Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

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of 40%.) localized instabilities (tearing modes, edge localized modes) were mitigated or eliminated via lithium application, and record stability levels (normalized beta of 7.2) were reached. kinetic theory has provided understanding of the complex relationship between global instabilities and plasma rotation. The connection between observed fast particle loss and toroidal alfvén instabilities/theory was established. • control of high beta st plasmas: active control of resistive wall modes and maintenance of favorable plasma rotation profiles decreased the disruption probability for long-pulse plasmas while exceeding the stability limit for nonrotating plasmas by over 50%. Rotation is controlled by 3-d magnetic fields in plasmas with strong momentum input. • integration and sustainment at low aspect ratio: stability levels approaching that needed for a fusion component testing device were sustained for significant duration (3-4 resistive diffusion times) with a majority of the plasma current provided noninductively. Reversed Field Pinch The reversed field pinch (RFP) is an axisymmetric configuration in which electrical current in the plasma generates most of the magnetic field. The requirements on the external magnets are therefore greatly reduced. The RFP has a high ratio of plasma pressure to magnetic pressure. The ohmic heating from the plasma current could reduce or eliminate the need for complicated auxiliary heating systems. These features could yield a high power density fusion energy system with simple construction. highlights of RFP research include: • a 10-fold increase in energy confinement is obtained when fluctuations in the magnetic field are reduced using active control of the plasma current profile. This confinement is comparable to that in a tokamak of the same size and plasma current. high-temperature plasmas are produced without auxiliary (non-ohmic) heating, with electron temperature t e ~ 2 kev and ion temperature t i ~ 1 kev. • high-current plasmas (up to 1.5 ma in RFX-mod) spontaneously generate a helical magnetic field in the plasma core. The energy confinement time is improved in these selforganized, quasi-helical plasmas. The confinement time is increasing with plasma current. • Plasmas with thermal pressure exceeding theoretical limits for interchange and magnetic tearing stability are produced without exhibiting fast disruptive behavior. • active feedback stabilization is now routine when the plasma is contained in a thin-walled metal shell. discharge lengths up to 0.5 s are obtained, which is more than ten growth times for thin-shell instabilities that occur without feedback control. • Up to 10% of the plasma current has been sustained using low frequency ac induction (helicity injection), a promising approach for efficient steady-state operation of the RFP. • The physics of magnetic self-organization has been advanced by RFP (and compact torus) research, with strong connections to plasma astrophysics. areas include dynamo processes, momentum transport, collisionless ion heating, and magnetic reconnection and turbulence. 174
Compact torus a compact torus (ct) is a toroidal plasma configuration, but no physical structure threads or links the hole in the plasma. compact tori are formed in cylindrical chambers, greatly simplifying assembly and maintenance. There are two distinct ct types: the (i) field-reversed configuration (FRc) and the (ii) spheromak. The FRc has the highest possible value of beta (ratio of thermal plasma pressure to magnetic pressure) for confined plasmas. it is diamagnetic, with a plasma current perpendicular to the magnetic field. The spheromak has moderately high beta, and like the RFP, the plasma current generates most of the magnetic field. These features could lead to compact fusion systems with properties that promote high availability. highlights in ct research include: FrC • high-density, high-temperature FRcs have been routinely produced in field-reversed theta-pinch devices. in the large S experiment, a 1.0×1021 m –3 density, 0.575 kev electron temperature, and 1.225 kev ion temperature were simultaneously obtained in a transient discharge; in the FRX-l experiment, much larger densities at lower temperature were obtained. • FRcs that overcome impurity radiation barriers and have t e +t i > 0.2 kev have been produced and sustained using low-megawatt, steady-state power. The required excellent vacuum environment has been obtained via baking and glow discharge cleaning. titanium gettering has eliminated uncontrolled recycling so that FRcs can now be fueled by gas puffing. (tcsU experiment). • FRcs formed and sustained by rotating magnetic fields are found to have central conductivity ~5 times higher than the average, edge-dominated value. (tcsU experiment). • electron temperatures > 0.3 kev have been sustained for >3 ms in small plasma columns heated by
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Research Needs for Magnetic Fusion
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Research Needs for Magnetic Fusion
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ExEcutivE SuMMaRy nuclear fusion
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Magnetic confinement magnetic confi
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The thrusts span a wide range of si
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eactor, most heat comes from fusion
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thrust 18: achieve high-performance
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confinement is measured by the so-c
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PART I: ISSUES AND RESEARCH REQUIRE
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ReneW Organization: Themes The stru
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22 Table 1. ReNeW Thrusts Address R
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ON PREVIOUS PAGE Nonlinear simulati
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extended operation phase. The optim
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Figure 2. Alpha particles can cause
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Figure 3. Spectrogram of the time-v
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Do the alpha particles couple to th
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• improved understanding of the e
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most relevant to iteR. Recent obser
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H-mode access: access to the h-mode
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although present-day devices have m
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estimates indicate that it will be
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can enter the plasma core and dimin
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ent drive alone cannot account for
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Figure 10. Control involves the ele
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to operation of iteR. solutions for
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• identification and stabilizatio
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Disruption prediction accurate pred
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Figure 12. The application of non-a
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ion losses, a quantitative predicti
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due to incompatibility of the measu
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agnostic measurements of critical p
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quires assessment of when potential
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suggesTions for furTher reading 1.
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miTigaTing TransienT eVenTs in a se
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ON PREVIOUS PAGE Nonlinear simulati
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increasing power density and pulse
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of recent accomplishments that have
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ity limits have been maintained. in
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highly risky in such an environment
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proximity-coil-based magnetics is ~
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will dominate the external sources
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The barrier gradient is generally l
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interaction with plasma boundary an
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itER-at aRiES-i aRiES-at b n (%) 3.
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and morphology, are needed. new mea
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field and temperature fluctuations
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large-scale process control problem
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tics. integrated control methods fo
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ing and design include computationa
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dated in the corresponding structur
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These requirements are applicable t
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• assess computationally, on test
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Research Requirements for Electron
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the launcher design is partly “tr
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tunities and goals for a few of the
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front layers of the field magnets c
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R&D Strategy a number of critical t
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formance burning plasmas are covere
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CreaTing prediCTaBle, high-performa
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magneTs JosePh mineRvini, massachus
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ON PREVIOUS PAGE Design of the ITER
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Page 130 and 131: Promising new ideas have been devel
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Page 134 and 135: • liquid surface PFc operation in
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Page 138 and 139: Taming The plasma-maTerial inTerfaC
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Page 142 and 143: ON PREVIOUS PAGE Design of an ITER
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Page 146 and 147: Safety and Environment • developm
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Page 150 and 151: gaps: need to select and test the t
Page 152 and 153: • neutron and other radiation tra
Page 154 and 155: emphasis on modeling and expertise
Page 156 and 157: gap: Current understanding of stren
Page 158 and 159: Research needs critical research ne
Page 160 and 161: • Proposing integrated safety des
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Page 164 and 165: Qualifying DEMO Components Possible
Page 166 and 167: • developing the design of an eff
Page 168 and 169: harnessing fusion power Theme memBe
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Page 172 and 173: ON PREVIOUS PAGE Reconstruction of
Page 174 and 175: Figure 1. Configuration space for t
Page 178 and 179: • Reduction of spheromak magnetic
Page 180 and 181: ment, but also micro- and macro-ins
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Page 184 and 185: the banana regime, low turbulent tr
Page 186 and 187: in stellarator discharges with ohmi
Page 188 and 189: • investigate how demountable coi
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Page 192 and 193: functions, edge flows, and edge neu
Page 194 and 195: Development of predictive capabilit
Page 196 and 197: Edge localized modes (ELMs): edge l
Page 198 and 199: theory predictions for alfvén inst
Page 200 and 201: coils, to permit replacement of the
Page 202 and 203: stand the relative roles of long-to
Page 204 and 205: Table 1. 202
Page 206 and 207: primarily electrostatic, in the cas
Page 208 and 209: to be important in present experime
Page 210 and 211: PLaSMa bOunDaRy intERaCtiOnS The ex
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Page 214 and 215: needed Theory, Computation, Modelin
Page 216 and 217: Scientific Issues and research requ
Page 218 and 219: esearch requirements new facilities
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Page 222 and 223: tRanSPORt: DEtERMinE unDERLying tRa
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nEEDED FaCiLitiES nEEDED tHEORy, CO
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connections Between Research Requir
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opTimizing The magneTiC ConfiguraTi
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Proposed actions: • Prioritize bu
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3) as planning matures for the rese
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that have high impact, that benefit
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could have an impact on the identif
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The Us fusion program is well posit
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Mitigation of disruptions in the ev
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elevant plasmas for very long pulse
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and stability, and mitigation requi
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• control alpha heating feedback
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heavy ion beam probes (already in u
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alpha particles (ash removal). mode
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• determine minimum heating power
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Research should focus on developing
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estal structure need to be coupled
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• sufficient heating with little
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Proposed actions: Short-term: begin
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Demonstrate active control of the p
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Demonstrate burn control and contro
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Develop the means for and demonstra
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Medium-term: Test and optimize full
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• Recruit, train and support dedi
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With this information in hand, phys
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to carry out the validation program
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and new devices could be designed w
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• high-field sc magnets for stead
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Element 2 — High current conducto
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Element 7 — integration of conduc
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many other scientific fields are be
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• based on these assessments, pro
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systems include neutral beams, ion
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The Us d-t facility, studied in 1b,
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300
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• design and implement innovation
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the controlling instabilities and s
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cross-field transport in the pedest
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The modeling of near-surface plasma
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310
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• build large-size test stands wh
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trol of the energy, impact angle, a
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ties that take advantage of simple
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ased materials development with adv
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introduction Thrust 11 addresses th
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technology is now evolving to inclu
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The elements of a thrust to develop
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The plasma facing components in a d
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to demonstrate that steady and tran
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mum of nuclear activation and prese
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introduction harnessing fusion powe
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each Thrust 13 element includes the
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Figure 3. System concept for perfor
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equirements. Understanding the fuel
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• Use a combination of existing a
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chemical interactions between the s
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dose fusion-relevant environment wi
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Use a combination of existing and n
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350
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evaluate, through advanced design a
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at the time when the demo design is
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3. Computational analysis managemen
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Materials and Components: Fuel Cycl
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• employ energetic particle beams
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• develop and validate theoretica
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• develop new diagnostics for int
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• increase sustained noninductive
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368
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Proposed actions: 1. conduct two qu
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The key areas in which new knowledg
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• exploration of high-temperature
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• availability of high-power radi
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378
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• study FRc stability at small io
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techniques for integrated data anal
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4. based on the outcome of actions
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2. With information from action 1,
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388
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aCROnyMS anD abbREViatiOnS (continu
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aPPENdix c: tHEME WoRKSHoPS tHEME W
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14. d.l. humphreys, Active Realtime
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tHEME 2: CREating PREDiCtabLE HigH-
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43. t.W. Petrie, White Paper: Some
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tHEME 3: taMing tHE PLaSMa MatERiaL
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37. e.J. strait, J.c. Wesley, m.J.
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20. s.a. maloy and e. Pitcher, Fusi
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tHEME 5: OPtiMizing tHE MagnEtiC CO
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39. P.W. terry, a. boozer, J.s. sar
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don coRRell, lawrence livermore nat
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GeoRGe mckee, University of Wiscons
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tony tayloR, General atomics RichaR
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