Shinya Yagura

Measurements of Fast Time Evolutions of Plasma Potential Using Emissive Probe

We present a new method of measuring the floating potential of an emissive probe when the floating potential is very close to the plasma potential. The probe potential at which the probe current becomes zero in the current-voltage curve of the probe is automatically biased by a new probe circuit connected to a bipolar voltage source. This method enables direct measurement of rapid changes in the floating potential with a time resolution of 1 µs, giving a continuous data trace. The method was verified experimentally using a DP machine.

An Influence of a Heating Voltage on an Emissive Probe Characteristic in a Plasma

An influence of a heating voltage on potential measurements by an emissive probe immersed in a plasma is studied. It is found that a peak point of the first-derivative curve of the current-voltage characteristic shifts even during the off cycle of the heating voltage with a half-wave rectified sinusoidal form. Calculations predict that this comes from a joule heating effect.

V-Shaped Potential Distribution with a Virtual Cathode Generated by an Electron Beam Injection

Spatial distributions of the potential and space charge density with a virtual cathode are described both experimentally and theoretically. A V-shaped potential profile is formed by injecting an electron beam which provides an ionization on the high potential region. The analys is with applying water bag energy distribution functions of beam and ionized electrons and with integrating Poisson equation is found to fully account for the experimental results.

Control of plasma parameters and electric fields in a microwave‐rf hybrid plasma

Control of electron energy and electric field in a low‐pressure argon plasma produced by a hybrid (2.45 GHz microwave and 13.56 MHz rf) discharge was studied for thin‐film preparation. The hybrid plasma was found to be useful over a wide range of magnetic field strengths, unlike conventional microwave plasma. A novel probe measurement revealed that the electron temperature and density were effectively controllable by the microwave power and the magnetic field strength, rather than the rf power, and the potential profile describing the electric field was controllable by the magnetic field strength. The control of an ion beam injected from the microwave into the rf plasma is described.

Potential double layer in a magnetic field free ion sheath with ion beam reflection

The spatial profile of potential in an ion sheath formed in front of a grid with a large cross-section is studied experimentally using a triple plasma device in the absence of a magnetic field. A potential double layer is established by injecting the ion beam into the ion sheath from the low potential side. The reflection of the injected ions produces a crest of the ion density, resulting in the formation of a knee on the potential profile. A relationship d varies as Delta phi 3/4 corresponding to space charge limitation is obtained where Delta phi and d are the height and the width of the potential double layer, respectively.

Coupling between wall and exciting grid in a collisionless plasma

Abstract The coupling mechanism of a wall and an exciting grid immersed in a collisionless plasma is c;arified by addition of electron emission from the grid. The amplitudes of the excited waves are found to increase strongly resulting in a clear observation of ion acoustic waves which are simultaneously excited at the wall.

Measurement of electron energy distribution function in a low-pressure rf discharge plasma

Electron energy distribution functions in a low-pressure rf discharge (<1 mTorr) were measured with an electrostatic energy analyzer facing the powered electrode and the bulk plasma. Electrons with high energy were observed in the former case, whereas the distribution of electrons was almost Maxwellian in the latter case.

Formation of a negative potential dip on a double layer created by a localized additional discharge in a magnetized plasma

Abstract A negative potential dip with a depth as high as (3–5) T e / e is transiently formed on the low potential tail of a double layer during the current limited phase, when a localized pulsed additional discharge is produced in a magnetized plasma column.

Observation of Potential Relaxation Instability in a Bounded Discharge Plasma

A potential relaxation instability (PRI), which causes a periodic motion of a potential jump and plasma expansion accompanying a high-density fluctuation level (¿60 percent), is observed in a bounded discharge plasma. The instability is found to create a high electron drift velocity and a spatial growth of density and potential fluctuations, and to accelerate a test wave. An additional supplement of a plasma into the boundary suppresses the instability. At the same time, the fluctuation decreases (<5 percent) and the frequency difference of the wave spectrum between nth and (n - 1) th (n is an integer) higher harmonics decreases as the frequency increases. However, when the potential relaxation instability is excited, this frequency difference keeps constant.

Observation of plasma production in a multipole device

Plasma production is observed in a simple discharge model of one filament cathode and a multipole magnet anode with variable electrode separation. Two‐dimensional velocity distribution functions of electrons and ions and two‐dimensional spatial profiles of the potential and electron density are measured with a directional energy analyzer, an emissive probe, and a Langmuir probe. The electrode distance is found to affect the plasma production for isotropic velocity distribution, quiescent plasma, and homogeneous spatial distributions of the potential and electron density. The results may help to explain the fundamental plasma physics of a multipole double plasma machine.