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Broadband microwave propagation and absorption processes and backscatter from objects immersed in a magnetized, finite, warm plasma column is addressed. In particular, the propagation, absorption, and backscatter of electron cyclotron waves are measured and compared with bounded vacuum hot plasma wave propagation, absorption, and ray tracing theory. The nonreciprocal nature of the transmission and absorption in an anisotropic plasma is measured. A homodyne technique which isolates the scattering from a single object in the plasma from the scattering from all other objects in the plasma and the walls of the containment device is developed and utilized. The range of absorption frequencies and nonreciprocity of the transmission signal are shown to be well correlated with wave trajectories in the associated regions of the Clemmow-Mullaly-Allis (CMA) diagram. It is shown that quasi-parallel propagation of electron cyclotron waves near resonance is present and that the transverse effects of wavenumber on propagation in the cylindrical plasma are small. >

We study the effects of an L-to H-mode transition in a tokamak on the loading of fast wave launchers in the Ion Cyclotron Range of Frequencies. For analytical simplicity, a dielectric-filled waveguide is chosen for analysis. However, other apertures or coils can readily be accommodated within the formalism. The H-mode density at the edge is modeled as a pedestal followed by a region of Gaussian variation. We calculate the waveguide reflection coefficient, the equivalent surface plasma impedance and the electric field profile at the aperture, for conditions appropriate to CIT (Compact Ignition Torus). It is concluded that an L- to H-mode transition can impose substantial loading variations on the launcher system. These variations can be matched by appropriate fast response tuner systems, similar to those used for coil antennas.

An excimer-laser ({lambda} = 193 nm) produced plasma in an organic gas (TMAE) has been generated and studied. These studies have determined the ion-electron recombination coefficient and the photon absorption cross-section, of the neutral gas. The dependences of wave transmission, reflection and absorption on plasma density are obtained. A new optical system with an array of cylindrical XUV coated lenses has been implemented to form a plasma sheet to study its usage as agile mirror microwave reflector. The lens system expands the incident laser beam in X direction and compresses it in Y direction to form a sheet beam. The expanded beam then passes through a vacuum chamber filled with TMAE at 50--500 nTorr to produce the plasma sheet. Space-time measurements of the plasma density and temperature as measured by a Langmuir probe are presented. XUV optical measurements of the laser beam as measured by a photodiode are presented. Initial experiments have generated a plasma sheet of 5--10 mm x 11 cm with peak plasma density of 5 {times} 10{sup 13} cm{sup {minus}3}. A microwave source will be utilized to study the agile mirror character of the plasma sheet. Modeling of the microwave reflection from the plasma profile will alsomore » be discussed.« less

Summary form only given. A Vacuum Ultra-Violet (VUV) laser pulse is used to create a plasma sheet in a low-ionization-energy organic gas. Microwaves from a highly directive X-band horn antenna impinge on the sheet where they are reflected. A bi-static antenna system is used for transmitting and receiving the microwave radiation. Both heterodyne and homodyne detection systems are investigated for maximum sensitivity. Reflected signals are measured for amplitude and phase analysis. Comparable amplitude and phase shifts are noted when compared to an aluminum conducting sheet placed in the same position as the plasma. The working gas is tetrakis(dimethylamino)ethylene (TMAE) with an ionization energy of 5.36 eV. The ionizing source is a VUV excimer laser operating at 193 nanometers (6.4 eV). The laser and plasma properties are diagnosed by an optical detection system and by Langmuir probes. The laser beam is transformed into a sheet using VUV coated Suprasil lenses (96% transmission efficiency). A plasma sheet with a peak density of 2.5/spl times/10/sup 13/ cm/sup -3/ and T/sub e/=0.8 eV is formed. Additional measurements of transmitted signals are utilized to determine plasma density and collision frequency. A computer model of the microwave transmission and reflection levels has been developed to optimize reflected signal levels as a function of density and thickness and to interpret experimental results. Comparison between the experimental results and the model show that this system is attractive for use as a microwave reflector.

Summary form only given. Agile microwave reflectors are of interest as potential replacements for large phased arrays on mobile crafts. Microwave reflection from an VUV(/spl lambda/=193 nm) excimer laser produced plasma (W=20 mJ, /spl tau/=17 ns) in an organic gas (TMAE: tetrakis-dimethylamino-ethylene) contained in a 22 mm/spl times/7 mm rectangular column, has been demonstrated. This work investigates the reflection of X-band microwaves at normal and oblique incidences by a planar TMAE sheet of dimensions: 9 cm W/spl times/2-7 mm H/spl times/10-20 cm L, produced by the same excimer laser. Suprasil VUV coated (96% transparent) lenses are used to generate the sheet laser beam profile. Both triple probes and reference probes are used to determine the 3-D laser produced plasma density and temperature profiles, at TMAE neutral pressures in the 25-150 mTorr range. The plasma diffusion during its lifetime is very small. Densities and temperatures in the ranges of n=5/spl times/10/sup 12/-2/spl times/10/sup 13/ cm/sup -3/ and T/sub e/=0.5-0.7 eV are obtained. An examination of the microwave reflection is carried out using X-band horns and rectangular guide apertures. The amplitude and phase of the transmitted and reflected microwave signals are measured using both homodyne and heterodyne systems with hybrid-tee mixers. A time history of the plasma and temperature density is obtained with Langmuir probes and compared with. a measurement based on microwave transmission through the plasma. Reflected and transmitted signals are compared with those from an aluminum sheet of the same dimensions as the plasma. Future plans for the agile mirror reflector and absorber are discussed.

Summary form only given. Agile microwave reflectors are of interest as a potential replacement of phased arrays in radar applications. Microwave reflection from an XUV (/spl lambda/=193 nm) excimer laser (Wmax=20 mJ, r=17 ns) produced rectangular Tetrakis(dimethyl-amino)ethylene (TMAE) plasma column of dimensions 2.2 cm wide, 0.7 cm thick and up to 40 cm long has been demonstrated. This work demonstrates reflection of X-band microwaves at normal incidence by a planar TMAE plasma sheet of dimensions 7.8 cm wide, 0.7 cm thick and up to 40 cm long generated with the same excimer laser. Suprasil XUV lenses coated for 98% transparency at /spl lambda/=193 nm are used to generate the sheet beam profile. The plasma is in the far field of an X-band rectangular aperture antenna used to launch the microwaves. Amplitude and phase measurements of the reflected and transmitted microwave signal is achieved with microwave interferometers utilizing magic-tees. Three dimensional plasma density and temperature profiles as a function of time are obtained with Langmuir probes and compared with a measurement based on microwave transmission through the plasma. Langmuir triple probe measurements indicate that the peak plasma temperature is about 1 eV and densities are on the order of 10/sup 13/ cm/sup -3/.

Summary form only given. Measurements and analysis of the absorption, reflection, and scattering of electromagnetic waves due to electron cyclotron absorption zones and the presence of modulated scatterers in a plasma are presented. Measurements using a modulated homodyne detection system have been made that are sensitive to the backscatter from a movable probe in the plasma. The phase sensitive system is used to measure the local k-spectrum in the inhomogeneous plasma and is compared with WKB (Wentzel-Kramers-Brillouin) theory. A 12-cm-diameter by 2-m laboratory plasma is produced by a 2.45-GHz microwave source. Wideband wave absorption of 30-50 dB due to the electron cyclotron resonance zone in the 1.5-3.0 GHz range is measured. Experiments examining the microwave scattering frequency sensitivity of modulation-launched magnetoacoustic modes from a ceramic encapsulated PIN diode and from a disc Langmuir probe scatterer have also been performed.

Summary form only given. Measurements and analysis of the absorption, reflection, and scattering of electromagnetic waves due to electron cyclotron resonance zones and the presence of scatterers in the plasma were carried out. The 12-cm-diameter by 2-m laboratory plasma was produced by a 2.45-GHz microwave source in a local mirror field, with wave measurements carried out in a larger mirror region. The plasma density that could be created was in the range of 5t109 to 5t1011/cm3 with electron temperatures in the 3-6-eV range and 0.5-2-kG magnetic fields. Wave absorption measurements of 25-50 dB due to the electron cyclotron resonance zone in the 1.5-3.0-GHz range were performed. A modulated homodyne detection system that isolates the backscatter from a single object in the plasma and suppresses the scattering from the walls. probes, and other background was constructed. This system was used to measure the shielding produced by the plasma, including the shielding by cyclotron resonance. The effect of collisional absorption for particular density profiles in weakly magnetized plasmas was analyzed to determine their effect on reflectivity. For collisional. low-magnetic-field plasma conditions comparable to those that can be obtained in the present experiments, the electromagnetic wave reflectivity was calculated using various Epstein profiles

We present an analysis of a rectangular dielectric‐filled waveguide, suitable for ICRF heating. To simulate the H‐mode, we take the edge plasma to consist of a pedestal of variable length followed by a region with either a parabolic or a gaussian variation. We present numerical results for the waveguide reflection coefficient, the equivalent surface plasma impedance and the electric field profile at the aperture, for a wide range of edge plasma conditions. A dielectric‐filled rectangular waveguide launcher has been designed, fabricated and tested for the ICRF wave coupling. Our theoretical analyses and measurements over the 60–130 MHz range indicate that a very high power coupling efficiency (≥90%) can be obtained for a matched launcher with appropriate tuning of the noncontacting sliding short. An input reflection coefficient model has been developed for a matched or plasma‐loaded waveguide launcher and compared with measurements.