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OPENING FOR A 3 YEAR PhD GRANT : “EFFECT OF ADSORPTION ON FIELD EMISSION IN HIGH VOLTAGE DEVICES”
Applications are invited for a 3 year PhD fellowship starting september 2012 in LCAR laboratory, University Paul Sabatier, Toulouse, France, in cooperation with Atomic Energy Authority (CEA), Cadarache, France. The grant is co-funded by Région Midi-Pyrénées and CEA. The work will be performed under the supervision of Bruno Lepetit in Toulouse, as well as Alain Simonin and Hubert De-Esch in Cadarache. The successful candidate will be involved in modeling of the electronic emission induced by the electric field in high voltage devices. Such devices are part of the Neutral Injection System currently under development for future nuclear fusion reactors (DEMO, ITER [1]…). This Neutral Injection System is used to bring energy to the fusion plasma and heat it up. Cathode emission of dark currents under vacuum has been measured recently in the Cadarache group [2]. Such currents can trigger arcing and induce damages to the device, thus they should be controlled and avoided as much as possible. It was shown in particular that these dark currents are dependent on the surface state of the emitting electrode, and in particular on the presence of adsorbates on it.
The proposed work will consist in developing models to gain better understanding and control of these currents. The work will quantify these effects through quantum physics simulations. Several steps will be followed: first, evaluate sticking probabilities of adsorbates as a function of the gas type (hydrogen, helium, other rare gases), pressure conditions and electric field. This part of the work will use the methodology described in [3-4]. Then, the effect of the presence of the adsorbate on emission conditions, its influence on work function and electronic density, will be studied, using Density Functional Theory type models.
The modeling work will be performed mainly at the University in Toulouse but will require close interaction with the experimental team at CEA, Cadarache, near Marseille. The candidate should have basic knowledge in plasma physics and/or quantum mechanics. As the present PhD work mixes engineering and basic science, it may be of interest for an engineering school or master student who has not decided yet between engineering and academic careers, but who is highly motivated by the development of numerical models, involving programming and use of software on high performance computers.
[1] For a general presentation on the Nuclear Fusion Project ITER : http://www.iter.org
[2] “Enhanced High-voltage Holding under Vacuum by Field Induced Adsorption of Gas on Metal Surfaces”, A. Simonin, L. Christin, L. Doceul, F. Faisse, F. Villecroze, H. de Esch, Proc. IPAC 2011, San Sebastian, Spain, http://accelconf.web.cern.ch/accelconf/IPAC2011/papers/tups004.pdf
[3] "Sticking and desorption of hydrogen on graphite : a comparative study of different models", B. Lepetit, D. Lemoine and B. Jackson J. Chem. Phys., 134, 114705 (2011)
[4] «Sticking of Hydrogen on Supported and Suspended Graphene at Low Temperature », B. Lepetit and B. Jackson, Phys. Rev. Lett., 107, 236102 (2011)
Information and application :
Bruno LEPETIT
LCAR laboratory
Université Paul Sabatier - Bât. 3R1 B4 - 118 route de Narbonne
31062 Toulouse Cedex 09, France
Tel: (33) 5 61 55 85 50
Alain SIMONIN
Institute for Magnetic Fusion Research
Plasma Heating and Confinement Department
13108 St Paul les Durance, France
Tel: (33) 4 42 25 47 41
Mail : [log in to unmask]
http://www-fusion-magnetique.cea.fr/
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