Flow measurements are accomplished with a Mach Probe -- a device that measures the current due to ion flows in opposing directions. With this device, the flow's mach number -- its speed normalized by the speed of sound in the plasma -- can be determined. These probes were used to measure axial and azimuthal flows at different radii during merging.
People: Jason Horwitz
The energy released during magnetic reconnection is the likely cause of the solar corona's extremely high temperature. Using the vacuum ultraviolet monochromator (VUV) and a soft x-ray detector (SXR), the photons emitted by electrons are measured and their temperature is determined. The data was compared to the results of a computer simulation and to emissions from carbon atoms that exist as impurities in SSX.
Simulations of spheromak merging were preformed by Elena Belova at PPPL. After some processing with IDL, this data can be compared with the the observations from various sensors. So far, density weighted velocity histograms have been created for comparison with the results from IDS.
People: Leon Maurer
By measuring the doppler shift in the wavelength of photons emitted by ions in SSX, the speed of the ions can be calculated. The sensor looks along a chord through the midplane of the device allowing the speeds of ions along that line can be calculated. When this data is arranged in a histogram, bi-directional flows resulting from spheromak merging can be observed.
Although we try hard to only let H2 in to the gadget, inevitably some impurities sneak in. However, these can be use for measurements. In this case we looked at CIII ions to find information on temperature, flow, and density.
People: Chris Cothran
NOTHING HERE YET
While experimental measurements of the magnetic field within a reconnection layer have been taken over a planar grid, spatial data has not yet been achieved. We are constructing a 3D magnetic probe that will measure the B field vector for each position in a 5x5x8 grid of points. Our data acquisition process will use a novel multiplexer system to reduce the number of expensive digitizer channels required. Interpretation of the large data sets will be facilitated by a customized IDL visualization program. By the end of summer 2000, we hope to produce 3D movies of reconnection dynamics.
The available external diagnostics provide only a limited picture of the processes inside SSX, and usually return values averaged over a large space rather than at a specific point. We have developed a simulation of the plasma dynamics in the SSX geometry, which returns a detailed spatial map of every important parameter (density, magnetic field, etc.) By manipulating the simulation parameters so that the appropriate averages match our experimental measurements, we can infer that the simulation provides an accurate and more detailed picture of the internal dynamics of the plasma. Our code is based on the TRIM simulation, running on a Cray supercomputer. With collaborators from Bartol Research Institute, we are also working to develop a new code that models the trajectories of energetic particles within the device. Output from this code will be compared with experimental data of energetic particles from out Retarding Grid Energy Analyzer device.
Impurities in the plasma are ionized, releasing photons whose energy depends on the identity of the element and the specific drop in energy levels. The plasma's temperature determines how many ions have a given energy state. Thus, an analysis of the ratios between the magnitudes of each spectral line can provide the plasma temperature as a function of time. The photon emissions are detected with a vacuum UV monochrometer.
A movable Langmuir probe has been installed to measure the temporal and spatial dependence of temperature and density in SSX. Measurements will be taken of the current that flows when the four probe tips are biased to given voltages. From these data we can calculate the plasma density and temperature. This information is critical to make comparisons of magnetic reconnection results to theoretical values, as well as to corroborate results from spectroscopy.
In both the sun and the earth's core, a rotating mass of conducting fluid generates a strong magnetic field. This mechanism is poorly understood. A small-scale model of the system is under study in the SSX lab, a project separate from but related to the other spheromak experiments. A sphere of liquid sodium is rapidly rotated, and measurements are taken of the surrounding magnetic field.