Z-Pinches in the Western Part of the United States

Size: px

Start display at page:

Download "Z-Pinches in the Western Part of the United States"

William Parker
6 years ago
Views:

1 Z-Pinches in the Western Part of the United States Robert A. Schill, Jr. University of Nevada, Las Vegas Dept. of Electrical and Computer Engineering 4505 Maryland Parkway; Box Las Vegas, NV (702) /4183 Lab: (702) FAX: (702) URL:

2 References and Special Thanks Special Thanks Dr. John Maenchen & Dr. David Johnson, Radiographic Physics Dept. - SNL Dr. Rick Spielman, High Energy Plasma Physics - SNL Dr. Bruno Bauer & Dr. Victor Kantsyrev, Physics, University of Nevada, Reno Dr. Frank Wessel, Physics, University of California, Irvine Dr. H.U. Rahman, Physics, University of California, Riverside Dr. John DeGroot, Physics, University of California, Davis Dr. David Scudder & Dr. Jack Schlachter, Los Alamos National Laboratory Gordon MacLeod & Sheldon Freid, Bechtel Nevada Interesting References ABCs of Zs: Z-Pinch Technology Workshop Proc., May 21-22,1998. G. Yonas, Fusion and the Z Pinch, Scientific American, Aug K. Matzen, Z Pinches as Intense X-Ray Sources for High-Energy Density Physics Applications, Physics of Plasmas, 4 (5), 1997, pp Ronald Riley, Jr., Instability Heating of Solid Fiber Z-Pinches, thesis, Univ. California San Diego, D. Mosher, Phy. & Tech. of Z-Pinches, US Part. Accel. Sch., Berkeley, CA, Jan Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 2

3 ZOT- Staged Z- Pinch Flow Diagram Differences Why All The Interest? NTF - HDZP II Issues? Z PINCHES Brief History. Mechanisms What? Motivation? Components NTF - Nevada Terawatt Facility PBFA Z - Particle Beam Fusion Accel. Z ZOT - UC Irvine Sandia Nat. Lab- PBFA Z Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 3

4 Z-Pinch Effect Z-Pinch Geometry Plasma column Large current flow along its longitudinal axis Mechanism Current generates a large magnetic field Magnetic field in turn interacts with the local current By a Lorentz force (J x B), radial confinement or a radial compression Magnetic energy concentrated near plasma surface; efficient Instabilities - Currents seek paths of low inductance di/dt = V/L; Coaxial geom. with rigid return -- L ~ ln(r c /r) NOTE: NO External Coils!!! SIMPLICITY!?!? Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 4

5 Graphical Picture of the Z-Pinch Effect J x B B I Plasma J x B Z-Pinch Mechanism B Rigid Return Conductor I r I r c Plasma Z-Pinch Coaxial Geometry Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 5

6 Artist s View of the Radiation from a Z-Pinch Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 6

7 Brief Historical Background 1934 Bennett -- (Bennett Pinch - Equilibrium) W.H. Bennett, Magnetically Self Focusing Streams, Phys. Rev. 45, (1934), p Plasmas thermal and magnetic pressures are balanced. Around 1950; Pinch Exp. for B-Confined Fusion Easy to build & operate but NOT a promising approach Testbed for plasma physics and plasma diagnostic dev. Niche in Material Radiation Studies Z-Pinch Classifications (Non-Equilibrium Pinch) Shock-Heated Z Pinch Resistive Heated Z Pinch Gas-Embedded Z Pinch Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 7

8 What s the Problem? Early Shock-Heated Pinch Exp. (Snowplow) Low density gas & large pulsed voltage supplied by Inductive storage device Capacitive storage device Required electric field needed ~ 1.6 MV/m Achieved only ~ 0.1 MV/m FLASH OVER Problem - surface becomes ionized by high voltage allowing current to arc & hence short out Early Resistively Heated Pinch Experiments Current carrying electrons being slowed by ion collisions Resistance ~ T -3/2 ; less effective at high temperatures Simple pinch is unstable Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 8

9 What s the Problem? (conti.) Early Gas Embedded Z Pinch Z-pinch is initiated in a narrow column immersed in a medium of neutral gas (~1960) Inhibit wall impurities in the plasma Suppress some instabilities by inertially coupling the pinch to the ionized corona around the pinch Column expansion was driven by an accretion of neutral gas surrounding the pinch which increased the pinch line density and cooled the plasma (~1982) Suggested solution was to increase the current rise rate Summarized Major Problems in Early Days Instabilities -- non-uniform compression for req. time scale State of the art in pulse power not mature Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 9

10 Z-Pinches Throughout the United States Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 10

11 Motivation & Goals Driving Z-Pinch Exp. Mid 1960 s to 1990 s Limited power output for fusion race TW ( mid 1960s) Focus on optimizing subkiloelectron-volt X-ray output (Nuclear weapon) Radiation studies on materials & electronics Radiation-Materials & Stockpile Stewardship - Present 1-5 kev Spectral region: radiation-material interaction studies Simulate different stages of a nuclear explosion Inertial Confinement Fusion [ICF](Origins 73) - Present Emphasis - generation of softer X-rays that can be thermalized Pulse power - charged particles (electrons 70s, ions 80s, X-rays 90s) Ablator physics and radiation symmetrization experiments Applications in Shock Physics & Astrophysics - Present Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 11

12 Specific Energy Densities Explosives Bituminous Coal Natural Gas Crude Oil D-T Fusion 4 x 10 3 J/gm 22 x 10 3 J/gm 35 x 10 3 J/gm 36 x 10 3 J/gm 2 x J/gm Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 12

Fusion Process Forcing together Deuterium and Tritium nuclei Fuse into a form of Helium Emits large amount of energy Pellet must be squeezed uniformly

13 Fusion Process Forcing together Deuterium and Tritium nuclei Fuse into a form of Helium Emits large amount of energy Pellet must be squeezed uniformly to high density for a fusion reaction to ignite and burn - Major Problem Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 13

TUNGSTEN WIRE ARRAY SECONDARY (FUSION FUEL) HYDROGEN BOMB PRIMARY HOHLRAUM PROPOSED

14 ICF Uses the Principle of the Hydrogen Bomb PRIMARY (FISSION DETONATOR) PRIMARY HOHLRAUM FOAM RADIATION CASE SECONDARY HOHLRAUM RADIATION DEUTERIU M TRITIUM PELLET TUNGSTEN WIRE ARRAY SECONDARY (FUSION FUEL) HYDROGEN BOMB PRIMARY HOHLRAUM PROPOSED FUSION REACTION CHAMBERS Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 14

The Inertial Confinement Fusion Concept Laser energy Laser Fusion Blowoff Inward transported thermal energy Atmosphere formation Laser beams rapidly heat the surface of the fusion target forming a

15 The Inertial Confinement Fusion Concept Laser energy Laser Fusion Blowoff Inward transported thermal energy Atmosphere formation Laser beams rapidly heat the surface of the fusion target forming a surrounding plasma envelope. Compression Fuel is compressed by the rocket-like blowoff of the hot surface material. Ignition During the final part of the laser pulse, the fuel core reaches 20 times the density of lead and ignites at 100,000,000 o C. Burn Thermonuclear burn spreads rapidly through the compressed fuel, yielding many times the input energy. Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 15

Inertial Confinement Fusion (ICF) Requirements Pulsed Power Fusion X-rays vaporize outer layer of fuel pellet which bursts outward and imparts inward momentum to the hydrogen fuel.

16 Inertial Confinement Fusion (ICF) Requirements Pulsed Power Fusion X-rays vaporize outer layer of fuel pellet which bursts outward and imparts inward momentum to the hydrogen fuel. Pellet implodes to 1 / 1000 to 1 / 10,000 of its original volume, fusion begins as temperature reaches 120 million degrees or more. Wavefront of burning hydrogen expands outward and cools until fusion ceases. Ignition Requirements - Laser or Pulse Power 500 TW 2 MJ of X-ray radiation at 3 million degrees 4 ns Pellet size ---. Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 16

17 Fusion Experiment Alternatives Magnetic Confinement -- Tokamak Magnetic field confines the energy and particles (traps hot deuterium-tritium plasma statistically long enough for fusion) International Thermonuclear Exp. Reactor (ITER) - ~$6 to $10 B Break-even? - Techn. and political diff. (US, Japan, Europe, Russia) Inertial Confinement -- Laser Fusion Inertia confines the energy and particles (lasers used to heat the fusion fuel, blow-off results causing the pellet to implode) National Ignition Facility (NIF) - ~$1.2 B Ignition - 0.1% to 0.5 % equivalent efficiency due to laser technology Magnetic Insulation - Inertial Confinement -- Z Pinch B-field confines the energy and inertia confines the particles X1 Facility - ~$0.4 B (Note: Z s equiv. eff. is 15%; X1 s equiv. eff.?) HIGH YIELD - fusion energy output >>energy input to the system Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 17

18 US Z-Pinch Programs Directed Towards Weapons & ICF R&D Diagnose Intense X-Ray Sources DOD & DOE Nuclear Weapons Effects Sim. (NWES) X-rays in the 1 kev and above regime to study transient response and damage due to exo-atmospheric nuclear bursts DOE Weapons Physics (WP) and ICF Programs Soft X-rays below 1 kev Radiation transport and trapping Equation of state Opacity properties of high energy density matter X-ray Diagnostics Study initiation and evolution of imploding pinches-optimize X-ray performance Material response to X-ray heating Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 18

19 Z-Pinch Advances at Sandia National Lab. Saturn (1996) Input: 10 MA, 20 TW Out: 40 TW (90 wire array) PBFA Z or Z Input: 20 MA, 50 TW, 25 TW/cm 2, few ns Output: ~ 3MJ, 290 TW 1.8 million deg. (~233 ev) X1 (High yield) Input: 60 MA, 150 TW, 75 TW/cm 2, ~10ns Output: 16 MJ, 10 3 TW 3 million deg. (~390 ev) Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 19

20 Cartoon Picture of PBFA-Z or Z Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 20

21 PBFA-Z or Z Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 21

22 Building a Wire Array - Close-Up View Wire Array - Single/Double ~1/10 th Dia. human hair 0.7 microns thick Array dia. ~ shot glass Wire Material Trial & error approach Al, Ti, Cu, W (Tungsten) K Shell Rad. & Rad. Emissivity Wire Placement Symmetry - crucial Small interwire spacing - cont. plasma shell Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 22

23 Experimental Setup of Double Nested Wire Arrays Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 23

24 Close-Up View of a Double Nest Wire Array Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 24

25 The Hohlraum - Vacuum Hohlraum Radiation chamber-x-ray oven Composite -Gold Coated Chamber High Z (atomic number) lined material Secondary Hohlraums - Physics Factories Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 25

Target Concepts for X1 - Hohlraum Types Dynamic Hohlraum (a) High Z imploding plasma shell stagnates on an inner low Z cylinder (foam) Plasma stagnates in the low Z Radiation permeates low Z Outer

26 Target Concepts for X1 - Hohlraum Types Dynamic Hohlraum (a) High Z imploding plasma shell stagnates on an inner low Z cylinder (foam) Plasma stagnates in the low Z Radiation permeates low Z Outer cooler regions of imploding plasma act as a high Z hohlraum wall Static-Walled Hohlraum (b) Dynamic hohlraum concept Min. capsule preheat at expense of x-ray drive eff. Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 26

27 Temperatures for 90 TW Pinch Power Computer Simulation Temp. (ev) Nonuniformity: due to sec. hohlraum Active Shock Breakout Diagnos. Measure nonuniformity of rad. field VISAR - Velocity Interferometry Al/LiF VISAR sample ~ 1.2 Mbars Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 27

28 Magnetically Insulated Vacuum Transmission Line - MITL High E-field vacuum systems emit electrons above ~ 250 kv/cm MITLs use the aximuthal magnetic field generated behind the leading edge of the high current power pulse to trap subsequent electrons into high efficiency (low loss) insulated flow This technique has been in constant use since the 1960s Anode Trapped Electron Sheath Pulse Front Electron Leakage Current C.L. Cathode Self- Magnetic Field Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 28

29 Standard Pulsed Power Components - Marx Banks, Intermediate Store, Pulse Forming Lines Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 29

30 Typical Closing Switch Pos. Water Oil Neg. SF 6 SF 6 Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 30

31 Equipotential Plots for Typical Closing Switches Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 31

32 ARCS AND SPARKS: OPEN SHUTTER PICTURE OF Z Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 32

X-Ray Pinhole Images on Nested Shot 180 1 ns intervals Experimental Data Pinch Compression 40 to 1 Tightest

33 X-Ray Pinhole Images on Nested Shot ns intervals Experimental Data Pinch Compression 40 to 1 Tightest pinch achieved on Z 1 mm diameter Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 33

34 Why does Z appear to be so Successful? What is its Secret to Success? Instability Problems Addressed? Pulse Power Problems Addressed? Secret to Success MITL - Magnetically Insulated Transmission Lines Extract the energy quickly, form of x-rays, before instabilities destroy the pinch geometry (FAST PINCH Machine) More thin wires in array allows for a more uniform plasma pinch Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 34

35 Nevada Terawatt Facility - University of Nevada, Reno High Density Z Pinch - II (HDZP-II) Existed at Los Alamos National Laboratory Moved to Reno in Summer 1998 Smaller Pinch - Couple of Terawatts Purpose Z studies at Sandia Limited to about 200 shots / yr Difficult to study pinch properties due to tremendous energies/powers generated Will fill a need for short-pulse, high power, low cost z- pinch with good diagnostics and high repetition rate. Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 35

36 High Density Z Pinch - II (HDZP-II) Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 36

37 HDZP-II Uses Three Stages of Pulse Compression Pulse power depends on the fast rise time of the current to the load. Induction effects hinder ideal pulse power operations and need to be minimized. Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 37

Staged Z-Pinch: University of California, Irvine Laboratory Facility Name: ZOT Projected to Achieve Break-even Fusion in a Compact Laboratory Device Two Dim codes suggest that ignition and near unity

38 Staged Z-Pinch: University of California, Irvine Laboratory Facility Name: ZOT Projected to Achieve Break-even Fusion in a Compact Laboratory Device Two Dim codes suggest that ignition and near unity yield is possible in a staged Z-pinch driven by 50 kj energy bank Definitive experiments have not been performed to date Slow Pinch Machine MHD instability time scales are important Low Cost, Low Maintenance Machine Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 38

39 to high power driver cathode (injector/ nozzle) What Is Meant By Staged? imploding liner (z-pinch) co-axial target (fiber target) anode Objective is Stable Energy and Power Compression Energy is coupled in stages Pulse power driver Imploding liner pinch Squeezes magnetic field lines Helmholtz coils Heats prepulsed DT fiber target Pinch is multi-shell configuration Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 39

40 Stabilization of Linear Pinch End-On Kerr Cell Photos Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 40

41 2-D Illustration of Staged Z-Pinch Facility and Discharge-Load Region Capacitor Bank Cryogenic Extruder High Pressure Gas Valve To Cryogenic Extruder H.V. Interface Rail Gap Switches Bz Coils Diagnostic Windows High Density Plasma Injector Vacuum Pumps High Pressure Gas Valve 16 Plasma Gun Array High Density Plasma Injector To Vacuum Pumps Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 41

42 3-D View of Staged Pinch Facility 3 m Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 42

43 Vacuum Load Region Underside of Staged Z Device Z-Pinch Vacuum Chamber Anode-cathode gap is 15 mm I sc =2 MA Quarter period rise time=1.8 µs Vacuum Pumps Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 43

44 Upper Deck Load Region Maxwell Rail Gap Switches Plate Transmission Line (1.25 m x 2.0 m) 6.4 mm thick Al plates Insulated 1.8 mm thick mylar film Capacitor Banks 2 sets of Cap. banks each consisting of ten 2.5µF, 50 kv Cap. Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 44

Cryogenic Extruder Deuterium Fibers are Extruded Deuterium freezes at 14 K In vacuum it can live at room temperature Transparent to room temperature infrared Fiber diameters

45 Cryogenic Extruder Deuterium Fibers are Extruded Deuterium freezes at 14 K In vacuum it can live at room temperature Transparent to room temperature infrared Fiber diameters ~110 to 130 µm Gravity is used to maintain a vertical orientation of the fiber in the Z pinch chamber Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 45

46 What Are The Key Mechanisms? Staging Process Coupling of energy in different stages. Non-equilibrium, Transiently Stabilized, Composite Pinch Two plasmas employed. Dynamic magnetic compression inhibits the instability process. Simulations have shown microsecond orders in stability. Compressing the magnetic field increases the implosion time compared to Fast Pinches. Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 46

47 Conclusion Z-Pinches May Be Used As A Testbed For Plasma Experiments and Diagnostics Z-Pinches Are Now Strong Contenders In The Fusion Race Z-Pinches Are Useful Tools In The Stockpile Stewardship And Nuclear Weapons Programs Someday, Compact University ICF Laboratory Reactors May Be Feasible Robert A. Schill. Jr., UNLV University of Wisconsin, Madison [Oct. 12, 1998] 47

Inertial Confinement Fusion DR KATE LANCASTER YORK PLASMA INSTITUTE

Inertial Confinement Fusion DR KATE LANCASTER YORK PLASMA INSTITUTE In the beginning In the late fifties, alternative applications of nuclear explosions were being considered the number one suggestion