Near-Field Effects in Radio Frequency Emission from Particle Showers in a Dense Medium

The SLAC T-510 Experiment studied the effects of a magnetic field upon the radio- frequency emission from particle showers in high-density polyethylene. Ultra-High Energy (UHF) and Very High Frequency (VHF) antennas were used to measure the radio frequency (RF) radiation from particle showers in the target. Special near field data runs were performed with the UHF antenna array positioned closer to the target (along the beam axis). The signal was split into two linearly polarized components, vertical and horizontal, arising from two different mechanisms: the Askaryan and Magnetic effects, respectively. Peak voltage data from the near-field runs was used to determine the behavior of the radiation amplitude as a function of distance from the target and angle made with respect to the beam line. Power spectral densities were produced using near field runs to analyze how various frequency ranges behaved as a function of distance. Initial results indicate that the amplitude dependence of the peak voltage on angle remains consistent even as the antennas are moved further from the target. A 1/R correction describes the effects of moving away from the target well. Spectral analysis reveals unclear effects in the lower frequency ranges. Although near field interference might be expected, such variations are likely dominated by reflections of RF emission within the target