A rate-equation model with greatly improved quantitative rigour is detailed for the CW optogalvanic effect on the 1s-2p transitions of neon atoms in the positive column of a dc normal glow discharge. This work constitutes one part of a wider complementary programme which also includes CW laser collisionally-induced fluorescence, optical emission spectroscopy and optical absorption spectroscopy for the excited-state populations, all employing the same atomic and discharge data set. Our aim has been to produce a theoretical model and test it with stringently collected data, to demonstrate that tunable laser CW optogalvanic spectroscopy (OGS) can provide a truly quantitative diagnostic of the excited-state kinetics in low-temperature discharges. The model is deliberately restricted to just six essential perturbed rate equations, four for the 1s states, one for the charged particles and one for the discharge current. Our formulation, via the 1s and 2p CW-induced pump rate perturbations, allows very direct identification of the important excited-state kinetics producing the OGE. The principles and scope of our theory are demonstrated for a neon filling pressure of 2.0 Torr and currents of 1-10 mA, based on fitting the model for three carefully selected transitions, the 1s5 -2p4 (594.5 nm), 1s4 -2p4 (609.6 nm) and 1s5 -2p9 (640.2 nm). Results show that the magnitudes of the CW optogalvanic effect on the 1s-2p transitions are strongly dependent on the discharge pumping rates of the 1s states and their coupling, and confirms that cascade effects must be included in the 1s excitation rate coefficients.

We utilize an array of related optical diagnostics to deliver quantitative description of each process involving the 15 lowest levels in neon, for reduced electric fields ranging from 3 × 10 −16 to 2 × 10 −16 V cm 2 (3-20 Td). Description of the kinetics between the 1s and 2p excited states (Paschen notation) has been obtained using CW laser collisionally induced fluorescence (i.e. fluorescence from a non-excited upper level). We have employed this technique in combination with the traditional optical emission and absorption spectroscopic studies to determine the rate coefficients describing electron-collisional excitation from the ground to the 1s and 2p states. These values, along with previously determined 1s-2p rate coefficients, have been used with current literature cross sections to provide information on the electron distribution function for energy bands of 2-8, 16.9-23.0 and 19.0-25.5 eV. Values of the electron temperatures obtained from our 1s coefficients were used for an extensive study of the ground state to 1s excitation functions. From 3 to 20 Td, the average values of the temperature corresponding to the 1s excitations ranged from 1.8 to 3.1 eV, while those from 2p excitation were in the range 1.6-2.9 eV. Our investigation of the bulk temperature using data for 1s-2p excitation suggests a scaling of ∼0.5 for the published theoretical excitation function, which is supported by the new experimental cross sections of Boffard et al.A quantitative description of cascade to the 1s states is also presented, showing that at the top of our reduced field range, cascade from the 2p states contributes 29-35% of the total excitation rates from the ground state.

Spectral analysis of the vacuum conditions within the JET tokamak provides unique challenges due to the complex interactions of Hydrogen, Deuterium and Tritium with the large amounts of Carbon forming the plasma facing first wall. Overlapping masses and low resolution of the quadrupole Residual Gas Analyzer (qRGA) means discrimination of individual species is not possible operating in a conventional mode. Baking the vessel to temperatures in excess of 300 degrees Celsius further complicates an already difficult task.Here, we present and demonstrate a complimentary technique operating the qRGA in a mode where the energy of the electrons emitted within the ionization source is variable. Different elements have defined ionization energies required to remove an orbiting electron, this energy is dependent on the electron orbital, i.e. outer shell electrons generally have weaker ionization energies due to the greater distance and lower electrostatic forces from the nucleus. Using this technique known as "Soft Ionization" de-convolution of the mass spectra obtained at JET could lead the way to providing a better understanding of the chemistry within the vacuum vessel as well as providing invaluable diagnostic information during vessel conditioning.Initial experimental data has proved encouraging demonstrating ionization energy discrimination of D 2 and 4 He at 4amu and D 2 O /Ne /Ar ++ at 20amu. De-convolution of hydrocarbon and deuterated hydrocarbon molecules in the mass spectrum is also currently ongoing, with initial results revealing clear discrimination of CH 4 and CD 2 molecular ions at 16amu. Using electron ionization cross-section theory we also demonstrate the generation of algorithms within the qRGA software to automatically discriminate quantitatively between overlapping peaks in the mass spectra. This technique can be applied to historical as well as real time data. 2010 brings the installation of the Beryllium plasma facing wall at JET and an opportunity to accurately determine the vessel chemistry during commissioning. The results from this phase of JET operations and further applications of the technique including leak detection and cryogenic pumping regeneration inventory determination could prove valuable for ITER commissioning and operations.

Very fast current transients (10 A, 5 GHz) have been measured using the Faraday rotation in CdMnTe sample. RF magnetic fields with an amplitude of < 10 G have been measured, despite the laser intensity noise (at these bandwidths) and the noisy environments. This paper describes a technique whereby the insertion loss is minimised and the effect of the laser intensity noise reduced, enabling these small RF fields to be measured for the first time.