advanced icrf antenna for adx€¦ · 21st rf top conf 2. wukitch –sofe 2015 3 adx: advanced...

Wukitch – SOFE 2015 1

ADVANCED ICRF ANTENNA FOR ADX

S.J. Wukitch, P.T. Bonoli, Y. Lin, W.M. Beck, J. Doody, R. Vieira, and L. Zhou

Symposium on Fusion Engineering 2015May 31-June 4 2015

MIT Plasma Science & Fusion Center


ICRF Antenna Performance has Strong Impact on System Reliability

For robust operation, ICRF antennas require:• Coupling - require high coupling efficiency through SOL.• Load tolerance – critical to handling ELMs and confinement transitions• Impurity production – seek to minimize.• Robust long-distant coupling – gas puffing can be useful tool.• Voltage and power handling – 15 kV/cm for E||B• Antenna conditioning – minimize time required to obtain high power

For efficient heating/current drive, antenna should excite wave spectrum that has good core absorption.

• Seek strong single pass absorption.• Avoid cavity modes.

21st RF Top Conf 2


ADX: Advanced Divertor and RF TokamakEXperiment

Mission: Test innovative solutions to divertor and RF sustainment challenges on the pathway to fusion electricity

• Purpose built device to investigate integrated innovative divertor, PMI, and RF solutions at reactor relevant parameters, field and density, in a tokamak device with high core plasma performance.

Key Elements:• Flexible divertor poloidal field coil sets allows

variety of advanced divertor concepts.• Reactor-level heat flux width, SOL q|| and

plasma pressures.• Integrated reactor-relevant RF heating and

current drive systems.

Rmajor = 0.73 m BT = 6.5 T (8T)

Rminor = 0.2 m IP = 1.5 MA (2 MA)

= 1.7 tpulse = 3 s

10 MW ICRF4 MW LHCD

W/Mo


Like C-Mod, ADX will use ICRF for Auxiliary Heating

An outstanding milestone is to demonstrate efficient, robust actuators capable of scaling to a thermonuclear environment.

• Robust wave coupling.• SS operation with low plasma-wall

interaction

Utilize two Field Aligned 4-strap antennas on low field side to provide up to 10 MW source.

Test high field side two strap antenna with up to 2.5 MW source.


Field Aligned ICRF Antenna: Successfully Developed on C-Mod

Field aligned antenna has current straps that are normal to the total B-field, ~10.

• And is helical to conform to plasma shape.

Classic antenna has straps and side protection tiles normal to the toroidal B-field and is cylindrical.

B-field line

B-field line

Field Aligned Antenna Classic Antenna

View of C-Mod Invessel Outer Wall


Field Aligned Antenna has Reliable Coupling

FA antenna has improved load tolerance.• Reflection coefficient is the square root of

reflected power to forward power.• Impedance variation is reduced and• Depends primarily on the real part of the

antenna load.

21st RF Top Conf6


Field Aligned Antenna has Reliable Coupling

FA antenna has improved load tolerance.• Reflection coefficient is the square root of

reflected power to forward power.• Impedance variation is reduced and• Depends primarily on the real part of the

antenna load.

With pre-matching, FA antenna coupled power is more robust.

• On C-Mod, prior to installation of stub average reflected power is 65%.

• Average reflected power after installation is ~17%.

• Maximum achieved power increased to 3.7 MW (4 MW source).

21st RF Top Conf7

11

9

7

5

3

1

VSW

R

with pre-match

no pre-matchField Aligned Antenna VSWR

200 400 600Discharges

Decoupling Stub~

Fixed Stub

Mechanical Stub Tuner and Phase Shifter

2 MW Amplifier

2 MW Amplifier

Antenna


16

12

8

4

1 21.50.5Injected RF Energy [MJ]

Classic Antenna

Estim

ated

Ene

rgy

[kJ]

Energy Deposited onto FA Antenna

Field Aligned Antenna has Low Plasma Material Interaction

Field alignment eliminates RF enhanced heat flux.

• Additional heat flux that appears on the antenna only when the antenna is powered.

21st RF Top Conf8





• Discharges heated with the FA antenna have lower total energy deposited on FA antenna.

21st RF Top Conf9

16

12

8

4

1 21.50.5Injected RF Energy [MJ]

Classic Antenna Field Aligned Antenna

Estim

ated

Ene

rgy

[kJ]

Energy Deposited onto FA Antenna




• Additional heat flux appears on the antenna only when the antenna is powered.


Local RF enhanced antenna impurity source is eliminated.

• Weak antenna source when antenna is NOT energized.

21st RF Top Conf10

1

2

4

3

0.6 0.7 0.8 0.9 1.0Time (s)

.1

2

6

5

PICRF [MW]

reference

Mo I Source


1

2

4

3

0.6 0.7 0.8 0.9 1.0Time (s)

.

PICRF [MW]

1

2

6

5

reference

Mo I Source

Classic antenna






• antenna increases with each power step for Classic antenna.

21st RF Top Conf11


1

2

4

3

0.6 0.7 0.8 0.9 1.0Time (s)

.1

2

6

5

PICRF [MW]

reference

Mo I Source [a.u.]

Classic antenna

Field Aligned antenna






• Antenna source increases with each power step for Classic antenna.

• Antenna source at FA antenna is near reference level – no enhancement.

21st RF Top Conf12


4-Strap, Field Aligned ICRF Antenna for ADX

Based on successful 4-strap, field aligned antenna used in C-Mod.




Utilize purpose built space for antenna field thrus.

• Allows for proper wave spectrum to be launched.






• Allows for robust end fed center grounded current straps.






• Allows for robust end fed center grounded current straps.

ICRF antenna power capability is 5 MW, 60-90 MHz.• Maximum average electric field is not to exceed 15 kV/cm where E||B.• Maximum voltage 50 kV.

Mechanical stress based upon disruption: 1.5 MA, 3 ms, 6.5 T


Key Innovation: High Field Side RF Launch

Motivated by remaining impurity contamination and requirements for reactors.

Injecting power from high field side removes the launcher from high heat flux region.

• Conventional approach has launchers facing into high heat exhaust and turbulent plasma.

RF

Laun

cher

Conventional






• Innovative compact RF launchers can be accommodated on high field side.

RF Launcher

> 0.5 m activelycooledshield&blanket

Innovation






• Innovative compact RF launchers can be accommodated on high field side.

Second innovation is to integrate RF into machine design.

RF Launcher

> 0.5 m activelycooledshield&blanket

Innovation


Increased Engineering Complexity has Potential for Significant Benefits

Robust coupling.• Quiescent high field side SOL - no ELMs or load variations from density

perturbations.• Distance to last closed flux surface is significantly reduced from 10s of

cm to few cm.• Density control through magnetic geometry.

Reduced erosion, impurity source and contamination.• Reduced erosion, sputtering, and RF enhanced convection• 10x better impurity screening• Safe haven from energetic ions/electrons.

Minimized impact on neutronics and tritium breeding ratio.Improvement in wave absorption and propagation - 100% single

pass absorption.


HFS Launcher Design is Based on C-Mod ICRF Launchers


• Vacuum feedthrus enter at top of vacuum vessel.• Critical region for ERF||B.

Coax to strip line transition minimizes radial build.

• ~10 cm radial build for antenna and transmission line.

• RF electric field in transmission line is perpendicular to the toroidal field.

• Voltage limit perpendicular to magnetic field is <40 kV/cm.


HFS Antenna Specifications

ICRF antenna power capability is 2.5 MW, 60-90 MHz.

• Robust end fed center grounded current straps.

• Maximum average electric field is not to exceed 15 kV/cm where E||B.

• Maximum voltage 50 kV.

Mechanical stress based upon disruption: 1.5 MA, 3 ms, 6.5 T

• HFS has twice the magnetic field compared to LFS.

Protection tiles and Faraday rods are TZM.


Utilize Reactor Relevant Materials and Manufacturing Techniques

Plan to 3-D print antenna strap in Inconel with water cooling passages directly included.

Plate current strap with tungsten.• SBIR with Plasma Processes, Inc. to

begin mechanical and RF testing.• RF voltage limits were increased by

~40% - path to higher power.

Single unit construction of refractory metal Faraday rod, protection tile and cooling channels.

• Effort to minimize joints.


Summary: ADX ICRF Antennas

LFS ICRF launchers are based on Field Aligned antenna.• Robust and proven technology.• Provide a comparison high field side launch.

High field side ICRF antenna provides an opportunity investigate the many potential benefits to high field side launch RF.

• Robust coupling - no ELMs or load variations from density perturbations.

• Reduced erosion/impurity generation and better impurity screening.• Safe haven from energetic ions/electrons.

Begin testing of reactor relevant materials and manufacturing techniques in harsh RF and plasma environment.

advanced icrf antenna for adx€¦ · 21st rf top conf 2. wukitch –sofe 2015 3 adx: advanced...

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