Latin American Experiment - First Data
The new FFS-LPP collaboration with a Latin American plasma focus group has produced its first data. The data is being used for calibration of the five scintillators that measure neutron flux, x-ray flux and x-ray temperature. Such calibration must be done carefully, because temperature measurements are based on the ratios of the signals from the scintillators when they are placed behind metal filters of different thicknesses. This data ends a long (four-year!) drought of experimental data for our project.
Calibration is being carried out by comparing the data from different scintillators for the same shots. The plasma focus produces three pulses for each shot: gamma rays when the electron beam from the plasmoid hits the inner electrode or anode; x-rays from the heated electrons in the plasmoid and neutrons from the fusion reactions in the plasmoid. (The calibration runs are using deuterium as the fuel.) For calibration purposes, the x-rays are being blocked by metal shields, which both the neutrons and the energetic gamma rays can penetrate. Since the neutrons travel much slower that the gamma rays, they arrive at the scintillators much later, so the two are easily distinguished. Both gamma rays and neutrons produce pulses of light when they hit the plastic scintillators. These pulses of light are then converted to electric pulses and amplified by photomultiplier tubes and fed to the oscilloscopes, which collect data every 0.4 ns (billionths of a second).
Calibration between the scintillators is done by taking the ratio of the signals at each time point. Absolute calibrations is then achieved by comparing the total signal (the area under the curve) to the total number of neutrons observed by an already calibrated neutron detector. Knowing the relative sensitivity of the scintillators to gamma rays and neutrons, the scintillators can then be calibrated for gamma rays was well.
Calibration is expected to be completed in a few weeks. The next step will be to take base-line x-ray observations of the plasm focus, before modifying it to see the effects of adding angular momentum.