1. 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

2. 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

3. 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

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

5. 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

6. 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

7. Our Choice: Botzmann vs. PIC/MC
BC – time slower than fluid
6D EDF > 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

8. 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

9. 3D simulations (PIC/MC)
Plasma Dynamics Corp., USA

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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

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

18. “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

19. “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

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

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

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

23. “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

24. 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

25. 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

26. 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