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

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and morphology, are needed. new measurement requirements include profile, flow and fluctuation measurements with better geometric coverage; measurements of ly-a and other radiation sources in dense divertor plasmas to account for radiation transfer and opacity effects; and neutral density in the divertor, sol and edge pedestal to understand fueling and divertor performance. measurements of radiofrequency sheaths and heat flux measurements on plasma facing components using infrared thermography and calorimetry with extensive 3-d coverage, and in-situ erosion and redeposition measurements, are needed for rigorous testing of thermal load predictions as well as prediction of impurity generation rate and distribution. data from integrated high heat flux, steadystate confinement devices with relevant wall conditions, complemented by basic plasma physics devices and plasma-wall interaction test stands, will be required for validation. Energetic Particle Physics Science Opportunities: • Will the formation of energetic particles in burning plasmas lead to the generation of new instabilities? if so, what types of instabilities? What are their thresholds for excitation? how do they grow and saturate? • do these instabilities lead to a state of turbulence and in what way might this turbulence couple to the thermal pressure gradient-driven turbulence? • how do the energetic particles and/or the background plasma turbulent transport, mhd equilibrium and RF driven currents respond to energetic particle modes and/or turbulence? research requirements Theory, computational, and experimental work is needed to understand the nonlinear saturation and development of a new regime of turbulence and associated transport due to fast-particle physics. new methods for long-term simulations are required that can track the evolution of fast particle generation (which occurs on confinement time scales) while simultaneously capturing the short time scale fast particle/wave interactions driving the turbulence. emerging diagnostic techniques (e.g., energetic ion distribution and loss diagnostics) should be incorporated into existing laboratory-scale and confinement experiments, and coupled to direct measurements of alfvén eigenmodes (ae) and alfvén turbulence using, for example, reflectometry, beam emission spectroscopy (bes), correlation electron cyclotron emission and other emerging spatiotemporally resolved diagnostics that have traditionally been used to study drift turbulence and transport. development of local magnetic field fluctuation measurements for determining amplitude and mode structure would also be valuable. synthetic diagnostic development in models is also needed. Disruptions: Prediction, avoidance, and Mitigation Science Opportunities: • can the probability of a disruption event be reduced to something less than one disruption per year while operating a steady-state advanced tokamak at high performance? • can we successfully and accurately predict the approach to a disruption event and initiate control techniques to avoid the disruption? 90
• if a disruption becomes unavoidable, can we then predict the onset, evolution and final termination of disrupting discharges due to all possible instability mechanisms (e.g., density limit radiation collapse, vertical displacement event, beta-limit, etc.) in a demo device and use this capability to design a mitigation scheme that will perform with high confidence? research requirements The fundamental question of disruption probability can only be definitively answered by a new generation of very long pulse (likely many days long) discharges coupled with extensive operational experience of such devices. no such experiment exists today. integrated modeling of disruptions, which would feature nonlinear mhd simulations for realistic tokamak geometry, including core, scrape-off layer, plasma facing components, and eventually even coil structures to calculate halo currents, must occur. such a capability could first be developed and experimentally validated for elms, then resistive wall modes (RWms), and finally disruption events. modeling must eventually successfully predict performance of disruption mitigation techniques with sufficient confidence to make design selection for demo. Reduced physics disruption models must be integrated into a real-time control system for disruption prediction and detection, avoidance, and mitigation. improved diagnostics of disruptions, including runaway electron generation and transport, as well as development and study of potential mitigation techniques, must be performed in existing experiments. validation experiments using emerging models of unmitigated and mitigated disruption events can provide predictive capabilities for iteR and then demo. Pedestal and ELM Science Opportunities: • can we accurately identify the physics trigger(s) for formation of the edge transport barrier, and translate this into a physics-based “l-h mode” transition threshold prediction? • can these predictions then be extended to fully saturated, steady-state wall conditions? can we predict the height of the pedestal with a physics-based understanding? can we accurately predict elm onset, dynamics and the associated heat and particle load on PFcs? • can we understand the behavior of elm control and mitigation schemes sufficiently well to confidently predict their performance and impact upon the pedestal conditions that will occur in a demo? • can we predict the coupling of radiofrequency, beam and pellet sources across the pedestal? research requirements a successful predictive pedestal model is inherently a multi-scale problem involving the long-time evolution of a turbulent system coupled with the evolution of the plasma profiles. new approaches are needed if a first-principles model of this system is to be created. validation will require new measurements (e.g., neutral fueling of the pedestal, field penetration from elm control coils) as well as significantly improved multipoint measurements of turbulent density, potential, magnetic 91
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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
Page 42 and 43: although present-day devices have m
Page 44 and 45: estimates indicate that it will be
Page 46 and 47: can enter the plasma core and dimin
Page 48 and 49: ent drive alone cannot account for
Page 50 and 51: Figure 10. Control involves the ele
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Page 54 and 55: • identification and stabilizatio
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Page 58 and 59: Figure 12. The application of non-a
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Page 62 and 63: due to incompatibility of the measu
Page 64 and 65: agnostic measurements of critical p
Page 66 and 67: quires assessment of when potential
Page 68 and 69: suggesTions for furTher reading 1.
Page 70 and 71: miTigaTing TransienT eVenTs in a se
Page 72 and 73: ON PREVIOUS PAGE Nonlinear simulati
Page 74 and 75: increasing power density and pulse
Page 76 and 77: of recent accomplishments that have
Page 78 and 79: ity limits have been maintained. in
Page 80 and 81: highly risky in such an environment
Page 82 and 83: proximity-coil-based magnetics is ~
Page 84 and 85: will dominate the external sources
Page 86 and 87: The barrier gradient is generally l
Page 88 and 89: interaction with plasma boundary an
Page 90 and 91: itER-at aRiES-i aRiES-at b n (%) 3.
Page 94 and 95: field and temperature fluctuations
Page 96 and 97: large-scale process control problem
Page 98 and 99: tics. integrated control methods fo
Page 100 and 101: ing and design include computationa
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Page 104 and 105: These requirements are applicable t
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Page 108 and 109: Research Requirements for Electron
Page 110 and 111: the launcher design is partly “tr
Page 112 and 113: tunities and goals for a few of the
Page 114 and 115: front layers of the field magnets c
Page 116 and 117: R&D Strategy a number of critical t
Page 118 and 119: formance burning plasmas are covere
Page 120 and 121: CreaTing prediCTaBle, high-performa
Page 122 and 123: magneTs JosePh mineRvini, massachus
Page 124 and 125: ON PREVIOUS PAGE Design of the ITER
Page 126 and 127: to stabilize deleterious plasma mod
Page 128 and 129: longer than the (solid) thermal equ
Page 130 and 131: Promising new ideas have been devel
Page 132 and 133: to handle 10 mW/m 2 , and elms with
Page 134 and 135: • liquid surface PFc operation in
Page 136 and 137: integrated effort that includes fun
Page 138 and 139: Taming The plasma-maTerial inTerfaC
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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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• techniques and instruments to a
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Qualifying DEMO Components Possible
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• developing the design of an eff
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harnessing fusion power Theme memBe
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168
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ON PREVIOUS PAGE Reconstruction of
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Figure 1. Configuration space for t
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of 40%.) localized instabilities (t
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• Reduction of spheromak magnetic
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ment, but also micro- and macro-ins
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esearch requirements • evaluate t
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the banana regime, low turbulent tr
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in stellarator discharges with ohmi
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• investigate how demountable coi
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tion using a central solenoid is al
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functions, edge flows, and edge neu
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Development of predictive capabilit
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Edge localized modes (ELMs): edge l
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theory predictions for alfvén inst
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coils, to permit replacement of the
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stand the relative roles of long-to
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Table 1. 202
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primarily electrostatic, in the cas
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to be important in present experime
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PLaSMa bOunDaRy intERaCtiOnS The ex
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calized field errors that can cause
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needed Theory, Computation, Modelin
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Scientific Issues and research requ
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esearch requirements new facilities
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small, concept exploration experime
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tRanSPORt: DEtERMinE unDERLying tRa
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esearch requirements analysis of ne
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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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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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