M.A. Bohnet

Results from current drive experiments on the Helicity Injected Torus

The Helicity Injected Torus [T. R. Jarboe, Fusion Technol. 15, 7 (1989)] is a low aspect ratio tokamak that is formed and sustained by coaxial helicity injection with no transformer. Toroidal plasma currents of over 200 kA have been achieved with electron temperatures in the 100 eV range and electron density between 1019 and 1020 m−3. The major radius is 0.3 m and the minor radius is 0.2 m. New results from equilibrium and stability analysis of the external magnetic diagnostics and new results from the Transient Internal Probe (TIP), an internal magnetic field diagnostic, are presented. A mechanism for the transfer of current drive on the open to the closed flux regions is presented.

The transient internal probe: A novel method for measuring internal magnetic field profilesa)

The transient internal probe (TIP) diagnostic is designed to permit internal magnetic field measurements in hot, high density plasmas. A small probe is fired through the plasma at high velocities and magnetic field measurements are accomplished using Faraday rotation within the Verdet glass probe. Magnetic field resolution of ±40 G and spatial resolution of 5 mm have been achieved. System frequency response is 10 MHz. Ablative effects are avoided by minimizing both the probe size and the time the probe spends in the plasma. A two‐stage light‐gas gun is used to accelerate the probe (held by a sabot) to 2.2 km/s. The sabot is removed using gas dynamic forces and a gas interface system prevents the helium muzzle gas from entering the plasma chamber. Work is underway to integrate the TIP diagnostic with laboratory plasma experiments.

Magnetic field measurements using the transient internal probe (TIP)

The transient internal probe (TIP) is a novel diagnostic technique for measuring magnetic fields in hot plasmas. The concept involves shooting a diamond clad magneto‐optic probe through the plasma at high velocity allowing measurement of the local magnetic field before ablation occurs. Magnetic field measurements are obtained by illuminating the probe with an argon laser and measuring the amount of Faraday rotation in the reflected light. The diagnostic was tested by measuring a permanent magnetic field inside a vacuum chamber with a probe traveling at 2 km/s using an unclad probe. The purpose of this experiment was to demonstrate the capability of the TIP diagnostic and to verify compatibility with plasma vacuum requirements. Magnetic field resolutions of 20 G and 1 cm spatial resolution were achieved. The response time of the detection system is 10 MHz. Introduction of a helium muzzle gas into the plasma chamber was limited to less than 0.4 Torr l.

Development of a transient internal probe diagnostic

The transient internal probe (TIP) diagnostic is a novel method for probing the interior of hot magnetic fusion plasmas. In the TIP scheme, a probe is fired, using a two‐stage light gas gun, through a hot plasma at velocities up to 5 km/s, and makes direct, local measurements of the internal magnetic field structure. The data are relayed to the laboratory optical detection system using an incident laser that is directed through a Faraday rotator payload acting as a magneto‐optic sensor. Ablative effects are avoided by minimizing the probe size, limiting the time that the probe is in the hot plasma, and encasing the probe with a diamond cladding. The degree to which the diamond probe cladding is susceptible to ablative effects will determine the plasma density and temperature regime in which the TIP diagnostic can be used. If the TIP suffers significant ablation it is an indication that the diagnostic is not usable on this hot and dense of a plasma (or that greater velocity must be imparted to the probe to...

INTERNAL TOROIDAL FIELD MEASUREMENTS ON THE HELICITY INJECTED TOKAMAK USING THE TRANSIENT INTERNAL PROBE

Measurements of the local toroidal magnetic field have been achieved on the helicity injected tokamak (HIT) using the transient internal probe (TIP). HIT is a low aspect (a=1.5, R=0.35 m) ratio tokamak designed to study steady state current drive. The TIP diagnostic involves accelerating a small diamond clad magneto-optic probe through the plasma at high velocities (∼2 km/s) using a light gas gun. The local field is obtained by illuminating the probe with a laser and measuring the amount of Faraday rotation in the reflected beam. Measurements were conducted using unclad magneto-optic probes directed along a chord tangent to the toroidal field. Plasma conditions were typically ne∼7×1019 m−3 and Te∼40–80 eV. Measurement uncertainty is less than 2%. No changes in plasma parameters were observed during the first 200 ms (∼40 cm) of probe travel in the plasma. A temporary dip in plasma current, probably due to ablation of the retroreflecting material on the probe, is observed as the probe exits the plasma. Dens...

Internal magnetic field measurements using the transient internal probe on the helicity injected tokamak

Summary for only given, as follows. The transient internal probe (TIP) uses a high velocity (2 km/s) magneto-optic probe to measure internal magnetic fields in hot plasmas. TIP has both accurately (2%) measured the internal toroidal field profile and directly measured internal magnetic fluctuation levels of the helicity injected tokamak (HIT). HIT is a low-aspect-ratio (A=1.5) spherical tokamak designed to investigate steady state current drive using coaxial helicity injection. Operating parameters are T/sub e//spl sime/100 eV, n/sub e//spl sime/5/spl times/10/sup 13/ cm/sup -3/ and I/sub p/=250 kA. These tokamaks are characterized by a 30-70 kHz rotating n=1 magnetic distortion. Measurements using TIP confirm that this n=1 mode is present only on the outer edge of the plasma in the bad-curvature region. Fluctuation levels of 150 G in the vicinity of the separatrix dramatically decrease in the core of the plasma.

Internal magnetic field measurements on the helicity injected tokamak (HIT) using the transient internal probe (TIP)

Summary form only given, as follows. The transient internal probe (TIP) is a novel diagnostic designed to measure internal magnetic fields in hot plasmas. The diagnostic involves shooting a magneto-optic probe through the plasma at high velocities (greater than 2 km/s) using a two stage light gas gun. Local fields are obtained by illuminating the probe with an argon ion laser and measuring the amount of Faraday rotation in the laser light reflected from the moving probe. Currently, internal magnetic profile measurements are being conducted on the helicity injected tokamak (HIT). HIT is a low aspect ratio (A=1.5) tokamak designed to investigate steady state current drive using coaxial helicity injection. Operating parameters are T/sub e/=100, n/sub e//spl ap/5/spl times/10/sup 13/ cm/sup -3/ and I/sub p/=250 kA. Internal magnetic field profile data will be presented. The TIP diagnostic has a spatial resolution of 1 cm and 20 Gauss magnetic field resolution. System frequency response is 10 MHz.

Magnetic field measurements using the orthogonal transient internal probe

Summary form only given, as follows. The transient internal probe (TIP) diagnostic is designed to measure the internal magnetic field profile of hot plasmas. A small magneto-optic probe is illuminated from the front with 514.5 nm laser light while being fired through the plasma at velocities in excess of 2 km/s. Magnetic field profiles are obtained by measuring the Faraday rotated laser light reflected from the probe. First generation TIP probes have the ability to measure only the axial component of the magnetic field. The orthogonal TIP probe, however, has the capability of measuring fields which are perpendicular to the direction of probe travel. Orthogonal measurement capability can provide a full radial scan of the poloidal field profile and will serve as a technology base for for future multi-dimensional TIP probes. Magnetic field resolution is 20 G, spatial resolution is 5 mm, and the system frequency response is 10 MHz. Measurements using the orthogonal TIP probe will be presented.

Development of an orthogonal transient internal probe

Summary form only given, as follows. The transient internal probe (TIP) diagnostic is designed to measure the magnetic field profile internal to hot, high density plasmas. A small magneto-optic probe is fired through the plasma at velocities in excess of 2 km/s. Magnetic fields are obtained by illuminating the probe from the front with an argon ion laser and measuring the amount of Faraday rotation in the reflected beam. First generation TIP probes are limited in that only one component of the magnetic field can be measured. The orthogonal TIP probe, however, has the capability of measuring magnetic fields which are perpendicular to the direction of probe travel. Orthogonal measurement capability can provide a full radial scan of the poloidal field profile and serves as a technology base for future multi-dimensional TIP probes. Magnetic field resolution of /spl plusmn/20 gauss and spatial resolution of 5 mm is expected with a system frequency response of 10 MHz. Progress in the development of the orthogonal TIP probe is presented.

Development Of Transient Internal Probe (tip) Magnetic Field Diagnostic

Development of Transient Internal Probe (TIP) Magnetic Field Diagnostic. J.P. Galambos, MA. Bohnet, T.R. Jarboe, A.T. Mattick, t h d j