Yasuyuki Funato

LaB6 coating to reduce the outgassing rate of a vacuum wall

Abstract Use of LaB6 is proposed to develop a low outgassing wall for vacuum chambers in which baking is not possible. Sputter deposition of LaB6 was performed in a device equipped with a d.c. plasma source, and the pumping characteristics of the chamber were investigated before and after depositioning the LaB6 coating onto the wall. The chamber with the LaB6 coating reached a lower ultimate pressure than that without the coating, and the residual water vapor pressure was remarkably reduced with the coating. The pumping speed on the coated surface was estimated to be 0.45 1 s−1 cm−2.

Prebreakdown Phenomena and Formation Processes of Low-Pressure Glow Discharges in Ar, Ar/N2 and Ar/O2 Mixtures

In this research, both the prebreakdown phenomena and the transient processes from the prebreakdown phenomena to the glow discharge in low-pressure Ar gas, Ar/N2 and Ar/O2 mixtures were investigated by electrical and optical methods. The prebreakdown phenomenon in the Ar/N2 mixture was similar to that of Ar gas, and a pulseless component has been observed. The prebreakdown phenomenon in the Ar/O2 mixture differed from those in the Ar gas and Ar/N2 mixture, and formed a pulse discharge. Thus, the prebreakdown phenomenon in the Ar gas has been changed to pulse discharge by mixing a small amount of O2 gas which played an important role in the formation of pulse discharge.

Pumping experiment of water on B and LaB6 films with an electron beam evaporator

Abstract The pumping characteristic of water vapor on boron and lanthanum hexaboride films formed with an electron beam evaporator have been investigated in high vacuum between 10 −4 and 10 −3 Pa. The measured initial maximum pumping speeds of water for the fresh B or LaB 6 films with a deposition amount from 2.3 × 10 21 to 6.7× 10 21 molecules/m 2 separately formed on a substrate are 3.2–4.9 m 3 /sm 2 , and the saturation values of adsorbed water on these films are 2.1 ×10 20 −1.3 × 10 21 H 2 O molecules/m 2 .

Deuterated Impurities Monitored by Microwave Spectroscopy during Glow Discharge Cleaning

Microwave spectroscopy was applied to monitoring of deuterated impurities produced by glow discharge cleaning (GDC). This method estimated the change in the quantity of the isotopic impurities by observing a rotational spectrum of water, HDO. For verifying the validity of the method, mass spectral behaviors of several light impurities (HDO, D2O, H2O, HD, D2 and H2) were studied simultaneously. The deuterated species decreased with time at their own diminishing rates, while normal water, H2O, showed no decrease during GDC. The rotational spectrum of HDO stood at the frequency of 22.3077 GHz. It was distant enough from the nearest neighbor (about 70 MHz) so that the observed line was identified definitely. The lowest partial pressure detected with a microwave spectrometer was 7×10-5 Pa.

Investigation of magnetic field properties in the helical axis stellarator: Asperator NP-4

Experimental measurements of the magnetic field properties of a helical axis stellarator were carried out. The results, together with the numerical calculation, are described herein. The toroidal device, Asperator NP-4, has a helical magnetic axis with a pitch angle of 45? and a multi-field period of n=8. The magnetic field of NP-4 is produced by the currents of helical solenoids and L=+1, -1 helical windings. By an electron beam mapping of field lines, the existence of a high rotational transform angle and magnetic surfaces are confirmed and the position if the helical magnetic axis is obtained. The other fundamental magnetic properties such as the shear and the specific volume of the configuration are also deduced from the measurements. Numerical calculations lead to a good agreement with the results of the experiment.

On the effect of bakeout for the pumping speed dependence of outgassing rate in a stainless steel chamber

In order to investigate the effect of bakeout on the dependence of outgassing rate on pumping speed in a vacuum system, the outgassing rates of a test chamber at room temperature without baking and after bakeout at 100 and 250 °C were measured as a function of pumping speed. The measuresd outgassing rate q(Torr · [ls · cm2) obeys power law q = C(S/A)m where C and m (0 < m < 1) are constants, S/A is the pumping parameter defined as the ratio of the pumping speed S(l/s) and the surface area A(cm2) of the chamber, and the variable range of S/A is from 2.46 × 10−5 to 1.26 × 10−2 (ls · cm2). The obtained power laws at RT and 100 °C have two different exponents but that at 250 ° has only one exponent. The experiment shows that the bakeout weakens the pumping speed dependence on outgassing rate. In addition the theoretical consideration for the effect suggests that the sticking probability of the wall plays an important role on the pumping speed dependence.

Current Equilibrium in a Toroidal Device with a Non-Planar Magnetic Axis (Asperator NP-3)

The results of the experiment on plasma equilibrium in Asperator NP-3, a toroidal device with a three-dimensional magnetic axis, are described. It is shown that the equilibrium of a current column in this system is mainly determined by the vacuum masnetic surfaces produced by solenoids with a spatial axis. By the application of an l =1 transverse field, a method for controlling the current position by the external field is confirmed experimentally.

Electron behaviour in cylindrical magnetron sputtering source

Abstract The characteristics of the glow discharge in a new type magnetron sputtering device are described. An azimuthal magnetic field produced by the current flowing through the center conductor is superimposed into a conventional cylindrical magnetron configuration. It is possible to change the configuration of the magnetic field and then to control plasma parameters in space by changing the ratio of the azimuthal field to the longitudinal one. Effects of such a magnetic field on the properties of magnetron discharges are examined expermentally. By adjusting the strength of the azimuthal field, the current-voltage characteristics for Ar gas with various discharge voltages were measured. With proper choice of the magnetic and electric configuration, the current flux density is apparently increased. To confirm the availability of the composed magnetic field, the density profile of electrons was measured by an electrostatic probe. The results show that the electron density was increased two-fold by applying the magnetic field with the azimuthal component. This result may be due to a decreased end loss of electrons.

Beta Limit for a System with a Closed Helical Magnetic Axis

The “critical β” at which an equilibrium either ceases to exist or becomes poor for confinement is determined for a non-axisymmetric system with a closed helical magnetic axis. The plasma is assumed to have a circular cross section through which a longitudinal current with a flat radial profile flows in a direction to either increase or decrease the rotational transform of the magnetic field. It is shown that an equilibrium does not exist in a certain range of current which increases the rotational transform due to the resonance of toroidal effects. It is also shown that there are the upper and lower limits of β value for a stable equilibrium.

A monitor for discharge cleaning using microwave spectroscopy

Abstract The measurement of the partial pressure of water is essential to monitor the conditioning during glow or ECR discharge cleaning. Usually QMF is adopted for this purpose, however, it has to be operated in better vacuum conditions of lower than 10 −2 Pa and with a hot filament for the electron source. The method described in this article is an application of the microwave spectroscopy so that measurement can be carried out with relatively high pressures of up to 100 Pa and needs no hot filament. The absorption rotational spectral line of water molecules at 22.235 GHz is used for this purpose. The spectrometer consists of a waveguide absorption cell with Stark electrode, a frequency-sweep microwave source and a phase-sensitive detector. The change in the intensity of the absorption spectrum of water could be detected during hydrogen glow discharge.