energetic ion losses in the alcator c-mod tokamak*...d.c. pace, et al., energetic ion losses,...

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


• 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


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


• 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


• 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


• 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


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


• 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


• 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


• 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


Field Aligned Orientation Increases Scintillator Coverage and Extends Detection to Smaller Pitch Angles

12


0.5

2.5 4.5

6.5 8.5

3040

5060 70 80 89

Pitch Angle (deg) Gyro

radiu

s (cm

)


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


• 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


• 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)


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


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


• 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


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


• 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

energetic ion losses in the alcator c-mod tokamak*...d.c. pace, et al., energetic ion losses,...

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