Extremely small-diameter, high-density, radio frequency, plasma sources and central gas feeding for next-generation electrodeless plasma thrusters.

Radio frequency (RF) waves including helicon waves can readily produce high-electron-density (ne up to 1013 cm-3) plasmas with a broad range of external operating parameters. Various featured RF and helicon sources in a wide range of scales are suitable for plasma propulsion schemes. Electrodeless RF plasmas have no direct contact between electrodes and antennas, which enables long-life operation. However, one of the crucial problems is to reduce the plasma size for future applications in nano- and pico-satellites. Diagnostics of the plasma parameters in a small area should also be improved. Furthermore, to increase plasma performance, it is important to consider the radial electron density (ne) profile with an increasing upper limit, observed in high-density helicon sources due to the depletion of neutrals. This problem may be controlled by the location of neutral gas feeding and knowledge of the gas pressure distribution. Here, production of RF plasmas, with extremely small diameters from 3-mm down to 0.5-mm including 1-mm, was demonstrated, and characterization of ne and the electron temperature was performed with a collisional radiative model. Finally, to improve plasma performance such as ne and the thrust force, internal gas feeding was demonstrated using a developed Pirani gauge to measure neutral density.

Spatial measurement in rotating magnetic field plasma acceleration method by using two-dimensional scanning instrument and thrust stand.

A two-dimensional scanning probe instrument has been developed to survey spatial plasma characteristics in our electrodeless plasma acceleration schemes. In particular, diagnostics of plasma parameters, e.g., plasma density, temperature, velocity, and excited magnetic field, are essential for elucidating physical phenomena since we have been concentrating on next generation plasma propulsion methods, e.g., Rotating Magnetic Field plasma acceleration method, by characterizing the plasma performance. Moreover, in order to estimate the thrust performance in our experimental scheme, we have also mounted a thrust stand, which has a target type, on this movable instrument, and scanned the axial profile of the thrust performance in the presence of the external magnetic field generated by using permanent magnets, so as to investigate the plasma captured in a stand area, considering the divergent field lines in the downstream region of a generation antenna. In this paper, we will introduce the novel measurement instrument and describe how to measure these parameters.

Development of 2-D horn-antenna millimeter-wave imaging device (HMID) for the plasma diagnostics.

The two-dimensional (2-D) Horn-antenna Millimeter-wave Imaging Device (HMID) has been developed for the O-mode Microwave Imaging Reflectometry (O-MIR) in the Large Helical Device (LHD). The detectable frequency range of the HMID is 23-33 GHz, which corresponds to the cutoff electron density of 0.8-1.5 × 1019 m-3 in the O-MIR. The HMID is a 2-D imaging device that improves on the horn-antenna mixer array, which had been developed for the X-mode MIR in the LHD. In the HMID, the signal (RF) wave from the horn antenna is transmitted to the microstrip line by the finline transmitter, and this is mixed by the double-balanced-mixer with the local oscillation wave that is fed by a coaxial cable. By using the HMID, the MIR optical system can be significantly simplified.

A 60-GHz interferometer with a local oscillator integrated antenna array for divertor simulation experiments on GAMMA 10/PDX.

In conventional multichannel/imaging microwave diagnostics of interferometry, reflectometry, and electron cyclotron emission measurements, a local oscillator (LO) signal is commonly supplied to a receiver array via irradiation using LO optics. In this work, we present a 60-GHz interferometer with a new eight-channel receiver array, called a local oscillator integrated antenna array (LIA). An outstanding feature of LIA is that it incorporates a frequency quadrupler integrated circuit for LO supply to each channel. This enables simple and uniform LO supply to the receiver array using only a 15-GHz LO source and a coaxial cable transmission line instead of using an expensive 60-GHz source, LO optics, and a waveguide transmission line. The new interferometer system is first applied to measure electron line-averaged density inside the divertor simulation experimental module (D-module) on GAMMA 10/PDX tandem mirror device.

Validation experiment of a numerically processed millimeter-wave interferometer in a laboratory.

We propose a new interferometer system for density profile measurements. This system produces multiple measurement chords by a leaky-wave antenna driven by multiple frequency inputs. The proposed system was validated in laboratory evaluation experiments. We confirmed that the interferometer generates a clear image of a Teflon plate as well as the phase shift corresponding to the plate thickness. In another experiment, we confirmed that quasi-optical mirrors can produce multiple measurement chords; however, the finite spot size of the probe beam degrades the sharpness of the resulting image.

Development of horn antenna mixer array with internal local oscillator module for microwave imaging diagnostics.

A new antenna array is proposed in order to improve the sensitivity and complexity of microwave imaging diagnostics systems such as a microwave imaging reflectometry, a microwave imaging interferometer, and an electron cyclotron emission imaging. The antenna array consists of five elements: a horn antenna, a waveguide-to-microstrip line transition, a mixer, a local oscillation (LO) module, and an intermediate frequency amplifier. By using an LO module, the LO optics can be removed, and the supplied LO power to each element can be equalized. We report details of the antenna array and characteristics of a prototype antenna array.

Development of very small-diameter, inductively coupled magnetized plasma device.

In order to miniaturize a high-density, inductively coupled magnetized plasma or helicon plasma to be applied to, e.g., an industrial application and an electric propulsion field, small helicon device has been developed. The specifications of this device along with the experimental results are described. We have succeeded in generating high-density (~10(19) m(-3)) plasmas using quartz tubes with very small diameters of 10 and 20 mm, with a radio frequency power ~1200 and 700 W, respectively, in the presence of the magnetic field less than 1 kG.

Development of 3D microwave imaging reflectometry in LHD (invited).

Three-dimensional (3D) microwave imaging reflectometry has been developed in the large helical device to visualize fluctuating reflection surface which is caused by the density fluctuations. The plasma is illuminated by the probe wave with four frequencies, which correspond to four radial positions. The imaging optics makes the image of cut-off surface onto the 2D (7 × 7 channels) horn antenna mixer arrays. Multi-channel receivers have been also developed using micro-strip-line technology to handle many channels at reasonable cost. This system is first applied to observe the edge harmonic oscillation (EHO), which is an MHD mode with many harmonics that appears in the edge plasma. A narrow structure along field lines is observed during EHO.

Simultaneous projection and detection system of four different frequencies for microwave imaging reflectometry in Large Helical Device.

A simultaneous projection/detection system of four different frequencies for microwave imaging reflectometry (MIR) was developed for three-dimensional observation of electron density fluctuations in the Large Helical Device (LHD). The microwave with four frequency components at 60.410, 61.808, 63.008, and 64.610 GHz is projected in a continuous-wave mode to illuminate the target LHD plasma. A two-dimensional horn-antenna mixer array (2D HMA) receives the reflected wave from the plasma as well as the wave from the local oscillator operating at 55.800 GHz. The first intermediate frequency (IF) signals at 4.610, 6.008, 7.208, and 8.810 GHz were confirmed to be obtained by downconversion of these microwaves using the 2D HMA. Each of these first IF components is filtered from each other and downconverted again for the superheterodyne detection. It was confirmed that both the amplitudes and the phases of the detected signals reflect the fluctuations in LHD plasmas.

Calibration of electron cyclotron emission radiometer for KSTAR.

We developed and installed an electron cyclotron emission radiometer for taking measurements of Korea Superconducting Tokamak Advanced Research (KSTAR) plasma. In order to precisely measure the absolute value of electron temperatures, a calibration measurement of the whole radiometer system was performed, which confirmed that the radiometer has an acceptably linear output signal for changes in input temperature. It was also found that the output power level predicted by a theoretical calculation agrees with that obtained by the calibration measurement. We also showed that the system displays acceptable noise-temperature performance around 0.23 eV.

Development of electron cyclotron emission imaging system on Large Helical Device.

A combined system of microwave imaging reflectometry and electron cyclotron emission (ECE) imaging has been developed for the Large Helical Device. This system includes a wide-band two-dimensional horn-antenna mixer array (HMA). The HMA consists of horn antennas, waveguides, mixers, and intermediate frequency circuits. The frequency response of the HMA is between 50 and 110 GHz. The ECE signal is selected using a 95 GHz local oscillator and a 93 GHz high-pass filter.

Development of microwave imaging reflectometry in large helical device.

Three key devices of the microwave imaging reflectometry (MIR) are under development in large helical device (LHD). The 2-D mixer array is developed by stacking the one-dimensional array of the planar Yagi-Uda antenna. The new type of the bandpass filter bank is modified to match the requirement of the MIR. The low-cost quadrature demodulator is also developed for the phase detection system. By using the low-price commercial wireless devices, the development cost becomes much lower than the expensive waveguide system. These devices enable the development of 2-D/3-D microwave imaging system for the plasma diagnostics and industrial applications.

[Resistance to Fas-mediated apoptosis in human papillomavirus type 16-immortalized human laryngeal epithelial cells after tumorigenesis].

Apoptosis plays an important role in such biological processes as multistep carcinogenesis. Human papillomavirus type 16(HPV16)-immortalized human epithelial cell lines are, for the most part, nontumorigenic in nude mice and useful for studying mechanisms involved in multistep carcinogenesis. We previously reported that HPV16-immortalized human laryngeal epithelial cell line HLEC16 formed tumors after treatment with 4-(methyl-nitrosamine)-1-(3-pyridyl)-1-butanone, and derived one tumorigenic cell line, HLEC16T. We compared sensitivity to Fas receptor-mediated apoptosis of nontumorigenic HLEC16 and tumorigenic HLEC16T. HLEC16 and HLEC16T expressed Fas protein (Fas) but not Fas-ligand (FasL) mRNA. We applied an anti-Fas monoclonal, antibody, CH11, to HLEC16 and HLEC16T, and monitored cell death. HLEC16T was found to be significantly less sensitive to CH11-mediated cell death that HLEC16. Western blot analysis showed no significant difference in levels of apoptosis-inducing protein, Bax, between HLEC16 and HLEC16T. Levels of apoptosis-inhibiting proteins Bcl-2 and Bcl-XL increased in HLEC16T. These results suggest that the inhibition of Fas-mediated apoptosis through apoptosis-inhibiting protein overexpression may promote tumorigenicity in HLEC16T.

[Resistance to Fas-mediated apoptosis in head and neck squamous cell carcinoma cells].

Various types of carcinoma cells have been shown to escape immune recognition by constitutive resistance to Fas receptor (Fas)-mediated apoptosis. The purpose of this study was to examine the sensitivity to Fas-mediated apoptosis of human head and neck squamous cell carcinoma (HNSCC) cells. We applied an anti-Fas monoclonal antibody (CH11) to HNSCC cell lines and monitored their cell death. All three HNSCC cell lines examined expressed Fas protein but not Fas-ligand mRNA. CH11 did not induce cell death (CH11-resistant) in any of the three HNSCC cell lines examined. Treatment with actinomycin D (ActD) converted the phenotypes of the CH11-resistant HNSCC cell lines from CH11-resistant to CH11-sensitive, suggesting that the resistance to CH11-induced apoptosis was dependent on RNA synthesis. Western blot analysis did not show any differences in expression of Bcl-2 between the non-treated and ActD-treated HNSCC cell lines. Expression of Bcl-XL, on the other hand, was greatly reduced in the ActD-treated HNSCC cell lines, implying that Fas signaling in the CH11-resistant HNSCC cell lines might be regulated by an Bcl-XL-inhibitable step.

Caspase-9 regulates cisplatin-induced apoptosis in human head and neck squamous cell carcinoma cells.

The aim of this study was to understand the molecular requirements for cisplatin-induced apoptosis in human head and neck squamous cell carcinoma (HNSCC) cell death. Cisplatin induced apoptosis in HNSCC cell lines, HSC-2, HSC-3 and HSC-4 in a dose-dependent manner. However, cisplatin did not induce the expression of Fas-ligand mRNA or upregulation of Fas protein. By caspase activation assays, cisplatin induced Caspase-3 (Casp-3), -8 and -9 activation. In all three lines tested, the use of a specific inhibitor of Casp-9 almost completely blocked cisplatin-induced apoptosis, while the use of Casp-3 and -8 inhibitors resulted in a partial blockade of cisplatin-induced apoptosis. Our results strongly suggest that Casp-9-dependent apoptosis plays an important role in cisplatin-induced HNSCC apoptosis.

Morphology of lymphatics in the canine large intestine.

The finer distribution of lymphatics in the large intestine of adult dogs was morphologically examined by puncture injection of colored dyes, intra-arterial injection of silver nitrate mixed with India ink, and electron microscopy. In the lamina propria there was a double-layer of lymphatic channels - a shallow network (near the mucosal surface) and a deep compartment (just above the muscularis mucosae). Sparse lymph capillaries also extended vertically paralleling intestinal glands. Some lymphatics penetrated into the submucosa where they demonstrated prominent valves and formed collecting lymphatic trunks alongside blood vessels.