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An electron emission microscope (EEM) constructed for electron emission sites observations is presented. This EEM consists of three unipotential lenses, a microchannel plate, and a phosphor screen, and has the advantage that it enables the observation of electron emission sites of not only a sharp point cathode, such as a field emitter, but also a broad area cathode surface. Experimental results obtained are as follows: 1. the operation of this EEM was confirmed by observing photoelectron emission sites irradiated with ultraviolet light, and 2. field emission sites in broad area Al and Cu could be observed.

We have successfully used the Spindt field emitter array (FEA) in the pressure measurements in ultrahigh vacuum (UHV) and extremely high vacuum (XHV). For applying the FEA to pressure measurements, we have made evaluation tests, focusing on gas exposure and outgassing characteristics. The cold cathode hardly influenced the vacuum conditions, compared to a hot-filament cathode.

Fusion performance of reversed shear discharges with an {ital L}-mode edge has been significantly improved in a thermonuclear dominant regime with up to 2.8 MA of plasma current in the JT-60U tokamak. The core plasma energy is efficiently confined due to the existence of persistent internal transport barriers formed for both ions and electrons at a large minor radius of r/a{approximately}0.7 near the boundary of the reversed shear region. In an assumed deuterium-tritium fuel, the peak fusion amplification factor defined for transient conditions involving the dW/dt term would be in excess of unity. {copyright} {ital 1997} {ital The American Physical Society}

For the purpose of quantifying surface roughness, the geometrical effect on heavy-ion RBS spectra is examined using optical grating bases coated with a thin film of Pb. It is shown that the RBS spectra from such surfaces with a periodic roughness can be well simulated by properly taking account of the system resolution including the detector response and published data of a stopping power of the substrate for the heavy ions. The spectral shape together with the fraction of the surface component reflects the microscopic structure of the sample surface strongly enough for the parameters characterizing the roughness to be determined from the measured spectra. Thus potential applicability of a “Pb coating-RBS” method to quantification of surface roughness is demonstrated.

Pressures in UHV and XHV have been successfully measured using a quadrupole mass spectrometer (QMS) with a Spindt-type field emitter array (FEA) as the electron source. However, two problems remained to be resolved: a reduction in the small amount of outgassing from FEA, and an elimination of ESD ions. Outgassing from FEA became negligible after degassing at 400 °C for 5 h in a vacuum of 10 −6 Pa. Thus, the degassed FEA allowed us to measure the pressure in UHV and XHV with little disturbance from the vacuum conditions. After that, the ESD effect on the partial pressure measurement with QMS was investigated through the use of the time-of-flight (TOF) technique. The ESD components for H 2 and CO were small compared with the gas-phase ions. However, mass 16 had a large ESD peak in the TOF spectrum as well as mass 19. The gas-phase peak for H 2 was proportional to the pressure, although the ESD component was not only a function of the pressure. The area measurement under the gas-phase peak in the TOF spectra was useful in measuring pressures of less than 10 −10 Pa.

The 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) was commissioned in October 2007, and successfully accomplished 3 GeV acceleration on October 31. Six run cycles through February 2008 were dedicated to commissioning the RCS, for which the initial machine parameter tuning and various underlying beam studies were completed. Then since May 2008 the RCS beam has been delivered to the downstream facilities for their beam commissioning. In this paper we describe beam tuning and study results following our beam commissioning scenario and a beam performance and operational experience obtained in the first commissioning phase through June 2008.

Recent lower hybrid current drive (LHCD), and heating (LHH) experiments on JT-60 are reported. The current drive product of neRpIRF approximately 12.5*1019 m-2 MA was achieved at the LH power of approximately 4.5 MW, and the CD efficiency, the energy confinement, the global power balance and the heat load on divertor plates were investigated in high power LHCD plasmas. Nearly steady state H-mode discharges were found during LHCD with two different frequency injections. Sawtooth suppression in NB heated plasmas by LHCD have shown an improvement in confinement near the plasma center. Parametric instabilities in LH heating experiments were significantly reduced by increasing the plasma current, and the stored energy increased linearly with heating power of up to approximately 9 MW at ne approximately 7*1019 m-3 and Ip=2.75 MA. Parametric instabilities near the plasma edge in the ion heating regime were also reduced in peaked density plasmas produced by pellet injection and LH waves increased the central plasma pressure at ne(0) > 1.4*1020 m-3.

Outgassing from the first wall made of graphite has been investigated with a newly developed pressure gauge. This gauge can measure the pressure near hydrogen plasmas in a short response time (

It was success to develop the radiation resistant components using for beam collimator. Turbo molecular pump could be operated more than 15 MGy of gamma ray irradiation dose. Stepping motor developed at JAERI could be operated with good performance in the gamma ray dose of more than 70 MGy. PEEK sheathed cables and connector have kept good performance during gamma ray irradiation more than the dose of 10 MGy. It was cleared that the function of the heat pipe disappeared at 30 kGy gamma ray irradiation dose.

It was success to develop alumina ceramics vacuum ducts for the 3GeV-RCS of J-PARC at JAERI. This duct has titanium flanges and exterior RF shield to reduce duct impedance. The longitudinal duct impedance was sufficient small for stable beam acceleration from impedance measurement by coaxial method. The temperature of titanium flange became 45 Co due to eddy current heating under dipole magnet operation. This duct is usable for the 3GeV-RCS of J-PARC.

Fast pressure gauges were installed in the JT-60 (JAERI Tokamak-60) to monitor the pressure near a plasma. They are Penning configuration gauges. A Penning discharge in the cell is sustained by the magnetic field which confines the plasma. The gauges are controlled by a personal computer. The response time of the system is fast ( >

In JT-60U, the highest fusion product of 1.2/spl times/10/sup 21/ keV sm/sup -3/ was recorded in July 1994, and the confinement performance has been also improved in the quasi-steady states (duration time /spl sim/1.5 s). The JT-60U has various wall conditioning methods. In particular, the boronization system using decaborane and B/sub 4/C-converted CFC divertor tiles was effective for reduction of the oxygen impurity and particle recycling. In the latest boronization session, gas mixture of deuterium and helium was used in glow discharge instead of helium only to reduce the hydrogen content in the boron film. On the other hand, the B/sub 4/C-converted CFC tiles caused, so called, the real-time solid target boronization (STB) by plasma impact, and then low concentration level of impurities was achieved. Water cooling of the divertor tiles, which was carried out in October 1994, was also effective for the reduction of impurity production. The amount of neutron and tritium generated by the D-D reaction have also increased with the improved plasma performance. From the measurement of the tritium in the first wall tiles, it is expected that tritium of 1.6/spl times/10/sup 10/ Bq, which corresponds to approximately 50% of tritium generated until 1993, still remained in the first wall.

A Spindt-type field emitter array (FEA) has been tested in an ultrahigh vacuum as the electron source for a commercial quadrupole mass filter. The FEA supplied the stable emission current of several mA. We demonstrated that the thermal effect of the filament could be avoided through the use of the FEA. However, outgassing was observed from the FEA. The main species were H 2 , CO, and CO 2 . In addition, and somewhat surprisingly, a large quantity of fluorine was detected. This is ascribed to the residue in the FEA.

The monitoring of conductive spinal cord evoked potentials (conductive SpEPs) has been widely used for the purpose of preventing damage to the spinal cord during operation [5, 7–9]. It has not been resolved whether changes in the conductive SpEPs correlate to the pathological condition of the spinal cord under chronic pressure or not. Excision of the tumor usually ensures recovery from paralysis caused by chronic pressure and circulatory disturbance due to extramedullary spinal cord tumors. Therefore patients with spinal cord tumors are useful models for studying changes of the con­ductive SpEPs in the spinal cord under chronic pressure. The purpose of this study is to investigate a correlation between changes in the conductive SpEPs and prognosis of the patients.

In the last year, ohmic heating experiments were performed in JT-60 for about three months; May–June 1985 and March 1986. The major experimental effort has been concentrated on the divertor configuration in anticipation of H-mode operation of JT-60 in high power supplementary heating experiments starting in August 1986. Stable discharges with a divertor have been obtained at Ip = 1.85 MA and ne = 5.7 × 1019m−3. Radiated power from the main plasma in divertor discharges is reduced to one third of that in material limiter discharges. The electron density has a broad radial profile and the effective safety reaches qeff = 2.5. The neutral gas pressure in the divertor chamber becomes significantly high and the control of particle recycling has been attempted.

Emphases in JT-60 experiments are placed on (1) lower-hybrid (LH) current drive characteristics with a multi-junction type launcher, and (2) the confinement study with combination of neutral beam injection LH current drive and pellet injection. The new multi-junction LH launcher provides a sharp N/sub /// spectrum with high directivity for N/sub ///=1-3.4. The current drive efficiency and the radial distribution of high energy electron production show clear correlation with injected N/sub ///: the current drive efficiency has the maximum at low N/sub ///( approximately 1.3) while flattening of plasma current is more effective in large N/sub ///. A broad radial distribution of high energy electron current and approximately 30% reduction in sawtooth inversion radius were obtained by high N/sub /// ( approximately 2.5) LH injection. To fully suppress the sawtooth activity, low N/sub /// ( approximately 1.3) injection was found to be more effective. Improved energy confinement has been obtained with hydrogen pellet injection. Energy confinement time was enhanced up to 40% relative to usual gas fuelled discharges. The discharge has a strongly peaked electron density profile with ne(0)/(ne) approximately 5 and ne(0) approximately 2.0*1020 m-3. The improved discharges are characterized by a strongly peaked pressure profile within the q=1 magnetic surface, and degrades when a large sawtooth recovers or the pressure gradient may reach a critical value. When large (3 mm, 4 mm) and fast (2.2 km/s) pellets were injected, 30% energy confinement improvement was obtained even during the NB heating of 14 MW. Further investigations of IDC characteristics have been made. The oxygen impurity lines from the main plasma and the main radiative loss drop first. Then the plasma stored energy starts to rise. The particle recycling is reduced around the main plasma, and is localized in the neighborhood of the X-point with a time lag of approximately 0.2 sec. Eventually the discharge shows a significant remote radiative cooling power at the divertor region.

Initial ohmic heating experiments in JT-60 were performed for a three month period of April-June 1985. A maximum plasma current of 1.6 MA was obtained for both divertor and limiter discharges. Low-q discharges of qeff=2.5 and high density discharges of 4.8*1019 m-3 in line-averaged density were obtained in the divertor configuration. In divertor discharges radiated loss from the main plasma can be kept at 20-30% of the ohmic input.

This paper describes a new method for using a Penning gauge to measure pressure in high magnetic fields. The intensity of the Hα and Hβ Balmer lines emitted from a Penning discharge is a function only of the discharge ion current and is independent of anode voltage and magnetic field from 0.1 to 2.0 T. The light intensity is proportional to the ion current below ∼0.1 Pa. The ratio of the light intensity to the ion current increases by 40% for pressures above ∼0.1 Pa because of a change in the type of discharge. The higher pressure discharge probably has a lower electron temperature.

Essential divertor functions — density and energy control — have been investigated in the JT-60 divertor with metal walls. Neutral pressure in the divertor chamber increases in proportion to n2e and high recycling state for particle exhaust is realized. At ne ≤ 6 × 1019m−3, wall pumping by the divertor plates is dominant in particle exhaust. However, at ne ≥ 6 × 1019m−3, particle exhaust by active divertor pumping systems becomes essential. Because of the effectiveness of the divertor, radiation loss in the main plasma is reduced to 5–10% of the absorbed power and impurity concentrations are significantly suppressed at very low level (Zeff = 1.5-2.0). In the experiments with graphite walls, short periods of H-mode phases were found in the outside X-point divertor discharges although improvement in energy confinement is limited to within 10%. In limiter discharges, combination of high vessel temperature (210–300 °C) and low current limiter discharges (1.5 MA) without gas puffing is effective as a wall conditioning in obtaining reproducible high density discharges. The maximum parameters, Ip = 3.2 MA, ne = 1.2 × 1020m−3, qeff = 2.2 at Bt = 4.8T, a Murakami parameter of 7.5, and a stored energy of 3.1 MJ have been attained. The maximum density is limited by the occurence of the MARFE. During high power neutral beam heating, enhanced carbon influx was observed possibly due to chemical sputtering. The wall pumping by the inner wall is still effective in decreasing the electron density from the high density region of ne ~ 1 × 1020m−3. An empirical energy confinement scaling of JT-60 has been drawn in terms of an offset linear function as τE = 0.19 I1.9PPabs + 0.062 a1.8p

The growth processes of bismuth films on Si(111) surfaces were studied using quadrupole mass spectrometry, AES, and LEED. At higher substrate temperatures, the adsorption occurs only in a tightly bound state. The LEED pattern from these surfaces shows a Si(111) √3 × √3−30° -Bi structure. At lower temperatures, the orientation relationship of Bi(0001) ∥ Si(111) was observed for thick films.

From June to October 1987, JT-60 achieved fusion product (ne(0). tau E*.Ti(0)) of 6*1019 m-3.keV.s with hydrogen plasma at plasma current of 2.8 to 3.1 MA with neutral beam power of approximately 20 MW. The central electron density of 1.3*1020 m-3 was obtained at plasma current of 3 MA with 13 approximately 20 MW neutral beam power and the confinement time reached 0.14-0.18 s. An offset linear scaling law like the Shimomura-Odajima scaling on confinement time will be able to reproduce experimental data better than that of the Goldston type scaling. With low beam energy injection approximately 40 keV, confinement degradation was found. Many short periods (0.05 approximately 0.1 s) of H-mode phase were found in outside X-point divertor discharges with NB or NB+RF(LH or IC) heating power above 16 MW. However, improvement in energy confinement time was limited to 10 %. The ballooning/interchange stability analyses were also made for the outside X-point divertor equilibrium in connection with H0-phase capability. Heating powers of 9.5 MW and 1.9 MW were obtained by LHRF, ICRF injection, respectively. In combined LHRF and NB heating, the incremental energy confinement time of 0.064 s was obtained, which is the same level of that of NB heating only. In combined NB and on-axis ICRF heating of low ne discharge, an incremental energy confinement time of 0.21 s was obtained, which is three times as long as those of NB or ICRF heating only. High energy beam ions were accelerated by ICRF in the central region of the plasma.

This paper describes a new type of hot filament ionization gauge for measurement of neutral gas density in a high magnetic field. The notable feature of the gauge is its spherical symmetry. The ion current varies linearly with the pressure from 10−4 to 1 Pa for N2 and Ar. The sensitivity changes by no more than +20% in a magnetic field of up to 1.2 T. The main reasons for this small change in the sensitivity are as follows: (i) The probability of ionization of gas molecules is almost independent of a high magnetic field, because the spherical symmetry causes electrons to be emitted from the filament to the region in which the electric field is almost parallel to the magnetic field; (ii) the probability of ion collection is independent of a magnetic field.