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AD-A157 445UNCLASSIIEDGNEUTRAL BEAM INTERACTIONS WITH MATERIALS(J) MICHIGANUNIV ANN ARBOR COLL OF ENGINEERINGRGILGENBACH ET AL. 18 JUN 85 AFOSR-84-8i3820/IlfllllliIIh fI/Nlfllflflflflfifl.fEiEEEBBEEIBBiEiIIDIEEIhE
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*.*I .'REPROOMcI) AT GOVIN W ".IAnnual,nI. . .--"-ll lIProgress Report to:The Air Force Office of Scientific Researchfor the Project:I-Neutral Beam Interactionswith Materials(AFOSR 84-0130)IR.M. GilgenbachNuclear Engineering Dept.J. J. DuderstadtNuclear Eng. Dept. andDean, College of EngineeringR.S. OngAerospace Eng. Dept.DTICELECTEJune 1985Intense Energy Beam Interaction Laboratory" ,LA---7.%C 3APProved for public roloaslie-.,Ditrifbution Unlimiteds85 7 o0 -185:
I fOflhI0CV. ) AlIW.lv is uD qg -UNCLASSIFIED("'4T041S PAO&EqSCLA&SS PICA? 1OFREPORT DOCUMENTATION PAGEIunclassified.l.RSRCIEMRIG3. OISTRISUTI*NjAVAILAGILITY*2& SECURITY CLASSIFICATION AUTHORITY1%release, distribution unlimiteda. MONITORING ORGANIZATION REPORT NUMBR(SlPILROORMaNG ORGANIZATION REPORT NUMERP(S)1AFOSR84-0130 7&. NAME OF MONITORING ORGANIZATIONb. OFFICE SYMBOL11AME OF PEAPOIRMING ORGANIZATIONAir Force Office of ScientificRsacdf.,Igbe,University of MichiganWb ADDRESS #City. SUN &v UIP CoujS.ADDRESS (Ciuy. SM## ad SIP CodPhysical and Geophysical SciencesBolling Air Force Base, Washington,DCNuclear Engineering DepartmentAnn Arbor, MI 48109PU0NORGAN IZAT IONfiAFOSR84-0130OSSUdIftc ADDRESS" ECy. ta,andIPhysicalBolling AFB,!IB.PROCUREMENT INSTRUMEONT 1OV.TIFICATION NUNERSIP. OFFICE SYMBOLISO, NAME OFP PUNDINGdSPONSORINGI.TITLE 'Ieudapproved for publicUnclassified,21. OILCASIP ICAT IN90101INRADING SCHOULE%OF REPORTOFFPPUOO fOB.16I. SOUR0111ceZIP Co&)Geophysical SciencesWashington, DCftvncv cbmi"gAIIUTASKNo0.N.PROGRAMELEMENT NO.PROJECTNO.WODRK UNITAnnual Report.'Neutral Beam Interactions with Iftrig12. FPRSONAL AUTHORS)'ach nd J7. J .R. M. Glznrpa1 June 18POjLLTO32LgAnnualII5. P114. DATE OF RIPOR111T (Ifi. Me. a"136. TIME1COVERED13. TYPE OF REPORTIt cOUNT19851I. SUPPLEMIENTARY NOTATION1.CPOSUBJECT TERMS orCendnue on FagveATCD8Is.ifa.m'adielyOi.mINeutral beams, radiation signatures, beam-material interactionssue 014GROUSETRATI.Aeeon Noer If tneeOrv "d iouft tiIby blocS ma*rIAbstractannual report describes experimental and theoretical research1 hhiwihconcerns the interaction of neutral or ion beams with surfaceablation plasmas. This problem is of interest in the case of particlepenetration to outgassing or ablating objects in a high va'cuum environment.* We have constructed a neutral beam-ablation plasma experiment which employslsaa dense altooidpnetygnrta Q-switched ruby laeother side)-'(continued020. DIST RI BUT IONIA VAI LAB LOTYVOP ABSTRACTUNCLASSIPISD/UmLimOTED1228%Dr.2 AMR AS RIPT. 0 OTIC USERS0Unclassified22b. TELEPHONE NoUMBERNAME OFP RESPONSIBLEK INDIVIDUAL(227Robert BarkerO FORM 1473, a3 APR21. ABSTRACT SECuRNITY CLASSIPICATIONEDITIONaOP ijAN 73 18 OBSOLETE.n-231j SFEUN.ASIIE
1IF-'ROINICMf Al VIVPANMU*;!PON*UNCLASSIFIEDgICUNSTV C*%SSPCAST@*40 T041PAGEE!I--The neutral beam is generated by a (5-20 keV) duopigatron ion source withExperimental results of beamcharge exchange neutralization cell.attenuation show excellent agreement with predictions based on availableIn studying the attenuation of the neutral beams wecross-section data.have considered primarily charge exchange processes although we areestimating the relative contributions of momentum scattering and impactionization. Line density values from a self-similar expansion model showgood agreement with attenuation data. Spectroscopic measurements of theablation plasma yield singly and doubly ionized lines.We have developed a one-dimensional computational physics code whichsimulates the ablation of a carbon target by a proton beam. This isaccomplished by coupling a sophisticated collisional-radiative equilibrium(CRE) ionization dynamics model, a one-dimensional, single temperature andfluid hydrodynamics model, and an energy deposition model. The totalpackage is then applied to simulating the beam-target interaction under avariety of beam conditions. Other applications considered include heatingdue to. inner-shell photon absorption and calculation of the amount of K.radiation emitted by the direct interaction of a beam proton with a targetatom.The basic approach involves coupling a one-dimensional hydrodynamicBecause thecode to an ionization dynamics and an energy deposition model.radiation emitted by the plasma is an important diagnostic tool, we havetried to model the ionization dynamics very carefully. This isaccomplished by developing an ionization dynamics model which considers alarge number of excited states and atomic processes.The atomic processes which are considered in our model are:1) collisional ionization2) three body recombination3) collisional excitation4) collisional de-excitation5) spontaneous emission6) radiative recombination7) dielectric recombination.We have developedcarrying electrons) inplasma approximation.which are likely to bea model for structured low Z projectile ions (those.cold (neutral) or ionized targets in the localSpecial attention has been paid to shell correctionsimportant in the energy regime of interest.Corrections to first Born calculations include polarization and Blochterms.S'V -i2
,10Annual Progress Report to:The Air Force Office of Scientific Researchfor the Project:"Neutral Beam Interactions with Materials"AFOSR84-0130R. M. Gilgenbach, J. J. Duderstadt, R. S. OngNuclear Engineering DepartmentThe University of Michigan,.AnnArbor, MichiganJune 1985I'.148109
CONTENTSI.Introductionp. 3Theoretical Progressp. 3a).4b)II.p. 3Computer Simulation of Ion Beam Target Dynamicsand Radiation Emissionp. 6Experimental Progressp. 18p. 18a)Neutral/Ion Interactions with a Laser AblationPlasmab)Duopigatron Based Experiments Concerning Neutral/IonBeam Interactions with Laser Ablation Plasmasp. 20c)::Stopping Power of Low-Z "Structured" ProjectileIons1)Beamline and Vacuum Systemsp. 232)Ruby Laser Systemp. 273)Beam Diagnosticsp. 294)Ion and Neutral Beam Probe Measurementsp. 295)Ablation Plasma Production and Diagnosticsp. 386)Beam-Plasma Interaction Experimentsp. 40Fabrication of an Applied-B Ion Diode for Febetronp. 46III. Graduate Students Supported Under this Contractp. 58IV.Publications and Doctoral Dissertations.p. 58V.Honors and Awardsp. 58Accession For-ITTIS GRA&IDTIC ability CodesAvail and/or].D t Spcial2*
IntroductionDuring the past year we have performed experimentaland theoretical research regarding the interaction of* "neutralbeams with independently generated ablationplasmas.Some of the results included in this annualreport were given in the 6 month interim report.We have,however, presented significant new data obtained duringthe second six months of this project.I.Theoretical ProgressIa. Stopping Power of Low-Z "Structured" ProjectileIonsWe have developed a model to calculate the stoppingpower of low Z "structured" projectile ions (those withbound electrons) in the local plasma approximation(LPA).The LPA averages a constant density free-electron stoppingpower expression over the target electron cloud.Theprojectile structure is accounted for through the screeningeffect of the bound electron distribution 22 .Binding effectsare introduced by comparing the high-velocity result with aBethe-like formula for partially ionized projectiles.3This formula is given by Kim and Cheng 3.We ignorelosses due to projectile excitation and extend the result tonext order term by the technique of Fano and Turner 4.inIt the9order to be able to account for shell effects.Theagreement with the LPA is very good provided the LindhardScharff binding parameteris introduced.Shell effects are likely to be important in the energyi 3
Jregime where projectiles can carry bound electrons into thetarget.For the bare ion case, in order to obtain agreementand experiment 6 , it had been necessary tobetween theory,:include the polarization (Z3)corrections.and Bloch ("Z4")For low Z projectiles, these contributionstend to cancel.Hence, the modeling here will not be asdetailed.theDeutsch 7 has given a compact formula forpolarization effect for bare ions.V'Since this contributionreplace thewe simplycollisions,distant chargefrom nucleararisesnet charge.with itsprojectileThe Bloch 8 correction arises from close collisions.Hence, it is tempting to leave the projectile nuclear chargealone, but this significantly overestimates the magnitude.Surprisingly, plausible results have been obtained byreplacing the nuclear charge with the net charge 9 though the0.soundness of such an approach has been questioned 10Wecontinue to search for the proper way to reduce thiscorrection due to the screening of the projectile.Target Ionization:As the target becomes ionized, free electronscontribute to the stopping power.This may be calculatedfrom our high-velocity expansion for bound electrons byreplacing the Fermi distribution for a degenerate gas witha Fermi-Dirac distribution of a nondegenerate gas withexpansion technique of Sigmund and Fu1 1 to structuredprojectiles.For the special case of bare ions, our4
. .--.-.--:--, -:- -:---,.- ,.1-:i:--,result agrees with a temperature dependent calculation ofDeutsch 12The remaining bound electrons will be reduced in numberand more tightly bound than the original neutral targetelectrons.This is partially accounted for in the LPA byusing appropriate wave functions 13 to describe the targetion electron distribution.The increased binding entersthrough the Lindhard-Scharff binding parameter (LSBP).Peek 14 was the first to recognize that the LSBP mustscale with the degree of target ionization in order to agreewith more detailed first Born calculations 1 5 .This scalingWithout it, the LPA waswas wholly empirical in nature.thought to break down for ionized targets.arguments 5 gave the LSBP a constant value.The originalHowever, thesearguments were based on a Thomas-Fermi (many-electron)picture of the atom, clearly not suitable for, say, a oneelectron ion.We have demonstrated that the appropriatescaling of the LSBP is observed when the Lindhard-Scharffargument 5 is repeated for a.one-electron ion.soundness of the LPA is strengthened.Thus, theThis affects both the"Z2" and the "Z3" stopping, both described by the LPA.The Blochcorrection will also be affected by theincreased binding since fewer collisions are likely to beclose encounters.However, the usual form of this term doesnot readily suggest ways to incorporate this effect.Modeling the Bloch correction in terms of the LPA ispresently being pursued.5."
I b.COMPUTER SIMULATION OF ION BEAM TARGET DYNAMICSAND RADIATION EMISSIONWe have developed a one dimensional computational physics codewhich simulates the ablation of a carbon target by a proton beam.Thisis accomplished by coupling a sophisticated collisional-radiativeequilibrium (CRE) ionization dynamics model, a one dimensional, singletemperature and fluid hydrodynamics model, and an energy depositionmodel.The total package is then applied to simulating the beam-targetinteraction under a variety of initial beam conditions.Otherapplications considered include heating due to inner-shell photonabsorption and calculation of the amount of Kradiation emitted by thedirect interaction of a beam proton with a target atom.The basic approach involves coupling a one dimensional hydrodynamiccodel to an ionization dynamics and an energy deposition model.Becausethe radiation emitted by the plasma is an important diagnostic tool, wehave tried to model the ionization dynamics very carefully.This isaccomplished by developing an ionization dynamics model which considersa large number of excited states and atomic processes.The atomic processes which are considered in our model are:1) collisional ionization2) three body recombination3) collisional excitation4) collisional de-excitation5)spontaneous emission6
"p.'-.,,6) radiative recombination7)* dielectric recombinationThese are incorporated into a set of rate equations which have the,.-2form: N(Z,J),,,,,[(NelN(Z-1,J")S(Z-1,J":Z,J) NeN (Z l,j')N.- 'dt[a(Z l,J' :Z,J) Ne (Z ,j' :Z,J)] Z N(Z,i)A(i,j) Ne i j N(Z,i)X -(iJ)i jNei jZ N(Z,i)X(i,j)]e -N(Z,j)[N S(Z,j:Z Ij') -eNe Ec(Z,j:Z-1,J")Ne(Z,j:Z-lj")] Z A(J,i) i jNee ZJX'. j ,E JX(j)J(j,i) Ne i where N(Z,J) is the population density of ion species Z in level J,3S(Z-l,j"; Z,j) is the collisional ionization rate (cm /sec) fromKN(Z-1,j") to N(Zj),ais the sum of the radiative and dielectronicrecombination rates (ar adr) in cm3 /sec, 8 is the collisional6recombination rate (cm /sec), A(i,j) is the spontaneous decay rate fromlevels i to j (1/sec), X(i,j) is the collisional excitation rate from itoj(o M/sec) and Xis the inverse reaction, collisionalde-excitation.(Note that since this is an equilibrium model, the left hand side of theabove equation is set equal to zero.).7-,-.1 ,",-.,.,-'' *."*"S. . "*".-", .,' '" ' .'. .- ,,'' ".,:*.'.-.:" .""-:' .' .".,.:.-.- ' ::: J "' .
.q.Schematically, the transitions and atomic processes considered inthis model are:L'i:':*N(Z , 0).(ZN(Z,0**O)Inthisset of coupledform the model consists of an infinitenon-linear equations, one for each available state of the ions and atomspresent inthe plasma.Fortunately,there are some methods andprocedures available for truncating the number of states.Though we arenot explicitly considering reduction in ionization potentials in thismodel, this phenomenon still sets an upper bound on the number of8", 7r.-7", v. ,.,.' ,' -,.' . - .;'i:.'*l.;.'' ' " t'' -;":.:''""-.' . " .%"' -".".'" %. .s.;" , . i'.''.' ".'L
%r V,.--rQ-rdiscrete quantum states available, i.e., we only need model those states"Umfor which E(n) E(Z) -AE(Z)."In our model we have considered only the 5-10 lowest states foreach ionization stage of carbon, including neutral carbon.Although alimited number of states have been considered in this model, they shouldstill be adequate for modelling the radiation field, specific heats andother equations of state information needed for the beam-targetsimulations.We have shown that the CRE model is applicable over the range ofplasma conditions considered in this work, i.e., for temperatures between1924-31 and 100 ev and ion densities between 10and 10cm . Both theCRE and LTE models give identical results for collisionally dominantplasmas.Similarly, the CRE model exhibits coronal behavior in the lowdensity limit.-This ability to model both collisional and radiativeplasmas is essential for a comprehensive ionization dynamics model.In addition, we investigated the time constraints placed upon theoverall simulation.In particular this consists of a consideration ofthe equilibrium aspects of the CRE model and the single temperature andfluid assumptions inherent in the hydrodynamics code.In all cases, wefound that the models are valid for the timing limitations encounteredin this study.We have calculated temperature, density and pressure profiles forevolving targets.We find that the deposition region heats very rapidlyuntil the processes of electron thermal conduction, radiative loss and-Ibeam deposition begin to equilibrate.i'-Once this occurs, we find thatthe pressure across the width of the deposition region remains fairlyduring the interaction.,'constant3'*.:'.i-.-.-,i." ?.-. .The pressure is responsible for9."'.-.- ., .-. ,.-.-.,-,.-.--.-.-.-,--'--i-.-?.-. ' i ,-, .i'i-; i -"-""'" .'i N
See the uwut fiurefor an *nlazood Viewthis region.*ofTIfM (lmuwucoesh)iZ1-00TARGET RADIUS (10-3 CM)iTOU RM S(1-3COLU5.m4aNI"10%1"WfymUnA
bibe*TIE seAVAEUIMICAG5AFNTOOFTXMUMSf10.6TAtlE (sec-1:::1:la,brTIEWpmAIINNSuclsnffa
!.".compression of the nondeposition region to densities as high as five toten times solid state.We provide diagnostic information that displaysvarious transition energies and power densities during the ablation.*.Inaddition, the partitioning of the deposited energy into internal,-kinetic and radiative components is examined.to a variety of plasma and beam conditions.V4have already been mentioned,This model can be appliedThe plasma restrictionsand the beam conditions must be such thatthe energy and power density is sufficient to heat the target to atleast several ev (1 ev represents the lower bound of the ratecoefficient table).An examination of the results of our parameter study suggests thedirection one might take in order to tailor the energy partitioning ofthe radiation field or ablation region for a specific application.example,ifcarbon isto be used as a x-ray laser pump,Forthen one mightwant to optimize the radiation conversion efficiency or the shape of theemission profile.,. *.-:be as large as 90%.!*;In our work, we find that conversion efficiencies canWe also find that the thermal emission profile isdependent upon both the energy and power density of the beam.This isillustrated by the observation that the hardness of the radiation field-can be increased by either using less energetic protons and maintainingthe same power density or else increasing the power density.parameter study also categorizes the dependence of internal, kinetic and,-Theradiative energy upon beam power density and proton energy.Theradiation field is further divided into relative contributions of line,-.recombination and bremastrahlung radiation.We also investigated the effects of including the inner-shell photonabsorption process.%'a.This is the only radiation transport we considered12
%'-,t, 9PARAMETER STUDY(Power density is 1012 v/cm 2)PS'ENERGY"PARAMETERS1INITIAL IONENERGYMevINITIAL IONENERGY2 MevINITIAL IONENERGY3 MevIENERGIES IN UNITS OF (103 J/CM 2 1 AND"OF TOTAL BEAM ENERGY) ARE 1.3(14%)(27%)(14%)(14%)LINE SPECTRUM ENERGIES (% OF RADIATIVE ENERGY)E" 10ev10 E 20ev20 E 60ev60C.l100 E 200ev3%15%31%200 E 350ev****00E 350ev**060 E ATION SPECTRUM ENERGIES (% OF RADIATIVE ENERGY)E 10ev10 Z 20ev20 E 60ev60 E 100ev100 E 200ev200 E 350evl.-E **00Ionization energy is included in internal energy . 5%13%6%
PARAMETER STUDYv/ca 2Paver density is 101PLASMA *ENERGY"PARAMETERSINITIAL IONEEGYIINITIAL IONENERGYINITIAL IONENERGY2 Mev3 MevevENERGIES IN UNITS OF (105 3/Q 2 ) AN(%OFTOTAL BEAM ENERGY) ARE 100%)(10%)( 5%)(85%)9.0.45.478.2(100%)C 5%)(5%)(91%)9.0.52.458.1IONIZATION.2(2%).17 ( 2%).18LINE2.3 (25%)2.6 (29%)1.5RECOMBINATION4.8 (53%)4.1 (45%)3.9BREMSSTRAHLUNG.60 ( 7%)1.5 (17%)2.6LINE SPECTRUM ENERGIES (% OF RADIATIVE ENERGY)(100%)( 6%)(5%)(90%)( 2%)(17%)(43%)(29%)E 10ev10 E 20ev20 E 60ev60 100ev100 E 200ev200 350ev 350ev"6%11%8%14%14%11%4%3%RE,CBINATION SPECTRUM ENERGIES (% OF RADIATIVE ENERGY)9 10ev10 3 20ev20 3 60ev60 100ev100 200ev*200 Z %Ionization energy is included in internal energy
41inour otherwise "optically thin" model.The results of the study showthat as much as 105 of the radiation field can be absorbed by theinner-shell process.Although, for an optically thick application thisvalue would be reduced because of competition with valencephoto-processes, it still represents an important absorption mechanismfor recombination radiation.An examination of the temperature, densityand pressure profiles show that inner-shell photon absorption primarilyaffects the temperature and density profiles of the ablation region.The nondeposition region appears t
RGILGENBACH ET AL. 18 JUN 85 AFOSR-84-8i38 UNCLASSIIEDG 20/ N IlfllllliIIh f I . June 1985 ELECTE" ,LA-- Intense Energy Beam Interaction Laboratory C 3 APProved for public roloas . agreement with the LPA is very good provided the Lindhard-Scharff binding parameter is introduced. Shell effects are likely to be important in the energy .
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