FRC FORMATION AND TRANSLATION EXPERIMENT AT AFRL

1. FRC FORMATION AND TRANSLATION EXPERIMENT AT AFRL C. Grabowski, D. Gale, B. Martinez, J. Parker, D. Ralph, and W. Sommars Science Applications International Corporation, 2109 Air Park Rd SE Albuquerque, NM 87106 USA J. H. Degnan, M. Domonkos, and E. L. Ruden Air Force Research Laboratory, Directed Energy Directorate, 3550 Aberdeen Avenue SE Kirtland AFB, NM 87117-5776 USA J. F. Camacho and S. K. Coffey NumerEx, 2309 Renard Place SE, Suite 220 Albuquerque, NM 87106-4259 USA G. Coulter Voss Scientific, Inc., 420 Washington St. SE Kirtland AFB, NM 87108-2737 USA S. C. Hsu, T. P. Intrator, R. M. Renneke, P. Sieck, W. J. Waganaar, and G. A. Wurden Los Alamos National Laboratory Los Alamos, NM 87545 USA Title � no addition comments needed.Title � no addition comments needed.

2. 2 ABSTRACT Over the past six years, the Air Force Research Laboratory in Albuquerque, NM has been working in close collaboration with Los Alamos National Laboratory on their field-reversed configuration (FRC) experiment, FRX-L. Through these joint efforts a second experiment has been designed and is now being assembled and tested at the AFRL. This new experiment has the goal of not only forming a plasma in a field-reversed configuration but also of translating it into an aluminum flux conserving shell (solid liner), where it will be subsequently heated through rapid compression of the liner. The FRC formation portion of this experiment has been designed to closely match the electrical properties of FRX-L so that FRCs of similar parameters will be formed. Likewise, though the translation portion of FRX-L is still currently under development, the AFRL translation section will be similarly designed to match that of FRX-L, as well. The design approach being taken to compressively heat the FRC relies on the experimental setup used during two earlier �deformable-contact� vacuum liner experiments1,2 that were performed with the Shiva Star Capacitor Bank in which the liner electrodes had 8-cm-diameter holes on their axes. Both tests were successful, allowing the ends of the 10-cm diameter, 30-cm long aluminum liner to stretch and maintain contact with the electrodes while the body of the liner glided radially inward to implode uniformly. As might be inferred from the three portions of the experiment (i.e., processes to be performed) that were described above � FRC formation, FRC translation from the formation region up to the liner, and adiabatic compression of the FRC in the liner � there are also three constituent systems in this experiment to carry out these tasks. This presentation focuses on the design and integration of the first two of these component systems. The status of each, with regard to assembly and recent test results, is discussed, along with the array of magnetic and plasma diagnostics that are being implemented in each area. Remaining tasks to be accomplished before a complete FRC formation, translation, and compression experiment can be performed are also outlined. Abstract � no additional comments needed.Abstract � no additional comments needed.

3. 3 EXPERIMENTAL GOALS FOR THE AFRL EXPERIMENT Duplicate (electrically) LANL�s FRX-L experiment Characterize the pulsed power system well enough to be able to reliably form FRCs with plasma parameters similar to those of the FRCs formed with FRX-L Demonstrate the ability to translate an FRC sufficiently far and through a liner electrode aperture Perform liner implosion experiments with an integrated formation, translation, and compression setup on Shiva Star to demonstrate fusion This experiment combines the knowledge base we have from the FRX-L FRC formation experiments at LANL and the �tall� (30-cm) liner implosion experiments performed at AFRL.This experiment combines the knowledge base we have from the FRX-L FRC formation experiments at LANL and the �tall� (30-cm) liner implosion experiments performed at AFRL.

4. 4 PLASMA PARAMETERS Present and Projected FRC Parameters3 In formation region of experiment n ~ 1017 cm-3 T ~ 100 � 300 eV Poloidal B ~ 2 - 5 T After solid liner compression n > 1019 cm-3 T ? several keV Poloidal B ~ 200 - 500 T Energy confinement time > 10 ms needed The initial plasma parameters indicated here are needed if we hope to obtain the parameters shown after liner compression, and these latter parameters are what are needed to initiate the D-D fusion reactions in the plasmaThe initial plasma parameters indicated here are needed if we hope to obtain the parameters shown after liner compression, and these latter parameters are what are needed to initiate the D-D fusion reactions in the plasma

5. 5 BACKGROUND Advantages of FRC�s for a fusion energy concept4: Simple cylindrical geometry High b (b ~ 1) and high power density ? compact system Translatable ? formation and adiabatic heating regions can be separated Natural separatrix diverter � isolation from walls, impurity barrier Some particular advantages for using the FRC plasma as opposed to some other plasma configuration.Some particular advantages for using the FRC plasma as opposed to some other plasma configuration.

6. 6 BACKGROUND (Cont.) How the FRC is formed5: How the FRC is formed � the formation scheme presently used with both FRX-L and our experiment.How the FRC is formed � the formation scheme presently used with both FRX-L and our experiment.

7. 7 ESTIMATED PULSED POWER AND FIELD COIL REQUIREMENTS Three banks required for FRC formation (with cylindrical Theta coil) Slow bank for Bias field (0.3 ~ 0.5 T) Fast bank to pre-ionize (PI) the D2 pre-fill (0.3 ~ 0.5 T, ~250 kHz) Moderately fast, high-energy Main bank for field reversal (3.0 ~ 5.0 T, ~3.0 �s risetime) For FRC translation to the liner region (and conical Theta coil for formation) three additional banks required Two slow banks for Cusp fields, applied at each end of the formation region (>0.5 T) One high-energy Slow bank for Guide fields (3.0 ~ 5.0 T) and Mirror field (>5.0 T) at the end of the liner This is essentially a list of the capacitor banks and the field coils they will be driving that are required to form the FRC plasma and then translate it into the liner. The approximate flux densities required by each of the field coils, and hence their current requirements from their banks, are also indicated.This is essentially a list of the capacitor banks and the field coils they will be driving that are required to form the FRC plasma and then translate it into the liner. The approximate flux densities required by each of the field coils, and hence their current requirements from their banks, are also indicated.

8. 8 STATUS OF PULSED POWER SYSTEMS Bias, PI, and Main banks are all operational FRC formation tests presently underway with these banks Cusp-I, Cusp-II, Guide/Mirror banks are in design and construction stage Bank status is given as well as a schematic diagram showing bank interconnections and the locations of the field coils that they are driving around the vacuum vessel. Note that not only are bank grounds lifted, but all power supply connections are also opened before firing the banks.Bank status is given as well as a schematic diagram showing bank interconnections and the locations of the field coils that they are driving around the vacuum vessel. Note that not only are bank grounds lifted, but all power supply connections are also opened before firing the banks.

9. 9 BIAS BANK Assembled with two cap bank modules, ~2.5 mF per module Switched with ignitrons 3.5 mH �Bias inductor� to isolate from PI and Main banks (soon to be decreased to 0.88 mH to allow a faster current rise time) The Bias bank parameters are given here.The Bias bank parameters are given here.

10. 10 PI BANK Single Maxwell 2.1 mF capacitor Switched with single rail-gap switch Oscillation frequency of ~230 kHz The high-frequency current (B-field) generates an E-field gradient that ionizes the D2 pre-fill in the vacuum vessel PI bank parameters are given here.PI bank parameters are given here.

11. 11 MAIN BANK Single Shiva Star bank module with caps turned sideways to reduce bank height Cupper = Clower = 72 mF Switched with quad set of rail-gap switches ~3.3 ms quarter-cycle rise time for the bank current Main bank parameters are given here. The bank is a modified Shiva Star bank module; the capacitors are turned sideways to reduce the height of the bank. As will be seen later, this is so that the bank can be moved under one of the Shiva bank arms.Main bank parameters are given here. The bank is a modified Shiva Star bank module; the capacitors are turned sideways to reduce the height of the bank. As will be seen later, this is so that the bank can be moved under one of the Shiva bank arms.

12. 12 The Main bank current is crowbarred near its maximum to extend FRC lifetime Comprised of quad set of rail-gap switches Theta coil and Main bank current loops through Crowbar switch have no shared volume to minimize modulation of the Theta coil current MAIN BANK CROWBARSWITCH Here are some details about the Main bank crowbar switch.Here are some details about the Main bank crowbar switch.

13. 13 AUXILIARY BANK TO DRIVE CROWBAR CLOSURE Because the Crowbar is triggered near Main bank current max, voltage across it is very low Once one rail-switch in the Crowbar begins to conduct, remaining voltage collapses Small bank (12 ?F) has been added in parallel to the Crowbar switch to try to apply voltage across it when it is triggered The problem with getting all four rail gaps that make up the Crowbar switch to trigger is brought up here. Having all four trigger consistently would be nice, not only for data reproducibility reasons, but the four-rail-gap-switch configuration provides the lowest inductance for the Crowbar path and results in the lowest modulation on the Theta coil current waveform. To hopefully get around this problem, therefore, an additional bank is being set up in parallel with the Crowbar switch to hopefully apply voltage across it at or just before the time it is triggered.The problem with getting all four rail gaps that make up the Crowbar switch to trigger is brought up here. Having all four trigger consistently would be nice, not only for data reproducibility reasons, but the four-rail-gap-switch configuration provides the lowest inductance for the Crowbar path and results in the lowest modulation on the Theta coil current waveform. To hopefully get around this problem, therefore, an additional bank is being set up in parallel with the Crowbar switch to hopefully apply voltage across it at or just before the time it is triggered.

14. 14 THETA COIL ANDVACUUM STAND Present Theta coil (horizontal orientation) has 4 single-turn segments; segment width is ~8.25 cm, 1-cm gap in between Two inner segments have inner radius of 6.16 cm; outer two segments have inner radius of 6.6.6 cm Quartz vacuum vessel inserted along the axis of the field coils; pre-filled with 10 ~ 100 mTorr of D2 before each shot As seen in the photo, the cable header for the Theta coil has been made fairly compact to fit under the center of the Shiva Star bank. The current design on FRX-L is flat and fan-shaped; for our experiment this matrix header will allow us to attach the 64+ cables from the Bias, PI, and Main banks in a more compact space.As seen in the photo, the cable header for the Theta coil has been made fairly compact to fit under the center of the Shiva Star bank. The current design on FRX-L is flat and fan-shaped; for our experiment this matrix header will allow us to attach the 64+ cables from the Bias, PI, and Main banks in a more compact space.

15. 15 DIAGNOSTICS Present diagnostic set B-dot probes along formation region axis for monitoring field profile and used with excluded flux calculation Flux loops around outside of quartz tube for excluded flux calculation Gated MCP camera 100 ~ 200 ns gate width minimum single frame provides visible light image of plasma profile at various times during formation The principle diagnostics we have in the formation region are discussed in this slide.The principle diagnostics we have in the formation region are discussed in this slide.

16. 16 DIAGNOSTICS (Cont.) Future diagnostic set Four-chord HeNe laser interferometer will allow measurement of the time history of plasma density at up to four radial or four axial locations Fiber optic light monitors can qualitatively provide time history of plasma density Hg line filter placed at end of fiber in front of PMT or photo diode A couple of the key diagnostics that we hope to add in the very near future are described here. There are many other useful ones, as well, but these will be most relevant as we prepare for a compression heating experiment.A couple of the key diagnostics that we hope to add in the very near future are described here. There are many other useful ones, as well, but these will be most relevant as we prepare for a compression heating experiment.

17. 17 RECENT DATA Short series of test shots to evaluate system and diagnostic performance have been taken with Bias current at ~110 kA (0.33 T), PI current slightly lower at ~75 kA (0.20 T), and Main bank current at ~738 kA (2.05 T) Main bank trigger time has been set at PI trigger time + 1 PI period (we plan to shift this to PI trigger time + 3 PI periods) MCP camera images have been obtained of both initial plasmas and FRC-like plasmas (see next two slides) Analysis of B-dot and flux loop data still in progress to determine excluded flux and (possible) separatrix radius More thorough experiments, with higher PI, Bias, and Main currents and varying pre-fill pressures, will be conducted shortly

18. 18 Plasma images taken during Bias-PI shots: Illustrate the appearance of the plasma during early formation Show a filamentary structure developing, as was also observed on FRX-L

19. 19

20. 20 FRC TRANSLATION � THE NEXT PHASE OF THE EXPERIMENT After the FRC is formed, it then must be translated into the liner The cylindrical Theta coil will be replaced with a conical Theta coil ? the Main bank discharge will not only form the FRC but also launch it into the translation region After formation, the FRC needs to be moved or translated up into the Aluminum liner. A Theta coil with a conical bore will allow the FRC to be pushed out of the formation region as the process of formation is nearing completion. After formation, the FRC needs to be moved or translated up into the Aluminum liner. A Theta coil with a conical bore will allow the FRC to be pushed out of the formation region as the process of formation is nearing completion.

21. 21 FRC TRANSLATION (Cont.) Mention is made here of the fields (and field coils) that need to be set up above the formation region to allow the FRC to be ejected from the formation region and subsequently travel into the solid liner where it will be trapped.Mention is made here of the fields (and field coils) that need to be set up above the formation region to allow the FRC to be ejected from the formation region and subsequently travel into the solid liner where it will be trapped.

22. 22 CUSP, GUIDE, AND MIRROR COIL BANK DESIGN Cusp and Guide/Mirror banks to be constructed from 1- or 2-mF capacitor modules Estimated capacitancs: Cusp I � 1 mF Cusp II � 1 mF Guide/Mirror � 12 mF Individual modules switched with their own ignitron Cusp and Guide/Mirror bank parameters are given here. Cusp and Guide/Mirror bank parameters are given here.

23. 23 INTEGRATED FORMATION, TRANSLATION, AND COMPRESSION Here is a conceptual layout for the coils under the Shiva bank. An eleven-segment Theta coil is shown, with a conical taper in the inner radius of the segments. This will help launch the FRC upwards as its formation is completed. Guide coils (not shown) will guide it to the liner (through an aperture in the lower liner electrode). A mirror coil above the liner (also not shown) will slow the FRC in the liner, and then by that time the liner will be moving inward to compress the FRC.Here is a conceptual layout for the coils under the Shiva bank. An eleven-segment Theta coil is shown, with a conical taper in the inner radius of the segments. This will help launch the FRC upwards as its formation is completed. Guide coils (not shown) will guide it to the liner (through an aperture in the lower liner electrode). A mirror coil above the liner (also not shown) will slow the FRC in the liner, and then by that time the liner will be moving inward to compress the FRC.

24. 24 STATUS AND SUMMARY Vacuum and static pre-fill (50 mTorr) tests with all three banks required for FRC formation have been performed MCP camera images of the plasmas before and after compression have been obtained; with one exception the expected annular FRC profile has not been observed yet Presently modifying the Bias bank to increase its current delivery Also setting up an auxiliary bank across the Crowbar switch to drive switch closure and obtain reliable multi-gap operation Will perform additional formation tests with these new hardware changes at other pre-fill pressures and PI-to-Main Theta Bank timings LANL/FRX-L personnel are currently working on translation hardware design and fabrication Focus will be shifted to setting up translation hardware as soon as it is available; FRC translation tests are then expected begin shortly thereafter Summary � fairly self-explanatory.Summary � fairly self-explanatory.

25. 25 REFERENCES [1] J. H. Degnan, et. al., �Full axial coverage radiography of deformable contact liner implosion performed with 8 cm diameter electrode apertures,� Digest of Technical Papers: 15th IEEE International Pulsed Power Conference, pp 1239-1241, (2005). [2] J. H. Degnan, et. al., �Liner Implosion Performed with 8 cm Diameter Electrode Apertures Using Deformable Liner � Electrode Contact with Full Axial Coverage Radiography,� presented at the 2006 ICC Workshop, Austin, TX, February 13-16. [3] G. A. Wurden, et. al., �FRC Plasma Studies on the FRX-L Plasma Injector for MTF,� to be published in Proc. from the 20th IAEA Fusion Energy Conference, Vilamoura, Portugal, 2004. [4] M. Tuszewski, �Field Reversed Configurations,� Nuclear Fusion 28, pp. 2033-2092, (1988). [5] J. M. Taccetti, et. al., �FRX-L: A Field-Reversed Configuration Plasma Injector for Magnetized Target Fusion,� Rev. Sci. Inst. 74, pp. 4314-4323 (2003). References � no additional comments needed.References � no additional comments needed.