Tim Mortensen

Swansea University | SWAN · Welsh Centre for Printing and Coating "WCPC"

This article details the development of a thin film piezoresistive screen printed pressure sensor on a flexible substrate using a composite ink based on functionalised graphene nanoplatelets (GNPs). The sensor operates through direct interfacial contact between two distinct films of the composite ink deposited over conductive substrates, without re...

A tunable, pulsed laser was used to excite the Lyman-α transition (1S-2P) of positronium (Ps). The laser system has a large bandwidth of GHz at nm, providing significant coverage of the Doppler-broadened, single-photon transition. The infra-red fundamental of a Nd:YAG laser was converted to ultraviolet by a series of solid-state, nonlinear processe...

The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the free fall acceleration of ultracold neutral anti hydrogen atoms in the terrestrial gravitational field. The experiment consists preparing anti hydrogen ions (one antiproton and two positrons) and sympathetically cooling them with Be + ions to less than...

The specific antiproton- and positron-beam requirements of the CERN AD-7 experiment, GBAR (Gravitational Behavior of Antimatter at Rest) are presented. GBAR will synthesize antihydrogen ions which will be sympathetically cooled before performing a free-fall experiment on the atom. Antiprotons delivered by CERN's ELENA facility in 100-keV, 300-ns pu...

The anharmonic component of the electric field of a Penning–Malmberg trap is exploited to manipulate a subset of the radial (r) distribution of trapped positrons, using a dipole field made to rotate about the long-axis (z) of the trap. This 'rotating wall' technique (RW) induces inward transport at frequencies associated with the motion of trapped...

We describe a simple and versatile method to manipulate the amplitude of the magnetron orbit of ions stored in a Penning trap, applied here to a cloud of low energy positrons. By applying a pulsed voltage to a split electrode in the trap, which is normally used for rotating wall compression of the particles, the size of the magnetron orbit can be c...

Positron clouds are compressed following accumulation in a Surko-type two-stage buffer gas trap using an asymmetric rotating wall electric field. An analytic theory used to describe measurements of the rate of compression is discussed. Furthermore, we describe measurements taken without the rotating wall applied and with the rotating wall compressi...

An asymmetric dipolar rotating electric field can be used to compress a trapped cloud of positrons when applied with a frequency close that of their axial bounce, and in the presence of a low pressure molecular gas to provide cooling. Measurements of the compression rate and associated parameters are presented and compared with results of a theory...

The application of an asymmetric dipolar electric field rotating at a frequency close to that of the axial bounce of a collection of trapped positrons has, in the presence of a low pressure molecular gas to provide cooling, been used to achieve compression of the cloud. A theory of this effect has been developed for a Penning trap potential, with t...