Kunihiko Hattori

Characteristics of electromagnetically accelerated plasma flow in an externally applied magnetic field

In order to clarify the acceleration mechanism of applied-field magneto-plasma-dynamic arcjet (MPDA) plasma, the spatial profiles of the flow field and electromagnetic field near the outlet of the MPDA were measured using magnetic probes and the spectroscopic method. The plasma current densities and Lorentz forces acting on the plasma were evaluated experimentally. It was found that the azimuthal rotation of the exhausted plasma in the applied magnetic field is determined by a balance among the E×B drift, the diamagnetic drift, and the centrifugal force drift. Three components of the Lorentz force, i.e., the radial, the azimuthal, and the axial, were measured experimentally for the first time. The radial component Fr was dominant among the three components and the axial one (Fz) was weakened by the deceleration force, which spontaneously appeared in the applied-field MPDA plasma due to a diamagnetic effect of the high-beta plasma. It was demonstrated that the deceleration force can be converted to an acce...

Control of radial potential profile and related low-frequency fluctuations in an ECR-produced plasma

Abstract Low-frequency fluctuations related with a radial electric field are investigated in a magnetized plasma produced by an electron cyclotron resonance. It is observed that flute mode fluctuations are predominantly excited in a range of positive electric fields and drift mode fluctuations are stabilized with an increase of the radial electric-field strength.

Alfven wave excitation and single-pass ion cyclotron heating in a fast-flowing plasma

Alfven wave excitation and ion heating experiments were performed in a fast flowing plasma. When rf waves in the ion cyclotron range of frequency were excited by right- and left-handed helically wound antennas, shear and compressional Alfven waves with azimuthal mode number m=−1 and m=+1, respectively were excited. The dispersion relations of the propagating waves were obtained experimentally and compared with the theoretical ones, including the Doppler effect of the plasma flow. Strong ion heating was observed in the fast-flowing plasma when rf waves were launched by the right-handed helically wound antenna in a magnetic beach configuration. The plasma thermal energy W⊥ and the ion temperature Ti drastically increased during the rf pulse. This large increase was observed under lower-density conditions, where the ratio of the ion cyclotron frequency to the ion-ion collision frequency becomes high. The resonance magnetic field was affected by the Doppler shift due to the fast-flowing plasma.

Generation of supersonic plasma flows using an applied-field MPD arcjet and ICRF heating

A quasi-steady, supersonic plasma flow was produced by using a magneto-plasma-dynamic arcjet (MPDA) in a divergent magnetic nozzle. The ion acoustic Mach number, Mi, evaluated by spectroscopy and Mach probe measurement, was unity in the uniform field near the MPDA and reached almost 3 in the divergent magnetic nozzle. In the case of a subsonic flow near the exit of the MPDA, a magnetic Laval nozzle was effective in converting it to a supersonic flow with Mi = 1 at the throat. We heated ions of the fast-flowing plasma by ICRF (ion-cyclotron-range of frequency) in a magnetic beach field. The increased thermal energy was converted to flow energy as it passed through the divergent magnetic nozzle in accordance with the constant magnetic moment. We were able to successfully control the plasma flow with a wide range of densities for basic magnetohydrodynamic (MHD) studies and space thruster applications.

ICRF Heating and Plasma Acceleration with an Open Magnetic Field for the Advanced Space Thruster

The ion cyclotron resonance heating and acceleration in a magnetic nozzle are performed in a fast-flowing plasma in the HITOP linear device in order to investigate an advanced space propulsion system. When radio-frequency (RF) waves are excited by a helically-wound antenna, plasma thermal energy W[perpendicular] and ion temperature drastically increase during the RF pulse. Thermal energy of the heated ion is converted its flow energy when the ions pass through a diverging magnetic nozzle. The plasma thermal energy changes so as to keep the magnetic moment constant. The exhaust plasma flow energy can be controlled by changing an input RF power only.

Transonic Plasma Flow Passing Through a Magnetic Mirror

Dynamics of a fast-flowing plasma through a magnetic mirror field was investigated. A highly-ionized, high-density, He plasma produced by a quasi-steady MPD arcjet (MPDA) was injected into a magnetic mirror. In a uniform magnetic field region, ion acoustic Mach number (Mi) was almost unity, while in a diverging field region the Mach number increased up to 2-3. When the supersonic plasma flows into a converging field region, a shock-like structure was formed. The subsonic flow downstream of the shock was re-accelerated up to Mi of 2-3. The sonic condition (Mi=1) is satisfied at the magnetic mirror throat as in a conventional Laval nozzle. The adiabatic exponent of ions was evaluated by comparing measured spatial profiles with the prediction from 1D isentropic model.

Beam extraction from a Hall-type ion accelerator

Fundamental characteristics of beam extraction from a Hall-type accelerator working with permanent magnets were investigated. Ions were extracted by an axial electric field E(z) in a small annular plasma channel with a radial magnetic field B(r). Effects of discharge current and voltage, length of discharge channel, and gas flow rate were examined. It can deliver a large beam current density of more than 100 mA/cm(2) with low beam energy of 50 eV. By biasing an additional plasma chamber attached at the extraction area, the beam energy was controlled independently of the beam current.

Improvement of Flow Characteristics for an Advanced Plasma Thruster

A higher specific impulse and a larger thrust are required for a manned interplanetary space thruster. Until the realization of a fusion-plasma thruster, a magneto-plasma-dynamic arcjet (MPDA) powered by a fission reactor is one of the promising candidates for a manned Mars space thruster. The MPDA plasma is accelerated axially by a self-induced j × B force. Thrust performance of the MPDA is expected to increase by applying a magnetic nozzle instead of a solid nozzle. In order to get a much higher thruster performance, two methods have been investigated in the HITOP device, Tohoku University. One is to use a magnetic Laval nozzle in the vicinity of the MPDA muzzle for converting the high ion thermal energy to the axial flow energy. The other is to heat ions by use of an ICRF antenna in the divergent magnetic nozzle. It is found that by use of a small-sized Laval-type magnetic nozzle, the subsonic flow near the muzzle is converted to be supersonic through the magnetic Laval nozzle. A fast-flowing plasma is successfully heated by use of an ICRF antenna in the magnetic beach configuration.

Excitation of an Axisymmetric Shear Alfvén Wave by a Rogowski‐Type Antenna

Characteristics of wave excitation in a high speed plasma flow are investigated experimentally. Axisymmetric, azimuthal mode number m = 0 shear Alfven waves (SAW) are excited by a Rogowski‐type antenna in a high density (more than 1013 cm−3), high speed, magnetized helium plasma flow with ion Mach number (Mi∼ 1). The Rogowski‐type antenna with Faraday‐shield for the SAW excitation consists of a solenoid coil, so the magnetic field is not generated around the antenna in vacuum. Dispersion relations of excited SAW are in good agreement with the theoretical curve which is obtained by taking into account the effect of a Doppler shift due to a high speed plasma flow. Ratio δBy/ B0 of the excited magnetic perturbation δBy to the uniform magnetic field B0 is as large as 1% . Spatial profiles and damping rate of the SAW are also obtained experimentally.

Application of millimeter-wave phase-imaging interferometry to the tandem mirror GAMMA 10

A millimeter-wave phase-imaging interferometer has been applied to the tandem mirror GAMMA 10. The interferometer consists of a 70 GHz klystron oscillator and a quasi-optical transmission system. The probe beam is expanded so as to fill orthogonal views of the plasma cross section. The views are imaged onto an 11-channel Schottky barrier diode array. The feasibility of measuring density profiles has been demonstrated.