Good question.
The basic SF premise of TNL is that human beings have a "real" soul.  That
is to say, that there is a physical thingy in which human consciousness
resides.  It is not defined scientifically, but it may be thought of as a
sort of electromagnetic Kirlan field that can have an independent exitence,
The presumpton is that there is an extensive technology based round it.
It is called "pneuma" and the technology is "pneumatechne".
The human being is a sort of pneuma-flesh hybrid, but there are also beings
entirely of pneuma.   These are technically known as pneumasomatic entities.
colloquially known as Eaters
Many "Eaters" are **pneumavores** - soul-eatsrs.  They consume human souls
if they can get them.
They also consume each other and raw energy in electrical form.
They are locally native to the Van Allen belts, but may have come there from
elsewhere  -
All this is straight from Hodgson's own work.  There is an essay on it here
http://home.clara.net/andywrobertson/nightsoul.html
Pneumatechne involves investigating the whole pneuma realm, of which the
human being (a pneume/flesh symbiote) is a part.
In practical terms it involves
1) building technology to protect people against the Eaters.   The multiple
physical and electromagnetic shields of the Redoubt are primarily directed
to this end.
2)  Finding out about the Eaters - Khresten's work as a Seer invlves
mechanically amplified telepathy, and  telepathy in this sense is a normal
sensory ability of the human pneumea/symbiote/
3)  Finding ways to destroy the Eaters.
The Eaters also go back to Cordwainer Smith's Dragons - in fact you may have
noted the Ragnarok extract made the connection explicitly.
They are vunerable to intense electromagnetic energy, much as we are
vunerable to an iron spike through the head.  They may also be hurt by
intense light (Smith's photonuclear bombs).  But some vibrations and 
wavelengths, or combinations, can also poison, confuse, and destroy 
them at low intensity.
SO, essentially the watchmen at the end are armoured - not necessarily in
heavy armour, but in something that has an electromagnetic pulse running
through it that the Eaters will find intolerable and flee from.      .
They will be shepherding VERY heavy equipment - things the size of cars -
essentially designed to split the "infected" volume of the tower up by into
sections with electromagnetic force screens, and then to saturate each
section in turn with plasma discharges and electric vibrations which will
kill the Eaters in that section.   Then move on to the next.
They will have sensors that warn them where the Eaters are
The final scene, if you like, I would envisage them as first, setting up a
screen across the door.   Then "electrifying" the floor and walls of the
room, so the Eaters can no longer endure contact with it.
Then they would push the screen forward into the room by electromagnetic
distortion (imagine it like a curved wall of lightening pushing in: behind
it they can barely be seen)  and two would enter the room carrying equipment
to "anchor" the screen at some point within the room.   This is the point of
risk for them - if the Eaters penetrate the screen they can be attacked and
soul-destroyed.   But if they succeed they have a corridor pushing into the
room which they can then use to repeat th process, moving in equipment and
extending the screens furthur, sectioning the room up with "overlapping
floods of briliance", till finally only the central console is left.
They would not have anti personal weapons becaus they would be useless in
this context.   However they might be "carrying" equipment that looked like
extremely distorted guns.   Think "projector" not "gun".      Screen
deformers.  Ionisers (to make the air conductive).
The equipment might be based on a loony-Tesla vibe.  Scalar electromagnetic
wave projectors.  Stuff
Wonderful site
http://www.cheniere.org/books/part1/teslaweapons.htm
Also
http://www.wolfenstein.nl/sitegfx/wolfenstein.nl/wapens/tesla.jpg
http://www.physics.ncsu.edu:8380/courses/py202/pictures/tesla.gif
http://flyingmoose.org/truthfic/tesla.jpg
http://www.mtu.edu/studenthandbook/images/large-inverted-tesla-coil.jpg
http://www.alumni.caltech.edu/~decker/tesla.jpg
http://utenti.tripod.it/oiramilgrande/tesla.jpg
http://images.google.com/images?hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&q=tesla
+weapon
Also anything that has used heavy e/m work.  Pix of REAL particl
accelerators (not the ones from Ghostbusters).
http://www.aip.org/history/lawrence/larger-image-page/first-7a.htm
http://www.mindfully.org/Nucs/2002/LBNL-Bevatron-Particle-Accelerator7aug02.
GIF