IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 18, NO. 2, JUNE 2008 779

Application of the SMES for the Large ScaleAccelerator Magnet Power Supply

Hikaru Sato, Katsuya Okamura, Toshifumi Ise, Yushi Miura, Shinichi Nomura, Ryuichi Shimada,Takakazu Shintomi, and Shigeharu Yamamoto

Abstract—Power supply for the large-scale accelerator magnetsdraws a large amount of power from the utility network. For an ex-ample, the new proton accelerator complex for high intensity beam(Japan Particle Accelerator Research Complex, J-PARC) is underconstruction at the Tokai campus of Japan Atomic Energy Agency(JAEA) as a joint project between KEK and JAEA. The J-PARC50 GeV proton synchrotron (50 GeV-PS) magnets power suppliesare constructed with IGBT and IEGT, then the power factor is al-most 100%. However, the swing of an active power becomes almost170 MW, although the average power is about 50 MW. Such largepulse power will give un-allowed disturbances to an ac power line.A SMES system will be required for compensating such as pulseelectric power and reducing the disturbances. Case study on circuitconfiguration of the power supply with SMES and present statusof the R & D for the SMES system will be discussed.

Index Terms—Accelerator, power compensation, power leveling,SMES.

I. INTRODUCTION

THE accelerators for particle and nuclear experiments aregetting to large scale, then the electric power demand is

also very huge. For such case, the power line is connected to anultra high voltage power line and the compensation of the fluc-tuation is essential. On the other hand, compact accelerators formedical use have come into wide use. In these cases, electricpower is connected to a general commercial line, but the com-pensation of the power fluctuation is also necessary and loadleveling should contribute the good cost performance. For thesecompensating the power fluctuation and load leveling, Super-conducting Magnetic Energy Storage (SMES) is very attractive.SMES system has been investigated since 1970th and a verygood progress has achieved in research and development forseveral MJ class SMES system. In this paper, the R&D statusof the SMES and an example are introduced as an applicationof the SMES to the accelerator magnet power supply.

Manuscript received August 28, 2007. This work has been supported by theJoint Development Research at High Energy Accelerator Research Organization(KEK).

H. Sato and K. Okamura are with High Energy Accelerator Research Organ-ization, Tsukuba, Ibaraki 305-0801, Japan (e-mail: hikaru.sato@kek.jp).

T. Ise, Y. Miura, and Y. Yamamoto are with Osaka University, Suita, Osaka565-0871, Japan (e-mail: ise@eei.eng.osaka-u.ac.jp).

S. Nomura and R. Shimada are with Integrated Research Institute, TokyoTechnology, Meguro-ku Tokyo 152-8550, Japan (e-mail: shin@nr.titech.ac.jp;rshimada@nr.titech.ac.jp).

T. Shintomi is with Nihon University, Chiyoda-ku, Tokyo 102-0073, Japan(e-mail: shintomi-takakazu@arish.nihon-u.ac.jp).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TASC.2008.922240

II. R&D HISTORY AND STATUS OF SMES

SMES had been proposed to electric power leveling and hadbeen studied at the University of Wisconsin and Los AlamosScientific Laboratory so far, since the end of 1960’s [1], [2]. InJapan, research and development (R&D) to energy transfer andload leveling for the synchrotron magnet power supply at KEK[3], [4] were performed. In an electric power system society inJapan, a fundamental engineering study has been performed foryears, and the progress of power semiconductor has opened theavailability of SMES for stabilizing the power system and main-taining power quality, control the frequency fluctuation, protec-tion for the instantaneous voltage drop and so far. That is, threetimes national development projects for SMES have been per-formed. The basic technology to make the SMES feasible hadbeen established for eight years since 1991, and the reducingsystem construction cost have been performed for five yearssince 1999. At this present, field test of 20 MJ class SMESis under going since 2004. These projects were promoted byNEDO (New Energy and Industrial Technology DevelopmentOrganization established by the Japanese government).

Application study of SMES for the accelerator magnet powersupply project started under support by the Joint DevelopmentResearch at High Energy Accelerator Research Organization(KEK) and research of SMES for replacement FWG has beencontinued.

III. SMES FOR THE LARGE SCALE ACCELERATOR

MAGNET POWER SUPPLY

We will introduce the R&D study of the energy storagesystem for the J-PARC project for an example of the large-scaleaccelerator magnet power supply. There are following twocases of study for an accelerator magnet power supply re-placement. At the case of CERN-PS magnet power supply,SMES-based modular compensator system has been studiedfor a conceivable replacement of the existing flywheel with amotor-generator [5]. At the BNL-AGS, the simulation study ofa power supply where energy is stored in capacitor banks withdc to dc converter was presented [6].

A. J-PARC Project and Energy Storage

The J-PARC project is under progress as the joint project bythe Japan Atomic Energy Agency (JAEA) and the High EnergyAccelerator Research Organization (KEK) [7]. The facility islocated at the JAEA Tokai site and comprises a 600-MeV linac(in Phase I, an 181 MeV linac is already commissioning for a400 MeV linac), a 3-GeV rapid-cycling synchrotron (RCS), and

1051-8223/$25.00 © 2008 IEEE

780 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 18, NO. 2, JUNE 2008

TABLE IREQUIREMENTS FOR POWER SUPPLY OF BENDING MAGNET

Fig. 1. Typical excitation current pattern of the bending magnet for 50-GeVoperation.

a 50-GeV synchrotron main ring (MR). The 50-GeV MR com-prises 96 bending magnets, 216 quadrupole magnets, 72 sex-tupole magnets and 186 steering magnets. The power supplysystem for the magnets of the 50-GeV MR is made up of a largenumber of power supplies, one is for the bending magnets, 11 forthe families of the quadrupole magnets, three for the families ofthe sextupole magnets and 186 for the steering magnets. Thesepower supplies are operated with an excitation pattern of trape-zoidal wave form. For example, the requirements for the powersupply of the bending magnet and the excitation current patternof the bending magnet are shown in Table I and Fig. 1, respec-tively. The total amounts of active power of these power sup-plies become about 105 MW and 65.0 MW in peak withonly cable loss for 50-GeV operation [8].

The MR has a three-superperiod configuration and thebending magnets are divided into three sections and six groupsin total as shown in Fig. 2. Each group is excited with a unitof power supply. Therefore, the power supply for the bendingmagnets consists of six power supply units, while each familyof the quadrupole magnets has one power supply unit [8].

The pulse electric power is required to excite the magnetscorresponding to the resistive and inductive parts at the 50 GeVoperations. Since the power supply adopts the self-commutatedconverter system utilizing IGBT or IEGT, no reactive power isgenerated and power factor is almost unity.

The typical patterns of the active power for 50 GeV, 40 GeVand 30 GeV operations are shown in Fig. 3. The peak power isgenerated at the end of the full excitation and the beginning ofthe de-excitation of the magnets. The big active power swing,170 MW, affects a connected network with disturbances overa permissible level. In order to reduce such disturbances, somecompensation device has to be installed. When the MR is ex-cited up to 40 GeV in Phase-I, the pulse power will be about ahalf of that of the 50 GeV operation, and the disturbance levelis allowable. That is, the result of the original design indicates

Fig. 2. Configuration of the magnet connection with the power supply units forthe 50 GeV MR. The accelerator is a three super-period configuration.

Fig. 3. Typical patterns of the active power for 50 GeV, 40 GeV and 30 GeVoperation.

that the disturbance level is allowable if the total pulse poweramplitude is less than 100 MW which was calculated by TokyoElectric Company.

Two kinds of devices may be considered for the pulse elec-tric power compensation: one is the Flywheel Generator System(FWG) and the other is SMES.

For the original design of the energy storage system, adoubly-fed FWG system has been under consideration asshown in Fig. 4 [8]. The preliminary investigation has beencarried out for the FWG and performed the 75 kW class modelexperiment [9], [10]. A 50 MVA flywheel energy storagesystem should be installed for the MR 50 GeV operation.However, the number of pulse repetition will be times inthe lifetime of the MR. In case of the FWG, therefore, this largenumber of repetitions have to be carefully considered becauseof repetitive mechanical and thermal stresses.

B. SMES for J-PARC

As mentioned above, we assume that the pulse power overthat at the 40 GeV operation has to be compensated. This means

SATO et al.: APPLICATION OF THE SMES FOR THE LARGE SCALE ACCELERATOR MAGNET POWER SUPPLY 781

Fig. 4. Conceptual block diagram of the power supply system with FWG forthe 50-GeV MR.

Fig. 5. Various configuration of magnet power supply with SMES. (a) Config-uration using line commutated ac/dc converter; (b) configuration using forcedcommutated ac/dc converter; (c) configuration using forced commutated ac/dcconverter and dc type SMES.

that the pulse power over around 60 MW is to be compensatedand the energy for compensation over 60 MW is estimated asaround 30 MJ. If 30% of the stored energy in the SMES systemis assumed to be used with a conservative estimate, a SMESsystem, which has the capacity of 100 MJ, is necessary. Threetypes of configuration of magnet power supply with SMES areconsidered as shown in Fig. 5. Types (a) and (b) are simple caseat an ac line as like as the FWG system and we propose the otherexcellent system configuration (c), that is, six SMES units are

Fig. 6. Six SMES units are connected at the dc side of the power supply.

Fig. 7. Four solenoid coils configuration.

connected at the dc side of the power supply as shown in Fig. 6.The ac-to-dc converter supplies only the averaged compensatedpower corresponding to the loss by the resistive part of the mag-nets and the chopper does the pulse power corresponding to theinductive part of the magnets.

C. Design of SMES

In consideration of the six units power supply, supercon-ducting coil for SMES is also composed of six units. Aconfiguration of four solenoid coils with opposite polaritiesis presented as shown in Fig. 7, although we proposed alsothe 100 MJ class Force-Balanced Coil SMES [11], [12]. Atthe design, the parameters were fixed as that the maximummagnetic flux density was 5.0 T with the Rutherford type Nb-Ticonductor and the height of coil was twice the diameter. Thedesign study has been carried out for the cases that the storedenergy of one coil is 2.0 MJ and 5.0 MJ. Then, the total storedenergies by four pole coils and six units are 48 MJ and 120 MJfor the cases of 2.0 MJ and 5.0 MJ, respectively. In order tocompensate the pulse power of 21 MJ, 44% and 18% of the

782 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 18, NO. 2, JUNE 2008

TABLE IISOLENOID PARAMETERS OF SMES

Fig. 8. Calculated line voltage fluctuation. (a) 154 kV line; (b) 66 kV line.

stored energy of the 48 MJ and 120 MJ are used, respectively.Specifications of the coil unit are shown in Table II.

D. Simulation of SMES for J-PARC

The simulation of this 1/6 equivalent circuit, that is one unitcircuit in Fig. 6, has been performed using PSCAD/EMTDCsoftware [13]. Calculated results of the voltage fluctuation areacceptable for the power system as shown in Fig. 8.

IV. OTHER APPLICATIONS OF SMES FOR ACCELERATOR

A. Lord Leveling

A power supply of compact accelerator such as medical useis connected the general commercial power line. Power swingis expected not so large, but load leveling is very effective toreduce the running cost and control of voltage fluctuation is alsonecessary. SMES is available to do it.

B. Protect for Instant Voltage Drop

Although the storage ring for radiation photon source and col-lider experiments requires almost continuous power lording butnot pulsed power, instant voltage drops due to lightning forceunexpected beam aborts. SMES is superior to protect or recoverfrom the instantaneous voltage drop by high-speed input/outputof electric energy. For example, micro-SMES has been installedat National Synchrotron Light Source Facility in BNL [14] and

the SMES-UPS is under construction at National Institute forFusion Science in Japan [15].

V. CONCLUSION

A large scale SMES is expected the replacement for thepumped storage power plant and available at the time to need.On the other hand, several MJ to several hundred MJ classSMESs are available for the accelerator and the fusion plantpower supply. Status of the research and development wasintroduced especially in Japan and an application study hasbeen performed for the J-PARC accelerator magnet powersupply. The progress of power semiconductor has opened theavailability of SMES for stabilizing the power system andmaintaining power quality, control the frequency fluctuation,protection for the instantaneous voltage drop and so far. Ap-plications for these needs were also described. Field test ofthe 20 MJ class SMES for control of the voltage fluctuationstarted and the results would be expected. Further study shouldbe continued for the application to J-PARC accelerator magnetpower supply.

ACKNOWLEDGMENT

The authors would like to acknowledge with thanks thehelp and stimulating discussions of Research Association ofSuperconducting Magnetic Energy Storage (RASMES), Inter-national Superconductivity Technology Center (ISTEC) andthe Research Laboratory of Kyushu Electric Power Company.

REFERENCES

[1] H. L. Laquer, “Superconducting magnetic energy storage,” Cryogenics,pp. 73–78, Feb. 1975.

[2] R. W. Boom et al., “Superconductive energy storage for power sys-tems,” IEEE Trans. Magn., vol. MAG-8, no. 3, pp. 701–703, Sep. 1972.

[3] M. Masuda et al., “100 kJ superconducting coil energy storage,” inProc. 6th Int. Conf. on Mag. Tech., 1977, p. 254.

[4] T. Shintomi et al., “3 MJ magnet for the superconducting energystorage,” Adv. Cryo. Eng., vol. 25, pp. 98–104, 1979.

[5] R. Gehring et al., “SMES-based power supply for accelerator mag-nets,” IEEE Trans. Appl. Supercond., vol. 16, no. 2, pp. 594–597, Jun.2006.

[6] I. Marneris et al., “Simulations of the AGS MMPS storing energy incapacitor banks,” presented at the PAC’07, Albuquerque, NM, Jun.25–29, 2007, MOPAS096, unpublished.

[7] [Online]. Available: http://j-parc.jp/Acc/en/index.html[8] Accelerator Technical Design Report for J-PARC KEK Report

2002-13.[9] H. Akagi et al., in Proc. PAC’99, New York, 1999, p. 3749.

[10] H. Akagi and H. Sato, IEEE Trans. Power Electron., vol. 17, p. 109,2002.

[11] S. Nomura et al., “Demonstration of the stress-minimized force- bal-anced coil concept for SMES,” IEEE Trans. Appl. Supercond., vol. 13,no. 2, pp. 1852–1855, Jun. 2003.

[12] T. Shintomi et al., “SMES for electric power compensation of theJ-PARC high intensity proton synchrotron,” IEEE Trans. Appl. Super-cond., vol. 16, no. 2, pp. 628–631, Jun. 2006.

[13] I. Ise et al., “Magnet power supply with power fluctuation compen-sating function using SMES for high intensity synchrotron,” IEEETrans. Appl. Supercond., vol. 13, no. 2, pp. 1814–1817, Jun. 2003.

[14] T. R. Abel, in Power Quality/Power Value Proc., Sep. 1997, pp.404–417.

[15] A. Kawagoe et al., “AC losses in a conduction-cooled LTS pulse coilwith stored energy of 1 MJ for UPS-SMES as protection from momen-tary voltage drops,” presented at the Appl. Supercond. Conf., 4D04,unpublished.