[Slick]

Are you asking if theses would work in real life or for a fictional stroy?

For fiction, anything goes of course.

For real life (sorry to be so negative):

Q1: Unfortunately not. Most elements won't fuse to begin with [only those lighter than Fe are even possible], and adding lots of energy tends to make things fly apart whereas fusion requires containment with high temperatures and pressures. So, in short, no.

Q2a: We haven't the foggiest idea on how to manipulate gravity other than moving giant masses around so a gravity field generator is fictional.

Q2b: "Energy" field? Energy is a concept, not a physical thing in itself. It is a quantity which in essence means "the capacity to do work", and since it is not it is not a physical thing, it is meaningless to form it into a shield.

Q3c: This one is the closest to something that we could do. Some "rad" [radiation] is comprised of charged particles and thus can be shielded by a strong magnetic field. The earth is protected from nearly 100% of all cosmic radiation of this type by its magnetic field. There are uncharged kinds of radiation which would be unaffected by a magnetic field. Gamma (or any electro-magnetic) rays, neutrons, neutrinos, are some and there are many more examples. For most of these, some solid shield is required. Neutrinos, for example, are so penetrating that they could penetrate a light-year of lead; but on the positive side, they go right through you and your ship and cause no damage.

Now, of course the argument could be made that right now our understanding of physics is too rudimentary to perform these things and one day in the future we will be able do all these and more. If that's the approach you wanna take, then it falls back on fiction until we actually do figure it out.

As Jean Luc Picard once said: "Things are only impossible until they are not."

Personally, I'd prefer to read a fictional version which is made believable by providing some, but not exacting, detail such that the reader assumes it works by some not-yet-understood-to-earthlings technology. Just enough detail should be used so as to make the reader believe it is more than PFM. Most of the better SciFi writers approach future technology this way. I'd like to read the finished product.

PFM = trade language meaning "Pure F****** Magic"

edit: can you say a-b-c???