Rf Confinement Research Articles

The structure of planar Coulomb crystals in RF traps

We investigate the structure of one-component and multicomponent planar Coulomb crystals in RF traps. Due to the RF confinement particular features emerge, especially in the case of multicomponent crystals. After briefly discussing one-component planar crystals, we consider the case of multicomponent crystals and, in particular, planar bicrystals. We show that in the multicomponent case, the spatial separation among components depends on the strength of axial confinement which also imposes a limit on the number of ions that can exist in the innermost shell. These theoretical results are confirmed by molecular dynamics simulations. Finally, we discuss some experimental issues.

Impact of high-temperature superconductors on the possibility of radiofrequency confinement of fusion plasma

Recent discoveries of superconducting materials that operate at high temperatures may have both technical and economic consequences for magnetic confinement fusion. In addition, however, they could also open up the possibility of plasma confinement by radiofrequency fields. The new, high-temperature superconductors may impact the feasibility of rf confinement in two important ways: (1) higher temperature superconductors should have higher criticalB fields and consequently may allow higher critical electric fields to be sustained in the cavity, thus allowing the necessary confining pressure to be achieved; and (2) the higher temperature superconductors lower the refrigeration power necessary to maintain the superconducting cavity, thus allowing a favorable energy balance.

Impact of high temperature superconductors on the possibility of radio-frequency confinement

It is suggested that recent high-temperature superconductors may impact the feasibility of RF confinement in two important ways: higher-temperature superconductors should have higher critical B fields and consequently may allow higher critical B fields to be sustained in the cavity, thus allowing the necessary confining pressure to be achieved; and the higher-temperature superconductors lower the refrigeration power necessary to maintain the superconducting cavity, thus allowing a favorable energy balance. Issues discussed include the frequency condition and the pressure balance, the maintenance of a superconductor near a thermonuclear plasma, and the field configuration. It is concluded that the old bases for rejecting the possibility of RF confinement of thermonuclear plasma are no longer valid. >

A time-of-flight method for studying the properties of an ion cloud stored in an rf trap

We report here on an experiment undertaken to obtain information on the spatial and velocity distributions of ions within a radio frequency quadrupole trap. A time-of-flight technique was used in which the progression of the rf confinement voltage was suddenly arrested, thus allowing the ions to escape axially. The measured profile of the ion time of flight is related to the ion distributions in position and velocity at the moment when the confinement voltage ceases to change (the time or phase of ejection). We have developed a general procedure for calculating the time-of-flight profile for any given spatial and velocity distribution of the ions within the trap. Although, in general, the solution involves a numerical integration, we find that, for the case of Gaussian distributions, this calculation can be carried out analytically. Shifts in the time-of-flight profile due to changes in the phase of ejection and in the mean ion energy are calculated. These results are compared with experimental measurements made on trapped Xe + ions in the presence of helium buffer gas.

RF Confinement of a Plasma by Two Cylindrical Electrodes

Electron contribution in the RF confinement of a mirror plasma by two cylindrical electrodes is reported. It is effective at a frequency corresponding to a parallel resonance including the electrode and the plasma. The plasma is sufficiently confined by a voltage of 40 volts, peak to peak, externaly applied to the plasma with an electron density n e ∼10 10 cm -3 and an electron temperature T e ∼20 eV. The plugging force for the confinement is caused by the electric field E z parallel to the mirror axis, which produces the ponderomotive potential in electrons, and ions are confined by the ambipolar electric field. The measured distribution of the space potentials can explain well that the plasma is confined by RF field between two cylindrical electrodes.

Frequency Characteristics of RF Confinement of Plasma in a Mirror Magnetic Field (I)

Frequency Characteristics of RF Confinement of Plasma in a Mirror Magnetic Field (I)

PROPERTIES OF RADIOFREQUENCY‐CONFINED PLASMAS*

A theoretical review is given of rf confinement research from 1960 to the present. New results described here include measurements of the luminosity distribution and the floating potential of the confined plasma. (MOW)

COMPUTER SIMULATION OF RADIOFREQUENCY CONFINEMENT OF A PLASMA*

The basic theory of rf confinement is summarized briefly. Single- particle confinement and multiple-particle confinement are treated in separate sections. (MOW)

Theory and experiment on radio-frequency plugging of magnetically confined plasma in an open-ended system

The theory of the rf plugging of a magnetically confined plasma in an open-ended system is presented; it takes explicit account of the collective effect brought about by the dynamic screening action of the plasma. The theory predicts a maximum efficiency of the rf plugging at an optimum frequency corresponding to a zero of the longitudinal dielectric constant. The plugging efficiency is calculated as a function of the plasma density, the strength of the rf field, and the intensity of the magnetic field. These theoretical predictions are compared with experimetal observations, demonstrating satisfactory agreement in over-all features. The results provide a useful scaling law associated with the concept of the rf confinement. The theory also offers an explanation for the discrepancy between the experimental values of the optimum frequency and those predicted by a conventional theory based on an individual-particle model.

Computer simulation of radiofrequency confinement of a plasma

Computer simulation methods have been used to investigate the confinement of lowdensity plasmas in nonuniform rf electromagnetic fields. The basic problem is to obtain a numerical solution of the equations of motion of a single charged particle in two-dimensional cross sections of both confining and nonconfining electromagnetic field configurations in a resonant cavity. The occurrence of confinement in a quadrupole electric mode of a cavity is demonstrated and the Φ quasipotential well theory of rf confinement is verified. The problem is then extended to large equal numbers of positively and negatively charged particles and the particle-in-cell method is used to include the effects of the self-consistent fields. The effects of finite initial temperature and of starting conditions are investigated. Confinement effects are observed in a quadrupole electric mode for initial temperatures corresponding to energies less than the depth of the Φ well.

A Function Generator for Dynamic Control of a Plasma

A function generator is constructed to generate voltage as any given function of input voltage. The generator approximates any function including a nonmonotonic one by quantizing it into 11 steps. It has fast response (less than 100 nsec), good frequency characteristic (up to 10 MHz), and is easy to construct. It is to be used with a V-to-f converter in a feedback loop of rf confinement of a plasma, where the most favorable frequency is given as a nonlinear function of plasma density.