The referenced paper [18] is informative:
http://www.space-nation.org/images/a/a1/Mini-Mag_Orion_and_s...===
2.3. Deceleration: the canonical issue
While accelerating to a sizable fraction of the speed
of light is a daunting task, deceleration is a yet more
challenging task. The reason is that no realistic scenario
to provide the gravy-train approach to either momentum
transfer or pellet energy transfer at distances of 4+
light years seems within known physics. We are therefore
challenged with either sending sufficient numbers
of pellet-sheath elements so that the spacecraft can decelerate
with on-board energy, or to come up with some
other innovative concept.
2.3.1. Fueling at departure point
One option is to provide all necessary propellant at
the departure location. If the specific power and specific
impulse is sufficiently high, this is a potential approach.
However, for our MMO concept, it is not particularly
feasible. For example, our specific power is certainly
high enough, but our specific impulse is dictated by
the pellet-sheath combination, which limits the Isp to
128,955 s. While this may seem like a prodigious specific
impulse, the ratio of spacecraft speed .1 c to g * Isp
is 23. This means that the deceleration propellant must
be e^23 times the spacecraft mass, which is an unworkable
solution.
2.3.2. Mag Sail deceleration
In 2003 both Andrews and Lenard postulated using
a large superconducting ring to intercept charge particles
in interstellar space to slow the spacecraft down
from high speeds. Additionally, the solar wind emanating
from a star system provides an additional source
of charged particles that can interact with the magnetic
field. Deceleration can actually begin a sizable distance
from the target star system. The following two charts
indicate deceleration, velocity and time as a function of
distance from the target star system. In this case the first
phase of the deceleration starts at 21600 AU with a twoturn
superconducting carbon nano tube reinforced loop.
This loop captures the charged interstellar medium and
deflects it to decelerate the spacecraft. This initial hoop
size is 500 km in radius and carries 1,000,000 A of current.
The spacecraft decelerates from .1 c to 6300 km/s
by the time the spacecraft reaches 5000 AU. This will
be quite a light show, so if there are any intelligent life
forms with an observing system, they should be able to
see the arrival.