Some of the earliest civilizations regarded the universe as organized around four principles, the four "elements" earth. water, air, and fire. Fire, which was the source of light and as such possessed an immaterial quality related to the spiritual world. was clearly the most impressive of these elements, although its quanti tative importance could not have been properly discerned. M- ern science has changed the names, but macroscopic matter is still divided into four states. The solid, liquid, and gaseous states are ordinary states, but the fourth state of matter, the plasma state, has retained a somewhat extraordinary character. It is now recognized that most of the matter of the universe is in the ionized state. but on the earth. the plasma state is still the exception. Hence the importance and also the difficulty of investigations dealing with ionized matter, which have been greatly furthered by the development of thermonuclear fusion research. The study of matter in the ionized state comprises a large diversity of problems belonging to many different branches of phys ics. A number of them relate to the microscopic properties of plasmas and concern the structure and the collisional behavior of atomic constituents. Although they are clearly of basic importance, their relevance to thermonuclear research was at first overlooked, at a time when most of the effort was concentrated on designing fusion devices and understanding macroscopic phenomena, mostly of an electromagnetic nature. At present.

Some of the earliest civilizations regarded the universe as organized around four principles, the four "elements" earth. water, air, and fire. Fire, which was the source of light and as such possessed an immaterial quality related to the spiritual world. was clearly the most impressive of these elements, although its quanti tative importance could not have been properly discerned. M- ern science has changed the names, but macroscopic matter is still divided into four states. The solid, liquid, and gaseous states are ordinary states, but the fourth state of matter, the plasma state, has retained a somewhat extraordinary character. It is now recognized that most of the matter of the universe is in the ionized state. but on the earth. the plasma state is still the exception. Hence the importance and also the difficulty of investigations dealing with ionized matter, which have been greatly furthered by the development of thermonuclear fusion research. The study of matter in the ionized state comprises a large diversity of problems belonging to many different branches of phys ics. A number of them relate to the microscopic properties of plasmas and concern the structure and the collisional behavior of atomic constituents. Although they are clearly of basic importance, their relevance to thermonuclear research was at first overlooked, at a time when most of the effort was concentrated on designing fusion devices and understanding macroscopic phenomena, mostly of an electromagnetic nature. At present.

Four years after a first meeting in BADDECK, Canada, on the Physics of Ion-Ion and Electron-Ion collisions, a second Nato Advanced Study Institute, in HAl~/Lesse, Belgium, reexamined the subject which had become almost a new one, in consideration of the many important developments that had occured in the mean time. The developments have been particularly impressive in two areas : the di-electronic recombination of electrons with ions and the collisional processes of mUltiply charged ions. For dielectronic recombination, a major event was the obtainment, in 1983, of the first experimental data. This provided, at last, a non speculative basis for the study of that intricate and subtle process and strongly stimulated the theoretical activities. Multiply charged ions, on the other hand, have become popular, thanks to the development of powerful ion sources. This circumstance, together with a pressing demand from thermonuclear research for ionisation and charge exchange cross sections, has triggered systematic experimental investigations and new theoretical studies, which have contributed to considerably enlarge, over the last five years, our understanding of the collisional processes of multiply charged ions. Dielectronic recombination and multiply charged ions were therefore central points in the programme of the A.S.I. in HAN/Lesse and are given a corresponding emphasis in the present book.

This volume reviews the theoretical and experimental work about continuous electron emission in energetic ion-atom collisions over the last 30 years. General properties of the two-center electron emission are analyzed, and particular attention is given to screening effects. The book also offers an overview of multiple ionization processes.

Four years after a first meeting in BADDECK, Canada, on the Physics of Ion-Ion and Electron-Ion collisions, a second Nato Advanced Study Institute, in HAl~/Lesse, Belgium, reexamined the subject which had become almost a new one, in consideration of the many important developments that had occured in the mean time. The developments have been particularly impressive in two areas : the di-electronic recombination of electrons with ions and the collisional processes of mUltiply charged ions. For dielectronic recombination, a major event was the obtainment, in 1983, of the first experimental data. This provided, at last, a non speculative basis for the study of that intricate and subtle process and strongly stimulated the theoretical activities. Multiply charged ions, on the other hand, have become popular, thanks to the development of powerful ion sources. This circumstance, together with a pressing demand from thermonuclear research for ionisation and charge exchange cross sections, has triggered systematic experimental investigations and new theoretical studies, which have contributed to considerably enlarge, over the last five years, our understanding of the collisional processes of multiply charged ions. Dielectronic recombination and multiply charged ions were therefore central points in the programme of the A.S.I. in HAN/Lesse and are given a corresponding emphasis in the present book.