H." Sanuki

Y.N. "Nejoh

National Institute for Fusion Science (NIFS-Repository)

§ 26. An Investigation of Spacecraft-PlasmaInteractions- Plasmas Near the Thruster -Nejoh, Y.N. (Hachinohe Institute of Technology)Sanuki, H.TIle electric propulsion for space vehicles utilizeselectric and magnetic fields to accelerate a propellant to amuch higher velocity than chemical propulsion does, and,as a result, the required propellant mass is reduced.Among electric propulsion devices Hall thrusters offertnuch higher thrust density than conventional ion thrusters.Hall thrusters have a merit that it accelerates a quasineutralplasma and hence is not subject to a space-eharge limit onthe electric current. The impeded electrons can ionizethe propellant neutral atoms effectively and support asignificant a'cial electric field vvith equipotentials along themagnetic field lines. TIle a'cial electric field acceleratesthe ions from the anode towards the charmel exit, in adirection that is opposite to the a'cial direction of theelectrons. Hall thrusters have enjoyed bothexperimental and theoretical progress, however theyremain fur from a fully understood behavior. Atpresent modeling cannot be used for designing optunizedstructures Ul a fully confident way. Even if the basicidea is a rather sunple one, the behavior of such dischargesis complex and an improved understanding in terms ofphysics and modelulg remains required. However,there is still no model describulg adequately plasmadynamics u1Side the accelerating channel. TIleimportance of developing a reliable model that unprovesour understanding of the factors v.-luch control plasmastructure becomes evident when attempt to unproveupon existing Hall thruster designs,· particularly regardingthe ulstability of the discharge current the thrust and theefficiency ofthe tImlster.When "ve discuss tile discharge for tile production oftile plasma, tile instability of tile discharge current hasfrequently been reported[ 1]. We asswne tImt tileXenon gas is into tile charmel and tImt tile plasmacomponents are electrOl1S, Xenon ions and neutrals.Equations (1) and (2) are tile conservation la,,," of positiveions and neutral particles v.,itIl tile creation (positive sign)and amllhilation (negative sign) tenus of the right-handside, respectively, where y is tile coefficient of thecreatiolml velocity of iOl1S. In tile channel of thetI1illster, ions increase due to the creation and neutralsdecrease by the ionization.an au. (1)_t+_tn.=+yn.nat AX t t Tlan au_Tl+----2!-n =-yn.n (2)at AX Tl 1tlwhere nj, 'f1n, Vj, V n, X, Y =1JR a = A 'V (J are tile ion andneutral densities, ion and neutral velocities, the distancefrom the anode and tile creation rate of ions, respectively.Here, a = 7T r 2, A, 'V, 1JR=Vj-Vn denote the cross section of. , . .tile collision, mean free pa1:l\ the collisional frequency andthe relative velocity between ions and neutrals, respectively..In tills case, the period 0.00011s and the frequency 9.1kHzare obtained from Fig.l.0\) \J GU \J Uo 0.0002 0.0004 0.0006 0.0008tFig. 1. Oscillation of the ion density depending on timeWe perfonn tile simulation ofthe oscillation oftile densityand the ion current on tile discharge iOluzation, and compareour results with tile e>"'}JeriInental ones[2]. Since tilefrequency and tile electric current ObtaiJled here coincidewith tile previous ones, our model interprets tile u1Stabilityof tile ion current shown Ul experiInental results. Wetherefore show tl1at when we decrease tile cross-sectiOlmlarea of the chamleL tile discharge current becomes stable.Moreover, it is pOUlted out to W1derstand the basic featuresof tile plasnm is sigrllficant. TIus ulvestigation tImsoffers tile fil1diJlgs on tile stabilization of tile disclmrgeinstability associated ,vitIl tile ion-neutral collision Ul tileHall tI1lUster ofthe spacecraft.References[1] Fife,J.M., Martinez-Sanchez,M and lSzabo, 33rdAIAAJASEMISAEJASEE JOUlt Propul. Conf p.l (1997) .[2] Mitsuboslu,M. and Nejoh,Y.N., Proc. 46th Space Sci.Tech. Symp. (CRL, Tokyo), p.147(2002).203

An Investigation of Spacecraft-Plasma Interactions - Plasmas Near the Thruster - Magnetically Confined Plasmas

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An Investigation of Spacecraft-Plasma Interactions - Plasmas Near the Thruster - Magnetically Confined Plasmas

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