Search

Diatomic negative ions of Na(Na2 -) are extracted with atomic negative ions of Na(Na-) from a low-temperature Na plasma. The extracted currents of these negative ions are experimentally measured as functions of discharge parameters and wall temperatures. The measured extraction characteristics are discussed by comparing the results with those of negative hydrogen and negative lithium ions extracted from the corresponding plasmas. The maximum current ratio of Na2 - to Na- for a wall temperature below 235°C is on the order of 0.01, much smaller than that obtained in the sputtering experiment.

A heavy neutral beam probe was developed for simultaneous measurements of local space potential and density fluctuations in a plasma. It was applied to both electron cyclotron heated (ECH) and radio frequency heated (RF) plasmas in the bumpy torus NBT-1M, and the feasibility of this method was successfully demonstrated by observing a low frequency m=1 interchange mode which was rotating poloidally at a frequency near the E×B drift frequency. It was shown that use of this probe results in extension of the range of fluctuation measurement by beam probe technique to relatively low temperature plasmas. It is applicable to a plasma with a strong RF field with which Langmuir probes cannot be used.

The energy distribution of Au- extracted from a plasma-sputter type negative ion source was measured. The energy spread ΔE, which was defined as the FWHM of the observed negative ion energy distribution, increased with increasing target voltage (V t). When V t was about 280 V, the energy distribution agreed well with the Thompson-Sigmund (T-S) theory. For values of V t less than 280 V, the high-energy component in the distributions fell off faster than those predicted by the T-S theory. This effect was exaggerated as V t was further decreased. The ΔE for V t below 280 V are less than 10 eV, which seems to be sufficiently small for application to a heavy ion beam probing (HIBP) method.

A method to measure the work function of the target surface in a plasma-sputter-type negative ion source has been developed. The method can determine the work function by measuring the photoelectric current induced by two lasers (He-Ne, Ar+ laser). The dependence of Au- production upon the work function of the target surface in the ion source was studied using this method. The time variation of the target work function and Au- production rate were measured during the cesium coverage decrease due to the plasma ion sputtering. The observed minimum work function of a cesiated gold surface in an Ar plasma was 1.3 eV. At the same time, the negative ion production rate (Au- current/target current) took the maximum value. The negative ion production rate indicated the same dependence on the incident ion energy as that of the sputtering rate when the work function was constant.

A high-temperature radiation source has been developed for the absolute calibration of diagnostic instruments for measuring electron cyclotron emission from high-temperature plasmas. The source has a radiation area of φ 150 mm and can be heated up to 500°C. The measured emissivity of the source is close to unity in the spectral region between 200 and 500 GHz. The grating polychromator has been calibrated using the radiation source developed. The obtained temperatures agree with those by the pulse height analysis of soft X-rays and Thomson scattering measurement within 10%.

A new method based on the laser-induced fluorescence method has been developed to measure the spatial electron density distribution in plasmas. The local electron density can be determined by observing the intensity ratio of the laser- to the collision-induced fluorescence. A spatial electron density distribution of a helium plasma (Te approximately 6 eV, ne:1011-12 cm-3) has been determined by observing the He(31P to 21S) laser-induced fluorescence and the He(31D to 21P) collision-induced fluorescence resulting from the He(31P to 31D) process due to collisions with electrons. The comparison of the result with that of a conventional method proves this new method is of practical use in the space-resolved measurements of plasma electron density.

Data of JIPP T-II ICRF heating experiments are presented. The experiment covers three typical cases: the low-concentration hydrogen minority case, the high-concentration hydrogen minority case, and the 3He-minority case. The best heating efficiency is obtained for the 3He-minority case. It is shown through power balance analysis that the two H-minority cases are different in the wave energy deposition profile. The difference is explained by the presence of a local cavity mode in the high-concentration minority case. The ion temperature stops rising at a power density level of 0.65 W-cm−3 for the hydrogen minority experiments. No such deterioration is found in the case of the 3He minority experiment up to a power density level of 0.45 kW-cm−3. This is the maximum possible to attain within the maximum power injection (180 kW) up to which the experiment is conducted. An analytic solution of the Fokker-Planck equation is derived in order to interpret the deterioration of the heating efficiency.

Suprathermal electrons which carry a seed current are generated by non-resonant parametric decay instability during the initial phase of lower-hybrid current startup in the JIPP T-IIU tokamak. From the numerical analysis it is found that parametrically excited lower-hybrid waves at the lower side-band can bridge the spectral gap between the thermal-velocity region and the low-velocity end of the pump power spectrum.

The use of a toroidal magnetic field as a lens system is proposed for producing an intense ion beam. The characteristics of the lens system are obtained both analytically and numerically. Some examples of ray-trajectories are presented for different focal lengths. The system is applicable to neutral beam injection heating and micro-pellet implosion for nuclear fusion, and to other fields such as ion beam X-ray lasers.

Current driven by injecting lower hybrid waves has been observed in low-density plasmas in the JIPP T-II. It is confirmed that RF-driven current is generated by momentum transfer from lower hybrid waves to suprathermal electrons with an energy of 8–25 keV. The driving efficiencies in tokamak and stellarator configurations are 1 kA·kW−1 and 0.3 kA·kW−1, respectively, at a power level of 40 kW. Enhanced electron cyclotron emission due to pitch-angle scattering of RF-driven suprathermal electrons is observed, and spikes in loop voltage and X-ray bursts appear coincidentally. In a long RF-pulse, these rapid changes advance to relaxation oscillations. It is concluded that the pulsating changes originate in the instantaneous scattering of RF-driven suprathermal electrons by the unstable waves excited at an anomalous Doppler resonance.

A new method using both techniques of a neutral beam and spectroscopy has been developed to measure the spatial electron density profile of a plasma. This neutral beam probing technique utilizes the photons emitted by impact excitation of the probing lithium beam with plasma electrons. The spatial electron density distribution of the plasma of Te approximately 10 eV, ne approximately 1011 cm-3 has been determined from the measurements of the local photon flux and beam intensity by using the excitation rate coefficient calculated from the available cross-section data. The comparison of these results with those of conventional methods proves this new method is of practical use in the space-resolved measurements of plasma parameters, especially when a Langmuir probe is no longer usable. The cross sections for excitation of the Li beam in collisions with He, Ar and H2 have been also measured and used to estimate the neutral lithium beam intensity.

The principle of Project MACETIE and the preliminary experiment are described. The basis of our plan is the thought that the goal of controlled thermonuclear fusion may be accessible by the multistage alternating processes of adiabatic compression and irreversible expansion of plasma. In the latter process, the plasma compressed by a strong magnetic field is expanded into a region of weaker magnetic field. A static consideration of this expansion suggests that plasma temperature will not change appreciably in this process, and a second adiabatic compression of plasma in the weak field may further increase its temperature. Preliminary experiments are being carried out to examine the foregoing principle of irreversible expansion.

A simple diagram method is applied to obtain the time evolution of the electron temperature from the time history of the impurity line radiation which appears during the early phases of lower hybrid current startup in the JIPP T-IIU tokamak. This method makes it possible to survey the dependence of the time behavior of impurity emission on various plasma parameters (impurity influx rate, impurity confinement time, etc.). The electron temperature thus obtained agrees well with that derived from the temperature-sensitive line ratio and from Thomson scattering.

A metal-film bolometer has been developed for reliable measurements of the radiation power from high-temperature plasmas. Its sensitivity and time response were improved by reducing the absorber thickness (10 µm) to the minimum limit in order to sufficiently absorb photons with high energies up to 3 keV. In addition, this detector has well-defined thermal characteristics. The deviation of the measured value arising from thermal cooling was investigated by numerically solving a heat conduction equation associated with the detector. The calculated results could explain the thermal characteristics well for a temporally constant power (at calibration) and showed that the deviation of the measured radiation power from its calculated value could be reduced by a precise correction (to the extent of 0.5%).

The characteristics of four crystals (LiF(200), Ge(220), LiF(220) and Quartz(2023)) for a Johann type crystal spectrometer with Photo Diode Array have been investigated from observations of FeKα1,2 characteristic X-ray. The results are tabulated with their resolution power and relative sensitivities. They were applied also to the X-ray spectroscopic measurements of a high-temperature plasma. The fine structure of the iron oxygen-like Kα lines has been resolved by the Quartz(2023) crystal.

The spatial profiles of electron density in Nagoya Bumpy Torus (NBT) have been measured with a fast neutral Li beam probing, which utilizes the photon emission due to the electron impact excitation of the injected atoms. It is shown that plasmas are well contained inside the hot electron annuli. The attenuation of thermally injected Li atoms has been measured for the estimation of electron density as a cross check.

The characteristics of a Johann-type crystal spectrometer with a photodiode array (PDA) are described. The crystal used is LiF(200) with a bending radius of 100 cm, and the sensitivity of the PDA is measured for X-rays of 4 to 17 key. The collection efficiency η of charges created in the PDA is determined as a function of the X-ray energy E(keV): η=-0.026E+0.68. An asymmetrical spectral profile is observed when a monochromatic X-ray beam is incident on the PDA with an angle larger than 40°. The sensitivity of the spectrometer is also calibrated against a conventional X-ray tube. The PDA is used for the observation of X-ray lines from a high-temperature plasma in a vacuum spark. The resultant Fe Kα spectrum shows a spread over several channels due to blooming, when compared with that recorded on Kodak no-screen X-ray film.

A 10-channel grating polychromator has been developed and applied for the measurements of the second harmonic electron cyclotron emission from the JIPP T-IIU tokamak plasma. The frequency resolution measured at 150 GHz is about 3 GHz which corresponds to the spatial resolution of 1.8 cm near the center of the plasma column. The grating efficiency is about 80% for S-polarization around 160 GHz. Its excellent time resolution, Δt≤2 µs, is favorable for studying MHD activities in hot plasmas. It has been found from the measurements in JIPP T-IIU that the grating polychromator is a powerful diagnostic tool for the measurements of electron temperature of the plasma.

By introducing into the single-collision model a flux-attenuation factor both in the incoming flux and in the outgoing flux, together with a reduced particle energy, we have derived more comprehensive analytical expressions for the number and energy reflection coefficients for all incident-target-atom combinations, leading to a simple explicit representation of the reflection flux under certain approximations. This gives the general qualitative tendency of the light-particle reflection, while a more quantative knowledge should be obtained from computer simulations or analytical approaches including numerical calculation for multiple collisions.

The magnetic field strength has been obtained from the Zeeman splitting. Thermal He atoms, as an impurity, were injected into a low density (n e∼5×1010 cm-3) hydrogen plasma produced by electron cyclotron resonance. A singlet line at 6678 Å from He atoms excited by the plasma electrons splits into a normal Zeeman triplet in the magnetic field. The line profile was measured with a high resolution Fabry-Perot interferometer. This diagnostic allows the determination of the Zeeman splitting at magnetic fields as low as 1.2 kG, lower than which the splitting is masked by the Doppler broadening of the injected atoms.

The efficiency vs operation voltage characteristics of a channel electron multiplier (CEM) with a negative voltage applied to the entrance cone are investigated in detail. In this negative bias operation, an abnormal increase in efficiency with operation voltage is found, arising from two main mechanisms. One is the change in potential distribution in the cone with the applied voltage. This is because the probability of secondary electrons ejected from the cone being pulled into the channel depends on the potential distribution in the cone. The other is the ionization of particles by leakage electrons from the gap between the CEM exit and the electron collector. Methods of solving these problems are also described.

The characteristics of a thermistor, a metal-film bolometer, and a pyroelectric detector were investigated with the aim of attaining a highly reliable bolometric measurement. The spurious signal which appears on a pyroelectric detector was sufficiently eliminated by setting a mask close to the detector, thus avoiding the direct incidence of photons at the electrode. Whether a signal was true or false could be determined from the integrated value of the signal. Calibrations were performed with a HeNe laser in consideration of reflections on the detector surface. No time drift was observed on the sensitivity determined in such a way. The radiation power measured with a pyroelectric detector agreed within 10% with that measured with a calibrated metal-film bolometer.

A high-current lithium ion beam of a few mAcm-2 with an energy of 12 keV and a minimum beam divergence of about 1.2° has been produced by using an ion source of the discharge type. Characteristics of the lithium ion beam regarding the intensity and divergence were experimentally investigated in detail. A lithium neutral beam has been produced using a sodium neutralizer. The neutralization efficiency of the lithium ion beam in the energy range of 2–15 keV was about 80% with a neutralizer at a vapor pressure of 1.7×10-3 Torr. A mass analysis was performed when a mixed discharge of lithium and argon was used. The ratio of R (argon-ion current/lithium-ion current) became less than 0.1 at the oven temperature of the ion source to about 700°C. The applicability of a fast neutral lithium beam to plasma probing is discussed.

The spectral line profiles produced by neutral hydrogen atoms have been measured using a high resolution Fabry-Perot Interferometer. The Hα line 6563 Å is found to have an asymmetric profile in non-magnetized and low density plasmas. The line profile calculated taking into account the fine structure of the Hα line shows a reasonable agreement with the experimental results. The atom temperature obtained from the Doppler broadening is about 0.1 eV.

Fundamental characteristics of a GaAs Schottky barrier diode mixer have been measured for the purpose of using it as the detector of a twin 118.8 µm CH3OH laser interferometer. The mixer sensitivity for beat oscillations of the twin lasers was measured in a frequency region from 1 MHz to 7 MHz. A signal to noise ratio of I.F. signal over 45 dB is obtained for the frequency up to 6 MHz. The dependence of the mixer sensitivity on local beam power was also measured. The I.F. signal level is approximately proportional to the local beam power in power level from 0.1 mW to 1.2 mW.

The ion temperature profile and the density distribution for the beam penetration in the plasma have been measured and evaluated using emissions produced by the charge exchange reaction between a heating neutral hydrogen beam and fully ionized impurities on the JIPP T-IIU tokamak. A 1 m spectrometer with a multichannel detector is used to detect ultraviolet and visible emissions from this reaction. The ion temperature profile during neutral beam heating (or plus ion cyclotron range of frequency heating) is obtained from the Doppler broadening of emission spectra. The central ion temperature agrees with those from other diagnostics. The beam density profile is also in good agreement with the simulational result. The availabilities are demonstrated on this technique to measure the ion temperature and the beam density profile which are necessary to discuss beam heating efficiency and thermal transport.

For the measurement of the profile of a spectral line, a high dispersive monochromator with an Echelle grating and 12 channels of photoelectric devices using thin glass sheets to separate the line profile was constructed. The measured resolving power is about 2×105 and the linear dispersion at the image plane is 1.2 mm/Å at 5000Å. This instrument was used to measure the ion temperature of a BSG device by employing the 4686Å line of He II.

N-type indium antimonide shows the photoconductive effect not only in the far infrared, but also in the millimeter-wave region. Millimeter-wave photoconductivity was observed in the 2 mm-wave region to clarify the origin of the effect. It is concluded that, in elements with low carrier concentration, the impurity transition between shallow donor levels is the main process for the photoconductivity, while the hot electron photoconductive effect is small as compared with the impurity photoconductivity. Performances as a millimeter-wave detector are also studied. Signal-to-noise ratio of InSb detector is superior to that of conventional silicon point contact diode. Rise and decay times of the detector without magnetic field are about 0.4 µs and 0.7 µs respectively. This detector is useful even for measurements of incoherent radiation.