Results from Alcator C-Mod ICRF Experiments · • For D(H) minority heating, the ΔVφ scales with ΔW/I p 1 For D(3He) MC absorption, the change in toroidal rotation, ΔV φ, is

Results from Alcator C-Mod ICRF Experiments

18th Topical Conference on RF Power in PlasmasJune 24-27, 2009

S J Wukitch Y Lin and the Alcator C-Mod TeamS.J. Wukitch, Y.Lin and the Alcator C Mod Team

Key Results:1 First demonstration of efficient RF flow drive by mode converted waves1. First demonstration of efficient RF flow drive by mode converted waves.

2. Observed direct fast wave heating on electrons with low single pass absorption.

3. RF sheaths were observed despite insulating protection tiles and were larger in H-mode than expected.

4. Demonstrated real time matching utilizing ferrite stubs at high power.

18th RF Topical Ghent 1

All C-Mod presentations can be found athttp://www.psfc.mit.edu/research/alcator/pubs/RFtopical/RF2009/rf2009index.htm

ICRF Mode Conversion Flow Drive (MCFD)

Background:• RF plasma flow actuator may offer a unique means to externally:

M i l t t t i fl h t bili ti d» Manipulate transport via flow shear stabilization and» stabilize of certain high-beta MHD instabilities.

• Theoretical calculations suggest RF flow drive is possible.1-3

• Limited experimental evidence of flow drive with RF waves• Limited experimental evidence of flow drive with RF waves.» Enhanced confinement attributed to ion Bernstein wave shear flow in PBX-M.4» Plasma flow observed with low frequency RF heating in Phaedrus-T.5» Sheared poloidal flow observed with IBW in TFTR.6p» Poloidal flow observed between mode conversion layer and minority resonance

in TFTR.7

Experimental Description:• Utilize mode conversion (MC) from long wavelength fast wave to two short

wave length modes: ion Bernstein and ion cyclotron waves.• Utilize L-mode discharges and• Compare mode converted absorption scenario with minority absorption.

1. G.G. Craddock et al., Phys. Rev. Lett. 67, 1535 (1991).2. L.A. Berry et al., Phys. Rev. Lett. 82, 1871 (1999).3. E.F. Jaeger et al., Phys. Rev. Lett. 90, 195001 (2003).


g , y , ( )4. B.P. LeBlanc et al., Phys. Plasmas 2, 741 (1995).5. S.J. Wukitch et al., Phys. Rev. Lett. 77, 294 (1996).6. B.P. LeBlanc et al., Phys. Rev. Lett. 82, 331 (1999).7. C.K. Phillps et al., Nucl. Fus. 40, 461 (2000).

Observe Toroidal and Poloidal Rotation with Mode Conversion

Toroidal rotation, Vφ, profile is peaked and approximately twice that observed in D(H) minority heated discharge. 60

80

km/s

]

Mode ConversionMinorityOhmic

y g• For D(H) minority absorption the

rotation profile is approximately flat and dominated by intrinsic rotation.

Change in poloidal rotation profile is 0204060

Rot

atio

n V

φ [k

Change in poloidal rotation profile is peaked off-axis in the ion diamagnetic drift direction.

• Vθ is up to 1.5 km/s and localized: 0.3 0.0 0.2 0.4 0.6 0.8-40-20

r/a

Toro

idal

R

< r/a < 0.7.• For D(H) minority absorption, Vθ less

than 0.5 km/s and has no clear spatial structure.

3.0

ion

Mode ConversionMinority

r/a

Discharge details: • Upper single null, L-mode plasmas

where the 3He concentration was modest (n3H /n ~ 10%) 1.0

2.0

θ [km

/s]

c dr

ift d

irect

i

modest (n3He /ne 10%).• D(3He) mode conversion layer is near

the magnetic axis for 50 MHz.• D(H) minority resonance is near the

magnetic axis for 80 MHz

0.0

1.0-Δ

Vθ

n di

amag

netic


magnetic axis for 80 MHz.• Injected power ~ 3 MW.

0.0 0.2 0.4 0.6 0.8 1.0r/a

-1.0

Ion

MCFD Scales with RF Power

100

D(3He) MC D(H) Minority

100100m

/sec

]

100

m/s

ec]

60

ΔV

φ [

km 60

ΔV

φ [

km

20 60 100

20

1 2 3

20

For D(3He) MC absorption, the change in toroidal rotation, ΔVφ, is i t l t i th i i l i t i i t ti li 1

20 60 100

ΔW/Ip [kJ/MA]

1 2 3PRF [MW]/<ne>[1020 m-3]

approximately twice the empirical intrinsic rotation scaling.1• For D(H) minority heating, the ΔVφ scales with ΔW/Ip

1

For D(3He) MC absorption, the change in toroidal rotation, ΔVφ, is scales


φas PRF / <ne> not with RF E-field.

1. J. Rice Nucl. Fus. 41, 277 (2001).

MCFD is largely Independent of Antenna Phase

The direction of rotation is independent of the antenna

hphase.• Vφ in co-current direction.• Vθ in ion diamagnetic

d if di idrift direction.• Phase scan showed only

10% variation between co-t d h ticounter- and heating

phase.The rotation magnitudes are

i il f ll tsimilar for all antenna phases.


Measurements Confirm Presence of MCICW

Mode converted ion cyclotron wave (MCICW) detected by phase contrast imaging about ~ 4 cm away from the 3He cyclotron resonance and onimaging about ~ 4 cm away from the 3He cyclotron resonance and on the HFS of magnetic axis.

Wave number kR ~ 3-7 cm-1, consistent l i f di i i d


• solution of dispersion equations and • to previous MC experiments (Y. Lin et al, PPCF (2005)).

TORIC Simulation Indicates Significant Power to Ions

2

3

4

5

W/m

3

6

8

1012

MW

/m3

ECE

Fit

Simulation

0

1

2

MW

0.2 0.4 0.6 0.8/

0

2

4 M

Using n(3He)/ne ~ 8-12% for TORIC simulation can reproduces

r/a

p• measured MCICW profile from PCI• And electron power deposition

profile.pThe MC ICW is damped strongly onto

3He ions through a substantially broadened IC resonancebroadened IC resonance.• Fast wave: k|| ~ 10 m-1

• MCICW: k|| ~ 40-50 m-1

k18th RF Topical Ghent 7

||||,3 vkHec +=ωω

Power to Ions Appears to be Important

Experimentally, no flow drive is observed when the power is absorbed by electrons.

2

3

4

40

60

80

km

/s]

km

/s]

V φ

Flux averaged power deposition to 3He from TORIC simulation is approximately at the same location where poloidal 10

MC ICW power to He3 (flux surface

0

1

0

20

[k [k

−ΔV θ(a)

at the same location where poloidal rotation is observed.

Suggests ICW ion interaction is key to 02

4

6

8

MW

/m3

MC ICW power to He3 (flux surface

averaged)

(b)Suggests ICW - ion interaction is key to MCFD. 0.0 0.2 0.4 0.6 0.8

r/a

0 (b)

Thought experiment: Assume toroidal force is proportional to ICW power deposition profile to ions.profile to ions.

• Solve the momentum transport equation in cylindrical coordinates and select diffusion and pinch velocities to match the observed profiles.

• Assumed force profile is consistent with observed rotation profile with χφ~0.1 m2/s.φ

• Estimated total toroidal force ~ 0.036 N per MW ICW or 0.018 N per MW total injected power to match experimental data.

» Injected fast wave momentum (P/vφ) is ~0.03 N/MW.» Mode converted ICW momentum content is 0 15 N/MW» Mode converted ICW momentum content is 0.15 N/MW.

• Sufficient wave momentum is injected but require asymmetry in plasma response.18th RF Topical Ghent 8

Future Directions

ExperimentalExamine dependence of flow drive on 3He concentration

0.54.5

)

PRF

k

TFTR MC flow drive

concentration.• Investigate importance of ion versus

electron absorption.Investigate flow drive scaling with plasma -0.5

0

3.5

Tim

e (s

km/s

MC

density.• Appears to scale inversely with density.• Density also changes the ICW

perpendicular wavelength hence the

-1.0

3.0 3.4R (m)

Ω3He

perpendicular wavelength, hence the radial wave pattern.

Investigate MCFD in He and H plasmas.• H mass density will change perpendicular

l th d di l tt

SimulationSeek scenarios for ITER and larger

devices where significant power i b b d b i i dwavelength and radial wave pattern.

Participate (pending approval) in JET experiments investigating MCFD.

• Data mining has produced evidence

is absorbed by ions via mode converted waves.

• Need to avoid direct electron and ion cyclotron absorption.Data mining has produced evidence

consistent with analysis of JET plasmas. Examine MCFD in H-mode plasmas.Assess influence of plasma current on flow d i

y pSimulate previous reported results

from TFTR.1Will require increased computational

drive. resources.

1. C.K. Phillips et al, NF (2000).

Direct Fast Wave Absorption Experiments

Motivation:Fast wave current drive is expected to

id l d fprovide central seed current for optimizing current profile in AT plasmas.

Background:FW damping is dependent on electron β and

electron temperature.1

2TωIm

2

2

Im

21 1 , ,

2 e

k x ee te

te e

pie e

TA T e vk v m

k e ζ

ωζ

ωπ ω β ζ

⊥− Δ

−⊥

= − = − = =

=

Estimates low single pass, 1-2%, is accessible from existing discharges.

Im 2 e eci

β ζω ω⊥

Fundamental

D resonance

Low single pass raised concerns since earlier work suggested 4% per pass edge loss.2

eso ce

42

30

18


10

80

4

1. M. Porkolab, AIP Conf. Proc. 314, 99 (1994).2. C.C. Petty et al, Nucl Fus. 35, 773 (1995).

Initial Results from Fast Wave Absorption

Successfully observed FW heating.• Utilized 50 MHz and heating

h ( ±10)4

PRF (MW)FW

BT~5.2 T, Ip=1.2 MA, USN

phase (nφ=±10)• Used D(H) minority at 80 MHz to

heat plasma to >4 keV at top of sawtooth

2

0.05

0.1

WMHD (MJ)

H minority

sawtooth.• Discharges were USN, L-mode

with an H-factor ~1.3.• Assuming L mode scaling

2

4

0.05

Te0 (keV)

• Assuming L-mode scaling, effective absorbed power fraction ~0.5.

» Central T increased ~ 1keV1

1.5

ne (1020 m-3)

neutrons (x1013s-1)» Central Te increased ~ 1keV.» Significantly higher density

production with FW compared to minority heating.

2

4

4 PRAD (MW)

neutrons (x1013s 1)

» Increase in neutron rate during FWEH.

» Significant impurity production but radiated power remains under 0.6 0.8 1.2

2

1.0

10

80

42

30

18

RAD ( )


but radiated power remains under control.

Time (s)

FW Absorption is Appears Dominant

Current drive phasing resulted in little or no heating.

C d i h i h 4PRF (MW)

FW

BT~5.2 T, Ip=1 MA, USNheating phase

current drive phase

• Current drive phasing has lower nφ=7 and faster wave phase speed.FW b i h

2

4

0.1

WMHD (MJ)

H minority

FW

• FW absorption has non-linear dependence on phase speed.S t f d t l 2

4

0.05

Te0 (keV)

• Suggests fundamental deuterium absorption is not significant.

L i t t l

2

1

1.5

ne (1020 m-3)

Lowering target plasma temperature resulted in reduced heating efficiency f h i h

2

4neutrons (x1013s-1)

for heating phase.• Target discharge had lower

Te(~3.6) which results in i l 1%

2

4

08

04

23

01

8,2

3

PRAD (MW)


single pass <1%.0.6 0.8 1.21.0

10

Time (s)

ICRF Impurity Production with Metallic PFCs is Challenging

A primary challenge to ICRF utilization in present experiments and future reactors is to reduce/eliminate impurity production specific to ICRF.• Boronization required for high performance discharges in C-Mod.1• Large gap, strong puffing necessary for ICRF H-modes in ASDEX-U.2

Metallic plasma facing components (PFCs) for fusion devices including p g p ( ) gITER are being considered.• Tritium retention is expected to be less than for carbon PFCs and • Have significantly better erosion resistanceHave significantly better erosion resistance.

Allowable high Z metallic impurity concentration is very restrictive. • Allowable W concentration is <10-4 for ITER.• W will radiate in the plasma pedestal region and may detrimentally effect• W will radiate in the plasma pedestal region and may detrimentally effect

H-mode performance.• High confinement modes have increased impurity confinement.

Prescription3 to ameliorate imp rit prod ction has been:Prescription3 to ameliorate impurity production has been:• Operate the antenna in dipole phasing, • Align the Faraday screen with total magnetic field, and

ili l fil d l f i f


• Utilize low Z film on antenna and plasma facing surfaces.1. B. Lipschultz et al., Plasma Phys. (2006).2. Neu et al., PPCF 49, B59 (2007) and Bobkov et al, 50th IAEA (2008).3. Jacquinot et al., Fusion Eng. Design 12, 245 (1990).

Low Z Film Lifetime is Limited

Following a boronization, successive discharges are heated by ICRF.

B i d d h i i l

1st Discharge

2nd Discharge• Boron is eroded when impurity control is lost during the H-mode

• Estimated erosion rate is ~15-20 nm/s ith RF h ti 0 1

0.15

d sc a ge

4th Discharge

with RF heating.JET utilizes beryllium coating on FS and

limiter to control high Z impurity i fl 1

0.05

0.1

WMHD (MJ)

H-modeinflux.1• Estimated erosion rate from Faraday

screen is 15 nm/80 MJ.1

1.5Prad (MW)

8-2

0

• Be layer is eroded from limiters faster but not specified.

Assuming similar erosion rate for Be in 1 00 7 0 8 0 9

0.5

1

1060421018

ITER (400 s discharge) • as B in C-Mod, lifetime of 5 mm layer

in ITER is ~1000 discharges.

1.00.7 0.8 0.9

Time (s)

1 M Bures et al Fusion Engineering and Design


• As Be on JET FS, lifetime of 5 mm is ~15000 discharges.

1. M. Bures et al., Fusion Engineering and Design 12, 251 (1990).

Can Plasma Performance be Improved by Insulating Limiters?

Replaced molybdenum protection tiles with insulating BN tiles to• Remove local antenna molybdenum source.• Eliminate sheaths on field lines that intersect the antenna protection tiles• Eliminate sheaths on field lines that intersect the antenna protection tiles.• Remove RF enhanced plasma potential.

Approach was similar to BN limited installed in the Phaedrus-T tokamak.*S f ll li i d l i i i i h i ll i f BN il d


• Successfully eliminated metal impurities with installation of BN tiles and removal of Faraday screen. *Majeski et al., 11th RF Power in Plasmas, AIP

Conf Proc 244, 322 (1992).

Insulating Tiles did not Improve Performance

Plasma performance was unimproved despite decrease in antenna limiter Mo source.

• Expected less RF power to obtain same stored

6RF power required to obtain

160 kJ < WTot < 180 kJ

• Expected less RF power to obtain same stored energy.

• Suggests RF limiters are not the only source of core Mo.

4

PR

F (

MW

)

Significant RF enhanced plasma potential is observed despite BN tiles.

• BN tile impedance is 100x the plasma-PFC

2

BN installed

sheath impedance.• RF voltage is dropped across insulating tile. • Plasma potential ~100 V in H-mode and would

have significant enhanced sputtering 1.5

RF Power [MW]

1998 2000 2002 2004Year

have significant enhanced sputtering.Contrasts with previous results.

• In Phaedrus-T, little residual plasma potential increase was observed but power density is 10-

0.5

1

1.5

H-modeincrease was observed but power density is 1040 times lower than C-Mod.1

• In C-Mod, BN merely covered metallic surfaces whereas in Phaedrus-T the BN replaced the 50

100


metallic antenna box.

1.4

0

1031120015

Plasma Potential [V]

Time (s)1.44 1.48

In L-mode, Sheath Voltage Scales as P1/2 only with Boronized Walls.

Sheath voltage is expected to scale with antenna power as

150unboronizedboronized

RF Power Density [MW/m2]2 6 10

100

a Po

tent

ial [

V]

,7,9

ITER PowerDensityplasma ant n RFV V C P=

• where Vant is the antenna voltage, Cn is constant depending on antenna loading, and Prf is the coupled power.1

50Plas

ma

5161

4-20

, 100

0621

002-

5,

Post-boronization, find the plasma potential is proportional to square root of power. 150

unboronized

1.51.00.50RF Power [MW]

1000

In a poorly conditioned machine, plasma potential scales with RF power.

100

ten

tial

[V]

unboronized

boronized

50P

lasm

a P

ot

20, 1000621002-5

,7,9

18th RF Topical Ghent 171.00.60.2Sqrt(RF Power) [MW1/2]

100051614-

1.4

1. D.A. D'Ippolito et al., Nuclear Fusion 38, 1543 (1998).

Sheath Potentials are Higher in H-mode

For similar power, the sheath voltage is expected to increase with antenna voltage.

• Measured antenna voltage in H-mode is ~20% than

H-mode

L-mode

H-mode with

150

[V]

comparible L-mode.• Expect RF enhanced plasma potentials to be ~20%

higher in H-modeObserve that plasma potentials are about twice as

BN tiles100

50ma P

ote

nti

al

[

1120015

p plarge in H-mode than L-mode.

Caveats:• RF power is affecting antenna loading.

» Density profile is modified during power power ramp1

50

Pla

sm

1000516014-2

0, 22, 1031

∼P1/2

» Density profile is modified during power power ramp.» Antenna loading is constant above 100 kW.

• RF sheath model needs to allow for cross-field currents.2,3

» Ion flows across the magnetic field along the length of

1.51.00.50RF Power [MW]

1Sorensen et al., Nucl. Fusion 36 (1996).2D.A. D”Ippolito et al., Nuclear Fusion 42, 1357 (2002).3

g g gthe flux tube are balanced by electron currents in and out of one end of the flux tube.

» Integrated flux tube impedance is less than or equal to the impedance through the sheath.

• RF is creating an energetic edge electron population

3E. Faudot et al., Phys. Plasmas 13, 042512 (2006).4D. Tskhakaya et al., Phys. Plasmas 9, 2486 (2002).5M. D. Carter et al, Phys. Fluid B 4, 1081 (1992).6V. Petržílka et al., in Proc. 32nd EPS Conf. on Plasma Phys. 29C, P-2.095 (2005).7 J. Gunn et al., 50th IAEA (2008).

RF is creating an energetic edge electron population.» Small energetic electron population, ~0.1% can double

the sheath voltage.4» Possible mechanisms are Fermi5 and near field6

acceleration.N id f i d l f TS


» No evidence of energetic edge electrons from TS measurements.7

Future Research: Proposed ICRF 4-Strap Antenna

Reduce coupled E|| by making antenna symmetric along a fi ld lifield line.• Integrated E|| along a field

line would be reduced.• Entire structure isEntire structure is

perpendicular to field line.Estimated reduction due to rotation is

~10-30x reduction in ∫E||·dl along fi ld lia field line.

• Compared tilted versus horizontal antenna load via lossy dielectric load antenna.

Feedthrus are 5” diameter (present are 4.5”).Power density at 2 MW (3MW) is 9.8 MW/m2 (14.8 MW/m2)

ossy d e ect c oad a te a.

Strip line impedance is 30 Ω (J is 50 Ω and D/E is 30 Ω)Screen is aligned to B-field and is 50% transparent (same as J)Peak nφ = 14 (0,π,0,π); 11 (0,π,π,0); and 8 (0,π/2,π,3π/2) in vacuumPeak nφ 14 (0,π,0,π); 11 (0,π,π,0); and 8 (0,π/2,π,3π/2) in vacuum

spectrum (bit higher than J antenna).

Reconciling C-Mod and AUG Results

C-Mod and AUG both have insufficient H-mode performance with ICRF and metallic PFCs.

C M d d i di h i RF i i i f h• C-Mod data indicates the primary RF impurity source is away from the antenna.

• AUG concludes the local ICRF limiters are primary source.L d hi h ffi d i d i i d i» Larger gap and high puffing reduce associated impurity production.

• JET in the ‘90s thought it was the Faraday Screen.C-Mod ICRF limiters are behind plasma limiters by ~0.8 cm whereas AUG

ICRF li it th fi t i t f t t ith th lICRF limiters are the first point of contact with the plasma.C-Mod antenna generates less E|| per MW than AUG.

• Straps are out of the antenna box in C-Mod and inside the antenna box in AUG.• Greater image currents with straps inside the antenna box.

For sputtering:• C-Mod is dominated by deuterium on Mo when plasma potential is >90 V y p p

(typical of H-mode).• AUG is dominate impurity sputtering from C and O on W.

If dominated by impurity sputtering of high Z, practically no safe E|| and do ed by pu y spu e g o g , p c c y o s e || dlifetime of low Z materials will be shortened.

18th RF Topical Ghent 20AUG data from Bobkov et al., 50th IAEA (2008).

Proposed ICRF Antenna

Challenge: Maintain Reliable Power Transfer

Edge plasma density and density profile determines the antenna coupling ffi i

1021

LCFS Main Plasma Limiter

Limiter

Near

SOL

efficiency.• Sets the distance to propagation and

propagation characteristics.d d i d i fil i d d

1020

Antenna L

Limiter

Shadow

Far

SOL

e [m

-3]

Edge density and its profile is dependent upon :• Plasma current, target density,

18

1019Cut-off density

Scrape-off Layer

ne

magnetic field, confinement mode, wall conditions, and RF power.

Transient phenomena modify the coupling

88 89 90 91 92

Rmajor [cm]

1018

on fast time scales:• ELMs,• Monster sawteeth, and• Confinement mode transitions


Utilize Triple Stub System

Tun

er #

1

ner

#2

Ferr

ite

T

FixedStubFe

rrit

e Tu

n

Antenna

Stub

Generator

System is installed in the E antenna matching network and operates at 80 MHz

DC1 DC3DC2DCC

MHz.• Fixed stub is used for pre-matching to prevent excessive voltages in the

ferrite stubs.• Ferrite stubs were originally designed for 60 MHz for hybrid ring systemFerrite stubs were originally designed for 60 MHz for hybrid ring system

at DIII-D and tested at ASDEX-U.Have directional couplers for forward power, reverse power, and phase at

four locations to enable analysis


four locations to enable analysis.

Ferrite System Characteristics

Electrical length is 35 cm for +/-150 A.

S d d i• Swept end to end is 4 msec.• Computational time is 200 μs

and presently limited by computational speed

Tuner #1computational speed.

• Calculating tuner settings from transmission line relations. Tuner #2

Comprehensive arc protection to prevent coupling to an arc.

• Optical arc detection in the f i

Tuner #2

Arc detection fiber

ferrite tuners.• Reflected to forward power

threshold set to 25%.

• Phase balance monitor utilizes current probes in the antenna strap near the strap ground.

» Detects loss of current in the current strap.» Primary defense against arcs at low voltage locations


» Primary defense against arcs at low voltage locations.

Smith Chart Representation of Matching Range

Admittance Smith Chart Y = G+jB1.0

To X

MTR

3B

80%

Example Admittance Smith Chart 1.0

oX

MTR

0.5

To

40% 3B

3A2B 5%

10%

20%

40%

0.5

To X

0.0

-Im

(Γ)

2A

1A

1%

G=

0.25

G=

0.5

0.0

-Im

(Γ)

-0.5

To AN

1B

-0.5T 5

010

-1.0 -0.5 0.0 0.5 1.0-Re(Γ)

-1.0

AN

T

<1% reflected <25% reflected-1.0 -0.5 0.0 0.5 1.0

-Re(Γ)

-1.0

To AN

T 108012

5

Design range covers wide range of plasma conditions in both L and H-


mode.

Overall FFT Performance is Good

With pre-matching, obtained 37 kV and 1.85 MW coupled into H-mode 0.15

0.20

tio

total loss in double stub

loss through first FFT

h t t i i li lmode.Found voltage limit to be ~25 kV

in one of the tuners.• Other tuner is higher by at

0.10

0.15

er

Loss

Ra short transmission line loss

Other tuner is higher by at least 30%.

Observed increased losses at high power. 0.00

0.05

Pow

e

p• Related to net magnetic field

in particular tuner rather than nonlinearity in losses due to

0 2 4 6 8Pcirculating (MW)

power.

• FFT characteristics show that for coil current >100 A will result in increased losses.

c cu at g

Pre-matching avoids:• High voltage in FFTs and• Avoids driving the net magnetic field to zero and increasing losses.


g g g

FFT Load Following is Reasonable

5

10

15

Dα (A.U.)

Ant. Loading (Ω)

10

15 Ant. Loading (Ω)

0

5

H-modeL-mode

1.0

MW

)

(MW

)

0.05

0

5

2

Dα (A.U.)

0.2

0.6

Pfo

rw (

M

Pre

lf (

100

t (A

)

Tuner 2

0.01

0.03

0.05

0.10

0.15 Γ2 = Prefl/Pforw

-100

0

100

Co

il C

urr

en

t

Tuner 1

Tuner 2

0.825 0.83 0.835 0.84 0.845 0.85

Time (s)

FFT follows load transitions associated with discharge evolution and

0.4 0.6 0.8 1.0 1.2 1.4

Time (s)

confinement transitions very well.Response is insufficient to maintain match <5% during entire ELM

because it is <50 μs but sufficient to reduce mismatch < fault level.


• Currently limited by computational time but ultimately will be the FFT power supply.

Summary

Observed significant toroidal and poloidal flow with D(3He) mode conversion.

T id l i d i i l li i h i i i /• Toroidal rotation exceeds empirical scaling with instrinsic/spontaneous rotation.

• Scales with RF power.M j i f i b b d b i• Majority of power is absorbed by ions.

First observation of Fast wave electron heating in C-Mod with low single pass absorption.

RF sheaths were:• Still present for an antenna with insulating protection tiles and • Observed increase with H-mode compared to L-mode was larger than p g

expected.A triple stub, fast ferrite matching network reliably maintains power

transfer to the plasma with low reflected power over wide range of p p gconditions.• To date, 1.85 MW coupled into H-mode.• Further improvements are possible in the voltage limit and time response


Further improvements are possible in the voltage limit and time response of these ferrite tuners.

Documents

Results from Alcator C-Mod ICRF Experiments · • For D(H) minority heating, the ΔVφ scales with ΔW/I p 1 For D(3He) MC absorption, the change in toroidal rotation, ΔV φ, is