[TallTroll]

>> High-energy gamma rays have a tendancy to decay into electron-positron pairs

True, the Pair Formation Threshold is only 1.022 MeV, but note that this only makes it POSSIBLE for a high-energy photon to decay. An interaction with matter is required to trigger the decay.

Pair production is a collision process, so as long as you are able to keep your photons away from heavy nuclei, you'll be fine.

The real problems occur when you consider that you need either a ridiuclously strong field, or a massive accelerator to achieve the required energy.

We either need to learn to produce stable magnetic fields many orders of magnitude stronger than anything we can manage today, or produce really high quality vacuums. If you need an accelerator than can realistically be measured in AU, you don't have much chance of getting a photon to survive the round trip without hitting something, unless you can COMPLETELY empty the chamber. Even interstellar space has a density of about 1 - 100 atoms/cm3.

As Pluto is about 38.5 AU away (approx. 3.6 billion miles, I think), you can see that you need a VERY clean acceleration chamber for any significant chance of a photon surviving the trip.

Theoretically possible to do it then, but much engineering needed first