Design & Testing of a Repetitively Pulsed Magnet for Neutron Scattering

Abstract

The National High Magnetic Field Laboratory in Tallahassee, Florida, USA has designed, built and tested a high field, split pair, Repetitively Pulsed Magnet (RPM) suitable for neutron scattering experiments. RPM magnets have the advantage of lower average power and lower construction costs than DC magnets. The NHMFL RPM program intends to build magnets with higher field and larger scattering space than those available elsewhere. Details of design and testing of the first prototype are presented.Index Terms-Neutron diffraction, repetitively pulsed magnet.

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“…Particle accelerator pulse (kicker) magnets are superconductive solenoids designed for identical requirements. Nb3Sn/Cu magnets can achieve 100T field pulses in fractions of a second and are sustainable for 10,000-200,000 pulse lifetimes [8]. They are rapidly activated as a particle beam approaches and the applied field pushes the beam onto a different path, allowing it to continue around the curve or exit accelerators.…”

“…The discovery inspired Kamerlingh Onnes to propose a 100,000 Gauss (10 T) solenoid two years later based on a superconducting coil cooled with liquid helium, yet it took more than 50 years to realize this design in practice [62]. In 1989 Motokawa et al at Tohoku University built the first of a series of a new class of magnets that were referred to as repeating pulse magnets [43] which provided pulsed fields of a few millisecond duration as high as 25 T once every 2 second [8]. These repetitively pulsed magnets were first built in a solenoid configuration [8][21] [44] for reliability and the same design is still in use today.…”

“…In 1989 Motokawa et al at Tohoku University built the first of a series of a new class of magnets that were referred to as repeating pulse magnets [43] which provided pulsed fields of a few millisecond duration as high as 25 T once every 2 second [8]. These repetitively pulsed magnets were first built in a solenoid configuration [8][21] [44] for reliability and the same design is still in use today. Pioneering design research is now being conducted by many high magnetic field centres [13][17][19] [37][54] [63] around the world which are achieving >100T strength fields and striving for second long pulse lengths but all still use solenoidal configurations.…”

“…The addition of multiple concentric coils each pulsing as the successive outer coils are energised is the key to reaching 100T fields [23][56] and beyond [54]. Magnet designers frequently trial improvements on 0.5m to 2m test coils [14][41] [63] and a review of papers on small bore coils [8][12][13] [40] shows that high field pulses are achievable in a small package. The evolution of lithium capacitor systems is the other key advancement that many facilities [17] have now integrated.…”

“…There are three highly stressed sections of a Rutherford cabled pulsed solenoid, the copper wire matrix around the filaments, the epoxy reinforcement and the cable (or core strip) midplane. [8][23] [46] Fig. 3 Rutherford cable Von Mises stress distribution: (a) non-cored cable, (b) cored cable [34] The feasibility of fabricating Rutherford cables with internal austenitic steel strips was demonstrated for the rapidcycling synchrotron project at GSI in 2005 [36][61].…”