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D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
D.C. Pace1, R.S. Granetz2, A. Bader2, P. Bonoli2, D.S. Darrow3, C. Fiore2, T. Golfinopoulos2, Y. Lin2, R.R. Parker2, R. Vieira2, S. Wolfe2, S.J. Wukitch2, and S.J. Zweben31ORISE, 2MIT, 3PPPL
53rd Annual Meeting of the APS Division of Plasma PhysicsSalt Lake City, Utah
November 14 - 18, 2011
Energetic Ion Losses in the Alcator C-Mod Tokamak*
*Work supported by US DOE through an appointment in the Fusion Energy Postdoctoral Research Program and under DE-FC02-99ER54512.
1 MeV Proton in Alcator C-Mod
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Ion cyclotron resonance heating (ICRH) produces an energetic ion tail in hydrogen [D(H)] or helium [D(3He)] minority heating scenarios– H (proton) energies ≤ 2 MeV measured by neutral particle analyzers (NPAs)– Alfvénic instabilities observed
• Fast ion loss detector measures the pitch angle and energy of tail ions that reach the outer midplane– optimized for high pitch angles produced by ICRH– compact design and fast response scintillator (2 MHz) improve detection
• Measured losses will contribute to the extensive ICRH experimental and simulation/modeling effort– confined energetic ion measurements: fast ion charge exchange and NPAs– full wave modeling of ICRH coupled to Fokker-Planck solvers used in synthetic
diagnostics
New C-Mod Fast Ion Loss Detector Increases Measurement Ability in Energetic Ion Experiments
2
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011 3
• R = 0.67 m, a = 0.22 m
• B = 2.3 - 8.0 T
• Ip ≤ 2.0 MA
• ne = 0.4 - 2.0 x 1020 m-3
• Te ≤ 8 keV, Ti ≤ 5 keV
• PRF ≤ 6 MW– minority heating: D(H), D(3He)– in-shot phasing adjustment
Alcator C-Mod Employs a Versatile ICRF Heating System at ITER Field and Density
z [m]
0.4
0.2
0.0
−0.2
−0.4
−0.6
R [m]1.00.80.60.4
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
Fast Ion Loss Detector is Installed and Ready for Plasma Operations
4
Secured toVessel Wall
B
IonTrajectory
Plasma
Vessel
(a)
Vacuum FiberOptic Cable
Aperture
(b)
3.8 cm
z = 0.0 m
z = -0.02 m
Aperture
Bt, Ip
• Fixed position near limiting surfaces: RFILD = 0.923 m, Rlim = 0.910 m
• Field aligned to increase maximum detectable pitch angle, α ≈ 85o
• Four scintillator regions fiber optically coupled to photomultipliers for 2 MHz acquisition
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Toroidal transit distance in one gyroperiod (m):
µ = m / mp, χ = v||/v = cos(α)
• Expected C-Mod ΔL values are smaller than in other devices, e.g., 80 keV at χ = 0.2– DIII-D deuteron, ΔL = 4.9 cm– C-Mod proton, ΔL = 1.3 cm
• Actual value of ΔL is decreased according to probe head geometry
Short Toroidal Transit Distances Limit the Size of the Detector, Requiring Thin Shield Walls
5
Δφ
α
BT, Ip
DetectableOrbit
Undetectable Orbit
Molybdenum Shield
Scintillator
Collimator
Scintillator
MolybdenumShield
Ion Orbit
BT, IpPlasma
a
b
∆L = v�Tci = 8.328× 10−16 µχ
ZBT
�2E
m
ΔL
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Maui-535 scintillator from Lightscape Materials*, Inc.– emission peak: λ = 534 nm– emission width: Δλ = 49 nm– decay time: Δt = 490 ns
• Secured in place within slot cut into molybdenum shield– minimizing radial distance from
plasma increases ion collection – poor thermal contact to plasma
facing surface keeps scintillator below 100 oC
Fast Response Scintillator is Tightly Integrated into Probe Head to Improve Sensitivity
6
Aperture
Stainless Substrate
Scintillator
3.2 cm
*Maui-535: http://www.lightscapematerials.com/02_pdfs/M535.pdf
Slides into
position
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Strike maps are calculated using the Monte Carlo code NLSDETSIM*
• Energy dependence is determined based on value of the magnetic field at the detector
Modeling of Ion Impact Locations Indicates that the FILD is Sensitive to a Wide Phase Space
7
ApertureScintillator
0.5
2.5 4.5 6.5 8.5
2030
4050Pitch Angle (deg) Gy
rora
dius (
cm)
60 70 80 89
0.5e6 ions
1.7e6 ions
*S.J. Zweben, et al., Nucl. Fusion 30, 1551 (1990).
Strike Map for Optimized Aperture Geometry
• Color contour represents ion number density– grid points mark the average position of all impacts from 3.2 × 106 orbits– 432 × 106 orbits calculated for this map
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
Ion TrajectoryApertureScintillator
0.5
2.5 4.5 6.5 8.5
50
Pitch Angle (deg)
Gyro
radiu
s (cm
)
70 80 89
Viewing Region of Single Fiber Optic Channel
6040
• In-vacuum fiber optics custom prepared by LEONI Fiber Optics*
• Future replacement by a coherent fiber bundle will provide full scintillator imaging
Scintillator is Imaged by Four Fiber Optic Cables Transferring Light to Photomultiplier Tubes
8
Fiber OpticCoupler
Aperture
*http://www.leonifiberoptics.com/contact-leoni-fiber-optics.html
Stainless Lid
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Shield thickness limits ability to utilize edge of scintillator
• Extending aperture across the lid and shield significantly increases measurable phase space
Extending the Aperture into the Molybdenum Shield Greatly Increases the Usable Scintillator Area
9
-6 -4 -2 0 2Y-position (toroidal, cm)
-2
-1
0
1
2
Z-po
sition
(ver
tical,
cm)
ApertureScintillator 0.5
2.5 4.5 6.5 8.5
2030
40 50 60 70 80 89Pitch Angle (deg)
Gyro
radiu
s (cm
)
-4 -2 0 2 4Y-position (toroidal, cm)
-2
-1
0
1
2
Z-po
sition
(ver
tical,
cm)
ApertureScintillator 0.5
2.5 4.5 6.5 8.5
20
3040 50 60 70 80 89Pitch Angle (deg)
Gyro
radiu
s (cm
)
Lid/TZM Aperture
Lid-only Aperture
Stainless SteelLid
Molybdenum (TZM)Shield
Aperture
v||,ion
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Ion trajectories begin at the position of the FILD aperture:
Toroidal Clearance of Δϕ ≈ 40o Allows for Detection of Most Orbits with E > 50 keV
10
Toro
idal P
ositio
n (de
g)
380
360
340
320
300
280R (m)
0.94 0.92 0.90 0.88 0.86
0.7v|| / v = 0.3
1100309032, 1.0 s
E = 500 keV
0.7v|| / v = 0.3
1100309032, 1.0 s
E = 500 keV
Toro
idal P
ositio
n (de
g)
380
360
340
320
300
280R (m)
0.94 0.92 0.90 0.88 0.86
50 keV500 keV
1100309032, 1.0 s
v|| /v = 0.5
50 keV500 keV
100309032, 1.0 s
v|| /v = 0.5• Necessary toroidal
clearance is Δϕ ≈ 40o for all energetic ions of interest
Rap = 0.931 m
zap = -0.024 m
Limiter
Limiter
LimiterR = 0.900 m
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Minimum toroidal clearance is Δϕ ≈ 40o
• Primary obstacle is a split limiter of reduced footprint
• Maximum clearance is Δϕ ≈ 108o
Installation Location Provides Ideal Toroidal Clearance
11
RF Antenna
RF
RF
Ip, BT
A
B
CFILD
Ro = 0.67 m
SplitLimiter
D
E F
G
H
J
K
∆φ # 40o
LH
Split Limiter
C-Mod Top View
FILD
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
Field Aligned Orientation Increases Scintillator Coverage and Extends Detection to Smaller Pitch Angles
12
ApertureScintillator
0.5
2.5 4.5
6.5 8.5
3040
5060 70 80 89
Pitch Angle (deg) Gyro
radiu
s (cm
)
ApertureScintillator
0.5
2.5 4.5 6.5 8.5
2030
40 50 60 70 80 89Pitch Angle (deg) Gy
rora
dius (
cm)
Field Aligned
Horizontal (midplane)
BFILD = 4.0 TrL = 0.5 cm → E = 19 keV
rL = 5.0 cm → E = 1916 keV
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Orbits calculated across all FILD-acceptable gyrophases: Δθgy = ±5o
• Spatial localization determined by ensemble of all orbits – Δϕbounce ≈ 5o
– ΔR, Δz ≈ 1 cm
Detectable Orbits are Spatially Localized
13
0.4 0.6 0.8 1.0R [m]
-0.6
-0.4
-0.2
0.0
0.2
0.4
z [m
]
11003090321000 ms
phi [rad]
z [m
]
BoIp
1100309032, 1000.00 ms
0 60 120 180 240
FILD
300 360phi [degrees]
0 1 2 3 4 5 6-0.4
-0.2
0.0
0.2
0.4
op
Eo = 500 keV, v||/v = 0.50Δϕbounce = 5.5o
Single OrbitAll Orbits
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011 14
• Compact neutral particle analyzer array observes evolution of tail ion distribution
• I-mode* provides increased temperature at reduced density, an ideal RF tail environment
Marmar, YI2.00003, Friday AM
• ICRH tail temperatures same as JET in high temperature I-modes:White, poster 20 of this session
Reliable Ion Cyclotron Resonance Heating System Produces Significant Tail Ion Densities up to E = 2 MeV
1500
1000Count Rate (counts/s)
500
00.0 0.5 1.0t (s)
1.5 2.0
< 500 keV> 500 keV
J6
2.0
Ip (MA)
PRF (MW)
Te(0) (keV)
ne (x1020 m-3)1.5
1.0
0.50.0
Shot1110217040
6543210
Ip (MA)
PRF (MW)
Te(0) (keV)
ne (x1020 m-3)
R = 0.70 m
*D.G. Whyte, et al., Nucl. Fusion 50, 105005 (2010) A.E. Hubbard, et al., Phys. Plasmas 18, 056115 (2011)
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011 15
Diagnostic Suite Provides Wide Coverage of Energetic Ion Profiles and Instabilities
major radius [m]0.5 0.6 0.7 0.8 0.9
z [m] 0.0
+0.1
-0.1
-0.2
-0.3
+0.2
+0.3
ampli
tude [
a.u.]
+1
- 1*Adapted from Fig. 5: E.M. Edlund, et al., Phys. Rev. Lett. 102, 165003 (2009)
• Compact neutral particle analyzer array (CNPA): ffast(E)
• Phase contrast imaging (PCI): line-integrated ñ Ennever, poster 7 of this session
• Electron cyclotron emission (ECE): Te and Te– FRCECE: profile, 32 channels – CECE: fluctuations, 1 cm spot size
Sung, poster 19 of this session
• Fast ion charge exchange (FICX): ffast(E) Liao, poster 28 of this session
~
n = 3 RSAE Density Perturbation (a.u.)*
PCI/CNPAChords
FILD
FICX
1 cm4 cm
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
ICRH Antenna Phasing is Adjusted in-shot, Modifying Sawteeth and Tail Ion Confinement
16
t = 1.14 s
• H-minority heating scenario
• J-antenna phase is modulated– first five cycles: -90 phasing
– last four cycles: +90 phasing
• Significant neutron reduction during +90 phasing
I p (M
A), n
L04 (
1020 m
−2) 1.2
1.00.80.60.40.20.0
nL04
Ip
T e (k
eV)
6543210
FRCECE 1
FRCECE 32
P RF (
MW),
Neut.
(1013
s−1) 5
43210
t (s)1.41.21.00.80.6
FRCECE 1
FRCECE 32
Neutrons
PRF
-90 J-phasing +90 J-phasing
Core Te
Edge Te
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• Activity at f > 500 kHz is consistent with Alfvénic activity• Fluctuation at f ~ 275 kHz is unidentified• Intriguing environment for investigating tail ion-driven MHD
High Frequency Coherent Modes are Driven During the Co-current +90 Phasing
17
0
200
1.00 1.05t (ms)
1.10 1.157.0e-5
6.5
400
600
800Magnetics Cross-power: BP10_GHK, BP11_GHK
log(cross-power) 1/2f (
kHz) -90 J-phasing +90 J-phasing
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
0.4 0.6 0.8 1.0R [m]
-0.6
-0.4
-0.2
0.0
0.2
0.4
z [m]
11003090321000 ms
v||/v = 0.80.4
• Tritons are produced from DD-fusion:D + D → T (1.0 MeV) + p (3.0 MeV) [50%] → He (0.8 MeV) + n (2.5 MeV) [50%]
• Gyroradius of a 1 MeV triton during BT = 8 T (BFILD = 6 T) operation is rL > 4 cm
• Detectable orbits overlap with r/a = 0 m, the likeliest source of fusion products
FILD May Identify Fusion Products During Operations at BT = 8 T
18
1 MeV TritonBFILD = 4.0 T
D.C. Pace, et al., Energetic Ion Losses, APS-DPP 2011
• FILD is capable of measuring energetic ions produced in magnetic fields of BT > 4 T– ICRH tail ions featuring energies of
E ≤ 2 MeV and pitch angles of α > 70o
– BT = 8 T may provide for the detection of fusion products
• Measured losses will contribute to the extensive ICRH experimental and simulation/modeling effort
Fast Ion Loss Detector (FILD) has been Installed on Alcator C-Mod to Measure ICRH Tail Ion Losses
19
FILD