V.P. Nagorny, V.N. Khudik Plasma Dynamics Corporation, USA Three-Dimensional Fully Kinetic Simulations of the Discharge Pulse in an AC-PDP cell V.P. Nagorny, V.N. Khudik Plasma Dynamics Corporation, USA

Numerical Simulations: Achievements Provided valuable information about discharge evolution and parameters. Helped to form basic concepts and understand many features of the discharge. Helped improve PDP parameters. Plasma Dynamics Corp., USA

Advantages of Numerical Approach Allows to investigate pdp without building a pdp. Provide time-space information about discharge characteristics (electric field, electrons, ions, …), often unavailable otherwise. Provides “clear” view of the discharge features, not obscured by apparatus, driving, etc. Allows to “look inside” the discharge, even to manipulate with its parameters in order to uncover hidden relationships. Numerical simulations proved to be a powerful and useful tool Plasma Dynamics Corp., USA

PDP Simulations: Status ~ 99.9% Fluid simulations ~ 0.1% - Kinetic simulations (2D PIC/MC) Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Fluid Simulations Pros: Fast  can work on slower computers Easy to interpret results Cons: Assumptions (close to equilibrium-not real EDF) Assumptions (rates; rate scaling) Numerical diffusion, especially ions Qualitative rather than quantitative Ideal for investigation of general discharge features, ramp stability, multi-cell, … when details of high-energy part of the EDF are not critical. Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Kinetic Approach Necessary when detailed EDF is required (efficiency, striations) or for investigating statistical effects like jitter, or very small currents. Pros: Uses only fundamental data (c-s, probabilities) Self consistent simulation of EDF, rates, fields; No a-priory assumptions about EDF Cons: Requires a lot of memory Very slow  require powerful computers. Plasma Dynamics Corp., USA

Our Choice: Botzmann vs. PIC/MC BC – 105-106 time slower than fluid 6D EDF >109-1010 elements (3Dv x 3Dr) for reasonable accuracy, even if “one” electron in the gap. Numerical diffusion (both ions and electrons). Unrealistic “for everyday use” even now MC – only ~1-103 times slower than fluid Number of elements = Ne – can be small. Even strong discharge has only ~108 electrons – without problems one can use <~106 macroparticles. No numerical diffusion, if ions also treated kinetically MC - realistic already for modern computers Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Subject of this work In this work we investigate a strong PDP discharge (general features) using 3D PIC/MC code. Using freedom of manipulating with physical parameters, perform a number of specially designed numerical experiments. Plasma Dynamics Corp., USA

3D simulations (PIC/MC) Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Real Discharge L. F. Weber, EuroDisplay 1999 (Courtesy of L. F. Weber) Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Discharge - in details 7%Xe + 93%Ne mixture L1=650m L2=220m L3=160m SW=155m SG=90m PG=90m g(Ne)=0.5 g(Xe)=0.01 V1=-220V V2=220V Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Discharge - Phase 1 Ions accumulation phase, field is almost the same as in empty gap Ion density (top view) Ion density (side view) Electric potential (side view) Charge deposition rate on sustain electrodes the dielectric surface above Xe-excitation rate (top view) Ne-excitation rate (top view) Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Discharge – Phase 2 Plasma forms near anode and protrudes from the anode toward the cathode; First striations appear Ion density (top view) Ion density (side view) Electric potential (side view) Charge deposition rate on sustain electrodes the dielectric surface above Xe-excitation rate (top view) Ne-excitation rate (top view) Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Discharge – Phase 3 Plasma region reaches the cathode area, abnormal CF is formed; Anode deposition wave covers new areas of the anode Ion density (top view) Ion density (side view) Electric potential (side view) Charge deposition rate on sustain electrodes the dielectric surface above Xe-excitation rate (top view) Ne-excitation rate (top view) Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Discharge – Phase 3 CF expands in the form of ionizing wave – speed of the wave ~ vi Anode deposition wave covers new areas of the anode Ion density (top view) Ion density (side view) Electric potential (side view) Charge deposition rate on sustain electrodes the dielectric surface above Xe-excitation rate (top view) Ne-excitation rate (top view) Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Discharge – Phase 4 Positive charge covers most of the cathode, discharge extinguishes Ion density (top view) Ion density (side view) Electric potential (side view) Charge deposition rate on sustain electrodes the dielectric surface above Xe-excitation rate (top view) Ne-excitation rate (top view) Plasma Dynamics Corp., USA

“Metal anode” experiment Metal anode, regular cathode No discharge spread above the anode (no striations), no changes above the cathode Plasma Dynamics Corp., USA

“Frozen ions” experiment Immobile ions above the part of the anode Striation are even more pronounced.==> They are not a result of ion motion. Plasma Dynamics Corp., USA

“No Cathode” experiment To separate physical phenomena near the anode from those near the cathode – no cathode at all!!! Current, initial EDF controlled by the source S, ions – frozen. Plasma Dynamics Corp., USA

“No Cathode” experiment Ion density (side) Potential (side) Ion density (top) Charge Deposition Rate Plasma Dynamics Corp., USA

“No Cathode” experiment Ion density (side) Potential (side) Ion density (top) Charge Deposition Rate Plasma Dynamics Corp., USA

“No Cathode” experiment Ion density (side) Potential (side) Ion density (top) Charge Deposition Rate Plasma Dynamics Corp., USA

“No Cathode” experiment No significant difference between narrow (0-1eV), and wide (0-8eV) EDF of the source S. Area is proportional to Qe d/eE. Qe -deposited charge. Anode wave IS a discharge deposition wave, and speed is proportional to the current. si si/10 completely different behavior, no striations; e  10e restores original picture with striations. Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Summary PDP is a very complicated system which is difficult to experiments with. Results always have room for multiple interpretations. As a result – lack of experiments. PIC/MC code is an ideal tool, that one can and should use for PDP “experiments”. Experiments must be carefully designed to avoid any misinterpretation or uncertainty of the results. Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA Summary In a strong discharge phenomena in the cathode and anode areas weakly influence each other. Charge deposition progresses in a wave-like manner with pronounced fronts. Cathode wave – expansion of the cathode fall, ionization is the main factor. Speed ~vi . Decreases with increasing d /e Anode wave – charging wave, independent on the ion velocity. Speed proportional to Id /e. Plasma Dynamics Corp., USA

Plasma Dynamics Corp., USA The last word In the last decade computers have become so powerful, that in the very near future 3D kinetic simulations will probably become the main tool for investigating PDPs. Even more, the ultimate goal in simulating of PDP – to track each particle (and photon) is quite feasible nowadays. This type of code will enable us to focus on optimizing PDP parameters, and to leave justification of physical approximations behind. Plasma Dynamics Corp., USA