Evidence is presented of acoustic cavitation generated by a Dornier extracorporeal shockwave lithotripter. Using x-ray film, thin aluminium sheets, and relatively thick metal plates as targets, evidence of liquid jet impacts associated with cavitation bubble collapse was observed. The jet impact was violent enough to puncture thin foils and deform metal plates. Furthermore, numerous jet impacts were generated over a volume of greater than 200 cm 3 . It is likely that such violent cavitation will also occur in tissue, and observed biological effects (e.g. renal calculus disintegration and tissue trauma) may be related to cavitation damage.

Acoustic cavitation generated by an extracorporeal shockwave lithotripter

Cavitation microjets as a contributory mechanism for renal calculi disintegration in ESWL.

A kinetic description of the dc Hg-Ar mixture plasma of fluorescent lamp discharges is given on the basis of the main microphysical processes and corresponding atomic data. The investigation comprises particle balances for the excited Hg atoms of the triplet 63P0,1,2 and singulet 61P1 state, the balance of the discharge current and an adequate form of the electron Boltzmann equation for such a mixture plasma, the latter including also the various binary collision processes with excited Hg atoms and the Coulomb interaction between the electrons. By simultaneously solving the balances together with the kinetic equation the densities of electrons and excited Hg atoms, the electron energy distribution, the resulting mean energy, mobility and various energy transfer rates of the electrons and the ultraviolet radiation output were determined and in part compared with measured data from the literature. This paper presents and analyses the macroscopic plasma properties mentioned for a wide range of the wall temperature or the corresponding Hg partial pressure variation, where a good agreement of calculated results with experimental data is obtained. In a second paper the change of the macroscopic plasma behaviour due to variation of buffer gas pressure and discharge current will be dealt with.



Kinetik des Ar-Hg-Plasmas von Leuchtstofflampenentladungen I. Modell — Grundgleichungen — Hg-Partialdruckvariation



Die Arbeit befast sich auf der Grundlage der wesentlichen mikrophysikalischen Prozesse und der entsprechenden atomaren Daten mit der kinetischen Beschreibung des de Hg-Ar-Mischplasmas von Leuchtstofflampenentladungen. Die Untersuchung verwendet die Teilchenbilanzen fur die angeregten Hg-Atome des Tripletts 63P0,1,2 und des Singuletts 61P1, die Bilanz fur den Entladungsstrom und eine adaquate Form der Elektronen-Boltzmann-Gleichung fur ein solches Mischplasma, wobei in letzterer auch die verschiedenen Zweierstosprozesse mit angeregten Hg-Atomen und die Coulomb-Wechselwirkung zwischen den Elektronen berucksichtigt wird. Mittels simultaner Losung der Bilanzgleichungen zusammen mit der kinetischen Gleichung wurden sowohl die Dichten der Elektronen und angeregten Hg-Atome, die Elektronenenergieverteilung, die sich ergebende mittlere Energie, Beweglichkeit und die verschiedenen Energieubertragungsraten der Elektronen als auch die Ausbeute an ultravioletter Strahlung bestimmt und teilweise mit in der Literatur verfugbaren Mesdaten verglichen. In dieser Arbeit werden die genannten makroskopischen Plasmaeigenschaften fur einen weiten Variationsbereich der Wandtemperatur und damit des Hg-Partialdruckes dargestellt und analysiert, wobei gute Ubereinstimmung von berechneten und experimentellen Ergebnissen erhalten wird. In einer weiteren Arbeit wird das makroskopische Plasmaverhalten bei Variation des Puffergasdruckes und des Entladungsstromes dargestellt und diskutiert.

Kinetics of the Ar-Hg Plasma of Fluorescent Lamp Discharges. I. Model — Basic Equations — Hg Partial Pressure Variation

In this work, the second in a series of two, a spatially averaged model of an electron beam generated Ar?N2 plasma is developed to identify the processes behind the measured influence of trace amounts of N2 on the development of the electron energy distribution function. The model is based on the numerical solution of the electron Boltzmann equation self-consistently coupled to a set of rate balance equations for electrons, argon and nitrogen species. Like the experiments, the calculations cover only the low-energy portion (<50?eV) of the electron energy distribution, and therefore a source term is added to the Boltzmann equation to represent ionization by the beam. Similarly, terms representing ambipolar diffusion along and across the magnetic field are added to allow for particle loss and electrostatic cooling from the ambipolar electric field. This work focuses on the changes introduced by adding a small admixture of nitrogen to an argon background. The model predictions for the electron energy distribution function, electron density and temperature are in good agreement with the experimentally measured data reported in part I, where it was found that the electron and ion energy distributions can be controlled by adjusting the fraction of nitrogen in the gas composition.

https://iopscience.iop.org/article/10.1088/0963-0252/22/6/065005/pdf

Controlling the electron energy distribution function of electron beam generated plasmas with molecular gas concentration: II. Numerical modeling

Dual pulse shock wave lithotripsy: in vitro and in vivo study.

The present paper is devoted to the investigation of the kinetics of the electron component in the stationary beam discharge plasma in molecular nitrogen. Using the Boltzmann equation with the inclusion of the elastic and the main inelastic binary collisions and also the Coulomb interaction between the charged particles we have calculated the energy distribution function and some macroscopic quantities of the electrons within a large range of parameters. Using our earlier results for the beam discharge plasma in hydrogen, also the dependence of the macroscopic quantities on the kind of molecular gas is discussed. Finally, the comparison of some macroscopic properties of the beam and the glow discharge plasma was performed under the condition of equal power input per volume unit in both types of plasmas in nitrogen.

Kinetics of the Electron Component in the Turbulent Electron‐Beam Discharge Plasma in Diatomic Gases and Comparison of some Macroscopic Properties between the Plasmas of the Beam and the Glow Discharge

In a recent paper the stationary beam plasma discharge in partially dissociated hydrogen was investigated where the electron component was described by the Boltzmann equation for a mixture of atomic and molecular hydrogen and the main heavy charged and neutral particles by balance equations. It was assumed that, via the quasilinear beam plasma interaction, the electron beam produces only the turbulent electric field whilst an additional production of plasma electrons due to direct ionization by the beam and thus a direct influence on the balances of charge carriers were neglected. Now the additional production of plasma electrons due to direct ionization by the beam is studied on the basis of a generalized Boltzmann equation but for the simpler model of a purely molecular hydrogen plasma. For experimentally obtainable values of the turbulence energy density, beam energy, beam ionization degree and electron life time the calculation of the electron energy distribution function and of the direct beam contribution to the electron particle balance shows a marked influence of the direct beam ionization with increasing degree of beam ionization.



Der Einflus der durch Strahlelektronen verursachten Direktionisation auf die Elektronenkinetik des Strahl-Entladungsplasmas in molekularem Wasserstoff



In einer kurzlich erschienenen Arbeit wurde das stationare Strahl-Entladungsplasma in teilweise dissoziiertem Wasserstoff, untersucht, wobei die Elektronenkomponente durch die Boltzmann-Gleichung fur ein Gemisch von atomarem und molekularem Wasserstoff und die wesentlichen schweren geladenen und neutralen Teilchen durch Bilanzgleichungen beschrieben wurden. Hierbei wurde angenommen, das der Elektronenstrahl vermittels der quasilinearen Strahl Plasma-Wechselwirkung nur das turbulente elektrische Feld erzeugt, wahrend eine zusatzliche Erzeugung von Plasmaelektronen infolge direkter Ionisation durch den Strahl und somit ein direkter Einflus auf die Bilanzen der geladenen Teilchen vernachlassigt wurde. Im folgenden wird die zusatzliche Erzeugung von Plasmaelektronen infolge direkter Strahlionisation auf der Grundlage einer verallgemeinerten Boltzmann-Gleichung jedoch fur das einfachere Modell des rein molekularen Wasserstoffplasmas untersucht. Fur experimentell realisierbare Werte der Turbulenzenergiedichte, der Strahlenergie, des Strahlionisierungsgrades und der Lebensdauer der Elektronen zeigt die Berechnung der Elektronenenergieverteilungsfunktion und des direkten Strahlbeitrages zur Elektronen-Teilchenbilanz einen ausgepragten Einflus der direkten Strahlionisation mit anwachsendem Strahlionisierungsgrad.

The Impact of Direct Ionization by Beam Electrons on the Electron Kinetics of the Beam Discharge Plasma in Molecular Hydrogen

The present paper considers the plasma-beam instability of a space limited electron beam in a strong magnetic field (ωH ≫ ωo). The form of the beam was taken to be both cylindrical and plane. The threshold of the non-linear regime turned out to be weakly dependent on the beam form and independent of the magnetic field intensity. It is defined by the current and the directed velocity of the beam particles.

On the plasma beam instability of the space limited electron beam in a magnetic field

Comparison between some macroscopic properties of the beam and glow discharge plasma in nitrogen

The investigation of the impact of the vibrationally excited molecules in the electronic ground state was performed by simultaneously solving a balance equation system for the main charge carriers, the H atoms, the metastable H atoms, the H2 molecules in the different vibrational states and for the power transfer of the electrons in the beam discharge mixture plasma. The balance equations for the vibrational states include in particular one-quantum step excitation and deexcitation, electronic excitation, dissociation and ionization from each vibrational level in electron collisions as well as the finite life time of these states because of the gas transfer through the band-like plasma. A main finding is that due to the additional impact of vibrationally excited molecules there is a marked enhancement of the resulting dissociation and ionization degree in the beam discharge plasma at medium power input from the turbulent electric field. For discharge parameters of practical interest the ionization and dissociation budget, the population of the vibrational states, the different energy dissipation processes and the energy pumping into the ladder of the vibrational states were calculated and discussed in detail.



Der Einflus schwingungsangeregter Zustande auf das makroskopische Verhalten des bandformigen Elektronenstrahl-Entladungsplasmas im H/H2-Gemisch



Die Untersuchung des Einflusses der schwingungsangeregten Molekule im elektronischen Grundzustand erfolgte durch simultane Losung eines Bilanzgleichungssystems fur die wesentlichen Ladungstrager, die H-Atome und die metastabilen H-Atome, die H2-Molekule in den Schwingungszustanden sowie fur die Energieubertragung der Elektronen im Strahlentladungs-Mischplasma. Die Bilanzen fur die Schwingungszustande erfassen insbesondere einquantige An- und Abregungen, elektronische Anregung, Dissoziation und Ionisation von jedem Schwingungsniveau in Elektronenstosen sowie die endliche Lebensdauer dieser Zustande infolge des Gastransportes durch das bandformige Plasma. Als ein wesentliches Ergebnis wurde erhalten, das auf Grund des zusatzlichen Einflusses schwingungsangeregter Molekule ein merkliches Anwachsen des Dissoziations und Ionisierungsgrades im Strahl-Entladungs-Plasma bei mittlerer Leistungsaufnahme aus dem turbulenten elektrischen Feld erfolgt. Fur praktisch interessierende Werte der Entladungsparameter wurden der Ionisation- und Dissoziationshaushalt, die Besetzung der Schwingungszustande, die verschiedenen Energiedissipationsprozesse und die Energieeinspeisung in das System der Schwingungszustande berechnet und im einzelnen diskutiert.

J. Wilhelm

Papers

Kinetics of the Electron Component in the Turbulent Electron‐Beam Discharge Plasma in Diatomic Gases and Comparison of some Macroscopic Properties between the Plasmas of the Beam and the Glow Discharge

The Impact of Direct Ionization by Beam Electrons on the Electron Kinetics of the Beam Discharge Plasma in Molecular Hydrogen

On the plasma beam instability of the space limited electron beam in a magnetic field

Comparison between some macroscopic properties of the beam and glow discharge plasma in nitrogen

Impact of the Vibrationally Excited States on the Macroscopic Behaviour of the Band‐like Electron Beam Discharge Plasma in H/H2‐Mixture