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

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• improved understanding of the effect of non-axisymmetric fields on plasma confinement. • development of the capability to model transport and the conditions for transport barrier formation sufficiently well for simulating potential iteR scenarios. The Us fusion energy science community is a world leader in confinement and transport research, with flexible and comprehensively diagnosed experimental facilities (equipped with very good turbulence diagnostics), as well as excellent theory, modeling, and simulation capabilities. The field of confinement and transport provides a good mix of short and long-term research opportunities, both experimental and theoretical. answering the questions that are motivated by the need to understand transport in burning plasmas prior to and during iteR operation will require a solid base program and ancillary facilities with the tools necessary to reproduce, study, and control plasma conditions as similar as possible to those of iteR. Given these capabilities, the Us fusion energy science community will be well positioned to contribute strongly in this area. Recent accomplishments and progress significant progress has been made toward a predictive understanding of energy, particle, and momentum transport, including detailed comparisons of experimental observations with theoretical predictions. highlights include: • detailed measurements of fluctuations over a wide range of spatial scales. • agreement between experimental measurements of turbulence characteristics and kinetic profiles and predictions from gyrokinetic turbulence and gyro-landau-fluid codes. • direct measurements of turbulence-induced zonal flows. • models developed that accurately predict the structure of the h-mode pedestal. • correlation found between the power threshold for low to high-confinement mode (l-h) transition and the edge plasma flow. • observation of self-generated plasma rotation in the absence of external torque. • clear evidence of inward convection of particle density. • identification of trigger mechanisms for internal transport barrier formation. • improved scalings with dimensionless parameters for projecting confinement to future devices. SCiEnCE CHaLLEngES, OPPORtunitiES, anD RESEaRCH nEEDS Improved characterization of confinement in plasma conditions specific to anticipated ITER operating scenarios The burning plasma regime is expected to have specific characteristics. simulations indicate that the optimum operating point for iteR has high density (~ 10 20 m -3 ), high temperature (> 15 kev), and strong magnetic field (~ 6 t). These requirements imply a specific range of values for dimen- 34
sionless parameters of importance for transport. These values are somewhat different from those generally obtained in present-day devices. Particular examples include: • The ion and electron characteristic gyro-orbit size relative to the machine size (known as the normalized gyroradius r*) is nearly an order of magnitude smaller in iteR than in present-day devices. • The collision frequency of the ions and electrons in iteR relative to the frequency at which these particles transit a full circuit of the confining magnetic field (known as the collisionality n*) is at the low end of the range of values obtained in present-day devices. • The thermal equilibration time between ions and electrons in iteR is much smaller than the thermal confinement time, which implies close coupling between the ion and electron energy channels. because these parameters are important in the transport of energy, particles, and momentum, there is therefore still some uncertainty in projecting iteR confinement. Energy transport: Whereas the thermal transport of ions is thought to be reasonably well understood, additional work is needed to show that the present understanding is complete and correct. in particular, quantitative estimates of the role of rotation in suppressing turbulence and improving transport should be further refined. For electron thermal transport, there is no consensus on the identity of the underlying mechanism, which appears to be sensitive to physics related to spatial scales ranging from the ion to electron gyroradius. diagnostic capability for both profile and fluctuation measurements needs to be ex pand ed to solve this extremely demanding problem. determining the scaling of transport phenomena with dimensionless parameters has proven to be a valuable tool in developing a better physics basis for extrapolation to iteR. a transport extrapolation to smaller normalized gyroradius (r*) and perhaps smaller collisionality (n*), while keeping the other dimensionless variables fixed, is the preferred scaling path. multi-machine studies of the r* and n* dependences are needed to increase the range covered and thereby reduce projection uncertainties toward iteR. several enabling tools are required in this area. in particular, measurements capable of resolving fluctuations in the magnetic field, velocity, density, temperature, and electric potential on scale lengths comparable to the electron gyroradius (~ 5 × 10 -3 cm in a typical fusion plasma) are needed to probe turbulence that drives electron transport. in addition, more electron heating than is currently available on existing machines will be needed to access electron-loss-dominated regimes. such electron heating could also be used to better simulate the burning plasma regime with strong alpha particle heating of electrons and low torque injection. Momentum transport: The magnitude, direction, and detailed profile of the plasma flow are determined by the interplay of rotation sources, momentum transport, and any sink mechanisms that are present. Rotation is generated in a burning plasma (1) intrinsically or spontaneously, (2) externally by radiofrequency waves, (e.g., from the wave’s momentum), and (3) through radiofrequency heating not externally driven. While extrapolation of intrinsic rotation from a multiple-machine database appears favorable (see Figure 6), it is important to determine the physical origin of spontaneous rotation and validate its size scaling. Pure electron heating cases are the 35
Page 1 and 2: Research Needs for Magnetic Fusion
Page 3: Research Needs for Magnetic Fusion
Page 7 and 8: ExEcutivE SuMMaRy nuclear fusion
Page 9 and 10: Magnetic confinement magnetic confi
Page 11 and 12: The thrusts span a wide range of si
Page 13 and 14: eactor, most heat comes from fusion
Page 15 and 16: thrust 18: achieve high-performance
Page 17 and 18: confinement is measured by the so-c
Page 19: PART I: ISSUES AND RESEARCH REQUIRE
Page 22 and 23: ReneW Organization: Themes The stru
Page 24 and 25: 22 Table 1. ReNeW Thrusts Address R
Page 26 and 27: ON PREVIOUS PAGE Nonlinear simulati
Page 28 and 29: extended operation phase. The optim
Page 30 and 31: Figure 2. Alpha particles can cause
Page 32 and 33: Figure 3. Spectrogram of the time-v
Page 34 and 35: Do the alpha particles couple to th
Page 38 and 39: most relevant to iteR. Recent obser
Page 40 and 41: 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
Page 52 and 53: to operation of iteR. solutions for
Page 54 and 55: • identification and stabilizatio
Page 56 and 57: Disruption prediction accurate pred
Page 58 and 59: Figure 12. The application of non-a
Page 60 and 61: ion losses, a quantitative predicti
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
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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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• 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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230
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232
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234
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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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