Two photon absorption laser induced fluorescence (TALIF) measurements of neutral hydrogen and its isotopes are typically calibrated by performing TALIF measurements on krypton with the same diagnostic system and using the known ratio of the absorption cross sections [K. Niemi et al., J. Phys. D 34, 2330 (2001)]. Here we present the measurements of a new calibration method based on a ground state xenon scheme for which the fluorescent emission wavelength is nearly identical to that of hydrogen, thereby eliminating chromatic effects in the collection optics and simplifying detector calibration. We determine that the ratio of the TALIF cross sections of xenon and hydrogen is 0.024 ± 0.001.
Here we describe a novel infrared laser-induced fluorescence scheme for the 1s2 state of Ar-I using an 841.052 nm (vacuum) Sacher tunable diode laser oscillator and compare it to an established 667.913 nm (vacuum) 1s4-pumping Ar-I LIF scheme using a master oscillator power amplifier laser [A. M. Keesee et al. Rev. Sci. Instrum. 75, 4091 (2004)]. The novel scheme exhibits a significantly greater signal-to-noise ratio for a given injected laser power than the established scheme. We argue that this is caused by less intense spontaneous Ar-I radiation near the LIF emission wavelength for the 1s2 scheme as compared to the 1s4 scheme. In addition we present an updated iodine cell spectrum around the 1s4 LIF scheme pump wavelength.
Microwaves are injected into argon and helium helicon plasmas at 6 to 20 mTorr neutral pressure, 1.2 kW pulsed microwave power, up to 500 W continuous RF power, and up to 1 kG magnetic fields, with the objective of heating the tail of the electron energy distribution function (EEDF) and populating ion metastable states. Langmuir probes are used to measure the EEDF and optical emission spectroscopy is used to monitor ion emission. The injection of microwave power in argon helicon plasmas is shown to heat the high energy tail of the EEDF without increasing the plasma density. Argon ion emission is shown to increase by a factor of 4. Injection of microwaves into a helium helicon plasma is shown to cool the bulk of the of the EEDF and increase the plasma density. Previously absent helium ion emission lines are observed with the injection of microwaves. All the microwave results are shown to be independent of RF power within the limits of the system.
Direct laser induced fluorescence measurements are shown of cross-field ion flows normal to an absorbing boundary that is aligned parallel to the axial magnetic field in a helicon plasma. We show Langmuir and emissive probe measurements of local density and plasma potential in the same region, as well as floating probe spectra near the boundary. With these measurements, we investigate the influence of ion-neutral collisionality on radial ion transport by varying the ratio of the ion gyro-radius, q i , to the ion-neutral collision length, k, over the range 0.34 q i k À1 1.60. Classical drift-diffusion transport along density and potential gradients is sufficient to describe flow profiles for most cases. For two parameter regimes (q i k À1 ¼ 0.65 and 0.44), low-frequency electrostatic fluctuations (f < 10 kHz) and enhanced cross-field bulk ion flow to the boundary are observed.
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