Laboratoire de Physique des Gaz et des Plasmas<\/h3>\n\n\n\n
Bat 210, rue Henri Becquerel<\/p>\n\n\n\n
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T\u00e9l : (33) 01 69 15 72 51<\/p>\n<\/div>\n\n\n\n
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Mentions l\u00e9gales<\/a><\/p>\n\n\n\n <\/p>\n\n\n\n Annuaire<\/a><\/p>\n\n\n\n <\/p>\n\n\n\n Contact<\/a><\/p>\n\n\n\n <\/p>\n\n\n\n Acc\u00e8s<\/a><\/p>\n<\/div>\n\n\n\n MOD\u00c9LISATION DE L\u2019\u00c9MISSION \u00c9LECTRONIQUE POUR LA TENUE ULTRA-HAUTE TENSION ET LES SOURCES D’\u00c9LECTRONS CONTACT : TIBERIU MINEA Cet axe de recherche du LPGP se concentre sur la compr\u00e9hension de l\u2019\u00e9mission \u00e9lectronique de- puis des micro\/nano-structures pr\u00e9sentes \u00e0 la surface d\u2019une cathode \u00e0 haute tension sous vide [1]. Notre mod\u00e8le d\u00e9crit l\u2019\u00e9mission induite par effet de … <\/p>\n Lire la suite de\u00ab\u00a0Mod\u00e9lisation de l\u2019\u00e9mission \u00e9lectronique pour la tenue ultra-haute tension et les sources d\u2019\u00e9lectrons\u00a0\u00bb<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_en_post_content":"\n CONTACT : TIBERIU MINEA<\/strong><\/p>\n\n\n\n This area of research at LPGP focuses on understanding electronic emission from micro\/nano-structures on the surface of a high-voltage vacuum cathode [1].<\/p>\n\n\n\n Our model describes field-effect induced emission (AC or DC) with a thermionic contribution and in some cases includes photoelectric emission. The modelling work has two applications in view: the involvement of electronic emission from surface asperities in the vacuum breakdown of ultra-high-voltage devices, and the study of field-effect electron sources based on micro\/nano-emitter assemblies.<\/p>\n\n\n\n The most significant results have been brought together in a book [1] that introduces the physics and the main phenomena that govern electronic emission at high fields and temperatures. It presents recent approaches to numerical modelling and advanced developments, and is an important resource for Masters and PhD students wishing to study field emission, the behaviour of high-voltage devices, laser irradiation of surfaces and vacuum breakdown, as well as for researchers and industrialists in the field of accelerators and solid-state physics with an interest in these phenomena.<\/p>\n\n\n\n The first emission model was developed to evaluate the electronic emission from a single micro-structure. This model was first extended to an axially symmetric 2D geometry with time dependence and taking into account the self-heating of the micro-structure during emission. The results obtained in collaboration with the GeePS laboratory (CentraleSupelec) demonstrated that by applying a pulsed field (ns), it was possible not only to extract more electrons from the cathode, but also to increase the voltage withstand before breakdown. The shielding induced by the space charge during thermo-emission assisted by intense electric fields has been studied and, while maintaining the same maximum current emitted, it has been shown that voltage withstand is better when the space charge is present [2].<\/p>\n\n\n\n The continuation of this work (thesis by D. Mofakhami [3], 2018-2021) has made it possible - by refining the temporal evolution of the self-heating of the emitters - to differentiate between the stable evolution towards a steady state and the development, under certain conditions, of a thermal instability caused by the positive feedback loop between resistive heating and emitted current. In addition, a certain range of parameters has been identified for which the competition between resistive heating and the Nottingham effect, which becomes cooler (at high temperature), leads to the observation of a bi-stability around a threshold field. This bi-stability is associated with a jump in temperature, as shown in Figure 1.)<\/p>\n\n\n\n In addition, the extension of the model to 3D geometry has opened the way to the study of real, or at least realistic, field emitter arrays (FEAs). These more or less regular arrangements are at the heart of a new field-effect electron source technology that could eventually achieve intensities equivalent to their thermionic counterparts, without the disadvantages.<\/p>\n\n\n\n Working from independent experimental measurements, our simulations have recently made it possible to estimate the influence of the growth statistic of an emitter array on its emission performance (see [3], Chapter 6). Figure 2 shows, for example, for a given statistical distribution, the relative contribution of each emitter in an array to the total current. Combined with a thermal destruction model, this type of simulation could eventually become a good tool for assessing the effects of network parameters on source robustness and lifetime.<\/p>\n\n\n\n [1] <\/strong>Seznec, Tiberiu Minea, Ph. Test\u00e9, Ph. Dessainte, G. Maynard \u2013 Theoretical Treatment of Electron Emission and Related Phenomena - ISBN: 978-3-030-98418-2\/485780_1, Springer-Nature, 2022.<\/a><\/p>\n\n\n\n [2] Seznec, Ph. Dessante, Ph. Teste, T. Minea - Effect of space charge on vacuum pre-breakdown voltage and electron emission current - 2021 J. Appl. Phys. 129(15), 155102 \u2013 DOI: 10.1063\/5.0046135<\/a><\/p>\n\n\n\n [3] Darius MOFAKHAMI. \u201cMod\u00e9lisation Multiphysique de l\u2019\u00e9mission \u00c9lectronique Par Effet de Champ d\u2019une Surface 3D Micro\/Nano-Structur\u00e9e\u201d. Th\u00e8se de l'universit\u00e9 Paris-Saclay, mars 2022.<\/p>\n\n\n\n Bat 210, rue Henri Becquerel<\/p>\n\n\n\n 91405 Orsay Cedex<\/p>\n\n\n\n Phone: (33) 01 69 15 72 51<\/p>\n<\/div>\n\n\n\n <\/p>\n\n\n\n Terms of use<\/a><\/p>\n\n\n\n <\/p>\n\n\n\n Directory<\/a><\/p>\n\n\n\n <\/p>\n\n\n\n Contact<\/a><\/p>\n\n\n\n <\/p>\n\n\n\n Access<\/a><\/p>\n<\/div>\n\n\n\n CONTACT : TIBERIU MINEA<\/strong><\/p>\n\n\n\n Cet axe de recherche du LPGP se concentre sur la compr\u00e9hension de l\u2019\u00e9mission \u00e9lectronique de- puis des micro\/nano-structures pr\u00e9sentes \u00e0 la surface d\u2019une cathode \u00e0 haute tension sous vide [1].<\/p>\n\n\n\n Notre mod\u00e8le d\u00e9crit l\u2019\u00e9mission induite par effet de champ (AC ou DC) avec contribution thermo\u00efonique et inclut dans certains cas une \u00e9mission photo\u00e9lectrique. L'ensemble des travaux de mod\u00e9lisation ont en vue deux applications : l\u2019implication de l\u2019\u00e9mission \u00e9lectronique depuis des asp\u00e9rit\u00e9s de surface dans le claquage \u00e9lectrique sous vide des dispositifs ultra-haute tension et l\u2019\u00e9tude des sources d\u2019\u00e9lectrons \u00e0 effet de champ bas\u00e9 sur des assembl\u00e9es de micro\/nano-\u00e9metteurs.<\/p>\n\n\n\n Les r\u00e9sultats les plus marquants ont \u00e9t\u00e9 r\u00e9unis dans un livre [1] qui introduit la physique et les principaux ph\u00e9nom\u00e8nes qui gouvernent l\u2019\u00e9mission \u00e9lectronique sous fort champ et \u00e0 haute temp\u00e9rature. Il pr\u00e9sente les approches r\u00e9centes en mod\u00e9lisation num\u00e9rique et les d\u00e9veloppements avanc\u00e9s et constitue une ressource importante pour les \u00e9tudiants en Master et les doctorants d\u00e9sireux d\u2019approfondir l\u2019\u00e9mission de champ, la tenue des dispositifs \u00e0 haute tension, l\u2019irradiation des surfaces par laser, le claquage sous vide, mais aussi pour des chercheurs et industriels dans le domaine des acc\u00e9l\u00e9rateurs et la physique du solide avec un int\u00e9r\u00eat pour ces ph\u00e9nom\u00e8nes.<\/p>\n\n\n\n Le premier mod\u00e8le d\u2019\u00e9mission avait \u00e9t\u00e9 d\u00e9velopp\u00e9 pour \u00e9valuer l\u2019\u00e9mission \u00e9lectronique d\u2019une micro-structure unique. Ce mod\u00e8le a d\u2019abord \u00e9t\u00e9 \u00e9tendu en g\u00e9om\u00e9trie 2D \u00e0 sym\u00e9trie axiale avec d\u00e9pendance temporelle et prise en compte de l\u2019auto-\u00e9chauffement de la micro-structure au cours de l\u2019\u00e9mission. Les r\u00e9sultats obtenus en collaboration avec le laboratoire GeePS (CentraleSupelec) ont d\u00e9montr\u00e9 qu\u2019en appliquant un champ impulsionnel (ns), il \u00e9tait possible non seulement d\u2019extraire plus d\u2019\u00e9lectrons de la cathode, mais \u00e9galement d\u2019augmenter la tenue en tension avant claquage. L\u2019\u00e9crantage induit par la charge d\u2019espace lors de la thermo-\u00e9mission assist\u00e9e par des champs \u00e9lectriques intenses a \u00e9t\u00e9 \u00e9tudi\u00e9 et tout en gardant le m\u00eame courant maximal \u00e9mis, il a \u00e9t\u00e9 d\u00e9montr\u00e9 que la tenue en tension est meilleure lorsque la charge d\u2019espace est pr\u00e9sente [2]<\/a>.<\/p>\n\n\n\n La poursuite de ces travaux (Th\u00e8se de D. Mofakhami [3<\/a>], 2018-2021) a notamment permis \u2013 en raffinant l\u2019\u00e9volution temporelle de l\u2019auto-\u00e9chauffement des \u00e9metteurs \u2013 de diff\u00e9rencier l\u2019\u00e9volution stable vers un r\u00e9gime permanent et le d\u00e9veloppement, sous certaines conditions, d\u2019une instabilit\u00e9 thermique caus\u00e9e par la boucle de r\u00e9troaction positive entre chauffage r\u00e9sistif et courant \u00e9mis. Par ailleurs, une certaine gamme de param\u00e8tres a \u00e9t\u00e9 identifi\u00e9e pour laquelle la comp\u00e9tition entre chauffage r\u00e9sistif et effet Nottingham devenu refroidissant (\u00e0 haute temp\u00e9rature) m\u00e8ne \u00e0 l\u2019observation d\u2019une bi-stabilit\u00e9 autour d\u2019un champ seuil. Cette bi-stabilit\u00e9 est associ\u00e9e \u00e0 un saut en temp\u00e9rature comme le montre la figure 1).<\/p>\n\n\n\n Par ailleurs, l\u2019extension du mod\u00e8le en g\u00e9om\u00e9trie 3D a ouvert la voie \u00e0 l\u2019\u00e9tude des r\u00e9seaux r\u00e9els, ou tout au moins r\u00e9alistes, d\u2019\u00e9metteur \u00e0 effet de champ (FEA pour Field Emitter Array en anglais). Ces arrangements plus ou moins r\u00e9guliers sont au c\u0153ur d\u2019une nouvelle technologie de sources d\u2019\u00e9lectrons \u00e0 effet de champ qui pourrait \u00e0 terme atteindre des intensit\u00e9s \u00e9quivalentes \u00e0 leurs homologues thermo\u00efoniques, leurs d\u00e9savantages en moins.<\/p>\n\n\n\n En travaillant \u00e0 partir de mesures exp\u00e9rimentales ind\u00e9pendantes, nos simulations ont r\u00e9cemment permis d\u2019estimer l\u2019influence de la statistique de croissance d\u2019un r\u00e9seau d\u2019\u00e9metteur sur ses performances d\u2019\u00e9missions (cf. <\/em>3<\/a>], Chapitre 6). La figure 2<\/a> montre par exemple pour une distribution statistique donn\u00e9e la contribution relative de chaque \u00e9metteur d\u2019un r\u00e9seau au courant total. Combin\u00e9 \u00e0 un mod\u00e8le de destruction thermique, ce type de simulations pourrait \u00e0 terme devenir un bon outil pour \u00e9valuer les effets des param\u00e8tres du r\u00e9seau sur la robustesse de la source et sa dur\u00e9e de vie.<\/p>\n\n\n\n [1] <\/strong>Seznec, Tiberiu Minea, Ph. Test\u00e9, Ph. Dessainte, G. Maynard \u2013 Theoretical Treatment of Electron Emission and Related Phenomena - ISBN: 978-3-030-98418-2\/485780_1, Springer-Nature, 2022.<\/a><\/p>\n\n\n\nR\u00c9SEAUX SOCIAUX<\/h3>\n\n\n\n
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<\/figure>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/main>\n","protected":false},"excerpt":{"rendered":"Electron emission modelling for ultra-high voltage holding and electron sources<\/h1>\n\n\n\n
\n\n\n\nHigh voltage withstand under vacuum<\/h2>\n\n\n\n
Field effect electron sources based on emitter arrays<\/h2>\n\n\n\n
![\"\"](\"http:\/\/biblioconf.lpgp.universite-paris-saclay.fr\/wordpress\/wp-content\/uploads\/2024\/09\/ad3fe73c-2b33-4326-aac3-af28b66c6aa4.png\")
field for a single tungsten hemi-ellipsoid emitter. (a): Schematic
diagram of the modelled configuration.\u00a0(b) : Variation of the maximum temperature\u00a0 Tmax\u00a0\u00a0with the applied field E and of\u00a0the temperature at the top Ta\u00a0\u00a0in steady state. \u03b4=5kV\/m, so that \u03b4\/Eth=0.002%. (c): Steady-state temperature distribution at Eth\u00a0and\u00a0(d):at Eth+\u03b4. Parameter \u03a6N\u00a0\u00a0gives the heat flux density removed by the Nottingham effect at the emission surface.<\/em><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n\n![\"\"](\"http:\/\/biblioconf.lpgp.universite-paris-saclay.fr\/wordpress\/wp-content\/uploads\/2024\/09\/b74d4976-1445-4062-a883-bdcf6e3ce43a.png\")
contribution of the emitters to the total current of a regular array of
carbon nanocones. (a): 1cm\u00d71cm chip engraved on 1mm\u00d71mm.\u00a0(b) :
SEM micrograph of the carbon nanocones on the etched surface (c) :
Diagram of the simulated situation (25 emitters from a Gaussian draw on
the height H and the radius at the apex\u00a0Rs). (d): Contribution to total current Itot of each of the 25 transmitters at the field limit Elim\u00a0\u00a0just before the thermal destruction of emitter no. 10. J is the corresponding macroscopic current density.<\/em><\/figcaption><\/figure>\n<\/div>\n\n\n\nBibliography<\/h2>\n\n\n\n
Laboratoire de Physique des Gaz et des Plasmas<\/h3>\n\n\n\n
SOCIAL NETWORKS<\/h3>\n\n\n\n
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<\/figure>\n\n\n\n<\/figure>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/main>\n","_en_post_name":"","_en_post_excerpt":"","_en_post_title":"Electron emission modelling for ultra-high voltage holding and electron sources","_fr_post_content":"\nMOD\u00c9LISATION DE L\u2019\u00c9MISSION \u00c9LECTRONIQUE POUR LA TENUE ULTRA-HAUTE TENSION ET LES SOURCES D'\u00c9LECTRONS<\/h1>\n\n\n\n
\n\n\n\nTenue haute tension sous vide<\/h2>\n\n\n\n
Sources d\u2019\u00e9lectrons \u00e0 effet de champ bas\u00e9 sur des r\u00e9seaux d\u2019\u00e9metteurs<\/h2>\n\n\n\n
contribution relative des \u00e9metteurs au courant total d\u2019un r\u00e9seau
r\u00e9gulier de nano-c\u00f4nes de carbone. (a) : Puce d\u20191cm\u00d71cm grav\u00e9 sur 1mm\u00d71mm. (b) : Micrographie au MEB des nano-c\u00f4nes de carbone sur la surface grav\u00e9. (c) : Sch\u00e9ma de la situation simul\u00e9e (25 \u00e9metteurs issus d\u2019un tirage gaussien sur la hauteur H et le rayon au sommet Rs). (d): Contribution au courant total Itot de chacun des 25 \u00e9metteurs au champ limite Elim juste avant la destruction thermique de l\u2019\u00e9metteur n\u00b010. J est la densit\u00e9 de courant macroscopique correspondante.<\/em><\/figcaption><\/figure>\n<\/div>\n\n\n\nBibliographie<\/h2>\n\n\n\n