{"created":"2023-06-20T13:20:35.716174+00:00","id":624,"links":{},"metadata":{"_buckets":{"deposit":"9659cf77-fda4-4adc-8aa7-79c5beb54bc6"},"_deposit":{"created_by":1,"id":"624","owners":[1],"pid":{"revision_id":0,"type":"depid","value":"624"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00000624","sets":["2:428:14"]},"author_link":["7863","7862","7864"],"item_1_creator_2":{"attribute_name":"著者名","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"Rahman, Md. Mashiur"}],"nameIdentifiers":[{}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"ロホマン, エムディー マシュール "}],"nameIdentifiers":[{}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2004-03-24"}]},"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（学術）"}]},"item_1_description_12":{"attribute_name":"要旨","attribute_value_mlt":[{"subitem_description":"　Multipacting is a common phenomenon of spontaneous electron loading in resonant structures, either normal or super conducting. These electrons interact with the rf field inside the resonant structure and thus cause an abrupt and huge loss of rf field. As a result, multipacting appears as a performance limiting phenomenon of resonant structures, e.g., cavity and waveguide.\n　In the case of superconducting cavity, due to cool down to cryogenic temperature from room temperature, residual gas molecules adsorb on the inner surface of cavities and couplers. A common speculation is that these adsorbed molecules enhance the multipacting. In the research and development of superconducting Crab cavity for KEKB electron-positron collider, a severe multipacting is observed during the first time rf excitation after the cool down at 4.2K from room temperature. After processing the multipacting, if the cavity is kept at 4.2K, this multipacting is never observed during the following rf excitation. Also, in the case of KEKB superconducting accelerating cavities, multipacting is observed at and around the input coupler during the long time operation of KEKB. This observance of multipacting may be explained as that adsorption of residual gas molecules may cause this multipacting. Being inspired by these experimental hints, we have devoted our effort to understand the multipacting with respect to the adsorbed gas molecules. \n　Our study is different from the present trend of multipacting research-simulation of multipacting and study on secondary yield. In our study, we have focused our concentration in the origin of multipacting. What molecules are responsible in multipacting? Is there any difference between monolayer and multilayer of adsorbed molecules in multipacting? In our study, we have tried to find out this kind of fundamental answers in an attempt to trace out the seed of multipacting. \n　At first, we have designed and built up a dedicated experimental setup to lean the adsorption and desorption of residual gas molecules on cryo-cooled surface. Most exciting part of our experimental setup is to develop a Gas Flow Control System, by which we have efficiently controlled the number of molecules admitted into the vacuum chamber. This has enabled us to study the adsorption and desorption of gas molecules with respect to monolayer and multilayer. As the experimental surface on which adsorption and desorption has been studied, we have designed a cylindrical vacuum chamber. This vacuum chamber has been fabricated from the thick cylindrical pipe of oxygen free high conductivity (OFHC) copper so that the temperature distribution along the length of vacuum chamber becomes negligible. Since the most dominant residual gas molecule in ultra high vacuum is H<SUB>2</SUB>, we have extensively studied the adsorption and desorption of H<SUB>2</SUB>. We have found that H<SUB>2</SUB> has a saturated pressure of the order of 10<SUP>-4</SUP> Pa at 4.2K. Desoprtion of H<SUB>2</SUB> from monolayer as a function of temperature can be characterized by a broad peak at 14K. On the contrary, desorption of H<SUB>2</SUB> from multilayer occurs very sharply at around 5.6K.\n　Experience of the adsorption desorption experiment has been carried in the experiment of multipacting with respect to adsorbed gas molecules. For this study, we have designed and built up a coaxial type resonant cavity of resonant frequency is 1.5 GHz. Mode of excitation has been so chosen that different cutting parts, for example, vacuum opening at inner conductor, have been adopted at the places where rf surface current is zero.  This mode selection has enabled us to build up a coaxial cavity of rather high unloaded Q from OFHC copper. Another important feature of our design is that the inner and outer conductor can be easily separated from each other. This feature provides different options to study the multipacting. For example, besides the very easy access to the multipacting site, we can change the surface condition at the probable multipacting site. We have also designed and built up the unit coupling input probe, different monitor probes and the cryostat top flange. \n　To study the multipacting, we have used three parameters: i) vacuum pressure, particularly, for multipacting at room temperature,  ii) current due to multipacting electrons, and iii) reflected and transmitted signals from the cavity. In the study of room temperature multipacting, We have found that after processing of the multipacting observed below the peak electric field of 0.28 MV/m, these multipacting incidents do not occur during the subsequent rf excitations, if the cavity is not exposed to ambient air. \n　Multipacting above the peak electric filed of 0.28 MV/m occurs during every rf excitation, even if the cavity is not exposed to ambient air. Room temperature multipacting observed above 0.3 MV/m has been found not to become processed without baking at 100℃. This effect of baking hints that water molecule may cause or enhance multipacting. In contrast to room temperature, multipacting levels at 4.2K are few and soft. Once processed, multipacting dose not occur if the cavity is kept at 4.2K. We have studied the multipacting at 4.2K wiht respect to different amount of  adsorption of  H<SUB>2</SUB>-form saturated H<SUB>2</SUB> surface to partial monolayer of H<SUB>2</SUB>. Our experiment has revealed that adsorbed H<SUB>2</SUB> dose not act as the seed of multipacting, rather suppresses the multipacting. We have also studied the effect of other dominant residual gas molecules CO. We have found that CO too does not act as the seed of multipacting. Also, the development of multipacting in micro-second level has been studied.","subitem_description_type":"Other"}]},"item_1_description_18":{"attribute_name":"フォーマット","attribute_value_mlt":[{"subitem_description":"application/pdf","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743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":"2003"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"RAHMAN, Md. Mashiur","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743_要旨.pdf","filesize":[{"value":"346.3 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/624/files/甲743_要旨.pdf"},"version_id":"77605051-1e5d-495a-92ed-de83c2dbd2a3"},{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲743_本文.pdf","filesize":[{"value":"6.2 MB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"本文","url":"https://ir.soken.ac.jp/record/624/files/甲743_本文.pdf"},"version_id":"7d85c4cb-2313-4571-b05c-b3129938cb11"}]},"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 on Multipacting Phenomena of Low Temperature Cavity with respect to Condensed Gasses on its Surface","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Study on Multipacting Phenomena of Low Temperature Cavity with respect to Condensed Gasses on its Surface"},{"subitem_title":"Study on Multipacting Phenomena of Low Temperature Cavity with respect to Condensed Gasses on its Surface","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":"624","relation_version_is_last":true,"title":["Study on Multipacting Phenomena of Low Temperature Cavity with respect to Condensed Gasses on its Surface"],"weko_creator_id":"1","weko_shared_id":1},"updated":"2023-06-20T14:51:29.126615+00:00"}