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

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calized field errors that can cause wall locking of tearing modes, as shown in RFX-mod and mst. RFX-mod experiments have also established that locking of tearing mode phases to the wall can be mitigated by appropriate feedback using the full-coverage coil set. research requirements Present experiments suggest that it is possible to operate a RFP without a very conducting wall. however, key questions remain, and the optimal control system has not been identified. Will coils located inside the vessel be able to mitigate phase locking to the wall, optimize the plasma shape and help for power handling (as in iteR)? Will it be necessary to include special flux loops to control m=0 modes (m is poloidal mode number)? Will ad hoc saddle coils be able to compensate for the residual error fields due to the unavoidable asymmetries of the magnetic boundary? certain types of coils may be optimal for different instabilities. nonlinear coupling between m=1 and m=0 poloidal mode makes control of both harmonics important. separate coils optimized for m=0 control may be needed. The toroidal field coil set in RFX-mod could in principle provide significant m=0 mode control, but the precision of the currently installed power supply units is limited. in both RFX-mode and extrap t2R, the issue of sideband aliasing (unwanted perturbations in other modes) has been observed and improvements in control have been obtained by reducing it either by increasing the number of actuators (t2R) or by removing it from the measurements in real time (RFX-mod). it is vital to understand the required minimum number of control coils, and how advanced control algorithms can surmount issues such as sideband aliasing. The development of accurate models is essential for understanding the behavior of the present control systems and for predicting the performance and control requirements of future devices. several approaches are possible. an existing model of the electromagnetic boundary that includes simplified transfer functions for the feedback-controlled current power supply units in a multiinput, multi-output paradigm reveals the necessity to better understand and model the mutual couplings of the feedback coil hardware. in the near term, merging the electromagnetic code cariddi with the maRs code can advance this issue. The development of a full simulator of an RWm control system for existing devices will also allow testing different kinds of model-based control approaches, where standard Pid controllers will be replaced by more complex state-space controllers, and which may also take into account the 3-d structure of the magnetic boundary. a parallel approach to RWm control modeling is based on the development of a more complete physics model of the plasma in a simplified geometry, taking into account plasma pressure, compressibility, inertial, dissipation and longitudinal plasma rotation. in addition to RWm modes, optimization of the magnetic boundary for the control of tearing modes is important, for example, identifying the ideal non-axisymmetric deformation of the last closed magnetic surface. SELF-COnSiStEnt REaCtOR SCEnaRiOS in addition to the integration of current sustainment and improved confinement, a self-consistent scenario must also integrate RWm control and plasma boundary control to achieve high-performance RFP discharges and establish the knowledge base for a burning plasma experiment. The RFX-mod and extrap t2R facilities have capability to begin addressing the optimization of RWm control, but not for issues such as requirements on the proximity of feedback coils to the plasma surface. mst can apply current profile control and possibly enhance plasma pressure, but cannot 210
include reactor-relevant resistive wall mode stabilization (mst operates with a thick conducting wall), and is limited in oFcd capability. in general, the compatibility of boundary control is a large issue that cannot be addressed in present facilities. research requirements Experimental capabilities. The development of self-consistent scenarios requires a facility that includes all the aforementioned capabilities, probably at the performance extension level. This includes the capabilities for 100% current sustainment, heating, fueling, and RWm and edge control. testing feedback coil proximity and plasma rotation might be possible through extensive modification of existing facilities, or perhaps with a new, smaller facility optimized for this purpose. Reactor study capabilities. Further system code study is essential to develop such self-consistent scenarios, including both steady-state solutions and hybrid solutions with an oFcd phase and a current ramp-down phase. assessing the impact of special constraints imposed by the reactor environment is important, e.g., the proximity of active feedback coils if they need to be located outside the neutron shield. numerical capabilities. Three-dimensional nonlinear fluid computations, which could incorporate a toroidal divertor, are required to develop, predict and optimize self-consistent reactor scenarios. 211
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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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to stabilize deleterious plasma mod
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longer than the (solid) thermal equ
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Promising new ideas have been devel
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to handle 10 mW/m 2 , and elms with
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• liquid surface PFc operation in
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integrated effort that includes fun
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Taming The plasma-maTerial inTerfaC
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138
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ON PREVIOUS PAGE Design of an ITER
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trons in the breeding blanket. Thes
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Safety and Environment • developm
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plasma and gas to the scrape-off la
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gaps: need to select and test the t
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• neutron and other radiation tra
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emphasis on modeling and expertise
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gap: Current understanding of stren
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Research needs critical research ne
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• 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
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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
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Page 210 and 211: PLaSMa bOunDaRy intERaCtiOnS The ex
Page 214 and 215: needed Theory, Computation, Modelin
Page 216 and 217: Scientific Issues and research requ
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Page 222 and 223: tRanSPORt: DEtERMinE unDERLying tRa
Page 224 and 225: esearch requirements analysis of ne
Page 226 and 227: nEEDED FaCiLitiES nEEDED tHEORy, CO
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Page 230 and 231: opTimizing The magneTiC ConfiguraTi
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Page 238 and 239: Proposed actions: • Prioritize bu
Page 240 and 241: 3) as planning matures for the rese
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Page 248 and 249: Mitigation of disruptions in the ev
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Page 254 and 255: • control alpha heating feedback
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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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276
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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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332
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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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