J Low Temp Phys (2010) 159: 374–380 DOI 10.1007/s10909-009-0064-z
Progress in the Development of the Wuhan High Magnetic Field Center L. Li · T. Peng · H.F. Ding · X.T. Han · Z.C. Xia · T.H. Ding · J.F. Wang · J.F. Xie · S.L. Wang · Y. Huang · X.Z. Duan · K.L. Yao · F. Herlach · J. Vanacken · Y. Pan
Received: 22 July 2009 / Accepted: 1 December 2009 / Published online: 7 January 2010 © Springer Science+Business Media, LLC 2010
Abstract Since April 2008 the Wuhan High Magnetic Field Center (WHMFC) has been under development at the Huazhong University of Science and Technology (HUST) at Wuhan, China. It is funded by the Chinese National Development and Reformation Committee. Magnets with bore sizes from 12 to 34 mm and peak fields in the range of 50 to 80 T have been designed. The power supplies for these magnets are a capacitor bank with 12 modules of 1 MJ, 25 kV each and a 100 MVA/100 MJ flywheel pulse generator. The objective of the facility is to accommodate external users for extensive experiments in pulsed high magnetic fields. Up to seven measurement stations will be available at temperatures in the range from 50 mK to 400 K. The first prototype 1 MJ, 25 kV capacitor bank with thyristors, crowbar diodes and a mechanical switch has been developed and successfully tested. For the protection of the thyristor switch, a toroidal inductor is developed to limit the current at 40 kA. Five magnets have been wound with CuNb and copper wires and internal reinforcement by Zylon fiber; external reinforcement is a stainless steel shell encased by carbon fiber composite. Two Helium flow cryostats have been successfully tested and reached temperatures down to 4.2 K. Measurement stations for magneto-transport and magnetization are in operation. The design, construction and testing of the prototype system are presented.
Keywords Pulsed magnetic field · Capacitor bank · Magnet · Measuring system
L. Li () · T. Peng · H.F. Ding · X.T. Han · Z.C. Xia · T.H. Ding · J.F. Wang · J.F. Xie · S.L. Wang · Y. Huang · X.Z. Duan · K.L. Yao · F. Herlach · J. Vanacken · Y. Pan Wuhan High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan, 430074, China e-mail:
[email protected]
J Low Temp Phys (2010) 159: 374–380 Table 1 Main parameters of the three types of designed magnet
a C: capacitor bank, G: pulse
Field (T)
Short Pulse
Bore
Pulse duration
(mm)
(ms)
C
34
65
60
C
22
30
70
C
14
20
80
C
12
15
Long Pulse
50
G
22
2250/100b
60
C
26
200
Dual Stage
80
C
14
200/8c
b 2250/100: the total pulse
c 200/8: pulse duration of the outer coil is 200 ms and of the inner coil 8 ms
Power supplya
50
generator duration is 2250 ms and the flat top is 100 ms
375
1 Introduction A New Pulsed High Magnetic Field Facility is under development at the Huazhong University of Science and Technology (HUST), Wuhan, China [1]. The laboratory is funded by the Chinese National Development and Reformation Committee and the Chinese Education Ministry to establish a pulsed high magnetic field center for accommodating external users to perform extensive experiments in pulsed high magnetic fields. Various measurement stations will be available at WHMFC in the temperature range from 50 mK to 400 K in fields up to 80 T. The main parameters of the designed magnets are as shown in Table 1. Magnets are driven with two types of pulsed power supply, a modular 12 MJ/25 kV capacitor bank and a 100 MVA/100 MJ flywheel pulsed generator.
2 The Layout of the Wuhan High Magnetic Field Center The building of the Wuhan Pulsed High Magnetic Center (WHMFC) is under construction and scheduled to be finished in September 2009. It consists of three main parts: a machine shop, an experimental hall and an office building. The total area of the structure is about 9000 m2 . The layout of the experimental hall is shown in Fig. 1. The 12 MJ capacitor bank and rectifiers for the pulse generator will be installed in the power supply hall. The control center is adjacent to the power supply hall. Surrounding the power supply hall and the control center are 11 measuring cells to keep the distance short for easy communication. The laser will be placed between cells No. 8 and No. 9 and thus the transmission loss of laser light is minimized. For safety, all signals are transmitted by optical fiber links, and the walls of the measuring cells are reinforced. The cryogenic equipment is installed next to the cell No. 11. Liquid nitrogen is provided to the measuring cells via pipes. A small Helium liquefier system with a capacity of 150 liters per day will be installed to recycle the Helium consumed by all the measurement stations. All equipment for machining, coil winding, impregnation and assembly will be installed in the machine shop.
376
J Low Temp Phys (2010) 159: 374–380
Fig. 1 The layout of the experimental hall in the Wuhan High Magnetic Field Center
3 The Pulsed Power Supplies A modular 12 MJ/25 kV high energy density capacitor bank and a 100 MVA flywheel pulsed generator are used to energize the pulsed magnets as listed in Table I. Both are currently under construction and will be finally tested until the end of 2010. The modular concept for the capacitor bank is to enable the generation of different pulse shapes or rise time with variable energy and capacitance. The capacitor bank consists of 11 modules with a maximum energy content of 1 MJ (3.2 mF, 25 kV, modules 1 to 11) each and 2 modules with 0.5 MJ (1.6 mF, 25 kV, modules 12 and 13) each. The total stored energy of the 13 modules is 12 MJ. All modules are equipped with switches to connect them to current collectors for different measurement cells. This configuration also enables us to energize multistage coil systems with up to three separate sub-coils. The pulsed flywheel-alternator is used to energize a 50 T/100 ms long-pulse magnet via two 12-pulse power converter modules, which can provide a no-load voltage of 4.6 kV and a full-load voltage of 3.4 kV at the rated current of 20 kA. As a prototype of the capacitor bank, a 1 MJ capacitor module has been built, passed the tests and is now in operation as shown in Fig. 2. It consists of the capacitor (C), the protection coil (L), the main discharge switch (T), the crowbar circuit (D, RC1 , RC2 and S1 ), the discharging circuit (R and Relay2 ), the polarity changing switches (SP1 and SP2 ), the filter circuit (RF , CF and RS ), the charging unit and the switch gear. The charging time is less than 60 seconds with a charging current of 1.8 A. When relay No. 2 is closed, the full energy can be dumped into the resistor within 3 seconds. The resistances RC1 , RC2 , and RC3 of the crowbar circuit are
J Low Temp Phys (2010) 159: 374–380
377
Fig. 2 (Color online) A picture of the 1 MJ, 25 kV prototype capacitor bank and the schematic diagram of the electric circuit
400 m ceramic resistors with 25 kV and 35 kA voltage and current capability. The discharge switch consists of seven T1503N80T light triggered thyristors (LTT) made by the EUPEC Company. The diode stack (D) of the crowbar circuit is composed of nine DS3480Y50 diodes. For the protection of the thyristor switches, an inductor of 1.05 mH is developed and placed in series with the switch to limit the current at 40 kA in case of short circuit. In order to reduce the interference of the stray field of the inductor to the environment, the inductor is designed as a toroidal system consisting of 12 flat wound coils evenly distributed on the perimeter of a circle. If it is required, the inductance can be adjusted by reducing the number of coils.
4 Magnets A number of magnets with different bore size, peak field, energy, and pulse duration have been designed as shown in Table 1. These can be divided into three groups: short pulse magnets, long pulse magnets and dual stage pulsed magnets. All magnets are designed with the efficient pulsed magnet design package PMDS 2.2 [2]. The shortpulse magnets are energized by the capacitor bank to produce peak fields of 50 T to 80 T half-sine wave with pulse duration less than 100 ms in bore sizes ranging from 12 mm to 34 mm. There are two types of long-pulse magnets with pulse duration longer than 100 ms driven by capacitor bank and pulse generator. A dual stage magnet is designed to reach peak fields up to 80 T. Both inner and outer coils are energized by capacitor banks. The design philosophy of all magnets is to internally reinforce the inner layers of the conductor windings by fiber composite materials and
378 Table 2 Coil parameters of the wound magnets
J Low Temp Phys (2010) 159: 374–380 Magnet
No. 1
No. 2
No. 3
No. 4
No. 5
Field (T)
50
60
60
70
75
Bore (mm)
34
18
18
11.5
11.5
Conductor
copper
copper
copper
copper
CuNb
Cross section (mm2 )
24
24
25
24
25
Reinforcement
Zylon
Zylon
Zylon
Zylon
Zylon
Number of Layers
27
27
31
31
23
Pulse duration (ms)
30
20
25
20
25
Height (mm)
120
85
100
100
120
Fig. 3 (Color online) A picture of coil No. 3 ready for testing and the measured signal waveform during the test
allow for the separation at the interface of the reinforcement layer with the next outboard conductor layer wound on their top [3], and the outer compact part of the coil is supported by a stainless shell as an external reinforcement. The thickness of the internal reinforcement is optimized to nearly equalize peak stress in the layers of the composite. For the outer layers, there is still a thin layer of fiber composite inserted between the conductor layers for electric insulation. The deformation of the outer layers is mainly confined by the external reinforcement made from a stainless steel shell reinforced by composite materials on the outside. To verify the designs and to gather experience in coil winding, impregnation and assembly, five magnets with different bore sizes and peak fields have been developed. The parameters of these coils are listed in Table 2. Figure 3 shows a picture of coil No. 3 and the field waveforms during the coil testing.
5 The Control and Measurement System A user-friendly Control and Measurement System (CMS) is designed and realized at the pilot facility of WHMFC. The safety of personnel, the instrumentation and the
J Low Temp Phys (2010) 159: 374–380
379
Fig. 4 (Color online) A screen print of the interface of the control and measurement system of the prototype system during an experiment
data management are the main functions of the CMS. It consists of two parts: the central control system (CCS) in the control room and the Local Control and Measurement System (LCMS) at the measurement cell. The two systems are connected via optic fiber transmission for galvanic isolation. The CCS includes the user console (HMI), the trigger signal generator and the lock signal generator. All control and monitor commands including parameter settings, charging, dumping, discharging and so on, are issued on the interface of the CCS at the control room. These commands are then received and interpreted at the local control and measurement system. A DSP embedded system is developed to control the switches, relays and thyristors of the capacitor bank. The analog signals of dI /dt, dB/dt and the signals from the experimental sample are measured by a 24 bits, 200 kHz sample rate DAQ card made by National Instruments. Other functions, such as controlling, security, regulation and data logging are also realized in CMS. Figure 4 shows a screen print of the CMS interface during an experiment.
6 Measurement Stations Two experimental stations for electrical transport and magnetization measurements have been set up. A Helium flow cryostat and a G-M cryocooler system can be used to cool the samples for experiments in solid state physics. The lowest temperature
380
J Low Temp Phys (2010) 159: 374–380
that can be reached by the G-M cryocooler is 9.8 K. With the flow cryostat, temperatures down to 4.2 K can be obtained. Electrical signals as low as 10 microvolts can be recorded by using a commercial 24 bits DAQ card with 200 kHz sample rate. Experiments on double perovskite, alloy, and manganite materials are in progress. In a first series of magneto-transport and magnetization experiments, the magnetic phase diagram of double layered perovskite manganites has been explored. Moreover, magnetization and critical current density measurements of the new Fe-pnictides in fields up to 50 T will be pursued.
7 Conclusion A new pulsed high magnetic field facility is under development. It will provide a useful research tool for the scientific communities in China as well as in other countries, joining the word-wide community of pulsed field laboratories. Acknowledgements The work described in this paper was supported by the Chinese National Science Foundation (50888002, 50707011) and the bilateral project Flanders-China BIL 07/01.
References 1. L. Li, H.F. Ding, T. Peng, X.T. Han et al., IEEE Trans. Appl. Supercond. 18, 596 (2008) 2. T. Peng, L. Li, J. Vanacken, F. Herlach, IEEE Trans. Appl. Supercond. 18, 1509 (2008) 3. L. Li, F. Herlach, Meas. Sci. Technol. 6, 1035 (1995)
