How does electron positron plasma act compared to normal plasma? When an electron positron plasma is formed, will it react to magnetic fields the same way? With the gamma ray photons resulting from the annihilation, would the plasma be of greater energy?
Thanks!
 A: 
When an electron positron plasma is formed, will it react to magnetic fields the same way?

The short answer is yes and no.
The primary difference between an electron-positron plasma (also called a pair plasma) and an electron-proton plasma is one of scales.
In an electron-proton plasma, the cyclotron frequencies, $\Omega_{cs}$, plasma frequencies, $\omega_{ps}$, inertial lengths, $c/\omega_{ps}$, and gyroradii, $\rho_{cs}$, are all different for the different particle species $s$ (i.e., electrons and protons) due to the vastly different masses.  In a pair plasma, the first three are identical (for quasi-neutral conditions, i.e., $n_{e} = n_{i}$ or equal number densities) and the gyroradii are the same when the temperatures are the same, i.e., $T_{e} = T_{i}$ (where $e$ is for electron and $i$ is generic for ion).
The separation of scales in an electron-proton plasma allows for several interesting phenomena from wave modes to magnetic reconnection geometries that cannot exist in pair plasmas.
Finally, the other main difference is location.  Pair plasmas generally only exist in nature in extreme environments like the magnetospheres of pulsars and magnetars.  Under such high magnetic fields, much of the dynamics are also completely different (e.g., the gyroradii can become quantized), leading to different phenomena than is commonly found in an electron-proton plasma.

With the gamma ray photons resulting from the annihilation, would the plasma be of greater energy?

Electric fields generally do work on the system to eliminate themselves.  In plasmas, this results in Debye screening -- on scales larger than the Debye length the plasma is considered neutral, i.e., $n_{e} = n_{i}$.  Thus, pair annihilation is typically not a major issue.
The extreme environments under which pair plasmas form are generally responsible for their higher energies than pair annihilation.
