An Overview of Laser-Driven Magnetized Liner Inertial Fusion on OMEGA

Transcription

1 An Overview of Laser-Driven Magnetized Liner Inertial Fusion on OMEGA 4 compression beams MIFEDS coils B z ~ 1 T Preheat beam from P9 1 mm Ring 3 Rings 4 Ring 3 Target support Fill-tube pressure transducer J. R. Davies University of Rochester Laboratory for Laser Energetics 46th Annual Anomalous Absorption Conference Old Saybrook, CT 1 6 May 216 1

2 Summary Laser-driven magnetized liner inertial fusion (MagLIF) is being developed on OMEGA to study MagLIF scaling A energy scaled point design for laser-driven MagLIF on OMEGA has been developed that is 1 smaller in linear dimensions than Z targets* The key elements of preheating to >1 ev and uniform cylindrical compression at ~1 km/s have been demonstrated in experiments The first integrated laser-driven MagLIF experiment will be carried out later this year E24972 * S. A. Slutz et al., Phys. Plasmas (21); M. R. Gomez et al., Phys. Rev. Lett (214); P. F. Schmit et al., Phys. Rev. Lett (214). 2

3 Collaborators D. H. Barnak, R. Betti, E. M. Campbell, P.-Y. Chang, 1 G. Fiksel, 2 J. P. Knauer, and S. P. Regan University of Rochester Laboratory for Laser Energetics A. Harvey-Thompson, K. J. Peterson, A. B. Sefkow, D. B. Sinars, and S. A. Slutz Sandia National Laboratories 1 Currently at National Cheng Kung University, Taiwan 2 Currently at University of Michigan 3

4 MagLIF is an inertial confinement fusion (ICF) scheme using magnetized preheated fuel to allow for cylindrical implosions with lower velocities and lower convergence ratios than conventional ICF * Laser entrance hole with CH foil Laser entrance hole with CH foil Laser beam Axial field compressed by implosion 5 to 1 mm Azimuthal drive field Axial magnetic field Liner (Al or Be) Cold DT gas (fuel) Laser-heated fuel Start of liner compression Liner unstable but sufficiently intact Compressed fuel at fusion temperatures An axial magnetic field lowers electron thermal conductivity, allowing for a near-adiabatic compression at lower implosion velocities and confines alpha particles, allowing for a lower areal density Laser preheating to ~1 ev makes it possible for >1 kev to be reached at a convergence ratio <3 I2185c *S. A. Slutz et al., Phys. Plasmas 17, 5633 (21). 4

5 A point design for laser-driven MagLIF on OMEGA has been developed by scaling down the Z point design* by a factor of 1 in drive energy 4 compression beams SG2 phase plates up to 15.8 kj in 1.5 ns Preheat beam from P9 2- phase plate up to 395 J in 1.5 ns 1 mm MIFEDS** coils B z ~ 1 T Target support Fill-tube pressure transducer r (mm) Dr (mm) r/dr Ring 3 Rings 4 Ring 3 t fuel (mg/cm 3 ) B (T) T (ev) V imp (km/s) Convergence ratio T max (kev) Z (DT) OMEGA (D 2 ) TC12449a *S. A. Slutz et al., Phys. Plasmas 17, 5633 (21). **MIFEDS: magneto-inertial fusion electrical discharge system 5

6 The first two shot days were supported by the Laboratory Basic Science (LBS) program and Sandia National Laboratories (SNL) Laser entrance foil only targets (1.84 polyimide) Soft x-ray emission calorimeter Beam 46 Full targets Beam 25 3 (24.8 ) 25 ( ) H17C (16.6 ) Time-resolved spectra 3 (24.8 ) 25 ( ) H17C (16.6 ) Time-resolved spectra soft x-ray emission Soft x-ray diagnostic window optical emission Beam 25 3 (24.8 ) 25 ( ) H17C (16.6 ) Time-resolved spectra soft x-ray emission TC12451a Empty cylinders were used for compression-only shots 6

7 Foil transmission exceeds 5% with no backscatter from the gas and less than 1% sidescatter of transmitted light Intensity (MW/cm 2 ) Backscattered intensities measured for a full target and a foil Cylinder 25 Cylinder H17C Cylinder 3 Foil 25 Foil H17C Foil Power (TW) Total transmitted and backscattered powers calculated from two foil shots % forward transmission.8 Laser % absorbed 8.7% sidescattered transmission.5% backscattered Time (ns) Time (ns) Backscatter from foils and from full targets are very similar and contain a negligible amount of the laser energy. TC12456a 7

8 Three-channel soft x-ray imaging of the side window shows a gas temperature of >1 ev Transmission ( 1 22 cm 2 /ster) Soft x-ray framing camera (SXR) response Channel 3 Channel 1 Channel Photon energy (kev) SXR is not absolutely calibrated so it gives two channel ratios Used Spect3D to generate channel ratios for a range of gas and wall temperatures and densities (assumed uniform): four free parameters to fit the 2 channel ratios With the constraint T gas > T wall, one can determine T gas > 1 ev Channel 2/Channel Lower bound solution ns T gas = 17 ev Shot 2 Shot 3 T gas = 1 ev Shot Wall temperature (ev) T gas = 5 ev TC12574a According to 1-D models there is a preheat threshold of 1 ev. 8

9 X-ray emission recorded by Dante shows window, gas, and wall heating B52 Dante view 1 mm.54 mm Volume that Dante sees Diode (V) Channel 6 (9 to 98 ev) Foil only Cylinder with B = Signal from gas and wall Signal from foil Cylinder with B = 15 T Time (ns) TC12575a 9

10 Two-dimensional hydrocode predictions are in reasonable agreement with Dante measurements Channel 2 Channel 6 Signal (V) E = J E = J FLASH E = 2 J Signal (V) Time (ns) Time (ns) TC12575b 1

11 Streaked optical pyrometry (SOP) of the cylinder surface demonstrates energy coupling to the central.8 mm SOP view.8 mm Shield Laser Distance from laser entrance hole () Streaked optical pyrometry image Inner surface heats up Blanking Outer surface heats up Shock breakout Time (ns) E

12 The implosion of empty cylinders with rings 3 and 4 was measured separately using x-ray framing cameras Laser power (TW/cm 2 ) Intensity on target Position of peak x-ray self-emission Ring Ring 4 5 Ring z (cm) R () 4 3 Ring Time (ns) Ring 3 only t = 2.55 ns (end of laser pulse) Ring 4 only 52!19 V ring3 = 124.3!4. km/s 312!11 V ring3 = 178.1!1.2 km/s E24974 Overlap rings 3 at center and drive the ends with rings 4 12

13 A nine-shot day program is now being suported by the Advanced Research Projects Agency-Energy (ARPA-E) 1. Optimize ring-3 and ring-4 energy balance without preheat (1 Sept 15) 2. Complete optimization of ring-3 and ring-4 drive and reduce shell thickness without preheat (24 Nov 15) 3. Optimize preheat timing and vary preheat energy (19 July 16) 4. Complete B/no-B and preheat level dataset (22 Sept 16) 5. Measure axial B-field evolution 1: proton probing with D 3 He backlighter using H 2 fill to avoid proton production from target 6. Axial B-field evolution 2: use OMEGA EP if D 3 He is unsuccessful or extend dataset 7. Complete initial B-field scan including a higher value, if possible, with two MIFEDS and/or transformer coils (under development) with preheat 8. Fill-density and shell-thickness scans with B and preheat 9. Contingency: fill in missing data, address unforeseen issues, or extend dataset E

14 Compression-only shots have shown that axial uniformity can be controlled by beam balance and a.7-mm-long region can be compressed at >1 km/s r Sample x-ray framing camera (XRFC) Radius () of peak x-ray self-emission at 2.55 ns (end of laser pulse) z r () % ring 3 6 9% ring 3 8% ring 3 (r 43.8 ) z () 4--thick shells with 12 kj in 2.5 ns TC12532a 14

15 Hot-core formation and expansion have been observed with side-on x-ray framing cameras to 2.25 ns thick shell with 13.2 kj in 2 ns E

16 Hot-core formation and expansion have been observed with side-on x-ray framing cameras to 2.55 ns thick shell with 13.2 kj in 2 ns E

17 Hot-core formation and expansion have been observed with side-on x-ray framing cameras to 2.7 ns thick shell with 13.2 kj in 2 ns E24977a 17

18 Hot-core formation and expansion have been observed with side-on x-ray framing cameras to 2.95 ns thick shell with 13.2 kj in 2 ns E24977b 18

19 End-on x-ray framing-camera images show core emission earlier and a pentagonal structure to the shell Shadow of uncompressed end 2. ns 2.25 ns thick shell with 13.2 kj in 2 ns E

20 End-on x-ray framing-camera images show core emission earlier and a pentagonal structure to the shell Shadow of uncompressed end 2. ns 2.25 ns thick shell with 13.2 kj in 2 ns E24978a 2

21 End-on x-ray framing-camera images show core emission earlier and a pentagonal structure to the shell Emission from laser-heated plasma 2. ns 2.25 ns thick shell with 13.2 kj in 2 ns E24978b 21

22 End-on x-ray framing camera images show core emission earlier and a pentagonal structure to the shell No emission from cold gas inside shell 2. ns 2.25 ns thick shell with 13.2 kj in 2 ns E24978c 22

23 End-on x-ray framing-camera images show core emission earlier and a pentagonal structure to the shell Shock convergence heats gas 2. ns 2.25 ns thick shell with 13.2 kj in 2 ns E24978d 23

24 The pentagon corresponds to the azimuthal beam distribution in ring 4 and can be removed by repointing Standard beam distribution Direct laser power deposited (TW/cm 2 ) Uniform beam distribution Azimuthal angle ( ) z (cm) P laser (direct) E

25 A 3~ beam from P9 using Beam 35 is being implemented for preheating Current P9 system provides 2~ or 4~ using Beam 25 2~ has too low a critical density; 4~ has no diagnostics and no phase plate Beam 25 is required for compression A project to move Beam 35 at 3~ into P9 is underway First use date is 19 July 216 Current capabilities will be maintained P9 New 3~ lens Periscope (moveable) Final mirror Beam 35 Carts for 2~ and 3~ pickoff and final mirrors E

26 Summary/Conclusions Laser-driven magnetized liner inertial fusion (MagLIF) is being developed on OMEGA to study MagLIF scaling A energy scaled point design for laser-driven MagLIF on OMEGA has been developed that is 1 smaller in linear dimensions than Z targets* The key elements of preheating to >1 ev and uniform cylindrical compression at ~1 km/s have been demonstrated in experiments The first integrated laser-driven MagLIF experiment will be carried out later this year E24972 * S. A. Slutz et al., Phys. Plasmas (21); M. R. Gomez et al., Phys. Rev. Lett (214); P. F. Schmit et al., Phys. Rev. Lett (214). 26