The charactization of high-speed swept reflectometer for plasma diagnostics on the RFX reversed-field pinch

An ordinary mode IMPATT-based reflectometer operating over 26.5–110GHz has been developed for density diagnostic application on the RFX reversedfield pinch experimental fusion machine. The reflectometer uses polarization rotators located at the antennas for optimizing the polarization of the emitted E-field A sweep speed of 1.25ms for the full band is possible. Single subbands may be swept at a rate of 200us. The provision of polarization rotators and high-speed solid-state oscillators maximises the immunity of the system to the effects of high fluctuation frequencies and mode mixing due to high magnetic shear. The reflectometer uses an IMPATT oscillator system for the source which has not been used in previous reflectometer circuits. A previously unachievable temporal resulution is therefore available with this system. The reflectometer is the first to be developed for use on a reversed-field pinch (RFP) machine.Verification of reflectometer operation was achieved using plane metal targets to simulate the reflecting plasma cut-off layer. Targets were located at various distances from the antennas to cover the expected spatial reflection range. The theoretical and experimental characteristics were obtained by processing the intermediate frequency output of the detectors. Spurious signals are removed by calibrating the target data using residual fringe data. A zero-crossing detection algorithm was developed to accurately identify the beat fringes and to deduce the phase/frequency characteristic. Single subband and full sweep results are presented.     

THE FATE OF PYRIMIDINE DIMERS IN THE DNA OF ULTRAVIOLET-IRRADIATED CHINESE HAMSTER CELLS

Abstract —As an aid to understanding the relationship between dimer repair and cellular recovery, we have studied dimer removal and replication of dimer-containing DNA in Chinese hamster ovary (CHO) cells irradiated with ultraviolet light (254 nm). These investigations demonstrated that (1) dimers are not excised as polynucleotides of less than 500,000 mol. wt, (2) fractionation of the ultraviolet dose does not enhance dimer excision, (3) dimer-containing DNA is replicated in ultraviolet-irradiated CHO cells, and (4) the dimers are conserved in the replicated DNA. These findings support the proposed mechanism of bypass of photoproducts during DNA replication in mammalian cells.