Self-Organized Plasmas

LA-UR-99-2070 Self-organized plasmas

Briefing for the SEAB Task Force on Fusion Energy Princeton Plasma Physics Laboratory April 30, 1999

Richard E. Siemon Fusion Energy Program Manager Los Alamos National Laboratory

Magnetic Fusion Energy 1 Abstract

Self-Organized Plasmas

In the quest for fusion energy, sometimes Mother Nature helps. Certain plasma configurations exhibit properties known as “self-organization” where the plasma alters externally applied magnetic field in a way that improves the confinement properties needed for fusion. Examples in this talk include the reversed field pinch, the spheromak, the field-reversed configuration, and magnetized target fusion.

Magnetic Fusion Energy 2 Exploring the less familiar

Attractive Fusion Energy DEMO

Þ Fusion ITER Emphasis of this talk Energy FIRE * Development * Ignitor *

Performance Extension

i o Proof

R C of ( = Proposed ) Principle * * * *

Only U. S. Concept Experiments Exploration Shown Advanced Spherical Stellarator Torus Emerging Advanced RFP, FRC Tokamak Spheromak Fusion Technology & Plasma Theory

Magnetic Fusion Energy 3 Few equations; many applications

Electricity Maxwell + Boltzmann Ñ ´ B = j + ¶E / ¶t MHD Approximation Ñ · B = 0 ¶n / ¶t = -Ñ · (nu) Motors Astrophysics Ñ ´ E = -¶B / ¶t mnD(u) / Dt = j ´ B - Ñp

Ñ · E = q(ni - ne) 3nD(kT ) / Dt = Pheat + Ñ · q - Rad ICF (B=0)

Magnetic fusion Cell phones Plasma processing

Computers

Magnetic Fusion Energy 4 Holding a plasma in a torus (donut shape) requires: j x B = Ñ p Tokamaks

Spheromak

RFP FRC

Externally controlled Spherical Torus Self organized Stellarator In each case one investigates thermal 2 diffusivity c because tE = (size) / c

Magnetic Fusion Energy 5 Reversed Field Pinch: a self-organized plasma Small toroidal B reduces cost of magnet system

Magnetic Fusion Energy 6 RFP discovered experimentally; theory by J. B. Taylor

Helicity conservation even through nonlinear reconnection events Improved understanding and introduced by Taylor Proof of principle program proposed

1960 1970 1980 1990 2000

Self-reversal and quiesence Experimental studies throughout the world: observed on Zeta in Great Britain Great Britain, Italy, United States, Japan

Magnetic Fusion Energy 7 Magnetic fluctuations drive poloidal current

Magnetic Fusion Energy 8 Current profile control reduces dynamo-driven turbulence

10 Transient P (MW) J(r)-Control W Reduced ~ c global 5 Transport

0 from 120 Reduced B ˜ 2 2 60 (G) Magnetic Turbulence 0 MST 5 10 15 20 25 30 Time (ms) This major new insight gives strong justification for a Proof-of-Principle test of the Reversed Field Pinch

Magnetic Fusion Energy 9 Scientific progress leads to Proof-of-Principle

Understanding and improving transport is most critical RFP issue

Magnetic Fusion Energy 10 Spheromak: logical extension of RFP to unity aspect ratio (nothing on the axis)

• Based on helicity (Taylor states) like the RFP

• First wall becomes essentially spherical

• Engineering simplicity: No material object links plasma

IAEA 1978: Furth, Rosenbluth et. al.

Magnetic Fusion Energy 11 New experiment to address sustainment An example of exploratory research

Features - reduced field errors - controlled helicity injection - divertor and wall conditioning - advanced diagnostics - computed equilibria

Issues to investigate - sustainment - core energy confinement

SSPX experiment at LLNL

Magnetic Fusion Energy 12 Principle of helicity allows current drive Exploratory experiment U. Washington HIT experiment

Helicity injection to be tested on NSTX experiment at Princeton has potential for highly efficient current drive and may ease engineering requirements of the spherical torus central post. Magnetic Fusion Energy 13 SPHEROMAKS

Note by Paul M Bellan (California Institute of Technology)

Contents: Spheromaks are easily formed, self-organized ·Basic Concepts magnetized plasma configurations that have intrigued plasma physicists for over two decades. ·Magnetic Helicity Sometimes called magnetic vortices, magnetic ·Relaxation of an Isolated Configuration to the Taylor State smoke rings, or plasmoids, spheromaks first attracted attention as a possible controlled ·Relaxation in Driven Configurations thermonuclear plasma confinement scheme, but are ·The MHD Energy Principle, Helicity, and Taylor States now known to have many other applications. ·Survey of Spheromak Formation Schemes This book begins with a review of the basic ·Analysis of Driven Spheromaks concepts of magnetohydrodynamics and toroidal magnetic configurations, then provides a detailed ·Analysis of Isolated Cylindrical Spheromaks exposition of the 3D topological concepts ·The Role of the Wall underlying spheromak physics, namely magnetic helicity, Taylor relaxation, force-free equilibria, ·Helicity Flow and Dynamos and tilt stability. It then examines spheromak ·Confinement and Transport in Spheromaks formation techniques, driven and isolated configurations, dynamo concepts, practical ·Some Important Practical Issues experimental issues, diagnostics, and a number of ·Basic Diagnostics for Spheromaks applications. The book concludes by showing how ·Applications of Spheromaks spheromak ideas are closely related to the physics of solar prominences and interplanetary magnetic ·Solar and Space Phenomena Related to Spheromaks clouds. Imperial College Press, London (1999)

Magnetic Fusion Energy 14 Field Reversed Configuration: high-b self-organized plasma

• = 50-100%

• Power ~ b2B4

• compact torus like spheromak

Major issue: stability

Magnetic Fusion Energy 15 Theory of FRC behavior is incomplete

Experiments show slow decay MHD theory predicts fast decay

Hoffman and Slough, Nuc. Fus. 33, 27(1993)

More complete theory will include kinetic effects and sheared flow

Magnetic Fusion Energy 16 FRC sustained with current drive

New Exploratory experiment

U. Washington rotating- magnetic-field current drive

Magnetic Fusion Energy 17 Pulsed power: an enabling technology for fusion

Z Pinch cylindrical implosion Beam of Light Ions

Fast (100 ns) Slow (10 ms) V = 3 Megavolts V = 0.1 Megavolts I = 20 Megamps I = 30 Megamps Indirect drive pellet ablation Produce Xrays Produce megagauss magnetic field

High-yield Inertial fusion Indirect-drive Direct-drive plasma pellet fusion compression

Magnetic Fusion Energy 18 Z machine at SNL state-of-the-art pulsed power

Magnetic Fusion Energy 19 Elements of MTF Plasma preheater and injector Liner implosion system Guide-field coils Thin imploding liner

Magnetic guide field FRC

10 keV plasma

Typical parameters: Mega-ampere current Initial Final n 1017 cm-3 1020 cm-3 T 300 eV 10 keV B 100 kG 10 MG

Magnetic Fusion Energy 20 MTF Proof-of-Principle experiment

• Peer reviewed and judged ready for PoP status in July 1998. • Extends scientific study of self-organized plasma to high-field high-density regime • Expect DT-equivalent fusion energy gain 1-10% AFRL “Shiva Star” facility to drive PoP liner

Magnetic Fusion Energy 21 Magnetized Target Fusion Potential for low-cost development path

• After PoP, performance

enhancement (Qequiv ~ 1) could be tested on $50M- ATLAS facility

Los Alamos ATLAS facility operational in 2001

As with IFE, major issue is kopeck problem: cost to manufacture components destroyed on each pulse compared with small revenue generated per pulse of fusion energy.

Magnetic Fusion Energy 22 Summary

· Mother nature helps solve the quest for fusion by giving us “self-organized plasmas.” · More generally, fusion R&D is dynamic - new ideas and refinements in thinking are happening all the time. · Diverse portfolio results in valuable cross-fertilization of ideas. · By research on qualitatively different fusion approaches with different technologies, ranging from super-conducting magnets to high-power lasers, we ensure success for fusion even if a particular avenue encounters difficulty. · Roadmap is an ongoing R&D process with new ideas at exploratory level to be repeatedly encouraged for the foreseeable future.

Magnetic Fusion Energy 23