Wei Liu, Jing Li, Jia-Su Wang, and Su-Yu Wang
10 HTS Maglev launch technology
10.1 Introduction
The electromagnetic launch system can be divided into three typical modes depending
on the type of propulsion, such as rail gun, coil gun, and linear motor modes.
The rail gun mode is composed of two rails and a projectile to construct a closed
loop of current. A very high current pulse can be excited in the loop by a pulsed
power supply. The current pulse in the rails produces a highly magnetic field, which is
combined with the current in the projectile and produces a very large propulsion force.
The final muzzle velocity of railgun developed by the US Navy can achieve 2.5 km/s
with a 20-kg projectile [1]. In the rail gun mode, the projectile must contact the rail to
complete the pulse current loop. This creates mechanical friction so that this model is
not suitable for application of the HTS Maglev system.
The coil gun mode is based on the magnetic forces between a coaxial coil and
the projectile. The coaxial coil is usually designed as the barrel and can produ-
ce a highly magnetic field under a large current pulse. The projectile is made of
ferromagnetic materials or permanent magnets, which can produce a large force
with the high field of the coaxial coil. This force produces a high muzzle velocity.
Because of the axisymmetric magnetic force configuration in the radial direction, the
projectile in the coaxial coil could achieve stable suspension and have no mechanical
friction. Because the large magnetic force derives from the highly magnetic field
gradient, the length of coaxial coil should not be too long. The barrel of a coil
gun usually consists of several segments of coaxial coil to improve the gradient of
the magnetic field and thus of the force. However, the control of the coil gun is
more complicated than that of the rail gun, because it is necessary to control the
pulse current in each individual coil segment according to the location of projectile.
Limited by the performance of electronic power devices under high frequency and
large current, it is difficult to acquire a very high muzzle velocity for the coil gun.
The coaxial coils could be fabricated with superconducting wires or tapes which
have far lager current density than copper. A HTS bulk could acquire a high trapped
flux density up to 17.24 T [2], which is far larger than the residual flux density of a
PM. Thus, the magnetized HTS bulk is an ideal candidate for the projectile of the
coil gun.
The linear motor mode is composed of two modules: one is the propulsion
module, which is composed of segments of a linear motor, including an induction or
a synchronous style. The other is the support module, which can be divided into three
types: a mechanical slide type, the electromagnetic suspension (EMS) type, and the
HTS Maglev type.