole strengths are listed in Table 2. Dynamic apertures before and after WLS insertion were calculated using the BETA code [5]. It was found that the dynamic aperture is reduced by approximately 30% with the introduction of the WLS. 4. Radiation power distribution and absorbers Angular power distribution of the radiation generated by the WLS can be computed from [6] dP ðW=mrad2 Þ ¼ 5:42E 4 ðGeVÞ B ðTÞ I b ðAÞ dO " # 1 5g2 c2v 1þ , 7ð1 þ g2 c2v Þ ð1 þ g2 c2v Þ5=2
where E is the electron energy, B the WLS magnetic field, Ib the electron beam current, g the relativistic factor, and cv is the vertical angle. As shown in Section 2, the radiation Table 2 Quadrupole strengths before and after WLS insertion
QF1 QD2 QF3 QD4 QF1W QD2W QF3W
40.0
20.0
35.0
18.0
With WLS (m2)
2.4319 2.6096 2.3884 1.7439 – – –
2.4159 2.5482 2.3882 1.7609 2.4593 2.7123 2.3878
14.0
25.0
12.0 b (m)
b (m)
Original value (m2)
16.0
30.0
20.0 15.0
10.0 8.0 6.0
10.0
4.0
5.0 0.0 0.0
ð1Þ
2.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 s (m)
0.0 0.0
10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 s (m)
Fig. 1. SPS storage ring optics with the WLS, before (left) and after (right) correction.
ARTICLE IN PRESS P. Klysubun et al. / Nuclear Instruments and Methods in Physics Research A 582 (2007) 47–50
fan generated by the WLS has a horizontal angular spread of 772 mrad. In the vertical direction the radiation spread is defined by the factor 1/g, which in case of the SPS ring is 70.4 mrad. The WLS radiation power density from 200 mA electron beam current is shown in Fig. 2. From the above equation, maximum power density generated by the central pole and the side poles are 14.55 and 8.12 W/ mrad2, respectively. The maximum of the total power density is 21.69 W/mrad2, which occurs at 728 mrad (h), as shown in the figure. Total generated radiation power is 1.67 kW. Due to the facts that the opening at the exit port is only 20 mrad (h) and the planned hard X-ray beamline, which will have three branches, will utilize only 17 mrad (h) central radiation fan, radiation beyond 78.5 mrad (h) has to be masked by radiation absorbers in order to protect the downstream chambers. Because of the small size of the available brazing oven, the water-cooled copper absorber on each side of the vacuum chamber will be separated into two sections: ABS1 absorber which absorbs radiation fan from 8.5 to 30 mrad, and ABS2 absorber which absorbs WLS radiation from 30 to 72 mrad. The amount of radiation power passing through the beamline is
49
191.73 W, while the two absorbers on each side of the vacuum chamber will absorb 740.01 W. The absorbers will be made of oxygen-free copper (OFCU) with water-cooling channels made of aluminum. Heat load analysis was performed using finite element analysis (FEA) software COSMOS Works. The results are shown in Fig. 3. Due to the facts that the energy of the SPS ring is low and the beam current is not very high, the heat load on the absorbers is not large and the cooling can be carried out rather easily. 5. Other preparations Regarding liquid helium required for the operation of the WLS, a helium liquefaction system is now being installed at the SPS, and will be commissioned in the second quarter of 2008. The system has a capacity of producing 20 L of LHe/h in liquefaction mode without using liquid nitrogen. The WLS operation will be closedloop such that evaporated helium is taken back to the recovery compressor of the cryogenic system for reliquefaction. For this, several modifications to the cryostat are required. A new cryostat cover is fabricated to accommodate a helium gas return port, temperature and magnetic field sensors, new current leads which are helium vapor-cooled to reduce liquid helium consumption. Relief valves and burst disks will also be installed on the cryostat cover to provide pressure safety. Automatic filling of the liquid helium will be implemented. 6. Summary
Fig. 2. Total angular power density. Dash lines indicate separation in radiation delivered to beamline and radiation absorbed by ABS1 and ABS2 absorbers.
Installation of the 6.4 T WLS in the SPS ring will provide synchrotron radiation in the hard X-ray region that will enable researchers to carry out several experiments not currently possible. To study the effects of the WLS on the ring optics, beam dynamics calculations had been performed. It was found that distortion to the ring optics introduced by the WLS can be compensated by changing the focusing of the three adjacent quadrupole pairs, while the vertical tune shift is corrected using the rest of the quadrupoles. Reduction in the dynamic aperture is not substantial and still in the acceptable range. Characteristics of the WLS radiation were calculated in order to implement proper masking. Radiation absorbers were
Fig. 3. Heat load analysis for ABS1 (left) and ABS2 (right) absorbers.
ARTICLE IN PRESS 50
P. Klysubun et al. / Nuclear Instruments and Methods in Physics Research A 582 (2007) 47–50
designed and the heat load analysis was performed using FEA software. Acknowledgments The authors wish to thank Erik Wallen of MAX-LAB for his technical assistance and invaluable suggestions regarding the WLS. We also would like to express our gratitude to Prof. Mikael Eriksson of MAX-LAB for his contribution leading to the WLS donation.
References [1] J.T. Eriksson, et al., IEEE Trans. Magn. 28 (January 1992). [2] E. Wallen, Nucl. Instr. and Meth. A 495 (2002) 58. [3] H. Wiedemann, Particle Accelerator Physics II: Nonlinear and HigherOrder Beam Dynamics, second ed., Springer, Berlin, 1993, pp. 64–66. [4] H. Grote, F.C. Iselin, The MAD Program User’s Reference Manual, CERN-SL/90-13 (AP), March 1995 (Rev. 4). [5] L. Farvacque, J.L. Laclare, A. Ropert, BETA User’s Guide, ESRFSR/LAT-88-08, 1987. [6] F. Ciocci, Insertion Devices for Synchrotron Radiation, World Scientific, Singapore, 2000 (Chapter 2).
Nuclear Instruments and Methods in Physics Research A 582 (2007) 47–50 www.elsevier.com/locate/nima
A 6.4 T superconducting wavelength shifter for the generation of hard X-rays at the Siam Photon Source P. Klysubun, S. Rugmai, C. Kwankasem, W. Klysubun, P. Prawatsri National Synchrotron Research Center, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand Available online 12 August 2007
Abstract The Siam Photon Source plans to provide hard X-rays to synchrotron radiation users specifically those in the fields of macromolecular crystallography and X-ray absorption fine-structure spectroscopy. In order to generate synchrotron radiation in the hard X-ray spectral range from a low-energy (1.2 GeV) electron storage ring, installation of a high-field superconducting insertion device is necessary. A warm-bore superconducting magnet wavelength shifter, which was given to NSRC by MAX-LAB, Sweden, will be inserted into the storage ring in the middle of a straight section. The magnet consists of three pairs of iron-cored superconducting NbTi coils with a nominal peak field of 6.4 T. This report will discuss the characteristics of the WLS, the beam dynamics effects of the wiggler on the SPS storage ring optics and the necessary compensations, as well as radiation properties and radiation masking. r 2007 Elsevier B.V. All rights reserved. PACS: 41.85.Lc; 85.25.j; 07.85.Qe Keywords: Superconducting magnet; Wavelength shifter; Siam Photon Source
1. Introduction The Siam Photon Source is a dedicated 1.2 GeV synchrotron light source located in Nakhon Ratchasima, Thailand. Currently, there are three photon beamlines in operation, all of which utilize radiation in the VUV and low-energy (o8 keV) X-ray spectral regions generated by bending magnet. It had been decided that the light source should also be capable of delivering high-energy (8–20 keV) X-rays to researchers in order to expand research possibilities, specifically in the fields of macromolecular crystallography and X-ray absorption fine-structure spectroscopy involving heavy elements. For this purpose, a superconducting wavelength shifter with a peak field of 6.4 T will be inserted into one of the storage ring straight sections. The magnet was initially built for MAX-LAB, Sweden [1], where it was briefly installed and tested in the 1.5 GeV MAX-II ring [2]. Later, MAX-LAB decided that it had no use for the device and gave it to NSRC in late 2004. Corresponding author.
E-mail address: [email protected] (P. Klysubun). 0168-9002/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2007.08.084
The magnet was transported from Sweden and arrived in Thailand in 2005. 2. 6.4 T superconducting wavelength shifter The WLS magnetic structure is composed of three pairs of racetrack-shaped NbTi superconducting coils wound around iron poles. The central pole produces a nominal peak field of 6.4 T, while the two side poles generate 3.7 T opposing field for restoration of the closed orbit. The WLS utilizes two independent power supplies: a main power supply and a smaller correction power supply which supplies additive trim current to the side poles. This scheme provides the ability to adjust the first field integral (and thus, the total deflection of the beam) to zero at any wiggler field level, which eliminates the need for horizontal steerers. The maximum orbit displacement at the wiggler center and the maximum angular deviation are 7.4 mm and 772 mrad, respectively. Important characteristics of the WLS have been presented in Refs. [1,2]. The critical photon energy ec of synchrotron radiation generated from a dipole is c ðkeVÞ ¼ 0:665E 2 ðGeVÞB ðTÞ,
ARTICLE IN PRESS P. Klysubun et al. / Nuclear Instruments and Methods in Physics Research A 582 (2007) 47–50
48
which in the case of the SPS 1.2 GeV ring, ec will be increased from 1.4 keV with 1.4 T bending magnet radiation to 6.1 keV with the 6.4 T WLS field. Since the magnet had been out of commission for some time, preliminary test of the magnet coils had been carried out. Magnetic field measurements at low applied currents were performed, and the results were compared with the magnetic fields obtained from 2-D magnet simulation using the Poisson/Superfish code. The test shows good agreement between the measurement and the simulation. 3. Beam dynamics effects on the SPS storage ring To perform beam dynamics calculation, we first construct the hard-edge model of the WLS. For the main pole, the period length can be found directly from the field profile, while for the side pole it is found by comparing the field integral of the actual WLS with that of ideal sinusoidal wiggler field. This is done to ensure the same focusing strength between the two. After obtaining the period lengths, the lengths of the magnet in the hard-edge model were calculated following Ref. [3]. The bending radii of the hard-edge model were obtained from peak fields of the three poles. Finally, the bending angles were then derived from the magnet lengths and the bending radii of the hard-edge model. Parameters of the calculated hardedge model are listed in Table 1. Inserted in the SPS storage ring, the WLS distorts the ring optics and introduces +0.08 shift in the vertical Table 1 WLS hard-edge model parameters
Bending radius, rh (mm) Bending angle, yh (rad) Magnet length, 2lh (mm)
Main pole
Side pole
800.87 0.1403 112.36
1380.14 0.0702 96.89
betatron tune, as shown in Fig. 1. Matching calculation was done using the MAD code [4]. The optical functions were matched to the original unperturbed values using three pairs of quadrupole magnets adjacent to the WLS. Subsequently, the betatron tunes are adjusted to the original operating point (vx ¼ 4.749, vy ¼ 2.823) using the rest of the quadrupoles. Design and matched quadrupole strengths are listed in Table 2. Dynamic apertures before and after WLS insertion were calculated using the BETA code [5]. It was found that the dynamic aperture is reduced by approximately 30% with the introduction of the WLS. 4. Radiation power distribution and absorbers Angular power distribution of the radiation generated by the WLS can be computed from [6] dP ðW=mrad2 Þ ¼ 5:42E 4 ðGeVÞ B ðTÞ I b ðAÞ dO " # 1 5g2 c2v 1þ , 7ð1 þ g2 c2v Þ ð1 þ g2 c2v Þ5=2
where E is the electron energy, B the WLS magnetic field, Ib the electron beam current, g the relativistic factor, and cv is the vertical angle. As shown in Section 2, the radiation Table 2 Quadrupole strengths before and after WLS insertion
QF1 QD2 QF3 QD4 QF1W QD2W QF3W
40.0
20.0
35.0
18.0
With WLS (m2)
2.4319 2.6096 2.3884 1.7439 – – –
2.4159 2.5482 2.3882 1.7609 2.4593 2.7123 2.3878
14.0
25.0
12.0 b (m)
b (m)
Original value (m2)
16.0
30.0
20.0 15.0
10.0 8.0 6.0
10.0
4.0
5.0 0.0 0.0
ð1Þ
2.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 s (m)
0.0 0.0
10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 s (m)
Fig. 1. SPS storage ring optics with the WLS, before (left) and after (right) correction.
ARTICLE IN PRESS P. Klysubun et al. / Nuclear Instruments and Methods in Physics Research A 582 (2007) 47–50
fan generated by the WLS has a horizontal angular spread of 772 mrad. In the vertical direction the radiation spread is defined by the factor 1/g, which in case of the SPS ring is 70.4 mrad. The WLS radiation power density from 200 mA electron beam current is shown in Fig. 2. From the above equation, maximum power density generated by the central pole and the side poles are 14.55 and 8.12 W/ mrad2, respectively. The maximum of the total power density is 21.69 W/mrad2, which occurs at 728 mrad (h), as shown in the figure. Total generated radiation power is 1.67 kW. Due to the facts that the opening at the exit port is only 20 mrad (h) and the planned hard X-ray beamline, which will have three branches, will utilize only 17 mrad (h) central radiation fan, radiation beyond 78.5 mrad (h) has to be masked by radiation absorbers in order to protect the downstream chambers. Because of the small size of the available brazing oven, the water-cooled copper absorber on each side of the vacuum chamber will be separated into two sections: ABS1 absorber which absorbs radiation fan from 8.5 to 30 mrad, and ABS2 absorber which absorbs WLS radiation from 30 to 72 mrad. The amount of radiation power passing through the beamline is
49
191.73 W, while the two absorbers on each side of the vacuum chamber will absorb 740.01 W. The absorbers will be made of oxygen-free copper (OFCU) with water-cooling channels made of aluminum. Heat load analysis was performed using finite element analysis (FEA) software COSMOS Works. The results are shown in Fig. 3. Due to the facts that the energy of the SPS ring is low and the beam current is not very high, the heat load on the absorbers is not large and the cooling can be carried out rather easily. 5. Other preparations Regarding liquid helium required for the operation of the WLS, a helium liquefaction system is now being installed at the SPS, and will be commissioned in the second quarter of 2008. The system has a capacity of producing 20 L of LHe/h in liquefaction mode without using liquid nitrogen. The WLS operation will be closedloop such that evaporated helium is taken back to the recovery compressor of the cryogenic system for reliquefaction. For this, several modifications to the cryostat are required. A new cryostat cover is fabricated to accommodate a helium gas return port, temperature and magnetic field sensors, new current leads which are helium vapor-cooled to reduce liquid helium consumption. Relief valves and burst disks will also be installed on the cryostat cover to provide pressure safety. Automatic filling of the liquid helium will be implemented. 6. Summary
Fig. 2. Total angular power density. Dash lines indicate separation in radiation delivered to beamline and radiation absorbed by ABS1 and ABS2 absorbers.
Installation of the 6.4 T WLS in the SPS ring will provide synchrotron radiation in the hard X-ray region that will enable researchers to carry out several experiments not currently possible. To study the effects of the WLS on the ring optics, beam dynamics calculations had been performed. It was found that distortion to the ring optics introduced by the WLS can be compensated by changing the focusing of the three adjacent quadrupole pairs, while the vertical tune shift is corrected using the rest of the quadrupoles. Reduction in the dynamic aperture is not substantial and still in the acceptable range. Characteristics of the WLS radiation were calculated in order to implement proper masking. Radiation absorbers were
Fig. 3. Heat load analysis for ABS1 (left) and ABS2 (right) absorbers.
ARTICLE IN PRESS 50
P. Klysubun et al. / Nuclear Instruments and Methods in Physics Research A 582 (2007) 47–50
designed and the heat load analysis was performed using FEA software. Acknowledgments The authors wish to thank Erik Wallen of MAX-LAB for his technical assistance and invaluable suggestions regarding the WLS. We also would like to express our gratitude to Prof. Mikael Eriksson of MAX-LAB for his contribution leading to the WLS donation.
References [1] J.T. Eriksson, et al., IEEE Trans. Magn. 28 (January 1992). [2] E. Wallen, Nucl. Instr. and Meth. A 495 (2002) 58. [3] H. Wiedemann, Particle Accelerator Physics II: Nonlinear and HigherOrder Beam Dynamics, second ed., Springer, Berlin, 1993, pp. 64–66. [4] H. Grote, F.C. Iselin, The MAD Program User’s Reference Manual, CERN-SL/90-13 (AP), March 1995 (Rev. 4). [5] L. Farvacque, J.L. Laclare, A. Ropert, BETA User’s Guide, ESRFSR/LAT-88-08, 1987. [6] F. Ciocci, Insertion Devices for Synchrotron Radiation, World Scientific, Singapore, 2000 (Chapter 2).