Sounds, Images and Movies from
 

QuickLinks
 

CTX

Blake Shaw -- Fall Semester '03
 

Introduction

  • This website is a collection of the sounds, images, and movies I've created during my semester working at CTX. I have been working with Ben Levitt and Professor Mauel to try to better illustrate the data collected at CTX by using Mathematica and IDL. Furthermore, there are some images and movies created with a webcam which help to show how we make plasma at CTX.

    At CTX, we use a mechanically suspended dipole magnet to create a hot electron, ECRH plasma. We generally make a hydrogen plasma, although occasionally we use other gases. Microwaves are used to produce these energetic deeply-trapped electrons. We then use a variety of diagnostics to study the plasma.

Images

  • Here is a collection of images created using a simple webcam. We mounted an Apple iSight to the exterior of the chamber looking in through a port hole, and then recorded a variety of different kinds of shots. These are the best frames extracted from those movies. These pictures clearly show the geometry of the deeply trapped dipole plasma, characteristic of CTX.
  • The light that we see in these pictures is emitted from charged particles colliding with neutral particles. When a collision occurs, these neutrals become excited, and upon relaxation they emit photons. The number of neutrals is proportional to the density of the plasma. Therefore, in higher density shots we see more light emitted.
  • Furthermore, it is interesting that the high density region appears to be so well defined. Plasma density is inversely proportional to the radius^4. However, we see a clearly defined boundary of light.
  • High Density
  • In this picture one can clearly see the torus of plasma surrounding the polar grid detector, and one of the floating potential probes inserted into the plasma.
  • Medium Density
  • This view is more of a close-up of the polar grid detector and the tungsten mesh surrounding it. We can also see some microwave heating effects on the fringe of the tungsten mesh.
  • High Density
  • For many of the shots, we would get strange color variations, usually blue and purple. However, we believe that this effect had to do with the iSight trying to compensate for the quick flash of light and not because of the nature of the plasma.

 

Sounds

  • These sounds were generated using Mathematica and IDL to help illustrate the rotationally driven interchange instability. Ben Levitt is using the tungsten mesh to induce an electric field, which in turn, rotates the plasma, and drives this instability. The data was taken from one of the fast floating potential probes and converted into a data file using IDL. The data was then imported into Mathematica and used to generate time frequency domain plots (TFDs) and sound files of the frequency content embedded in the fast floating probe data. Here is the IDL script. Here is the Mathematica File.

 

Movies

  • These movies are the original footage that we took with the iSight. They are in real time. During roughly the first .6 seconds, microwaves are being used to heat the plasma. However, afterwards there is an afterglow period when, although the heating is off, the plasma persists. This period is the clearest part of the shot because we believe that the microwaves interfere with the CCD in the iSight.

 

  • High Density

 

  • Medium Density
  • In order to try to reduce the microwave interference, we built a Faraday cage. We used a fine wire mesh surrounding the iSight to try to reduce the effects of the microwaves. This did allow us to see more of the shot without interference. However, the wire mesh was still substantial enough to obscure the view.
  • High Density
  • w/ Faraday cage
  • These movies are created using the polar grid detector. The data from the detectors are processed in IDL and combined into movie files. The IDL code is adapted from Ben Levitt's original code. It uses cubic spline interpolation to create a polar contour surface from a set of irregular grid points. The orange and yellow colors represent areas of positive charge, and the blue and purple colors represent areas of negative charge. The black dots are the locations of the polar grid detectors.
  • With these movies, we are trying to observe drift waves rotating at roughly 5 khz. In the future we would like to use this setup to observe the rotation of the plasma when we induce an electric field with the tungsten mesh. However, currently the polar grid detector hardware isn't sensitive enough yet to be used in the lower density regime in which we currently use the meshes.
  • In these movies we can see some subtle signs of rotation. Not all the detectors are working, which can be clearly seen by some strange effects in the upper right corner of the plot. However, some drift waves are noticeable.
  • High Density
  • Shot 3830
  • .51 < time .512
  • 1000 frames

Source Code: download this zip package. Read Me included.

Thanks

  • Thanks so much to Professor Mauel for the opportunity to work at CTX this semester, and Ben Levitt for teaching me so much about how CTX works.