Below are just a few of the possibilities, which have been recognised already and which to some extent are already under investigation. Clearly, at present the more academic, fundamental research is primarily addressed. This is normal and good. Possible applications need to build up on the basic knowledge assembled in order to avoid costly mistakes.

• Plasma crystals are strongly coupled systems, where the coupling is electrostatic. The strong coupling properties should be investigated and compared with other strongly coupled systems, such as one-component-plasmas, liquid colloidal suspensions etc..
• Plasma crystals can be used as macroscopic model systems for studying certain generic aspects of crystal physics -- such as dislocations, phase transitions, annealing, wave propagation etc..
• Plasma crystals might be useful for investigating special aspects of colloid-physics, phenomena that involve e.g. rapid response times, easy control etc.. Particularly the interactions of granular media may become an exciting development. 
• Plasma crystals appear to be particularly suited as model systems for "nano-crystals", as it is fairly easy to "manufacture" small systems with only a few (to a few 10's) lattice planes. 
• In plasma technology "dust contamination" inside the reactors plays a major economic role. This dust nucleates in the reaction chamber itself. As smaller and smaller structures are manufactured, this contamination problem increases greatly. The reason is that the number of nucleated particles increases steeply with decreasing size, and that -- with smaller structures -- smaller particles can cause wafer contamination and break-down. Control of this contamination is of major importance. Research into plasma crystal formation, stability etc. may be of importance here, too.
  

The properties of plasma crystals are best evaluated in relation to other crystal systems. This highlights common properties as well as areas of complementarity, and illustrates where plasma crystals may be of special usefulness and significance.

• Plasma crystals are easy to produce in the laboratory. Whilst most workers so far have employed RF-plasma devices, the first DC-plasma discharge experiment was performed recently. This suggests that further novel possibilities for producing plasma crystals may exist yielding (possibly) different properties. This makes them more versatile than ion crystals produced in traps or storage rings.
• Plasma crystals are easy to control in the laboratory. Although research in this area is only just beginning, so far single hexagonal
  "cells" have been produced, linear chains, monolayers as well as flat multilayer crystals with several thousand cells.
• Characteristic time scales for plasma crystal formation are of the order of one second. This very fast response (about a million times
  faster than that of colloidal suspensions) allows investigations of dynamical properties which were not accessible before.
• Plasma crystals consist of three components, which in principle could be overall charge neutral (negatively charged microspheres, electrons and ions). In practice, gravity restricts the formation to parts of the plasma where a compensating electric field is built up, so that charge neutrality is not exactly met. In space -- under microgravity conditions -- ideal charge-neutral plasma crystals appear possible. Gravity does not play a role for ion crystals, of course, whereas for colloidal or surface crystals (e.g. Langmuir-Blodgett films) it is compensated by a suitable suspension medium -- which then may lead to massive overdamping and long equilibration time scales.
• Plasma crystals are easily visualised using suitable laser illumination and a CCD camera. In principle, full 3D monitoring is possible in this way, but this has not been achieved yet. This easy visualisation, including the direct storage and computer analysis, significantly enhances our diagnostic capacity with respect to the other crystal systems and makes a number of scientific investigations possible for the first time.
• The vertical positioning of plasma crystals in the electrostatic sheath can also be controlled, e.g. by using ultraviolet radiation. This may be quite important for testing the plasma crystal properties under conditions of differing ion flow. In RF-discharges ions are accelerated towards the lower electrode in the sheath. At the edge of the main plasma this flow velocity is about thermal, closer to the electrode it becomes highly suprathermal.
• Plasma crystals are easily manipulated by external electromagnetic forces. This opens up the possibility to perform active experiments serving carefully designed purposes. 
• The variety of plasma crystals that can be produced is large. The plasma parameters (mass, density, temperature) play a role, as do the RF-power input, microsphere size, shape, density and electrical properties. Add to this the as yet unexplored scope of DC-plasmas and one can readily see that this is a research area with a huge potential.

At present, plasma crystals are exciting more at a fundamental research level. They provide a Yukawa-type strongly coupled system and will undoubtedly influence the field of "strongly coupled plasmas" considerably over the next few years. In addition, they are seen as an interesting macroscopic model for crystal physics, perhaps allowing access to nonlinear phenomena (e.g. phase transitions) in a way not possible so far. Presumably -- as is the case with most new fundamental discoveries -- they might eventually be used for some commercial applications. Whatever the future holds, the discovery of plasma crystals has certainly enriched science and will continue to do so for a long time to come.