Feasibility of cooling positrons via conduction in conductive micro-tubes

A first order perturbation with respect to velocity has been employed to find the frictional damping force imposed on a single moving charge inside a conductive cylindrical micro-tube. The tensorial relationship between the force and velocity is derived and numerically estimated. Our results asymptotically match that of a flat geometry presented in the literature. Using the single particle analysis the cooling is formulated for an arbitrary density ensemble. It is shown that no further cooling via conduction occurs in the well-established non-neutral plasma equilibrium state. Also, the cooling rate for a weakly interacting ensemble is estimated. It is shown micro-tubes can be employed to cool down low density positron ensembles and/or to improve the beam emittance. A pack of tens of thousands of individual micro-tubes, each cooling only tens of positrons, is capable of cooling hundreds of thousands of particles in each cooling cycle. For example, with tens of particles per micro-tube in a 5cm long micro-tube stack with the resistivity of 0.46 Omega m and the tubes of radius 50 mu m, hundreds of thousands of positrons can be cooled down with a time constant of 103 mu s in longitudinal and 7 mu s in perpendicular direction. However, it must be noted that the cooling does not guarantee long term storage of particles in micro-tubes. (C) 2014 AIP Publishing LLC.