A CROWBARLESS HIGH VOLTAGE POWER CONVERTER FOR RF KLYSTRONS
Advances in power electronic components make feasible the production of switch-mode power converters in module sizes exceeding 100kW. The development of a power converter system in modular form for feeding high power CW RF klystrons will be described. It has the advantage that the stored energy at high voltage is so small that the conventional crowbar protection is unnecessary. Results of work to test the principle on a 50kW klystron used for power testing accelerating cavities at Daresbury will be presented.
New Magnet Power Converters for the SRS at Daresbury
A programme to replace 25 year old magnet power converters on the SRS at Daresbury is nearing completion. The roller regulator converters recovered from the NINA synchrotron beamlines are being replaced by commercially available switch-mode units for those rated up to lOkW, and by thyristor phase controlled units for those rated from 90kW to 750kW. The latter are designed to the CERN LEP standards, and incorporate the LEP control electronics. Some minor changes to the microprocessor software were made to facilitate interfacing to the SRS control system.
Copper Phthalocyanine Improving Nonaqueous Catalysis of Pseudomonas cepacia Lipase for Ester Synthesis
The nonaqueous catalysis of lipases is significant for synthesis of high pure esters, but they usually behave low catalytic activity due to denaturation and aggregation of enzyme protein in organic phases. To improve the nonaqueous catalysis, the inexpensive copper phthalocyanine was taken as a new carrier on which Pseudomonas cepacia lipase was immobilized by physical absorption, and used for synthesis of hexyl acetate, an important flavor, via transesterification of hexanol and vinyl acetate. Results showed that the desired loading was 10 mg lipase immobilized on 10 mg copper phthalocyanine powder. When the immobilized lipase was employed in the reaction system consisted of 1.5 mL hexanol and 1.5 mL vinyl acetate at 37℃ and 160 rpm, the conversion was five fold of that catalyzed by native lipase after 1 h, and reached 99.0% after 8 h. Undergoing six times of 8-h reuses, the immobilized lipase had an activity attenuation rate 1.22% h− 1, lower than 1.77% h− 1 of native lipase, which meant that the immobilized lipase was more stable. Even at the room temperature and the static state without shaking or stirring, the immobilized lipase could bring conversion 42.8% after 10 h and the native lipase gave 20.1%. Obviously, the immobilized lipase is an available biocatalyst in organic phase and has great potential in food industry.