Page 26 - libroBrevetti
P. 26
Department of Engineering, ICT and Technologies for Energy and Transport Patent Title Bolometric device with receiving cavity for high power microwave beam measurements at high frequency and procedure to coat the inner surface of the load. Ref. CNR 1657 Assignee(s): CNR CNR InƐƟƚute: IFP Main Inventor: Nicolò Spinicchia Countries: US Priority date: 24/02/2005 Abstract The development of powerful microwave sources requires the use of a cavity (“load”) in order to absorb the generated power and in some cases to provide a measure of the absorbed power (“bolometric load”). The microwaves, usually in concentrated beams, are injected in the load through an appropriate opening but a load can reŇect up to 10% of the injected power. An elevated ƌĞŇĞĐƟŽŶ, beyond to being harmful for the source, in the bolometric load case does not allow an accurate measure. For the development of these loads, advanced design and construĐƟŽŶ techniques are required, ƉĂƌƟĐƵůĂƌly in the ĚĞĮŶŝƟŽn of the thickness and the deposŝƟŽn of the ceramics layer, that has to be both microwave-absorbing and very resistant to thermal shocks. The ĐŽĂƟŶŐ, object of this inveŶƟŽn and selected ĂŌer a number of tests, allows a reĚƵĐƟŽn in reŇeĐƟŽn to less than 1%. Background The use of the bolometric loads concerns all sectors where high power microwave sources (gyrotrons) are employed. In the framework of thermonuclear fusion research the gyrotrons are employed in experiments of Plasma ,ĞĂƟŶŐ with frequencies in the range 28 GHz - 170 GHz. The expected increase of the power calls for new technological sŽůƵƟŽŶs in manufacturing bolometric loads, parƟcularly in making use of layer of microwave-absorbing ceramics very resistant to thermal shocks. Technology The invenƟon consists in a load of a hollow copper sphere (bolometric load) with a spreading mirror in front of the beam entrance. The millimeter-wave abƐŽƌƉƟŽn occurs in a thin ceramic ĐŽĂƟŶŐ deposited by Plasma Spray technology. An external cooling circuit removes the absorbed thermal energy. The power measurement is performed acquiring the ĚŝīĞrence between input and output temperature of the cooling ŇƵŝĚ and the ŇŽǁ rate. Advantages and ApplicaƟons The main advantage is due to the ĐŽĂƟŶŐ of Boron Carbide (B C) deposited in the inner wall of the load. The 4 B C has ďĞƩĞƌ resistance to the temperature and shows an improved microwave absŽƌƉƟŽn compared with 4 other ĐŽĂƟŶŐs. The bolometric load with ďĞƩĞƌ performances allows power measurements of gyrotrons of the new geneƌĂƟon (2 MW ĐŽŶƟnuous power). Development stage The device has been designed in diīĞƌĞnt versions and prototypes, coated with a tradŝƟonal absorber and tested in European Laboratories, thus demonsƚƌĂƟŶg the suitability of the design. The new ĐŽĂƟŶŐ has been deposited on small samples and tested in Laboratory, showing superior performances both for absorbance and for resistance to thermal shocks. 17