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The conditions for the existence of negative-energy perturbations (whichcould be nonlinearly unstable and cause anomalous transport) are investigatedin the framework of linearized collisionless Maxwell-drift kinetic theory forthe case of equilibria of magnetically confined, circularly cylindrical plasmasand vanishing initial field perturbations. For wave vectors with anon-vanishing component parallel to the magnetic field, the plane equilibriumconditions (derived by Throumoulopoulos and Pfirsch [Phys Rev. E {\bf 49}, 3290(1994)]) are shown to remain valid, while the condition for perpendicularperturbations (which are found to be the most important modes) is modified.Consequently, besides the tokamak equilibrium regime in which the existence ofnegative-energy perturbations is related to the threshold value of 2/3 of thequantity $\eta_\nu = \frac {\partial \ln T_\nu} {\partial \ln N_\nu}$, a newregime appears, not present in plane equilibria, in which negative-energyperturbations exist for {\em any} value of $\eta_\nu$. For various analyticcold-ion tokamak equilibria a substantial fraction of thermal electrons areassociated with negative-energy perturbations (active particles). Inparticular, for linearly stable equilibria of a paramagnetic plasma with flatelectron temperature profile ($\eta_e=0$), the entire velocity space isoccupied by active electrons. The part of the velocity space occupied by activeparticles increases from the center to the plasma edge and is larger in aparamagnetic plasma than in a diamagnetic plasma with the same pressureprofile. It is also shown that, unlike in plane equilibria, negative-energyperturbations exist in force-free reversed-field pinch equilibria with asubstantial fraction of active particles.Comment: 31 pages, late

Negative-energy perturbations in circularly cylindrical equilibria within the framework of Maxwell-drift kinetic theory