Positive Potential Well Research Articles

Observation of impurity ions during a plasma translation experiment in nested Penning traps

Charged-particle nested traps are considered to be free from impurity-charged particles. However, that is not always the case. We show that in addition to the original ions, charged particles are generated in nested traps during the plasma translation experiments. This study demonstrates electrons being accelerated by a pair of positive potential wells in a nested trap as soon as they are translated from the adjacent trap. The accelerated electrons cause ionization of the residual gas on impact and produce ions in addition to the ions already present in the nested trap. Well-known ions such as H2+, H2O+, and N2+, were also detected. We also explore methods for reducing experimental errors due to such impurity ions.

Intermittent ion leakage from a Penning trap during potential barrier closure

Intermittent leakages of trapped ions from a Penning trap are clearly explained. Two mechanisms are revealed by considering both experimental and numerical results. The initial leakage is due to ions energized by the potential barrier that is just closing to form a positive potential well. The following leakage is induced by an axial average oscillation of the bulk of the trapped ions. Some individual bounce ions are pushed out of the potential barriers owing to the space potential of the bulk.

Numerical simulation of the effect of lower positive charge region in thunderstorms on different types of lightning

Combined with the existing stochastic lightning parameterization scheme, a classic tripole charge structure in thunderstorms is assumed in the paper, and then 2-dimensional fine-resolution lighting discharge simulations are performed to quantitatively investigate the effect of lower positive charge (LPC) on different types of lightning. The results show: (1) The LPC plays a key role in generating negative cloud-to-ground (CG) flashes and inverted intra-cloud (IC) lightning, and with the increase of charge density or distribution range of LPC region, lightning type changes from positive polarity IC lightning to negative CG flashes and then to inverted IC lightning. (2) Relative to distribution range of charge regions, the magnitude of charge density of the LPC region plays a dominant role in lightning type. Only when the maximal charge density value of LPC region is within a certain range, can negative CG flashes occur, and the occurrence probability is relatively fixed. (3) In this range, the charge density and distribution range of LPC region jointly determine the occurrence of negative CG flashes, which has a linear boundary with the trigger condition of IC lightning. (4) The common effect of charge density and distribution range of the LPC region is to change the distribution of positive potential well of bottom part of thunderstorms, and inverted IC lightning occurs when the initial reference potential is close to 0 MV, and negative CG flashes occur when the initial reference potential is far less than 0 MV. lower positive charge, charge density, distribution range, lightning type, numerical simulation

Asymmetries in bidirectional leader development of lightning flashes

AbstractLightning flashes develop as a bidirectional tree, with a negative and a positive end propagating simultaneously into cloud charges of the opposite polarity. In recent years, this process has been modeled assuming that the bidirectional channel remains a zero‐net‐charge perfect conductor starting at the electric potential of its initial location. So far, both leader ends were treated identically. We summarize characteristics of bidirectional leader development of various lightning flashes registered by the Ebro 3‐D Lightning Mapping Array at the east coast of Spain, supplemented by high‐speed camera records. In order to follow the horizontal development of positive and negative leaders over time, a time‐distance‐altitude graph was designed, using the flash origin or a cloud‐to‐ground stroke as reference. The examples confirm that negative and positive leaders propagate at characteristic horizontal speeds (105 and 2 · 104 m s−1). The positive leader's low apparent speed corresponds to the phase when recoil processes are active. Very fast negative leaders (up to 8 · 105 m s−1) are detected in association with positive cloud‐to‐ground strokes. Negative leaders respawn repeatedly from the origin or as a retrograde negative leader at the positive branch. Positive leaders remain propagating throughout the flash or until reaching ground. We show that the velocity difference shifts the potential of the leader, increasing the gradient with cloud charge at the positive end while reducing it at the negative end. The positive section lowers its potential through retrograde negative leaders, eventually making it possible to emit a new negative leader into the upper positive potential well.

Arbitrary Amplitude Ion Acoustic Solitary Waves in An Unmagnetized Two Electron Population Ultra-Relativistic Dense Plasmas

The nonlinear wave structure of arbitrary amplitude ion acoustic solitary waves (IASWs) are studied in the Sagdeev’s pseudopotential framework for an ultra-relativistic degenerate dense plasma comprising cold and hot electrons and inertial ultra-cold ions. By employing standard normal-mode analysis the dispersion relation for linear waves is studied. The numerical results are presented to understand the features of ion acoustic solitary wave structures. It is shown that the present plasma model supports IASWs having positive potential well. Also, it is found that the small amplitude rarefactive double layer solution can exist in such a plasma system in some parametric region. It is shown that solitary structures and double layers are affected by relevant plasma parameters.

A Proposed Test of Extended MHD Plasmas by Merging of Lithium Ion Plasmas with Pure Electron Plasmas

Recently, extended MHD plasmas have been proposed, especially in both theoretical and computational fields of plasma physics. To test those experimentally, we propose a new project using two nonneutral plasmas: pure ion and electron plasmas. The experiment is performed on a linear machine in which a pair of positive and negative electrostatic potential wells is externally produced. In the positive potential well, an 7Li+ plasma is confined, while an electron plasma in the negative potential one. Then, those nonneutral plasmas are merged into an extended MHD plasma. The most remarkable advantage to employing nonneutral plasmas is that the ion skin depth, that is a typical scale length of the extended MHD plasmas, can be extended to the plasma radius. This actually alleviates experimental difficulties in diagnosing properties of the extended MHD plasmas. With precisely controlling densities of both pure 7Li+ ion and electron plasmas, the proposed method may explore an unrevealed research field of extended MHD plasmas.

Statistical Thermodynamics and Photographic Sensitivity

By the methods of statistical thermodynamics, it has been proved that a conduction electron cannot be trapped above 45 K in an AgBr microcrystal by a shallow positive potential well with a depth of about 0.05 eV. A trap with a depth of 0.2 eV cannot be effective above 155 K. The direct electron trapping process of the Hamilton nucleation and growth theory, in which an electron is trapped at room temperature by the shallow positive potential well of a silver ion on a surface kink site, without the participation of an interstitial silver ion in the actual trapping process at the trapping site, violates the second law of thermodynamics. This process would result in a decrease in the entropy and an increase in the Helmholtz free energy of the system.

Experimental study of potential structure in a spherical IEC fusion device

The spherical inertial-electrostatic confinement (SIEC) concept is designed to focus and accelerate ions and electrons radially inward towards the center of a negatively biased, highly transparent spherical grid. The converging ions create a high-density plasma core where a high fusion rate occurs. In addition, under proper conditions, the ion and electron flows create a space-charge induced well (a negative potential well nested inside a positive potential well). This structure traps high-energy ions within the virtual anode created by the double potential, providing a high fusion density in the trap volume. The present experiment was designed to verify double potential well formation and trapping by a measurement of the radial birth profile of energetic (3-MeV) protons produced by D-D fusion reactions in a deuterium discharge. This experiment was designed to operate at high perveance (0.4 to 1.4 mA/kV/sup 3/2/), where formation of a double well is predicted theoretically. Additional steps to aid well formation included: use of the unique Star mode of operation to obtain ion beam focusing down to -1.6 H the ballistic limit and the incorporation of a second electrically floating grid (in addition to the focusing/accelerating cathode grid) to reduce the ion radial energy spread to 0.34 mA/kV/sup 3/2/. As the perveance increased, the depth of the double well also increased. At the maximum perveance studied, 1.38 mA/kV/sup 3/2/ (corresponding to 80 mA and 15 kV), the negative potential well depth, corresponding to the measured proton-rate density, was estimated to be 22%-27% of the applied cathode voltage. This represents the first conclusive demonstration of double well formation in an SIEC, since prior measurements by other researchers typically yielded marginal or negative results.

Potential profile measurements using a collimated proton detector in spherical inertial-electrostatic plasma confinement

A collimated proton detector has been developed for spatial resolved proton measurements in inertial-electrostatic plasma confinement (IEC) fusion experiments. These are the first proton measurements used to infer potential well profiles on an IEC device. This paper describes a new technique for investigating the existence of multiple potential wells inside IEC devices. Analysis of the observed proton energy and source profile indicates that (for a 12-mA cathode current, a 30-kV cathode voltage in a 4-mTorr D2 background) predominantly beam-background fusion occurs. Computer simulation suggests that a positive space charge potential approximately half that of the applied voltage is formed inside the cathode. These results establish the first measurement of a positive potential well structure inside an ion-injected IEC device.

Solvation time of electrons in liquid ammonia

The phenomenon of solvation of an electron depends either on the presence of preexisting positive potential wells and/or on the orientation of the surrounding molecules by the field arising from the electron's charge. An effort was made to evaluate the solvation time for an excess electron in liquid ammonia at low temperature (-50oC).

Initiating and Maintaining a Discharge by a Transfer Mechanism

A new discharge is described which is radially contained by a magnetic field and is not sustained by electron emission from any surface. Two positive anodes of arbitrary but similar shape are lined up along the magnetic field. A control electrode, at a lower potential, is placed between them and creates a potential barrier and two positive potential wells in the vicinity of each anode. Electrons are axially trapped in these wells. An rf voltage in the megacycle range is applied, out of phase, to the two anodes and causes the trapped electrons to alternately spill across the barrier and pick up energy from the rf field. During each half-cycle they make many oscillations in the potential well which is most positive and make ionizing collisions. Every ion pair yields an electron which can gain energy in the same way. The process is very efficient and is characterized by rf breakdown voltages that approach the ionization potential of the gas.