Making clean energy with a Kerr black hole: A Tokamak model for gamma-ray bursts

In this paper we present a model for making clean energy with a Kerr black hole. Consider a Kerr black hole with a dense plasma torus spinning around it. A toroidal electric current flows on the surface of the torus, which ge nerates a poloidal magnetic field outside the torus. On the surface of the torus the magnetic field is parallel to the surface. The closed magnetic fi eld lines winding around the torus compress and confine the plasma in the t orus, as in the case of tokamaks. Although it is unclear whether such a mod el is stable, we look into the consequences if the model is stable. If the magnetic field is strong enough, the baryonic contamination from the plasma in the torus is greatly suppressed by the magnetic confinement, and a clea n magnetosphere of electron-positron pairs is built up around the black hol e. Since there are no open magnetic field lines threading the torus and no accretion, the power of the torus is zero. If some magnetic field lines thr eading the black hole are open and connect with loads, clean energy can be extracted from the Kerr black hole by the Blandford-Znajek mechanism. The model may be relevant to gamma-ray bursts. The energy in the Poynting f lux produced by the Blandford-Znajek mechanism is converted into the kineti c energy of the electron-positron pairs in the magnetosphere around the bla ck hole, which generates two oppositely directed jets of electron-positron pairs with superhigh bulk Lorentz factors. The jets collide and interact wi th the interstellar medium, which may produce gamma-ray bursts and the afte rglows.