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The H (n = 2) atomic density determination by means of vacuum ultra-violet (VUV) emission spectroscopy of the Lyman-α line in laboratory low pressure plasmas is strongly affected by self-absorption of emitted photons inside the plasma leading to an underestimation of this density. A correction of the densities obtained from VUV emission spectroscopy measurements is performed by using the escape factor method. The corrections applied can reach orders of magnitude even in low pressure plasmas. Assumptions on the spatial distribution of emitting and absorbing particles as well as on the corresponding line profiles have to be made. Consequently, additional measurements are performed, which raises the requirement of a benchmark of the applied correction procedure. In contrast, tunable diode laser absorption spectroscopy (TDLAS) on the Balmer-α line is a direct measurement of the H (n = 2) density and is thus suitable for a benchmark. For the ICP under consideration, H (n = 2) densities obtained via TDLAS are near 3 × 1015 m−3 whereas uncorrected VUV emission spectroscopy gives values in the range of roughly 1013 m−3 depending on pressure and applied RF power. The calculated escape factors are on the order of 2–8 × 10−3. An excellent agreement with TDLAS is observed by applying them to the results of the VUV emission spectroscopy.

Inductively coupled radio frequency (RF) ion sources operating at 1 MHz under the condition of a low gas pressure of 0.3 Pa are the basis of negative hydrogen/deuterium ionbased neutral beam injection systems of future fusion devices. The applied high RF powers of up to 75 kW impose considerable strain on the RF system and so the RF power transfer efficiency η becomes a crucial measure of the ion source’s reliability. η depends on external parameters such as geometry, RF frequency, power, gas pressure and hydrogen isotope. Hence, η along with the plasma parameters are investigated experimentally at the ITER prototype RF ion source. At only 45%–65% in hydrogen and an increase of around 5% in deuterium, η is found to be surprisingly low in this ion source. The power that is not coupled to the plasma is lost by Joule heating of the RF coil (∼26%) and due to eddy currents in the internal Faraday screen (∼74%). The matching transformer adds up to 8 kW of losses to the system. The low values of η and the high share of the losses in the Faraday screen and the transformer strongly suggest optimization opportunities. At high power densities well above 5 W cm−3, indications for neutral depletion as well as for the ponderomotive effect are found in the pressure and power trends of η and the plasma parameters. The comprehensive data set may serve for comparison with other RF ion sources and more standard inductively coupled plasma setups as well as for validating models to optimize RF coupling.

Collisional radiative (CR) models for molecular hydrogen are of high relevance for performing qualitative and quantitative analysis of excited-state population densities measured in plasmas or predicting the dependence of plasma emission on parameter variations. Although the development of such models for H2 started decades ago, major uncertainties still exist regarding the most important set of input parameters, namely the cross sections for electron-impact excitation. The deviations between cross sections from different datasets are particularly pronounced in the energy region close to the threshold energy, strongly increasing the uncertainty of CR models applied to low-temperature plasmas. This paper presents experimental validation of a set of newly calculated non ro-vibrationally resolved electron-impact cross sections calculated for the triplet system of H2 using the molecular convergent close-coupling method in the adiabatic-nuclei formulation. These cross sections are implemented into a CR model based on the flexible solver Yacora. A first comparison of CR calculations with the different datasets to experimentally-determined population densities is performed at a planar ICP discharge for varying pressure (between 1 and 10 Pa) and RF power (between 700 and 1100 W). For the experimentally-accessible electron temperature and density range (2.5–10 eV and 1.8–3.3 × 1016 m−3, respectively), very good agreement between the model and experiment is obtained using the new data set, in contrast to previously used cross sections.

The steady improvement of the analysis of atomic and molecular hydrogen emissivities together with the possibility to apply a high-resolution spectrometer motivated repeating at BATMAN Upgrade the detailed optical emission spectroscopy investigations performed at the BATMAN test facility in 2006. Although the test facility as a whole was upgraded, the RF-driven prototype source for the ITER NBI systems basically remained the same. The measurements were carried out in the first operation phase of BATMAN Upgrade i.e. in hydrogen in the volume operation mode of the negative ion source. The previously measured gas temperature of 1000 K in the driver, increasing to about 1200 K towards the grid is now determined to be 630 K in the whole source. Moreover, by evaluating now 12 rotational lines of the molecular Fulcher-α radiation instead of five, the presence of a two-temperature rotational distribution is demonstrated, revealing a hot ensemble with a temperature of about 4300 K. For the line of sight through the driver and the one parallel to the grid, the evaluation of the electron density and temperature showed similar values and trends as in the campaign of 2006. The third line of sight observes the expansion region and gives access, for the first time, to the plasma parameters in this region. Dependencies on the variation of the magnetic filter field strength and its topology are observed. The density ratio of atomic to molecular hydrogen is about 0.3 in all source regions, revealing no pronounced dependence on the filter field; however, due to the complex analysis procedure, the uncertainties are quite high for this parameter.

The power requirements of RF heated sources for negative hydrogen ions in fusion are substantial, which poses strong demands on the generators and components of the RF circuit. Consequently, an increase of the RF coupling efficiency would be highly beneficial. Fundamental investigations of the RF efficiency in inductively coupled hydrogen and deuterium discharges in cylindrical symmetry are conducted at the lab experiment CHARLIE. The experiment is equipped with several diagnostics including optical emission spectroscopy and a movable floating double probe to monitor the plasma parameters. The presented investigations are performed in hydrogen at a varying pressure between 0.3 and 10 Pa, utilizing a conventional helical ICP coil driven at a frequency of 1MHz and a fixed power of 520W for plasma generation. The coupling efficiency is strongly affected by the variation in pressure, reaching up to 85% between 1 and 3 Pa while dropping down to only 50% at 0.3 Pa, which is the relevant operating pressure for negative hydrogen ion sources for fusion. Due to the lower power coupling, also the measured electron density at 0.3 Pa is only 5 . 10(16) m(-3), while it reaches up to 2.5 . 10(17) m(-3) with increasing coupling efficiency. In order to gain information on the spatially resolved aspects of RF coupling and plasma heating which are not diagnostically accessible, first simulations of the discharge by an electromagnetic Particle-In-Cell Monte Carlo collision method have been conducted and are compared to the measurement data. At 1 Pa, the simulated data corresponds well to the results of both axially resolved probe measurements and radially resolved emission profiles obtained via OES. Thereby, information regarding the radial distribution of the electron density and mean energy is provided, revealing a radial distribution of the electron density which is well described by a Bessel profile.

CERN ’s new particle accelerator Linac4 is part of the upgrade of the LHC accelerator chain. Linac4 is required to deliver 160 MeV H− beam to improve the beam brightness and luminosity in the Large Hadron Collider (LHC). The Linac4 H− source must deliver 40-50 mA, 45 keV H− beam in the RFQ acceptance. Since the RF power coupled to the H− source plasma is one of the important parameters that determines the quality of the H− beam, the experimental investigation of the dependence of the load impedance on the operational parameters is mandatory. In this study, we have measured the impedance of the H− source plasma varying the RF power coupled to the plasma and the condition of the hydrogen gas. Also, optical emission spectroscopy (OES) measurements have been carried out simultaneously with the impedance measurement in order to determine the plasma parameters. The determination of the plasma parameters allows us to compare the experimental results with the analytic model of the plasma parameters, which is useful to discuss the results from a physical point of view.CERN ’s new particle accelerator Linac4 is part of the upgrade of the LHC accelerator chain. Linac4 is required to deliver 160 MeV H− beam to improve the beam brightness and luminosity in the Large Hadron Collider (LHC). The Linac4 H− source must deliver 40-50 mA, 45 keV H− beam in the RFQ acceptance. Since the RF power coupled to the H− source plasma is one of the important parameters that determines the quality of the H− beam, the experimental investigation of the dependence of the load impedance on the operational parameters is mandatory. In this study, we have measured the impedance of the H− source plasma varying the RF power coupled to the plasma and the condition of the hydrogen gas. Also, optical emission spectroscopy (OES) measurements have been carried out simultaneously with the impedance measurement in order to determine the plasma parameters. The determination of the plasma parameters allows us to compare the experimental results with the analytic model of the plasma parameters, which is usef...

Low pressure plasmas containing indium halides as radiators are discussed for lighting applications as an efficient alternative to mercury-containing fluorescent lamps. To gain insight into plasma parameters like the vibrational and rotational temperature of the molecule, the near UV emission spectra of the indium halides arising from the AΠ0+3→XΣ+1 and the BΠ13→XΣ+1 transitions are simulated. Such a simulation requires Franck–Condon factors and vibrationally resolved transition probabilities which are not available in the literature for InCl. Therefore, they have been calculated by solving the Schrodinger equation using the Born–Oppenheimer approximation. The values of the Franck–Condon factors and the transition probabilities are presented. For the A–X transition a good match of the simulated and measured spectra could be achieved but for the B–X transition neither the relative intensity nor the wavelength could be reproduced. This indicates that for the B state the values of the molecular constants, the potential curve and/or the electronic dipole transition moment of the B–X transition are inaccurate. Despite this mismatch the rotational and vibrational temperatures of the molecule can still be determined using the A–X transition.

Optical emission spectroscopy (OES) measurements of the atomic Balmer series and the molecular Fulcher transition have been carried out at the Linac4 ion source in order to determine plasma parameters. As the spectroscopic system was only relatively calibrated, the data evaluation only yielded rough estimates of the plasma parameters (T(e) ≈ 1.2 eV, n(e) ≈ 1 × 10(19) m(-3), and n(H/)n(H2) ≈ 0.5 at standard operational parameters). The analysis of the Fulcher transition revealed a non-thermal "hockey-stick" rotational population of the hydrogen molecules. At varying RF power, the measurements at the on-axis line of sight (LOS) showed a peak in the rotational temperatures between 25 and 40 kW of RF power, whereas a steady decrease with power was observed at a tilted LOS, indicating the presence of strong plasma parameter gradients.

CERN's 160 MeV H(-) linear accelerator (Linac4) is a key constituent of the injector chain upgrade of the Large Hadron Collider that is being installed and commissioned. A cesiated surface ion source prototype is being tested and has delivered a beam intensity of 45 mA within an emittance of 0.3 π ⋅ mm ⋅ mrad. The optimum ratio of the co-extracted electron- to ion-current is below 1 and the best production efficiency, defined as the ratio of the beam current to the 2 MHz RF-power transmitted to the plasma, reached 1.1 mA/kW. The H(-) source prototype and the first tests of the new ion source optics, electron-dump, and front end developed to minimize the beam emittance are presented. A temperature regulated magnetron H(-) source developed by the Brookhaven National Laboratory was built at CERN. The first tests of the magnetron operated at 0.8 Hz repetition rate are described.

The visual properties of a large plasmoid rising from a water container into the air for up to 450 ms are brought into correlation with the total energy dissipated into the system, and, in particular, with the energy used for plasma generation. The latter parameters are deduced from the time-resolved discharge current and voltage of the capacitor bank which is used as energy supply. By varying the experimental parameters, the energy dissipated to the system varies between 5 kJ and 30 kJ from which 10% to 30% is transferred to the plasma. Clear correlations are obtained for the size of the plasmoid changing from 15 cm to 35 cm in width, the ascent velocity ranging from 1 m/s to 2 m/s, and the rising height for which up to 85 cm is measured. For the relation of the autonomous phase with the energy transferred to the plasma, two trends are observed: 450 ms duration is achieved in maximum with the present setup being almost independent on the electrode gap, the voltage-on time, the water conductivity, or the type of salt dissolved in the water. On the other hand, an almost linear dependence is obtained by changing the capacitance.

A plasmoid in air at atmospheric pressure of about 20 cm in diameter and up to 500 ms duration is generated from a water discharge which is powered for a short time period by a capacitor bank. The analysis of the electrical circuit and the comparison with experimental values show that the energy dissipated into the system is given by the conventional equation for discharging capacitors. The resistance of the system is governed by the resistances of the water reservoir, the plasma, and the plasma-water transition, which are represented as one time-averaged resistance in the equation. Thus, the dissipated energy can be influenced by the energy available (capacitance and voltage), the voltage-on time, the conductivity of the water, the electrode gap and the size of the container (plate electrode) within the experimental boundaries. An estimation of the energy channels for a discharge at standard conditions revealed that the dominant part of the energy is dissipated into the water reservoir. About 25% of the energy is dissipated directly into the plasmoid and is available for plasma formation, plasma kinetics and chemical processes.

Inductively coupled low-pressure discharges containing InBr have been investigated spectroscopically. In order to obtain plasma parameters such as the vibrational and rotational temperature of the InBr molecule, the emission spectra of the and the transitions have been simulated. The program is based on the molecular constants and takes into account vibrational states up to v = 24. The required Franck–Condon factors and vibrationally resolved transition probabilities have been computed solving the Schrödinger equation using the Born–Oppenheimer approximation. The ground state density of the InBr molecule in the plasma has been determined from absorption spectra using effective transition probabilities for the A–X and B–X transition according to the vibrational population. The obtained densities agree well with densities derived from an Arrhenius type vapour pressure equation.