The Ionospheric Radar Integrated System (IRIS) includes (a) a portable HF/VHF radar, (b) a digital ionosonde, and (c) HF and VLF receiving systems. The HF/VHF portable radar consists of 4 transmitters, 4 receivers, 4 transmit/receive (T/R) switches, 7 power combiners, 3 sets of 4-element Yagi antennas and a controlling computer. The nominal operating frequency range is 10 - 60 MHz. The three sets of Yagi antennas with adjustable lengths can cover the frequency ranges: 11.5 - 22.5 MHz, 22.5 - 44 MHz, and 44 - 60 MHz, respectively. Each of the four amplifiers puts out 8 kW peak envelope power (PEP) at up to 15% duty cycle. Each 8 kW amplifier is composed of four 2 kW modules. The outputs of these 2 kW modules can be independently phased for purposes of beam steering. In turn, the four transmitters may be independently phased. Thus, in principle, 16 antennas can be used as a phased array in either a linear or square matrix. Multiple pulses can be combined to make coded sequences. The maximum length of any sequence is 2 mS at 4% droop. The pulse repetition frequency can be varied anywhere from 0 to 1 kHz, maximum duty cycle permitting. The entire system consumes about 13 kW at full duty cycle. Power is provided by means of four 5-kW diesel generators. The extra generation capacity may be used to power other components, such as lights and air conditioning/heating for the radar shelter building (currently a utility trailer).

Ionospheric Plasma Research Group, headed by Professor Min-Chang Lee, working at the VTF.

The Versatile Toroidal Facility (VTF) has been used for laboratory simulations of radio wave-induced plasma turbulence in space, and to cross-check Arecibo experimental results acquired by the PSFC's Ionospheric Plasma Research Group. Intense microwaves injected into the VTF plasma chamber can generate Langmuir wave turbulence having both cascading and anti-Stokes spectra, similar to what is observed in ionospheric plasma heating experiments at Arecibo, Puerto Rico. The successful reproduction of Arecibo experimental results in VTF corroborates that anti-Stokes Langmuir waves result from the nonlinear scattering of O-mode pump wave-excited Langmuir waves off the pre-existing lower hybrid wave.

Students set-up radar electronics at Arecibo.

77 Massachusetts Avenue, NW16, Cambridge, MA 02139, info@psfc.mit.edu