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Alcator C-Mod Research Highlights
Compact high-performance divertor tokamak research to establish the plasma
physics and engineering necessary for attractive
fusion reactors.fusion reactors.
55th Annual Meeting, APS-DPP, Denver, CO, November 11, 2013, CO4-01E. S. Marmar for the Alcator Group
Runaway Suppression May Not Require the Very High Density Implied by Collisional Theory
• Data from ITPA joint experiments and mining of previously existing data consistently show that the electric field required (Ecrit) to generate significant relativistic runaway e− populations is 5 to 10 times higher than expected from Connor, Hastie*
• Could be good news for runaway mitigation during disruptions in future facilities
V/m
)
Threshold for Runaway Production on Multiple Facilities
ric F
ield
(Vda
l Ele
ctr
Toro
i
0 0 2 0 4 0 6 0 8
• R. Granetz, BI2-03, Mon. AM*J.W. Connor, R.J.Hastie, Nucl. Fus. 15(1975)415.
Line-Average Density (1020m-3)0 0.2 0.4 0.6 0.8
Core transport, Gyrokinetic modeling
• Previous gyrokinetic modeling has shown sensitivity of ion transport to main ion dilution by impurities
• Series of nitrogen seeding experiments
• Under-prediction of electron heat flux increases with IP
• Series of nitrogen seeding experiments shows χi decrease, little/no change in χe
/s)
/s)
Unseeded
χ e(m
2 /
χ i(m
2 /Nitrogen Seeded
r/a r/a0.5 0.6 0.7 0.8 0.5 0.6 0.7 0.8
Nitrogen SeededUnseeded
• P. Ennever, CO4-07, this session• N. Howard, CO4-06, this session
Density (1020m-3)r/a r/a
• Correlates with absence of long-λ sub-dominant electron modes
Gyrokinetic Simulations of TEM Turbulence: Control of ITB Density Profile by ICRH
● Absolute fluctuation levels match experiment within
ncertainties
Gyrokinetic Simulations of TEM Turbulence in ITB match measured fluctuation level and transport within uncertainties
uncertainties
● Nonlinear upshift heightens TEM Sensitivity to Tey e
● Provides mechanism for density and impurity control
ith ICRHwith ICRH
Nonlinear upshift of TEM critical density gradient: strong sensitivity to Te
• D. Ernst, TP8-50, C. Fiore, TP8-35, Thurs. am
Additional gyrokinetic studies:C. Sung, CO4-08, this session, K. Liao, TP8-39
Current Profile Control with Lower Hybrid Waves Leads to Dramatic Changes in Core Plasma Rotation
• Unifies results from 4 facilities
s)
• Change in j(r) modifies core plasma rotation
cy (k
Rad
/s
ty (k
m/s
)
n fre
quen
c
ion
velo
cit
in ro
tatio
n
ge in
rota
ti
Cha
nge
i
Cha
ng
• J. Rice, CO4-09, this session
Magnetic Shear Scale Length, LS (m)
Lower Hybrid RF Edge Interactions Lead to Significant Confinement Increase of High Density H-modes
• ~25% increase in normalized confinement, with <15% increment in power
• LH waves absorbed in edge/SOL
• With LH, dramatic reduction in ped. d SOL d i fl i (GPI) power
• ~15% increase in absolute τEand SOL density fluctuations (GPI)
mal
ized
τE
ge in
Nor
mC
hang
• J. Terry, CO4-13, this session
I-mode Pedestal Peeling-Ballooning Stable;Pedestal βp scales with Density
• Poloidal beta of pedestal scales linearly with density
• Leads to linear increase of plasma pressure with input powernt
• ELITE modeling shows that I-mode pedestal is stable to peeling-ballooning
pressure with input power
esta
l Cur
ren
(kJ)
I modeNor
m. P
ede
d E
nerg
y (
I-modeN
Norm. Pressure Gradient (α) Sto
red
Power x IP ( MW-MA)• Favorable compared to H-mode, which
has ~constant pedestal pressure ⇒
• J. Walk, UI2-03, Thurs. PM
degradation of τE with power
Fluctuations and Energy Transport Reduced in I-mode Core
I-modeL-mode
● L-mode■ I-mode
Ĩ e/T e
(%)
T
Noise level
• Te fluctuations (CECE) reduced by at least 40% in core
• Energy transport reduced by similar amount across the core confinement region
ρ
Whit CO4 03 thi i
region
• White, CO4-03, this session
Additional I-mode studies: A. Hubbard, TP8-34, Thurs. am
Unique Mirror Langmuir Probe Reveals Unprecedented Details of Pedestal/Edge Modes
• Direct measurements of lag between density and potential fluctuations
• MLP electronics adjusts I-V in real-time to match that of an actual probe
• Yields Isat, Te, Vf, from single probe with μs real-time responseμs real time response
• EDA H-mode QCM very narrow (~3 mm) at LCFS
QCM i l t d ift ith• QCM is an electron drift-wave with significant interchange drive and electromagnetic contributions
• B. LaBombard, YI2-06, Friday, noon
Additional H-mode pedestal studies:T. Golfinopoulos, YI2-05, Fri. am, A. Diallo , CO4-04, this session; E. Davis, PP8-17, Wed. pm
Accelerator-based In-situ Materials Studies (AIMS):Between-shot measurements of surface changes
Isot
ope
hang
e in
I
1 M V D+ l t actio
nal C
h
• 1 MeV D+ accelerator
– Use toroidal and vertical B fields to steer beam
R lti l ti d tFr
aMeasurement Sequence
– Resulting nuclear reactions used to probe changes in surface conditions • In‐situ monitoring of evolution in
deuterium and boron surface concentrations at multiple locations during wall conditioning experiments
• Zach Hartwig, NI3-03, Wed. AM
wall conditioning experiments
With Continued Operation, C-Mod Ready to Provide Critical Results for ITER, FNSF and DEMO
Study/Exploit UniqueField-Aligned ICRF Antenna
Develop Advanced Off-Midplane LH Launcher
Deploy Actively Heated (900 0K) Tungsten DivertorExploit Unique
Capabilities for In-situ Measurementssitu Measurements
of Plasma Wall Interactions
Statistic:11 of 99 invited talks at this APS-DPP are by current or former MIT PSFC graduate students
Extreme Materials Challenge: Remove Heat and Particles with Close to Zero Erosion
• X‐Point Divertor: put the radiation where it belongs
• Concept of facility to test revolutionary approach: Alcator DX
• LaBombard, CO4-02, this session
Alcator C-Mod Presentations at 2013 APS-DPP Meeting
• Review– Martin Greenwald: Twenty Years of Research on the Alcator C-Mod Tokamak,
Monday, 8:00 am• Invited• Invited
– Robert Granetz: ITPA Joint Experiment to Measure Threshold E-fields and Densities for Runaway Electron Onset and Suppression, Monday, 10:30 am
– Zach Hartwig: The in-situ diagnosis of plasma-wall interactions on magnetic fusion devices with accelerators Wednesday 10:30 amfusion devices with accelerators, Wednesday, 10:30 am
– Jungpyo Lee: Ion intrinsic rotation in a tokamak caused by momentum transport due to diamagnetic flow effects, Wednesday, 4:00 pm
– John Walk: ELM Suppression and Pedestal Structure in I-Mode Plasmas, Thursday 3:00 pmThursday, 3:00 pm
– Ted Golfinopoulos: External Excitation of a Drift-Alfvén Wave Response in the Alcator C-Mod Edge Plasma and its Relationship to the Quasi-Coherent Mode, Friday, 11:30 am
– Brian LaBombard: New insights on boundary plasma turbulence and the Quasi-Brian LaBombard: New insights on boundary plasma turbulence and the QuasiCoherent Mode in Alcator C-Mod using a Mirror Langmuir Probe, Friday, 12 noon
• Oral Contributed (Monday, PM)• Poster Contributed (Thursday, AM)• ITER Oral Contributed (Wednesday, PM)ITER Oral Contributed (Wednesday, PM)
Research supported by USDOE
The mind is not a vessel to be filled, but a FIRE to be kindled. — Plutarch