Wolfram Knapp

Control of hot-filament ionization gauge emission current: mathematical model and model-based controller

The lack of adequate models for feedback-controlled emission current in hot-filament cathode ionization gauges (IGs) makes it difficult to achieve precision control over a wide range of emission currents (0.01 - 10 mA). A nonlinear mathematical model for transforming the filament heating power into emission current is developed. Experimental and theoretical results are shown. An electron emission regulator is described which was designed for use in the calibration of IGs, mass spectrometers and vapour rate measurements with IGs.

Electron emission characteristics of solidified gold alloy liquid metal ion sources

Abstract Solidified liquid metal ion sources (LMISs) operating with Au alloy wetted hair-pin emitters can be used as high-intensity electron point sources for application in the field of ultrahigh vacuum techniques. A nanotip emitter on a solidified LMIS emitter can be formed by quenching during ion emission mode. I–V characteristics and the performance of the electron emitting LMIS are presented.

CRT lighting element with carbon field emitters

Abstract Field electron emission from carbon fibres has been investigated. Measured current–voltage characteristics followed the Fowler–Nordheim equation. A cathode ray tube lighting element of a triode vacuum tube was manufactured as an application of a carbon fibre emitter by replacing conventional thermionic cathodes with carbon field emitters. Stable and intense electron emission, luminosity and long life of the emitters were demonstrated and discussed.

Hydrogen isotope inventories in the ASDEX-Upgrade tungsten coated divertor tiles

The total hydrogen isotope inventories in the tungsten coated divertor tiles of ASDEX-Upgrade were measured by thermal desorption spectroscopy (TDS) and - in the near surface region - by nuclear reaction analysis (NRA). The highest amounts of deuterium (≤ 5 x 10 22 D/m 2 ) are measured in the inner divertor region outside the separatrix due to the formation of a C:H layer on the tungsten by codeposition of deuterium with carbon. The inventories in the outer divertor - where erosion dominates - are generally smaller by an order of magnitude.

Formation of a nano-emitter for electron field emission on a liquid metal ion source tip after solidification of the alloy

Abstract Liquid metal ion sources (LMISs) operating with solidified Au alloys can be used as high-intensity electron point sources. A nano-emitter can be formed by quenching during ion emission mode. The I–V characteristics and the performance of the electron-emitting LMIS are presented.

Numerical investigations of hot cathode ionization gauges

Analytical or numerical methods for the investigation of hot cathode ionization gauges were described and discussed only rarely in the literature. This is due to various difficulties in the theoretical calculation of gauge sensitivity and other important properties. The rapid development of computer hardware gives the opportunity to apply numerical methods in the investigation of hot cathode ionization gauges. With the threedimensional numerical calculation program IONTRA3d it was possible to calculate the sensitivity and other important characteristics of hot cathode ionization gauges. The results of numerical calculations were compared with experimental data. The differences were discussed. By means of IONTRA3d it was possible to obtain results that can be achieved by experimental investigations only with large effort. These are the analysis of the distribution of electron current on the anode segments and the influence of anode support. The typical form of C-Uc-Plots (with 2 maximas) was explained.

Imidotitanium Complexes with Heteroallylic Ligands: Synthesis and Solid‐State Structure

Treatment of Ti(NtBu)Cl2(py)2 (1, py = pyridine) with bulky heteroallylic ligands in a 1:1 molar ratio affords the monosubstituted derivatives [PhC(NSiMe3)2]Ti(NtBu)Cl(py)2 (2), [MeOC6H4C(NSiMe3)2]Ti(NtBu)Cl(py) (3), and [Ph2P(NSiMe3)2]Ti(NtBu)Cl(py) (4). Similarly, 2:1 reactions afforded the disubstitution products [PhC(NiPr)2]2Ti(NtBu)(py) (6) and [Ph2P(NSiMe3)2]2Ti(NtBu) (7). The bis(pyridine) adduct Ph2P(NSiMe3)2Li(py)2 (5) was isolated as a by-product during the preparation of 4. The molecular structures of 7 has been established by X-ray crystallography.

Theoretical and experimental desorption investigations at ionization gauges

Abstract We have investigated the disturbing influence of outgassing and desorption effects on the pressure reading of three different types of ionization gauges with different methods. The behaviour of these gauges after exposure to gases, which are important in the Ultra-High-Vacuum region, after variation of the electron current, and for different potentials of the electrodes were studied. We have also determined the influence of the grid material on the outgassing and desorption effects for the Chen-Suen gauge. General statements of the influence of desorption phenomena on the pressure reading of ionization gauges at the lower pressure limit are given.

Investigations of the transition from field electron emission to stable plasma discharge in a micro electron source at vacuum pressure

We report on the transition from field electron emission to plasma discharges. During an experiment with a miniaturized field emission electron source a plasma discharge accompanied by a luminous effect was observed. A novel graphical evaluation method was used to interpret and to compare the observed phenomenon.

Energetic evaluation of the transition from field electron emission to plasma discharges with extended use of the Fowler-Nordheim plot

We report on an extended use of the Fowler-Nordheim plot for energetic evaluation of charge transfers in vacuum electronics. First results explained clearly, the transition from field electron emission to plasma discharge is physically conditioned, especially in the case of higher emission currents.