Neutralisation of intense ion beams at JET
Neutralization is an important issue in the design of neutral beam injection (NBI) systems for heating and fueling fusion plasmas. It has long been established that the neutralization efficiency of the JET injectors falls short of the theoretical value as determined by the expected gas target thickness and the well-known reaction cross-sections. This problem is even more acute in the recently upgraded 130 kV/60 Amp injectors at JET. An illustration shows the measured deuterium power delivered to JET as a function of extracted beam power. It has been proposed that the efficiency deficit is caused by a reduction in the line integrated gas density in the injector's neutralizer. This density reduction could be due to a number of factors including wall pumping and modification of the flow regime, but recent spectroscopic measurements of the neutralization system suggest that the density depletion is due to heating of the neutralizer gas. The mechanism responsible for this is thought to be indirect energy transfer from the beam to the neutral gas via the low temperature plasma that is formed in the neutralization process inside the neutralizer cell. This paper presents measurements of neutralization efficiency based on calorimetric data from the JET injectors. We also present some results from an experimental investigation at the JET Neutral Beam Test Bed including measurements of the low temperature neutralizer plasma. The plasma measurements are used as input parameters for a gas heating model and the outputs of this model are compared to a spectroscopic measurement of the neutralizer gas temperature. Overall, the results support hypothesis that the neutralization deficit is caused by gas density depletion due to indirect heating of the neutralizer gas.
On suitable experiments for demonstrating the feasibility of the beam-driven plasma neutraliser for neutral beam injectors for fusion reactors
Plasma neutralisers promise increased neutralisation efficiency of negative ion beams in neutral beam injection (NBI) beamlines compared with gas neutralisers. It has been suggested that, in the presence of an electron-confining magnetic cusp field along all neutraliser walls, the beam itself could ionise the neutraliser gas sufficiently to take advantage of this effect, avoiding the added complexity of external power coupling to the neutraliser. These predictions come from a zero-dimensional model by Surrey and Holmes (2013 AIP Conf. Proc. 1515 532) and Turner and Holmes (2019 Fusion Eng. Des. 149 111327). We have revisited and modified this model by introducing slowing-down energy distributions for stripped and Rudd electrons, including electron impact dissociation as an electron energy loss channel and taking into account dissociative recombination of molecular ions with electrons. Including the latter effect reduces the predicted plasma density by about a factor of four and the achievable neutralisation yield from ∼80% to 68% in the case of a negative deuterium ion beam with an energy of 1 MeV and a current of 40 A. With this revised model we estimate the expected performance of potential beam-driven plasma neutralisers (BDPN) on a variety of existing negative ion beam test facilities for NBI. Based on these results, we conclude that the most suitable proof-of-principle experiment would be a dedicated chamber, ideally of the same dimensions and with the same magnetic cusp configuration as a BDPN for the DEMO NBI, in which the plasma is not created primarily by the fast electrons stripped from the beam ions, but by electrons of similar current and energy emitted from biased filaments.
Rotational structure of the spectra of diatomic molecules
Автор(ы): Kovacs I. Год изд.: 1969 Описание: It is mainly since the early 1920's that the rotational spectra of diatomic molecules have been investigated. During this time it has become clear how deeply rooted are the connections between these spectra and the internal structure of the molecules and how important is the information they give about molecular architecture. It has become evident that these spectra are, say, coded messages from the molecules in secret writing and that to decipher these messages it is necessary to determine experimentally the position and intensity of the spectral lines and to establish the theoretical laws governing the spectra. Although the fundamental investigations about rotational spectra were published in the third and fourth decades of this century and the fundamental theory can be found in a number of excellent books, it seems appropriate and necessary to collate this material in the form of a unified system and to complete this system by adding new elements. This is especially true with respect to the formulas of intensity distribution, a systematic collection of which is in growing demand by physicists and astronomers. The author's aim is to meet this demand by the present book. It is the writer's hope that the present book will be useful to both theoretical and experimental research workers who want complete and unified information concerning the rotational structure in spectra. Оглавление: