Biomedical subjects

J Fajans

Publications and source records attributed to J Fajans.

13 recordsLinked to original sources

PubMed2005

Effects of extreme magnetic quadrupole fields on penning traps and the consequences for antihydrogen trapping.

Measurements on electrons confined in a Penning trap show that extreme quadrupole fields destroy particle confinement. Much of the particle loss comes from the hitherto unrecognized ballistic transport of particles directly into the wall. The measurements scale to the parameter regime used by ATHENA and ATRAP to create antihydrogen, and suggest that quadrupoles cannot be used to trap antihydrogen.

Journal Article↗

PubMed2003

Direct excitation of high-amplitude chirped bucket-BGK modes.

For the first time, high amplitude (Deltan/n approximately 40%), high Q (up to 100 000) Bernstein, Greene, and Kruskal modes have been controllably excited in a plasma. The modes are created by sweeping an excitation voltage downwards in frequency, thereby dragging a phase space "bucket" of low density into the bulk of the plasma velocity distribution. The modes have no linear limit and differ markedly from plasma waves and Trivelpiece-Gould modes.

Journal Article↗

PubMed2003

Quadrupole-induced resonant-particle transport in a pure electron plasma.

Small transverse magnetic quadrupole fields sharply degrade the confinement of non-neutral plasmas held in Malmberg-Penning traps. For example, a quadrupole magnetic field of only 0.02 G/cm doubles the diffusion rate in a trap with a 100 G axial magnetic field. Larger quadrupole fields noticeably change the shape of the plasma. The transport is greatest at an orbital resonance. These results cast doubt on plans to use magnetic quadrupole neutral atom traps to confine antihydrogen atoms created in double-well positron/antiproton Malmberg-Penning traps.

Journal Article↗

PubMed2000

Experimental dynamics of a vortex within a vortex.

We report the experimental dynamics of a new two-dimensional (2D) fluid phenomenon that occurs when an intense, pointlike vortex is placed within a diffuse, circular vortex. Our observations, made using strongly magnetized electron columns to model the 2D fluid, support the analysis performed by Jin and Dubin.

Journal Article↗

PubMed2000

Second harmonic autoresonant control of the l=1 diocotron mode in pure-electron plasmas

An oscillator whose frequency is amplitude dependent can be controlled by a drive whose frequency sweeps through a resonance with the oscillator's fundamental frequency. This phenomenon is called autoresonance, and has been previously investigated for drives with frequencies near the oscillator's fundamental or subharmonic frequencies. This paper examines autoresonance for drives at twice the fundamental frequency, i.e, second harmonic autoresonance. The l=1 diocotron mode in pure-electron plasmas, a very high Q nonlinear oscillator, is the focus of the paper. The theory for this oscillator is derived, and compared to experimental results. The results can be generalized to any Duffing-like driven nonlinear oscillator in which the coupling between the drive and the oscillator depends at least weakly on the oscillator amplitude.

Journal Article↗

PubMed1995