Axial Field Experiments

Two diagnostic systems, magnetic field probes and a high-speed framing camera, have been recently used to measure the effect of compression or reconnection when the compact toroid enters an axially directed external magnetic field that is either parallel or anti-parallel to the internal field of the SCT. The result is an unambiguous observation of magnetic reconnection in the anti-parallel case and magnetic compression in the parallel case. The data from this experiment may help in the development of a more accurate theoretical model of CT plasma dynamics, and also provides confidence in these diagnostic techniques, which may be in turn used to study other plasma phenomenon. The preliminary results from 60 shots are presented on the following pages including several movies and graphs of data.

 

CTIX Plasma Injector with Axial Field Solenoidal Coils

Four solenoidal coils have been wound around the accelerator section to produce an axially directed magnetic field for a sequence of interaction experiments. Coils can be run steady state at up to 200 Amps or pulsed at up to 500 Amps. They yield approximately 2 Gauss per Amp on axis.

 

CTIXAF

Parallel Axial Field Configuration

Parallel

Anti-parallel Axial Field Configuration

Antiparallel

Effect of Anti-parallel Axial Field

This movie shows the effect of reconnection of the SCT field with a 400 Gauss anti-parallel axial magnetic field (which is in the opposite direction to the SCT field). The effect is made clear by comparing images taken with axial field to images taken with zero axial field.
Blue => 400 Gauss case is brighter
Red => 0 Gauss case is brighter.
Black => equally bright

NP0m200_thmb

 

Click on the image to view a video clip.

Effect of Parallel Axial Field

This movie shows the effect of magnetic compression as the SCT interacts with a 400 Gauss parallel axial magnetic field (which is in the same direction to the SCT field). The blue ring at the end of the shot implies that the compression effect caused the SCT to remain in the accelerator section,
Blue => 400 Gauss case is brighter
Red => 0 Gauss case is brighter.
Black => equally bright.

RP0m200_thmb

 

Click on the image to view a video clip.

Magnetic Field Probe Signals with Zero Axial Field

Probe measurements of the z component of the magnetic field when zero external axial field is applied. The three traces plot the signals of as a function of time for magnetic probes located at z = 57 cm, 91 cm, and 142 cm

b0B_bz

Magnetic Field Probe Signals with Zero Axial Field

Probe measurements of the z component of the magnetic field when an anti-parallel external axial field of 400 Gauss is applied to the accelerator. The three traces plot the signals of as a function of time for magnetic probes located at z = 57 cm, 91 cm, 142 cm.

NPi200bz

Magnetic Field Probe Signals with Parallel Axial Field of 400 G

Probe measurements of the z component of the magnetic field when a parallel external axial field of 400 Gauss is applied to the accelerator. The three traces plot the signals of as a function of time for magnetic probes located at z = 57 cm, 91 cm, 142 cm.

rp200bz

Transport-Interpolation of SCT Magnetic Field

This is an animation of the approximate spatial dependence of the z-component of the internal magnetic field of the SCT throughout the length of the accelerator and the beginning of the drift section. The red curve shows the SCT Bz field as it interacts with the 400 Gauss parallel axial field and undergoes compression and slowing down. The blue curve shows the SCT Bz field as it interacts with the 400 Gauss anti-parallel axial field and undergoes reconnection and some acceleration. Each curve was made to agree with magnetic probe signals taken at z = 57cm, 91cm, 142cm, and 220 cm. The approximate magnetic field at locations between the fixed probes has been generated by doing a linear interpolation between adjacent probe signals, with respect to a frame of reference that is co-moving with the center of the SCT.

RP_NP_200_bz_thmb

 

Click on the image to view a video clip.

SCT Magnetic Field shot into Zero Axial Field

Animated 2D visualization of the Bz field as the SCT is accelerated down CTIX. Axial dependence of field is taken from the transport-interpolation of actual probe signals at z = 57cm, 91cm, 142cm, and 220 cm. Radial dependence of field is assumed to be Gaussian for the purpose of rendering the animation. The center electrode of CTIX is depicted by the rectangle along the lower edge of the screen. The contours represent approximate lines of constant Bz field intensity, which may or may not correspond to constant flux surfaces.

NP0_inj_thmb

Click on the image to view a video clip.

 

SCT Magnetic Field shot into Anti-parallel Axial Field

Animated 2D visualization of the Bz field as the SCT is accelerated down CTIX and reconnects with an anti-parallel Axial field of 400 Gauss.

NP200_inj_thmbClick on the image to view a video clip.

 

SCT Magnetic Field shot into Parallel Axial Field

Animated 2D visualization of the Bz field as the SCT is accelerated down CTIX and interacts with a parallel Axial field of 400 Gauss.

RP200_inj_thmbClick on the image to view a video clip.

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