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.
HIGH-VOLTAGE MODULATOR WITH SMALL ENERGY ACCUMULATION IN THE OUTPUT FILTER
A compact power source for the Injector of neutral atoms designed for diagnostics of plasma in thermonuclear installations is described. It forms output voltage up to 55 kV with an output current up to 3A during the two seconds pulse. The power source is constructed by the module method. It consists of six identical cells. Each cell includes an IGBT inverter operating at a frequency of 5 kHz, a high-voltage transformer with a 1:20 transformation ratio, bridge diode rectifier and capacitance filter. Outputs of the cells are set up in series. The inverters are phased-in such a way that the main frequency of output voltage ripple equals to 5kHz*2*6=60kHz. A capacitance filter with accumulated energy less than 2 J is enough for decreasing of ripple amplitude to level less than 1% under the nominal load. Combination of such an output filter with comparatively low leakage inductance of the high-voltage transformers and high speed of response of protection circuits of IGBT inverters allowed reliable protection for the grid system of the Injector against a break-down without expensive crowbar switch. The report presents the features of technical realization of the power source and its experimental and operational characteristics.
Study on essential drug use status and its influencing factors among cerebral infarction inpatients in county level hospitals of Anhui Province, China
Background and purpose Drug costs is one of the main components of hospitalization expenditure for cerebral infarction inpatients. In China, the National Essential Medicine System (NEMS) was created to relieve the heavy drug-cost burden for patients. The objective of this study was to investigate essential drug-use status and its influencing factors among cerebral infarction inpatients in county-level hospitals of Anhui province, China. Methods Three county-level hospitals were selected through a multi-stage cluster random sampling method. The hospitalization cost data of cerebral infarction inpatients in the three hospitals were extracted from the Anhui provincial information platform of the New Rural Cooperative Insurance System (NCMS), and whether the proportion of essential drug cost in the total drug cost reached the median value of 33.05% which was set as the evaluation index for essential drug-use status. Questionnaires for hospitals and physicians were designed and given to them to assess influencing factors. Results We retrieved the cost data of 2,189 inpatients from the NCMS platform and investigated 51 corresponding physicians in total. The drug costs accounted for 52.6% of the total hospitalization cost, and essential drug costs alone accounted for 37.0% of the total drug costs. The essential drug-cost proportion was high among physicians with a higher recognition degree on NEMS, older age, lower final academic degree, longer work experience and lower professional title. Married physicians and those with tight organizational affiliation also prescribed more essential drugs. Conclusions Increasing the proportion of essential drugs was an effective way to reduce the disease burden for cerebral infarction patients. Perfecting the NEMS, increasing government investment, reinforcing education and propaganda, and formulating relevant incentive and restrictive mechanisms were all effective ways to promote and increase the number of essential drug prescriptions written by physicians.