Search

A frequency multiplied microwave interferometer, a Hα line emission measurement system, and a high speed camera system were installed on the Pilot-PSI device for low frequency fluctuation study in the detached plasma condition. The two dimensional Hα line emission and its fluctuation were monitored with a fast visible camera with Hα filter. The coherent low frequency fluctuations of frequency of approximately 13 kHz were measured by all measurement systems. The stronger fluctuation intensities were observed in the downstream of the ionization front region in the detached plasma condition. Moreover, we show the clear difference between the strong fluctuation regions of the electron line density and Hα line emission for the first time. This means that the fluctuations of Hα line emissions was caused by not only electrons but also by hydrogen ions.

The multi-pass Thomson scattering (MPTS) system is a useful technique for increasing the Thomson scattering (TS) signal intensities and improving the TS diagnostic time resolution. The MPTS system developed in GAMMA 10/PDX has a polarization-based configuration with an image relaying system. The MPTS system has been constructed for enhancing the Thomson scattered signals for the improvement of measurement accuracy and the megahertz sampling time resolution. However, in the normal MPTS system, the MPTS signal intensities decrease with the pass number because of the damping due to the optical components. Subsequently, we have developed a new MPTS system with the laser amplification system. The laser amplification system can improve the degraded laser power after six passes in the multi-pass system to the initial laser power. For the first time worldwide, we successfully obtained the continued multi-pass signals after the laser amplification system in the gas scattering experiments.

The multipass Thomson scattering (MPTS) technique is one of the most useful methods for measuring low-electron-density plasmas. The MPTS system increases Thomson scattering (TS) signal intensities by integrating all multipass (MP) signals and improving the TS time resolution by analyzing each pass signal. The fully coaxial MPTS system developed in GAMMA 10/potential-control and diverter–simulator experiments has a polarization-based configuration with image-relaying optics. The MPTS system can enhance Thomson scattered signals for improving the measurement accuracy and megahertz-order time resolution. In this study, we develop a new MPTS system comprising a laser amplification system to obtain continuous MP signals. The laser amplification system can improve degraded laser power and return an amplified laser to the MP system. We obtain continuous MP signals from the laser amplification system by improving the laser beam profile adjuster in gas scattering experiments. Moreover, we demonstrate that more MP signals and stronger amplified MP signals can be achieved via multiple laser injections to the laser amplification system in the developed MP system comprising a laser amplification system.

We developed a multi-channel Hα array system to measure two-dimensional (2D) radial profiles of Hα emissivity in the central cell of the tandem mirror GAMMA 10/PDX. It consists of a 2D optical collection system, which contains twelve channels of lenses, Hα filters, and bundled optical fibers in vertical and horizontal directions. To study Hα emission behavior and its fluctuation in the hot-ion mode plasma experiments with additional plasma heating application, we used the modified Phillips-Tikhonov tomography method. After applying the fast Fourier transform analysis to the 2D Hα emissivity profiles, we could successfully obtain the 2D fluctuation images for the first time. These results are useful for the detailed study of fluctuations in magnetically confined plasma.

In GAMMA 10/PDX, divertor simulation studies have been started as a new research plan by using end-loss plasma flux at the end-mirror region. A divertor simulation experimental module (D-module) was installed in the west end-cell. Here we introduce a novel microwave interferometer system with a phase imaging method, and all the crucial components are designed and tested. Finally, we tested the interferometer system using a Teflon plate in substitution for plasma. In order to improve the system accuracy, the phase detection circuit was modified and the phase difference of each channel was verified.

In GAMMA 10/PDX, the divertor simulation experiment has been performed recently. Ion cyclotron range of frequency (ICRF) waves are used for plasma production and ion heating. It is necessary for obtaining better controllability and extending the operational regime to understand the excitation, propagation, and absorption of the waves. The density fluctuations accompanied by the ICRF waves propagating in the inner region of plasma has been measured by using a microwave reflectometer on the antenna-phasing experiments, where the propagation of the ICRF waves is actively controlled. The phase difference between two axially separated ICRF antennas remarkably affects the global plasma parameters. The density fluctuation caused by the interfered ICRF waves is shown to depend clearly on the phase difference between the waves excited from two antennas. The availability of a reflectometer for the evaluation of the internal wave propagation is shown.

Thomson scattering (TS) is one of the most reliable diagnostics to measure the electron temperature and electron density radial profiles in fusion plasmas. In GAMMA 10, a yttrium-aluminum-garnet (Y...

High time resolved electron temperature measurements are useful for fluctuation study. A multi-pass Thomson scattering (MPTS) system is proposed for the improvement of both increasing the TS signal intensity and time resolution. The MPTS system in GAMMA 10/PDX has been constructed for enhancing the Thomson scattered signals for the improvement of measurement accuracy. The MPTS system has a polarization-based configuration with an image relaying system. We optimized the image relaying optics for improving the multi-pass laser confinement and obtaining the stable MPTS signals over ten passing TS signals. The integrated MPTS signals increased about five times larger than that in the single pass system. Finally, time dependent electron temperatures were obtained in MHz sampling.

We developed an yttrium aluminium garnet (YAG)-Thomson scattering (TS) system for measuring an electron temperature and density in the divertor simulation experimental module (D-module) plasma in GAMMA 10/PDX. We applied a frequency multiplied microwave interferometer (MIF) system for measuring a line integrated electron density in D-module. In D-module, there are many electrostatic probes on the V-shaped tungsten target plate. However, they cannot measure the upstream plasma parameters. By using the YAG-TS system and MIF system, we can obtain the upstream plasma parameters. In the argon gas puffing D-module plasma, we successfully obtained the electron temperature and density of upstream plasma for the first time.

We developed an yttrium aluminum garnet (YAG)-Thomson scattering (TS) system for radial profile measurements of electron temperature and density in the GAMMA 10/PDX central cell. The optical collection system for TS light was constructed from three spherical mirrors and nine bundled optical fibers. The radial positions were intervals less than 5cm in the range of ±20 cm and were measured by moving the fixed fiber bundle position from shot to shot. We constructed a multi-pass TS system with laser amplification, which can increase the signal intensity and time resolution of the TS diagnostic system. In addition, we installed the end-TS system using the central-TS YAG laser in order to measure the electron temperature and density in a divertor simulation experimental module in the GAMMA 10/PDX end cell.

Beach heating using a slow Alfvén wave in ion cyclotron range of frequencies would be the first candidate for ion heating in a DEMO-relevant divertor testing linear plasma device if it is applicable to a high-density regime. To clarify its availability, the density dependence of a slow wave excitation is investigated using a full wave simulation with TASK/WF3D code in the GAMMA 10/PDX central cell configuration, where there is an extensive track record of a beach heating. A shielding effect is successfully demonstrated and well understood under a three-dimensional configuration in the limit of cold plasma approximation. As the density increases, excitable left-handed electric field, which contributes to ion cyclotron heating, degrades more and more from a core region, and resultantly the ion absorption region goes outwards with reducing its power. For core densities above 1020 m−3, the wave field exists only at a very edge, and ion heating becomes negligible unless the wave frequency is much increased with a correspondent magnetic field enhancement.

The suppression of the potential fluctuation was clearly observed by a gold neutral beam probe (GNBP) during the higher potentials and positive electric fields driven by electron cyclotron heating. The particle flux evaluated from the phase difference between the potential and density fluctuations measured by GNBP showed the radial outward flux and correlates with the decrease in the stored energy. When flux is suppressed by the potential formation, the quick plasma stored energy increase is observed.

In the tandem mirror GAMMA 10, plasma confinement is achieved not only by the magnetic mirror configuration but also by the high potentials at both end regions. Before applying plug–electron cyclotron resonance heating (P-ECH), drift-type fluctuations were observed in the potential and density measurements. The suppression potential and density of these fluctuations were clearly determined by using a gold neutral beam probe (GNBP) system during the potential formation by the application of P-ECH. We studied the relationship between the suppression levels of the potential fluctuations and the effects of potential produced by changing the applied electron cyclotron heating power. Moreover, the particle-flux-related values obtained by examining the phase difference between the potential and density fluctuations were measured by using the GNBP. We clearly show that radial anomalous transport induces radial particle transport, which decreases the stored energy of the plasma.

In the tandem mirror GAMMA 10/PDX, a neodymium-doped, yttrium-aluminium-garnet (Nd:YAG) Thomson scattering (TS) system have been constructed for electron temperature and density radial profile measurements. We can successfully measure the radial profiles of electron temperature and density in the central cell of GAMMA 10/PDX by using the YAG-TS system in a single laser shot. By using high speed oscilloscopes and their data collection program, we can measure time dependent electron temperatures and densities every 100 ms in a single plasma shot. Moreover, in order to increase the TS signal intensities, we have constructed a multi-pass TS system of the polarization based system with image relaying optics. The clear multi-pass TS scattering signals from first to eighth passing lasers through the plasma were successfully obtained. The five times larger TS signal intensity were indicated. The multi-pass TS system improves the measurement resolution and time resolution.

We developed the YAG Thomson scattering (TS) system for electron temperature and density radial profiles in a single laser shot in the tandem mirror GAMMA 10/PDX. The optical collection system for the TS light is constructed using spherical mirrors and nine bundled optical fibers. The measurable radial positions are 5-cm intervals in a region of ±20 cm due to the fixed position of the bundled optical fibers, which are set on a fixed-height optical platform. We replaced this with a lab jack to make the bundled optical fiber positions movable. Consequently, we can measure the radial profiles of the electron temperature in more detail. Moreover, we added a third spherical light collection mirror at the bottom of the main spherical collection mirror to increase the TS light intensity in the edge plasma region. In this way, we can obtain a slightly larger TS signal intensity than in the case without a third collection mirror. The radial electron temperatures and densities at 15 radial positions in GAMMA 10/PDX are successfully obtained. For the in-situ calibration of the electron density measurements of the TS system, we compare the TS system measurements to the electron line density measured using a microwave interferometer system.

Slow Alfven wave in ion cyclotron range of frequency (ICRF) is a powerful tool to heat ions confined in a mirror field. In spite of its efficient heating effect that has been attained in the central cell of GAMMA 10, there are still unknown characteristics concerning boundary condition, transient variation of heating effect, exact picture of cyclotron damping, and so on. To study these characteristics in detail, a multi-point measurement of the waves inside the hot plasma has been recently developed by using a microwave reflectometer. In addition to a radial profile measurement that is available by a usual reflectometer, an axial measurement has been achieved by arraying transmitting and receiving horn antennas in the axial direction, which are repeatedly switched in time during a discharge with PIN diode switches. Another transmitting and receiving horn antenna pair was newly added to the system and probing at five cross sections was achieved in a single discharge with time resolution of about 1 ms at each antenna pair position. With the upgraded reflectometer system, axial and radial distributions of wave-induced fluctuations and those temporal behavior were clearly observed, offering valuable data on wave physics in a hot mirror plasma.

Considerable interests have been focused on the study of turbulent fluctuations in magnetic confinement system, since various theories predict such turbulent fluctuations lead to anomalous transport and energy loss in the transverse direction. Density fluctuations during the formation of the confinement potential with application of electron cyclotron heating (ECH) in GAMMA 10 were studied by using both the multi-channel microwave interferometer and gold neutral beam probe. It is found that low frequency fluctuation, which corresponds to the diamagnetic drift, is suppressed during the formation of confining potential by the application ofplug-ECH.

It has been confirmed that the normal mode of a surface wave on a corrugated metal plate can be excited by a sheet electron beam. Two types of instabilities are analyzed numerically. One is the Cherenkov instability between the surface normal mode and the slow-space-charge mode of the electron beam. This instability is possibly absolute instability. The oscillation frequency of this instability can be controlled by the amplitude of the corrugation depth. The electron beam energy for this instability is determined by the ratio of the period length and the amplitude of the corrugation. Another is the Smith–Purcell-type instability. This instability is always convective-type instability. The oscillation frequency is higher than that of the above-mentioned Cherenkov instability and is in a broad band. The temporal growth rate of this instability is strongly reduced as the beam energy is reduced.

A multi-channel microwave interferometer can measure plasma density radial profiles in a single plasma shot. It has six observing channels for measuring the radial electron line integrated density ...

An electron density profile is observed by using an ultrashort-pulse reflectometry in the central cell of the GAMMA 10 device. The pulse having 65 ps FWHM is launched into the plasma in the O-mode and reflected at the cut off layer. The frequency range of the receiving system is 6 to 11 GHz. Time of flight of the received signal is measured via a time to amplitude converter and processed by a computer. Here, electron density profile lower than 1.5 x 10 18 m -3 is reconstructed within one-shot data. The time variation of the electron density profile is acquired. Reflected wave has information of fluctuation, simultaneously. Frequency spectrum of the fluctuation is also observed.

In the GAMMA10 tandem mirror, a strong ion cyclotron range of frequency heating is performed. As a result of the heating, the Alfven ion cyclotron (AIC) modes are spontaneously excited due to the strong temperature anisotropy. The AIC modes in the GAMMA10 are excited as the axial eigenmodes and detected at the whole of the device. In the recent experiments, the clear standing wave structure is observed with the magnetic probe measurements. Characteristics of the AIC modes and the measurement of the axial profile are presented.

The microwave reflectometry using FM and ultrashortpulse radar techniques have been applied to GAMMA 10 in order to diagnose plasma density profile and fluctuations. The reliability of profile measurement using the FM reflectometer is investigated for various sweep times and local path length. It is demonstrated that the reconstructed density profiles seem to be improved when the sweep time is faster than 50-100 μs. The several reconstruction algorithms are introduced to analyze the fast time-varying data, such as, the maximum-entropy method and wavelet analysis as well as zero-cross fringe counting and digital complex demodulation method. The reflectometers are applied to the measurement of density/magnetic fluctuations. The space- and time-resolving spectra of rf waves as well as low-frequency waves are obtained The density and magnetic-field fluctuations are evaluated from both the reflectometer and cross-polarization scattering diagnostic method.

Fluctuation of electron density is observed by using a microwave reflectometry in the central cell of GAMMA 10 tandem mirror. An ultrashort-pulse train, whose pulse width is 65 ps, is transmitted into the plasma in the ordinary-wave mode and reflected at the cut-off layer. The reflected wave is detected by the receiving system, and its time-of-flight, i.e., round trip time, is measured. Fluctuation of the time-of-flight is fluctuation of the cutoff layer and it means density fluctuation. The pulse has a broad frequency spectrum, so each frequency component is reflected at different layer corresponding to its frequency. The frequency range of the receiving system is 7 to 11 GHz, and cut-off density ranges 0.61 to 1.5 x 10{sup 18} m{sup -3}. Density on the central axis of the plasma is about 2 x 10{sup 18} m{sup -3}. Radial intensity distribution of the fluctuation is observed without any perturbation. Frequency of the fluctuation is around several kHz.

A new interferometer is installed on the west anchor cell of the GAMMA 10 tandem mirror. In GAMMA 10, we have used a heterodyne-type interferometer with a 70-GHz IMPATT oscillator and a 150-MHz oscillator for frequency modulation. The new interferometer consists of a 17.5-GHz phase locked dielectric resonator oscillator and a 37.5-MHz temperature-compensated crystal oscillator, as well as frequency multipliers. The main motivation for the new interferometer using frequency multipliers is to achieve a stable and cost effective interferometer. Direct anchor heating experiments with new anchor ion cyclotron range of frequency antennas in both the west and the east anchor cells are carried out. Density increases in both anchor cells are clearly observed using the new interferometer.

In the GAMMA 10 tandem mirror, the typical electron density is comparable to that of the peripheral plasma of torus-type fusion devices. Therefore, an effective method to increase Thomson scattering (TS) signals is required in order to improve signal quality. In GAMMA 10, the yttrium-aluminum-garnet (YAG)-TS system comprises a laser, incident optics, light collection optics, signal detection electronics, and a data recording system. We have been developing a multi-pass TS method for a polarization-based system based on the GAMMA 10 YAG TS. To evaluate the effectiveness of the polarization-based configuration, the multi-pass system was installed in the GAMMA 10 YAG-TS system, which is capable of double-pass scattering. We carried out a Rayleigh scattering experiment and applied this double-pass scattering system to the GAMMA 10 plasma. The integrated scattering signal was made about twice as large by the double-pass system.

We have developed an analysis method to improve the accuracies of electron temperature measurement by employing a fitting technique for the raw Thomson scattering (TS) signals. Least square fitting of the raw TS signals enabled reduction of the error in the electron temperature measurement. We applied the analysis method to a multi-pass (MP) TS system. Because the interval between the MPTS signals is very short, it is difficult to separately analyze each Thomson scattering signal intensity by using the raw signals. We used the fitting method to obtain the original TS scattering signals from the measured raw MPTS signals to obtain the electron temperatures in each pass.

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.

In the hot ion mode of the tandem mirror GAMMA 10/PDX experiments, increases in the flux and temperature of end-loss electrons were observed after the excitation of Alfvén ion cyclotron (AIC) modes. The increase of the electron temperature in the central cell is directly observed using a Thomson scattering system, confirming electron heating due to the electron Landau damping of AIC modes.

Microwave interferometer has newly been installed on GAMMA 10/PDX for divertor simulation study. A divertor simulation experimental module (D-module) is used to investigate the physics of divertor in the end-cell of GAMMA 10/PDX where an open magnetic field configuration is formed. D-module has a rectangular chamber with an inlet aperture. Two tungsten target plates are mounted in V-shape inside the chamber. In order to develop understandings of divertor simulation experiments the microwave interferometer using heterodyne scheme and a 1D horn-antenna mixer array (HMA) is applied to obtain electron density and density distribution inside the V-shaped target plates. Line-averaged electron density distributions inside D-module are first observed in H2 gas injection experiments.

I-Q (In-phase Quadrature) demodulator is one of key components in microwave interferometer system application. Normally, I-Q demodulator consists of amplifiers, mixers, 90 degree phase shifter, power divider and band-pass filters, and it is widely used in various microwave communication systems and measurement systems. In this paper, power divider and band-pass filters are newly designed as one single passive component, therefore, I-Q demodulator topology becomes simplified. The novel narrow band-pass filter type Wilkinson power divider not only provides extremely miniaturized circuit size, but also maintains the band-pass filter performance and power division function as well. One experimental circuit shows good agreement with the theoretical simulation.

A Thomson scattering (TS) system in GAMMA 10/PDX has been developed for the measurement of radial profiles of electron temperature and density in a single plasma and laser shot. The TS system has a large solid angle optical collection system and high-sensitivity signal detection system. The TS signals are obtained using four-channel high-speed digital oscilloscopes controlled by a Windows PC. We designed the acquisition program for six oscilloscopes to obtain 10-Hz TS signals in a single plasma shot, following which the time-dependent electron temperatures and densities can be determined. Moreover, in order to obtain larger TS signal intensity in the edge region, we added a second collection mirror. The radial electron temperatures and densities at six radial positions in GAMMA 10/PDX were successfully obtained.

Two dimensional (2D) plasma image analysis is useful to study the improvement of plasma confinement in magnetically confined fusion plasmas. We have constructed a 2D interferometer system with phase imaging method for studying 2D plasma density distribution and its fluctuation measurement in the tandem mirror GAMMA 10. 2D profiles of electron density and its fluctuation have been successfully obtained by using this 2D phase imaging system. We show that 2D plasma density and fluctuation profiles clearly depends on the axial confining potential formation with application of plug electron cyclotron heating in GAMMA 10.

A shear Alfvén wave at slightly below the ion-cyclotron frequency overcomes the ion-cyclotron damping and grows because of the strong anisotropy of the ion temperature in the magnetic mirror configuration, and is called the Alfvén ion-cyclotron (AIC) wave. Density fluctuations caused by the AIC waves and the ion-cyclotron range of frequencies (ICRF) waves used for ion heating have been detected using a reflectometer in a wide radial region of the GAMMA 10 tandem mirror plasma. Various wave-wave couplings are clearly observed in the density fluctuations in the interior of the plasma, but these couplings are not so clear in the magnetic fluctuations at the plasma edge when measured using a pick-up coil. A radial dependence of the nonlinearity is found, particularly in waves with the difference frequencies of the AIC waves; bispectral analysis shows that such wave-wave coupling is significant near the core, but is not so evident at the periphery. In contrast, nonlinear coupling with the low-frequency background turbulence is quite distinct at the periphery. Nonlinear coupling associated with the AIC waves may play a significant role in the beta- and anisotropy-limits of a mirror-confined plasma through decay of the ICRF heating power and degradation of the plasma confinement by nonlinearly generated waves.

A multi-pass (MP) Thomson scattering (TS) system modeled on the GAMMA 10/PDX TS system was constructed for enhancing the Thomson scattered signals. The MPTS system has a polarization-based configuration with an image relaying system. The former MPTS system in GAMMA 10/PDX can measure only four passing signals. We changed the larger aperture polarization control device for improving the MP laser confinement and obtaining the over four passing MPTS signals. The integrated MPTS signals increased about 1.2 times larger than that in the former system.

A multi-pass Thomson scattering (TS) system has the advantage of enhancing scattered signals. We constructed a multi-pass TS system modeled on the GAMMA 10 TS system; the new system has a polarization-based configuration with an image relaying system. For the first time, we used the new system to measure electron temperatures in the GAMMA 10 plasma. By using the multi-pass TS system with four passes, the integrated scattering signal was magnified by approximately a factor of three.

We applied Fraunhofer diffraction (FD) method to GAMMA10 plasma. The FD method can measure the density fluctuation in detail and the wave number of the fluctuation. We successfully obtained the density fluctuation spectra in GAMMA 10. Analyzing the FD method signals of radial fluctuation intensity profile, we can successfully obtain the wave number and the phase velocity of the low frequency density fluctuation.

Resection of pheochromocytoma is associated with potential risks of hypertensive crises and serious arrhythmias due to massive release of catecholamines from the tumor. We report our surgical experience with complete inferior vena caval isolation and extracorporeal charcoal hemoperfusion (IVCI-CHP), which were performed to prevent systemic exposure to catecholamines during surgical manipulation. The IVCI-CHP significantly reduced the postfilter and systemic catecholamine levels compared with the prefilter levels (P.01), indicating substantial catecholamine extraction (90%) by the CHP filter. Reflecting the reduction of systemic exposure to catecholamines during IVCI-CHP, the patient's blood pressures were markedly stable. Our findings suggest that IVCI-CHP may be useful to minimize the risk of hypertensive crises during surgical manipulation of pheochromocytoma, by preventing systemic exposure to high levels of circulatory catecholamines.

An yttrium-aluminum-garnet (YAG) Thomson scattering (TS) system was constructed and applied to the tandem mirror GAMMA 10 device to measure the electron temperature and density. We developped GAMMA 10 YAG-TS system to be able to measure multi-position electron temperatures and densities in a single laser and single plasma shots. The radialy multi-positions electron temperatures and densites are successfully obtained. We show the GAMMA 10 YAG-TS system and the results of multi-position measurements of electron temperatures and densities in the tandem mirror GAMMA 10.

An effective method to increase Thomson scattering (TS) signals is required in low-density plasmas. Multipass TS has the advantage of enhancing scattered signals. We constructed a double-pass TS system for a polarization-based system modelled on the GAMMA 10 TS system. In the second step, we have developed the multi-pass TS system based on the former double-pass TS system. In order to evaluate the effectiveness of the polarization-based configuration, the multi-pass system was installed in the GAMMA 10 TS system, which is capable of multi-pass scattering. We undertook Rayleigh scattering experiments. The integrated scattering signal was magnified to be approximately three times as large by using the multi-pass system with 6 passes. c

A novel configuration of the multi-pass Thomson scattering (TS) system is proposed to improve the time resolution and accuracy of electron temperature measurements by use of a polarization control technique. This configuration can realize a perfect coaxial multi-passing at each pass, and the number of round trips is not limited by the optical configuration. To confirm the feasibility of the new method, we installed this system in the GAMMA 10 plasma system. As a result, the integrated scattering signal of the double-pass configuration is about two times larger than that of the single-pass configuration. These results are in good agreement with the design.