{"created":"2023-06-20T13:20:34.909981+00:00","id":609,"links":{},"metadata":{"_buckets":{"deposit":"cc8c0f55-9546-47dd-af65-436904459621"},"_deposit":{"created_by":1,"id":"609","owners":[1],"pid":{"revision_id":0,"type":"depid","value":"609"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00000609","sets":["2:428:14"]},"author_link":["8858","8860","8859"],"item_1_creator_2":{"attribute_name":"著者名","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"方, 志高"}],"nameIdentifiers":[{}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"ファン, シッガオ"}],"nameIdentifiers":[{}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2001-03-23"}]},"item_1_degree_grantor_5":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"総合研究大学院大学"}]}]},"item_1_degree_name_6":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士（理学）"}]},"item_1_description_12":{"attribute_name":"要旨","attribute_value_mlt":[{"subitem_description":"　　Recently we observed strong spurious oscillations caused by the backstreaming electrons from the collector in the 324MHz 3MW 650μs klystrons developed at KEK. During the high-voltage processing of 324MHz klystron tube #1, unexpected oscillations were observed from both the output <br />and input cavities when there was no driving input power. These oscillations occurred when the beam voltage was 63～71kV or higher than 90kV, and had frequencies close to 324MHz. After some investigations, the oscillations were identified to be the results of the backstreaming electrons from the collector. The collector size was accordingly changed to evaluate its effect on the backstreaming electrons. The experiment results of klystron tube #1A and #2 with modified collectors of increased radiuses and lengths, indicated that the oscillations disappeared in the low beam-voltage region, and started from 95kV and higher than 104kV respectively.<br />　　In order to understand the oscillations and to improve the klystron tubes, this thesis has studied on these spurious oscillations due to the backstreaming electrons from the collector. These electrons originally come from the backscattering of the electron beam on the collector surface. According to the course of the oscillations, the study covers three parts: the production of the backscattered electrons on the collector surface, the formation of the backstreaming electrons into the drift tube, and the oscillation mechanism due to the interaction between the electrons and rf fields.<br />　　At first, the electron backscattering process has been investigated and simulated using the EGS4 Monte Carlo method. Electrons emitted from a bombarded material-surface are generally divided into two classes: the true secondary electrons whose energies are less than approximately 50eV, and the backscattered primary electrons whose energies vary continuously from the primary electron energy to lower energies. In this thesis, we concern those backscattered electrons that have high energies corresponding to the klystron applied-voltage from a few keV to several hundred keV. These backscattered electrons have been calculated by an EGS4 user code. The electron backscattering coefficients and energy distributions have been obtained under different conditions of incident energy and angle. For example, for the normal incidence on copper, the backscattering coefficient is equal to 0.3, and it increases with the incident angle. The trajectories of the backscattered electrons are also plotted out by a FORTRAN90 program. The EGS4 simulation results agree well with the experimental data of the reflected electrons.<br />　　After the above confirmation of the EGS4 code validity for the fundamental process, the simulations of the backstreaming electrons from the klystron collector have been performed by the EGS4 code. The simulation method includes three steps. (1) The trajectory calculation for the incident beam in the collector up to the collector wall. This step is performed by a FORTRAN90 program. Besides space-charge forces, relativistic effects, self-magnetic fields and external magnetic field effects are included in this calculation. The calculation results have shown a good agreement with the EGUN95 simulation results. (2) The simulation of the electron backscattering in the collector using the EGS4 Monte Carlo method. This step is performed by an EGS4 user code, which processes the initial conditions, collector geometry electron motion in the magnetic fields, and output of the backscattered and backstreaming electrons. (3) The post-process for the backscattered and backstreaming electrons. This step includes two FORTRAN90 programs; one is for the electron trajectory plotting, and the other is for the calculation of the z-component energy distribution of the backstreaming electrons. Some simulation results are also given in this thesis.The backstreaming electron coefficients and energy distributions have been obtained under different conditions of the klystron. The simulation results indicate that the backstreaming electrons are essentially independent of the beam voltage. For klystron #1, #1A, and #2, the backstreaming electron coefficients are 0.66%, 0.17%, and 0.13%, respectively. The contributions to the backstreaming coefficients from the cylindrical surface and cone-shaped surface of the collector have also been investigated. The former contribution mainly comes from the backscattering of the beam edge, and the latter contribution increases with the collector length shortening due to the direct reflection. The backstreaming coefficients have been carried out as function of collector diameter and length. Also the backstreaming electrons as function of various materials are obtained. It is clarified that a lower atomic-number material results in a smaller backstreaming coefficient. Furthermore, the transmission of the backstreaming electrons in the drift tube is investigated. It is indicated that most of the backstreaming electrons can pass through the drift tube to the input cavity region under the focusing fields of the klystron. <br />　　Finally, the study of the oscillation mechanism and conditions due to the backstreaming electrons has been performed, and relevant calculations of the oscillation conditions have also been executed using the previous results of the backstreaming electrons. Since the backstreaming electrons modulated by the gap voltage of the output cavity can induce an rf signal in the input cavity, they result in a formation of a feedback loop inside the tube. From the feedback theory, if an input cavity voltage can be regenerated by the backstreaming electrons, the oscillations will occur. Thus the oscillation conditions can be expressed by the complex product of the klystron voltage- gain and the feedback coefficient caused by the backstreaming electrons: (1) the amplitude of the product should be larger than unity, and (2) the phase of the product should be zero or integral times of 2π. The voltage gain of the klystron has been simulated by JPNDISK. Since we are interested in the beginning of the oscillations, which is in a small-signal linear region, the ballistic theory has been applied to calculate the feedback coefficient due to the backstreaming electrons by a FORTRAN90 program. Based on the calculations of the oscillation conditions, the beam-voltage regions of the oscillations for the 324MHz klystrons have been worked out. For klystron #1, the beam-voltage regions are 65~70kV and higher than 79kV. For the collector of #1A and #2, the regions are higher than 100kV and 105kV, respectively. These results show a good agreement with the experiments. With these analyses and calculations, the oscillation mechanism including the oscillation phenomena has been understood physically and numerically. Suitable collector dimensions are proposed for 324MHz klystron in order to suppress the oscillations due to the backstreaming electrons completely. Furthermore, some discussions and directions for future investigations on the oscillations are presented.","subitem_description_type":"Other"}]},"item_1_description_7":{"attribute_name":"学位記番号","attribute_value_mlt":[{"subitem_description":"総研大甲第505号","subitem_description_type":"Other"}]},"item_1_select_14":{"attribute_name":"所蔵","attribute_value_mlt":[{"subitem_select_item":"有"}]},"item_1_select_8":{"attribute_name":"研究科","attribute_value_mlt":[{"subitem_select_item":"数物科学研究科"}]},"item_1_select_9":{"attribute_name":"専攻","attribute_value_mlt":[{"subitem_select_item":"12 加速器科学専攻"}]},"item_1_text_10":{"attribute_name":"学位授与年度","attribute_value_mlt":[{"subitem_text_value":"2000"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"FANG, Zhigao","creatorNameLang":"en"}],"nameIdentifiers":[{}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲505_要旨.pdf","filesize":[{"value":"424.6 kB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"要旨・審査要旨 / Abstract, Screening Result","url":"https://ir.soken.ac.jp/record/609/files/甲505_要旨.pdf"},"version_id":"31fd47dc-a157-4089-995d-de96fe7cc7fa"},{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲505_本文.pdf","filesize":[{"value":"8.5 MB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"本文","url":"https://ir.soken.ac.jp/record/609/files/甲505_本文.pdf"},"version_id":"a8379283-4093-4469-a5be-419cb8766aac"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Study of Spurious Oscillations Due to BackstreamingElectrons from Collector in Klystron","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Study of Spurious Oscillations Due to BackstreamingElectrons from Collector in Klystron"},{"subitem_title":"Study of Spurious Oscillations Due to BackstreamingElectrons from Collector in Klystron","subitem_title_language":"en"}]},"item_type_id":"1","owner":"1","path":["14"],"pubdate":{"attribute_name":"公開日","attribute_value":"2010-02-22"},"publish_date":"2010-02-22","publish_status":"0","recid":"609","relation_version_is_last":true,"title":["Study of Spurious Oscillations Due to BackstreamingElectrons from Collector in Klystron"],"weko_creator_id":"1","weko_shared_id":1},"updated":"2023-06-20T14:51:42.403144+00:00"}