Current-free double-layer formation in a high-density helicon discharge

A strong, current-free, electric double-layer with eΦ/kTe∼3 and a thickness of less than 50 debye lengths has been experimentally observed in an expanding, high-density helicon sustained rf (13.56-MHz) discharge. The rapid potential decrease is associated with the “neck” of the vacuum vessel, where the glass source tube joins the aluminumdiffusionchamber, and is only observed when the argon gas pressure is less than about 0.5 mTorr. The upstream electron temperature Te appears 25% greater than the downstream Te, and there is a density hole on the downstream edge. This experiment differs from others in that the potentials are self-consistently generated by the plasma itself, and there is no current flowing through an external circuit. The plasma electrons are heated by the rf fields in the source, provide the power to maintain the double-layer, and hence accelerate ions created in the source out into the diffusionchamber

Simulation of main plasma parameters of a cylindrical asymmetric capacitively coupled plasma micro-thruster using computational fluid dynamics

Computational fluid dynamics (CFD) simulations of a radio-frequency (13.56 MHz) electrothermal capacitively coupled plasma (CCP) micro-thruster have been performed using the commercial CFD-ACE+ package. Standard operating conditions of a 10W, 1.5 Torr argon discharge were used to compare with previously obtained experimental results for validation. Results show that the driving force behind plasma production within the thruster is ion-induced secondary electrons ejected from the surface of the discharge tube, accelerated through the sheath to electron temperatures up to 33.5 eV. The secondary electron coefficient was varied to determine the effect on the discharge, with results showing that full breakdown of the discharge did not occur for coefficients less than or equal to 0.01

How to promote informal learning in the workplace? The need for incremental design methods

Informal Learning in the Workplace (ILW) is ensured by the everyday work activities in which workers are engaged. It accounts for over 75 per cent of learning in the workplace. Enterprise Social Media (ESM) are increasingly used as informal learning environments. According to the results of an implementation we have conducted in real context, we show that ESM are appropriate to promote ILW. Nevertheless, social aspects must be reconsidered to address users' needs regarding content and access, quality information indicators, moderation and control

Electron energy probability function and L-p similarity in low pressure inductively coupled bounded plasma

Particle-In-Cell (PIC) simulations are carried out to investigate the effect of discharge length (L) and pressure (p) on Electron Energy Probability Function (EEPF) in a low pressure radio frequency (rf) inductively coupled plasma (ICP) at 13.56 MHz. It is found that for both cases of varying L (0.1–0.5 m) and p (1–10 mTorr), the EEPF is a bi-Maxwellian with a step in the bounded direction (x) and non-Maxwellian with a hot tail in the symmetric unbounded directions (y, z). The plasma space potential decreases with increase in both L and p, the trapped electrons having energies in the range 0–20 eV. In a conventional discharge bounded in all directions, we infer that L and p are similarity parameters for low energy electrons trapped in the bulk plasma that have energies below the plasma space potential (eVp). The simulation results are consistent with a particle balance model

Pocket money and child effort at school

In this paper, we study the relationship between the provision of parental pocket and the level of effort undertaken by the child at school. Under altruism, an increased amount of parental transfer should reduce the child's effort. Our empirical analysis is based on a French data set including about 1,400 parent-child pairs. We find that children do not undertake less effort when their parents are more generous.

Labor opportunities against family intergenerational exchange

We study a model of domestic transfers based on exchange in which children can either work or provide services to their parents to earn some money. Using a French survey, we show that there exist attention-payment mechanisms to the young children from the parents, but these exchanges disappear when children can enter the labor market.

The role of cities in cohesion policy 2014-2020

Urban regions are an important factor in regional development. During the 2007-2013 programming period, the main input provided by cities and urban areas was at project level. For the 2014-2020 programming period, Cohesion policy enhances the role of urban areas. Nevertheless, in practice the role of cities still seems similar in scale. As the programming phase is almost completed, there is now limited scope for further influence on the design of the new programmes. The next opportunity to involve cities will be as part of partnerships during the programming perio

High source potential upstream of a current-free electric double layer

Large plasma potentials (up to ∼80V) are measured upstream of a current-free electric double layer generated in a helicon rf argon discharge for a constant rf power of 250 W (at 13.56 MHz) and for low operating pressures(<2mTorr) using an electrostatic ion energy analyzer. The energy of the Ar⁺ion beam formed by acceleration through the potential drop of the double layer is found to be strongly correlated with the large source potentials: both the source potential and the beam energy increase with decreasing pressure. The creation of the double layer depends on the magnetic field generated by the solenoid near the closed end (glass plate) of the helicon source

High density conics in a magnetically expanding helicon plasma

A two-dimensional mapping of ion density and plasma potential in a diverging magnetized low pressure (0.4 mTorr) carbon dioxide helicon plasma containing a double layer reveals the presence of high density conics (7 109 cm−3) along the most diverging magnetic field lines exiting the helicon source and connecting with the grounded expansion chamber. The density in the conic is about 30% greater than the density at the double layer and this results from local ionization associated with the presence of a high energy tail in the electron energy probability function. The plasma potential along the conic is constant at about 30 V