UCRL-JC-12SS63PREPRINT

Supernova Hydrodynamics Experiments on Nova

B.A. Remington, S. G. Glendinnin& K Estabrook, R J. Wallace,R London, R A. Managan, A. Rubenchilq D. Ryutov, K. S. Budil,

J. Kane, D. Arnett, R. P. Drake, R McCray, E. Liang

This paper was prepared for submittal to theInternational Conference on Superstrong Fields in Plasmas

Varenna, ItalyAugust 27-September 2,1997

DISCLAIMER

This document was prepared as an account of work sponsored by an agency ofthe United States Government. Neither the United States Government nor theUniversity of California nor any of their employees, makes any warranty, expressor implied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privately owned rights.Reference herein to any specific commercial product, process, or service by tradename, trademark, manufacturer, or otherwise, does not necessarily constitute orimply its endorsement, recommendation, or favoring by the United StatesGovernment or the University of California. The views and opinions of authorsexpressed herein do not necessarily state or reflect those of the United StatesGovernment or the University of California, and shall not be used for advertisingor product endorsement purposes.

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Supernova Hydrodynamics Experiments on Nova

B. A. Remington, S. G. Glendinnin~, K. Estabrook, R. J. Wallace. R.London, R. ~. Managan, A. Ruben;hik, D. Ryutav; and K. S. Budil

Lawrence Livermom National Laboratory, P. 0. Box 808, Livermore,CA 94550

J. Kane and D. Arnett

Stewart Observatory, University of Arizona, Tucson, AZ 85721

R. P. Drake

University of Michigan, Ann Arbor, MI 48109-2143

R. McCray

University of Colomdo-Boulder, JILA, Boulder, CO 80309-0440

E. Liang

Rice University, Houston, Tezas 77251

Abstract.We are developing experiments using the Nova laser to investigate

(1) compressible nonlinear hydrodynamic mixing relevant to the first fewhours of the supernova (SN) explosion and (2) ejects-ambient plasma in-teractions relevant to the early SN remnant phase. The experiments andastrophysical implications are discussed. We discuss additional experi-ments possible with ultra-high-intensity lasers.

Two phases of cor=ollapse supernova (SN) evolution, the core hydrody-namic mixing in the first few hours and colliding plasmas during early SN rem-nant formation, (Arnett et aI. 1989; McCray 1993) are areas rich with possibili-ties for supporting laboratory experiments. We report hereon two experimentsutilizing the Nova laser(Kilkenny 1992) to create the relevant plasma environ-ment. We conclude with a discussion of a new class of astrophysical experiment- radiative fireball relevant to gamma-ray bursts (GRB) - potentially possiblewith ultra-intense, short-pulse lasers.

We start with a progenitor for SN1987A simiIar to that shown in Pig. lafrom Arnett [1996), and calculate the hydrodynamic evolution using the SNhydrodynamics code PROMETHEUS ( Pryxell et al. 1991; MiiIler et al. 1991).We will focus on the instabtities at the He-H interface. To econom.= on com-puting time, we model only Mr/I& a 5, depositing the explosion energy, E =1.5 x 1051ergs at M./I% =5. Thw launches a strong radbl shotk that reachesthe He-H interface (M,/NL = 6) after a transit time of about 100 sec. We show

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fm$m,i~=L<”:’=mr)x:~

Radius (101 2 cm)02468103214%618

Mass coordinate (MjMo)

Figure 1. supernova simulations in lD of SN1987A.

(a)- (b) PROMETHEUSvs HYADE.S

..-Position (pm)

Figure 2. Supernovahydrodynamicsexperiment,

the density and pressure profiles at a time of 4000 aec in Fig. 1b. Note that atthe HI+H interface (R = 1.0 x 1012cm), the pressure and density gradients arecrceaed, that is, VP. VP <0, such that the He }ayer is behrg decelerated by thelower density H layer. This situation is unstable to the R.ayleigh-Taylor (RT)instability and perturbations at the interface grow in time. (Fryxell et al. 1991;Miiller et al. 1991)

The experimental configuration adopted for these laser experiments is il-lustrated in F]g. 2a and is described in more depth eIaewhere (Remington etal. 1995; Kane et al. 199~ Peyser et al. 1995). Eight of the ten Nova laserbeams at a duration of 1 ns and total energy of 12 kJ are focused into a 3.0 mmlong, 1.6 mmdiameterAu hohlraum (cylindrical rrdation cavity) convertingto a .-u 190 eV thermal x-ray drive. The experimental package is planar, a 85pm Cu (p =8.9 g/cm3) foil backed by 500pm of CHZ (p= 0.95 g/cm3). A A= 200 pm wavelength, qo = 20 pm amplitude sinusoidal ripple is impcsed atthis embedded interface. The package is mounted across a hole in the hohlraumwall, so that the inner (smooth) side of the Cu sees the x-ray drive. Dk+gnoaisof the interface is through side-on x-ray radiography, using the remaining twoNova beams focused onto an Fe backlighter dmk to generate a 5 IISpulse of He+x-rays at 6.7 keV. In th~ side-on view, the opaque Cu appears as a shadow, andthe CHZ is essentially transparent.

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In Fig. 2b we show the results of modeling in ID with HYADES,(Larsen& Lane 1994) and PROMETHEUS. (Fryxell et al. 1991; Miiller et al. 1991)HYADES is a lD Lagrangian code with multigroup ra&ation transport andtabular equation of state (EOS), and PROMETHEUS is a 3D Eulerian PiecewiseParabolic Method (PPM) code using (here) an ideal gas EOS. We use a measuredradiation temperature, Tr(t) ~as the source input to HYADES, and achieve animpulsive shock acceleration, followed by a protracted dderation, qualitativelysimilar to the He-H interface in the SN. We do a high resolution HYADES run,including multigroup radiation transport, for the first 2.45 ns, at which time theshock is approaching the CU-CH2 interface. We then map the results to ID or2D PROMETHEUS. We compare the results for pressure and density at 20 nsfrom a continuous lD HY~ES run including radiation transport versus thatfrom PROMETHEUS (F]g. 2b). The mapping works well. Note, the pressuresfor the Nova experiment, 1-2 Mbar, are not too different from those of the SN(10-15 Mbar), as shown in Fig. lb, though the SN densities, are lower by a factorof about 103.

We consider the difference of scales between the SN and the Nova experi-ment. If we assume that the mixing is dominated by the RT instability, thenin the nonlinear regime, the fluid flow can be characterind by a spatial scaleof order the perturbation wavelength ~ and velocity of order the perturbationterminal bubble velocity %’BO( (g~) 1/2. Here g corresponds to the accelerationand we have assumed constant Atwood number. A hydrodynamic time scaleis then given by ~ = ~/vB = (A/g)112, and the hydrodynamics equations areinvariant under the scale transformation (Hecht et al. 1994; Alon et al. 1995)A + al A,g -+ a2gt and T + (al/a2)112~. We illustrate this transformation, usingcharacteristic scales taken from the simulations shown in Figs. 1 and 2. At 4000sec for the SN, the deceleration of the H*H interface is gsN = -1.5 x 104cm/s2,the density gradient scale length is LsN = P/VP = 8X1010 cm, and the dominantperturbation wavelength is approximated to be ~sN = 10LsN = 8 x 1011cm. Forthe Nova experiment at 20 ns we have gN- = -2.5x 1013cm/s2, ~NOw= 2x10-2cm, and a characteristic time interval of ~0= = 5 ns. The scale transformationis given by al = ~SN/~~ = 4 x 1013,and az = @N/~ow = 6 x 10-1O. The cor-responding hydrod namically equivalent time interval for the SN is then given

7by 7SN = (al/aZ)’ 2~ova = 1.3 x ld see, which is a reasonable time scale forthe SN instability evolution that we are investigating. This scale transformationis not precisely correct, because we have not taken into account the effects ofdecompression, finite layer thickness, and shocks. Nevertheless, the Nova exper-iment appears to sddress the nonlinear compressible hydrodynamics similar tothat at the H~H interface of a Type 11SN during the first few hours.

In Fig. 3 we show a 2D image from the experiment at 33 ns (Fig. 3a)compared with results from the 2D simulations at 30 ns (Fg. 3b). The ex-perimentally observed perturbation has evolved into the classic nonlinear” RTbubbleand-spike shape with peak-to-valley amplitude ~fl s 1, and there arefaint indications of Kelvin-Helmholtz roll-ups at the tip of the spike and alongits sides. For the simulations we use the same mapping scheme in 2D as we dldin ID, only now the CU-CH2 interface has a A = 200 pm wavelength, qO = 20~m amplitude sinusoidal ripple. By 30 ns the perturbation has grown with theopposite phase to an overall peak-to-valley amplitude of WW s 180pm s ~,

3

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Figure 3. Comparison of data with the simulations.

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Figure4. Simulationof RT growth in the nonlinear regime of a 2Dversus 3D single mode perturbation. (2D=dotted, 3D=solid).

as shown in Fig. 3b. The shape of the perturbation has changed from sinu-soidal to bubbleand-spike, indicating that the interface has evolved well intothe nonlinear regime. In Fig. 3Cwe show the evolution of the spike and bubblefronts, compared with the predictions from both PROMETHEUS and CALE,a 2D ALE code (Tlpton 1996). The locations of the 2D bubble front and spikefront are reproduced very well by both hydrodynamics codes.

We have very recently designed an experiment to illustrate the differences insingl.+mode RT growth betwesn 2D and 3D, as illustrated in Fig. 4. For targetfabrication ressuns, the target materials used were changed to CH(Br) for thedense material (p = 1.53 g/cm3) and CH1.lOOX foam for the lower densitymaterial (p = O.O7g/cm3). These densities were chosen to maintain the sameinflight Atwood number (w 0.6). The 2D perturbation was a single si”uwid, ~ =q.co.s(kx), with k=2rr/,1, and A = 200 pm//2 = 141 pm and q. = 20pm. The3D perturbation corresponded to crassed sinusoids,v = V. ccs(k,x) coa(kyy),with kx~ = 2rT/Ax,Y,where Ax= Ay= 200jtm and rfo= 20pm. Results from thesimulations in the nonlinear regime(t = 30 ns) for the 2D case are shown inFig. 4a and for the 3D case in Fig. 4b. The spike and bubble front trajectoriesare juxtaposed in Fig. 4c, showing that the perturbation spike grows - 50~omore in 3D. The effect for the bubble is Ieea, but again the bubble grows morein 3D. SimiIar effects have been obserwd by a number of other groups doing 3Dsimulations (Tryggvason & Unverdi 1990; Dahlburg et al. 1993, 1995; Hecht et

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Figure 5. The density, velocity, and pressure profiles for a super-nova ejects-stellar wind interaction. (Reproduced from Chevaher et al.1992)

al. 1995). Experiments will be conducted on the Nova laser in the near futureto test this prediction. We are now doing simulations to investigate whether asimilar effect occurs in the supernova.

Supernovae remnant formation is one of the classic problems of astrophysics.With SN1987A, we have for the first time the opportunity to watch the time-dependent dynamics of the early stages of SN remnant as it evolves. High-velocity supernova ejects sweep up the surrounding ambient plasma, left overfrom the stellar wind of the SN progenitor. At the contact discontinuity (theplace where the two plasmas meet), shocks are launched forward into the ambientplasma (“forward shock” ) and backward into the SN ejects (’reverse shock”),as illustrated with the lD profiles of density, velocity, and pressure shown inFig. 5a (from Chevalier et al. 1992). At the contact discontinuity (at r/Rs =0.77 in Fig. 5a), the pressure and density gradients have opposite signs, that is,VP. Vp <0. Consequently, the shocked circumstellar plasma (of lower densitybut higher pressure) acts to decelerate the shocked SN ejects (of higher densitybut lower pressure). Such a situation is hydrodynamically unstable due to theRayleigh-Taylor instability, with strong RT growth at the contact d-ntinuitypredicted from 2D simulations (Chevaher et al. 1992; Chevs&er & B1ondin 199&Borkowski et al. 1997). This mixing at the contact discontinuity smeam out thedensity profile, as illustrated in Pig. 5b (reproduced from Chevr&er et al. 1992).The details of what to expect when the SN1987A ejects impacts the ring nebulawill depend on the structure of both the projectile assembly and the ring. Rwould be highly beneficial to be able to test these models experimentally priorto the awaited collhion.

Hence, our second experimentk fwwed on Ming our Unde-ring of.the colliding plasma dynamics in a situation qualitatively similar to that of theejects of SN1987A. Our goal is to develop the experiment and model it withthe astrophysics codes used to make the prdlctions of the upcoming ejecta-circumstellar ring col~lon expected for shortly after the year 2000.

Our initial approach to experimentally simulate the eject~wind interactionhydrodynamics is shown in Figure 6a. We use about 20 kJ of laser energy at0.35 pm laser wavelength, in a 1 ns pulse, to heat a 3 mm long by 1.6 mm

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F]gure 6. (a) A schematic of the laser experiment. (b) A firreo.t at 6ns from the data showing a ID density profiles at 6 ns. (c) Profiles fromthe ID LASNEX simulation at 6 ns showing density (g/cm3), pres-

sure/100 (Mbar), ion temperature (keV), and velocity (x 108 cm/s).(d) Iecdensity contours at 14 ns from a 2D LASNEX simulation. Theejects is flowing into the foam from left tu right.

diameter cylindrical gold cavity (a hohlraum) tu a temperature of about 220eV. The x-ray flux ablates a CH plug (doped with Br to reduce the transmissionof higher-energy x-raya) which is mounted in a 700 pm diameter hole in thehohlraum. The ablation drives a very strong (.w 50 Mbar) shock through theCH(Br), ejectirig plasma at about 30 eV from the rear of the plug. This plasma(the ejects) expands and cools. The leading edge of the expansion is a high-Mach-number plasma flow (about Mach 10), although it is at well below soliddensity. The ejects impacts a 700pm diameter cylinder of Si02 aerogel foamlocated 150 pm away and having a density of 40 mg/cm3. [n response, theflowing ejects stagnates and a shock is driven forward into the foam (forwardshock), as well as back into the ejects (reverse shock).

We diagnose these experiments by x-ray backlighting at 4.3 keV (.% Hea)to obtain radiographs of the shocked matter. We show a profile of-In (exposure)w density from the data in Fig. 6b and from a LASNEX (Zimmerman & Kruer1975) simulation in Fig. 6c, both at t = 6 ns. In both the data and simulation,we observe a clear forward shock in the foam, a reverse shock in the ejects, anda contact dkwontinuity in between. l+om the simulation, we see that the shockbreaks out of the CH(Br) at about 2 ns, at which time the back edge of theCH(Br) is at a density of abotrt 2 g/cm3 (compr~ion of N 2), pressure of 45Mbar, and temperature of 30 eV. The foam is impacted by the ejects about 1

6

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“- . ..

(a)

0.00 5.0 10.0 15.0 Om <0 li.o li.otime(m) time(m)

Figure 7. I.mok-ahead simulations of a similar e.iecta-ambient Plasmain~raction experiment at a higher drive of Tr = ’300 eV. “

ns later, suggesting that the high velocity tail of the ejects is moving at w ISOpm/ns = 150 km/s. We also show in Figure 6C the pressure, temperature, andvelocity of the ejects-foam assembly from the LASNEX simulation at 6 ns, thatis, about 3 ns after the ejects first starts sweeping up the foam. The contactdiscontinuity is located at a pasition of about 560 pm in both the data andthe simulation, and the peak densities from the simulation on either side of thecontact discontinuity in the ejects (foam) are 0.65 g/cm3 (0.25 g/cm3). Thepressure is continuous across the contact discontinuity at a peak value of 3.sMbar, the peak temperature is about 50 eV, and the velocity of the projectileassembly is about 1 x 107 cm/sec.

The region near the contact surface at the front of the ejects is RT unstable(Chevalier et al. 1992; Chevalier& Blondin 1995; Borkowski et al 1997). This isillustrated in Fig. 6d for a 2D simulation of the laser experiment. In the latter,a seed perturbation of wavelength A = 50 pm and initial amplitude q. = l~mwas imposed on the surface of the foam. By 14 ns, strong RT growth of theperturbation well into the nonlinear regime is visible, due to the VP” Vp <0configuration at the contact discontinuity (which is indicated by the dashedcurve). Comparing Fig. 6d with Fig. 10 from Che@er et al. (1992), we con-clude that both the Nova experiment and the early SN remnant evolution accessroughly similar levels of nonlinear RT hydrodynamics. A similar conclusion canbe arrived at by comparing linear regime RI’ growth rates, atin- (e.g. Eq. 6 ofMiiller et al. 1991), with total duration Ak of the growth: l/rein- < Atti~for both cases. We intend to use this experiment to test the theories and modelsbeing used to pre&ct the behavior of SN 1987A, well in advance of the upcomingSN ejects-ring nebula impact.

As a ‘look-ahead” exercise, we have done simulations where the drive ra-diation temperature was increased from 220 eV to T, = 300 eV. Such a driveshould be routine on the National Ignition F?adity (NIF) laser currently beingconstructed at LLNL (Paisner et al. 1994; Lhdl 1995). Density profiles areshown at 2 ns intervals in Fig. 7a for a nominal simulation (solid) comparedto a simulation where ra&ation is turned off after 3 ns (dashed curve). Thecorresponding temperature profiles are shown in Fig. 7b. The radiation servesto dwtribute the heat more evenly behind the forward shock, smoothing out the

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density valley at the contact discontinuity. The effects of the radiation on the en-suing hydrodynamics will become more prominent at higher drive temperatures,lower target densities, and upon the multiple shock reflections that will occurwhen the forward shock impacts a surrogate higher density ring. Experimentswhere the hydrodynamics depends on correct treatment of radiation transportshould be possible on the larger NIF laser currently being built.

As impressive as they seem, supernovae no longer occupy the status of mostenigmatic phenomena of the universe. That title almost surely belongs to themysterious gamma-ray bursts (GRB) (Flshman and Hartmann, 1997; Tavani,1997; Meszaros and Rees, 1997). As described by Fwhman and Hartmann, on theaverage of about 3 times a day, powerful pulses of gamma rays can be observed,each corresponding to the emis40n in the span of seconds or minutes more energyour sun will emit in its entire lifetime. The phenomenon has resisted study, sincethe flashes come from random directions in space and seemingly vanish wihtoua trace. This all changed on Feb. 28, 1997. The Italian-Dutch Beppo-SAXstellite detected GRB 970228, which lasted some 80 seconds. Within 8 hrs,the same spacecraft trained an x-ray telescope to that location in the sky andfound a source of x-rays that was fading fast. Thereafter, ground based, andeventually the Hubble Space Telescope turned to this location, finding a rapidlyfading source. If GRBs are extragalactic, as most currently believe, the representthe most powerful explosions in the univserse, eclipsing even supernovae. Notsurprisingly, GRBs are the hottest topic in the astrophysics community.

Data is sparse, and theories and models abound (Tavani, 1997). Possibili-ties include the coalescence of compact stars, neutron stars, or black holes; failedsupernova newborn spinars; or special jet phenomena in distant galaxies. Butat the heart of essentially all models is a rapidly expanding relativistic, fire-ball dissipating its energy in internal (reverse) and external (forward) radiativeshocks. The GR13s are initially observed with the bulk of the radiation in the0.1-1 MeV range, and cool subsequently through the x-ray into the UV andoptical regimes. Such high initial photon energies carrying the bulk of the ra-diation energy is most easily explain by a small, exceedingly hot source, T N0.1-1 MeV. Lasers such as the PetaWatt laser (Perry reference) are observedto produce such temperatures by focusing 0.5 kJ down to a w 30 pm spot ina 1/2 pa pulse. Simulations of the interaction lead to a strong hemisphericalblast wave bdng lauched in the first 100 ps after the laser pulse that propagatesradially outwards. Such a blast wave may be observable in current experiments,and bear the generic characteristics of the external and internal shock modelsproposed to explain gamma-ray bursts. This presents an exciting opportunity toemploy state-of-th+art laser facilities such as the PetaWatt laser to investigateone of most enigmatic events of current high energy astrophysics, gamma-raybursts.

In conclusion, we are developing experiments to investigate (1) hydrody-namic instabilities relevant to core collapse supernovae in the first few hours, and(2) ejects-ambient plasma interaction experiments relevant to the early stagesof SN remnant formation. Initial results from both experiments look promising.

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