M. C. Lin

An improved self-consistent fitting model for characterizing field emitters

We propose a new fitting model for better characterizing field emitters such as a field emission array (FEA) that may be operated at high current density. In this improved model, we employ both effective work function and effective enhancement factor approximations. The experimental data can be fitted perfectly and therefore the discrepancy between the experimental results of FEA at high current density and FN theory can be explained. It indicates the space charge effects play the key role.

Modeling a thermionic energy converter using finite-difference time-domain particle-in-cell simulations

A thermionic energy converter (TEC) is a static device that converts heat directly into electricity by boiling electrons from a hot emitter surface across a small inter electrode gap to a cooler collector surface. The main challenge in TECs is overcoming the space charge limit, which limits the amount of current that can transmit across a gap of a given voltage and width. In this preliminary work, it is found that the OOPD1 simulation results is in good agreement with analytical results. We have verified the feasibility of studying and developing a TEC using a bounded finite-difference time-domain particle-in-cell plasma simulation code, OOPD1 developed by PTSG, UC Berkeley.

Influence of ion effects on a space charge limited field emission flow: From non-relativistic to ultra-relativistic regimes

Influence of ion effects on a space charge limited field emission flow has been studied systematically, by employing both analytical and numerical approaches. The analytic calculations are carried out self-consistently to yield the steady states of the bipolar flow. It is found that the field emission currents in the presence of saturated ion currents can be enhanced to be nearly 1.8, 1.5, and 1.4 times of the cases with no upstream ion current in non-relativistic, intermediate, and ultra-relativistic regimes, respectively. The solutions have also been verified using 1D PIC simulations, as implemented in the OOPD1 code developed by PTSG of UC Berkeley.

Exact formulas for space charge limited flow in a planar diode: New relativistic Child-Langmuir law

Summary form only given. In this work, we have derived the exact formulas for the relativistic Child-Langmuir law to describe a space charge-limited flow in a planar diode under arbitrary applied voltages. Two hypergeometric functions are obtained to relate the classic Child-Langmuir law and the ultra-relativistic formula to exact relativistic Child-Langmuir law. Both nonrelativistic-to-relativistic hypergeometric function and ultra-relativistic-to-relativistic hypergeometric function are found to be dependent on applied voltages only. The formulas are elegant, compact, and intuitive, and can be easily employed.

Infuence of ion effects on a space charge limited field emission flow: From classical to ultrarelativistic regimes

The effects of ions in space charge limited field emission flow is studied using a self-consistent model, and confirmed by particle-in-cell (PIC) simulations. The field emission of electrons is described quantum mechanically by the Fowler-Nordheim equation. The cathode plasma and surface properties are considered within the framework of the effective work function approximation. Ionization effects at the anode as well as electron space-charge effects are described by Poissons equation coupled with the energy conservation equation including relativistic effects. The closed form of formulas has been derived and the numerical calculations are carried out self-consistently to yield the steady state of the bipolar flow from classical to ultrarelativistic regimes. The upstream ion current included in Poissons equation has been treated as a tuning parameter. The field-emission currents in the presence of saturated ion currents are enhanced by 1.8, 1.5, and 1.4 times of the case with no ion current in the classical, intermediate, and ultrarelativistic regimes, respectively. The solutions have also been verified using 1D PIC simulations as implemented in the OOPD1 code developed by the PTSG of UC Berkeley.

Output analysis of a coaxial virtual cathode oscillator [vircator]

Summary form only given. In this work, a coaxial virtual cathode oscillator (vircator) has been investigated. Horn antennas are widely used in the output of high power microwave tubes. The output characteristics of a vircator circular horn antenna with TM mode operations are studied. A 3D model has been constructed using the finite-element code, HFSS, and the numerical results have been carried out after time consuming simulations. The calculated far-field patterns of TE/sub 11/ and TM/sub 01/ modes for the vircator output are presented.

Influence of ion effects on relativistic field-emission-limited diodes

In a previous work, we investigated a relativistic field-emission-limited diode employing a high-transparency mesh anode via a self-consistent approach (M.C. Lin and D.S. Chuu, IVEC 2002, pp. 111-112, 2002, and Appl. Phys. Lett. vol. 80, pp. 4262-4264, 2002). Ionization effects at the high-transparency mesh anode were ignored. However, the ionization effects at the anode cannot be eliminated in the real world, even for the high-transparency mesh anode. It is well known that the emergence of upstream ion current would enhance the space-charge limiting current. In this work, we consider the anode plasma effects on the relativistic field-emission-limiting current. Thus, the previous theory is extended to the bipolar field-emission-limited flow. The ion current has been included in the relativistic Poissons equation and has been treated as a tuning parameter.