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4 th US-PRC Magnetic Controlled Fusion Collaboration Workshop, UT Austin, May 5-6, 2008 . Recent ICRF Results in the Alcator C-Mod Tokamak. Presented by Yijun Lin With contributions from S. Wukitch, A. Binus, A. Ince-cushman, E. Marmar, M. Reinke, and J. Rice Alcator C-Mod Project

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recent icrf results in the alcator c mod tokamak

4th US-PRC Magnetic Controlled Fusion Collaboration Workshop, UT Austin, May 5-6, 2008

Recent ICRF Results in the Alcator C-Mod Tokamak

Presented by Yijun Lin

With contributions from S. Wukitch, A. Binus, A. Ince-cushman, E. Marmar, M. Reinke, and J. Rice

Alcator C-Mod Project

MIT, Plasma Science and Fusion Center

Cambridge, MA 02139, USA

outline
Outline
  • Introduction of Alcator C-Mod
  • Overview of ICRF program
  • Recent ICRF results:
    • ICRF technology: fast ferrite tuning system
    • Fast wave direct electron heating
    • Mode conversion sawtooth modification
    • Mode conversion flow drive
  • Collaboration areas
c mod unique in world and us among high performance divertor tokamaks
C-Mod Unique in World and USAmongHigh Performance Divertor Tokamaks
  • Unique in the World:
  • High field, high performance divertor tokamak
  • Particle and momentum source-free heating and current drive
  • Equilibrated electron-ion coupling
  • Bulk all high-Z plasma facing components
  • ITER level (and beyond) Scrape-Off-Layer/Divertor Power Density
  • Approach ITER neutral opacity, radiation trapping
  • Highest pressure and energy density plasmas
  • Exclusive in the US :
  • ICRF minority heating
  • Lower hybrid current drive
  • A premier major US facility for graduate student training
present icrf system
Present ICRF System

D & E antennas

J antenna

c mod icrf research themes
C-Mod ICRF Research Themes
  • RF system R & D:
    • Antenna design, and real-time match for successful RF operation.
  • RF edge-plasma interactions:
    • Antenna coupling, dynamic loading, voltage and power limitations, RF sheath, and impurity production.
  • Wave propagation and absorption:
    • Fundamental minority heating, 2nd harmonic majority heating, direct fast wave, and mode conversion absorption regimes.
    • To validate simulation codes, scalable to ITER and reactors, to provide confidence in simulation codes used for discharge analysis.
  • Plasma current and flow drive:
    • To develop means to control plasma current profile and affect stability of MHD modes (e.g., sawtooth modification).
    • Investigate flow drive and application.
rf tech r d fast ferrite tuning system
RF Tech. R&D: Fast Ferrite Tuning System
  • A transmitter needs to be isolated from the antenna through impedance matching network.
  • Antenna loading changes with plasma conditions in real-time.
  • Ferrite material  varies vs. ambient B field  length variation in the line.
  • Digital control on the tuner current to achieve real-time matching.
  • Triple-stub design: one pre-match stub, and two with ferrite tuners.
fast ferrite tuning system
Fast Ferrite Tuning System
  • Equivalent length change up to 36 cm at 80 MHz with change of 300 A coil currents.
  • Power supply swing capability: 75 A/ms
  • Computation iteration: 250 s
  • Filled with SF6 for higher voltage handling
  • Water cooled
  • Optical arc detection
digital controller and power supply
Digital Controller and Power Supply

Linux server

PLC interfaces

RF power/phase detector

Power

Supply

Digital

Controller

fft performance in l and h modes
FFT Performance in L- and H-modes
  • Under real-time digital control, the FFT system can maintain the power reflection below 2% under significant antenna load variation.
  • First installed as a double-stub system in 2007, re-configured to triple-stub in 2008, and has been running successfully in the entire 2008 campaign.
  • Max net-power handled 1.85 MW in H-mode.
latest icrf physics experiments
Latest ICRF Physics Experiments
  • From 04/22 to 05/02/2008 (last two weeks), we ran experiments with J-antenna at 50 MHz, and D/E antennas at 80 MHz.
  • In this setup we can access many scenarios other than the normal D(H) minority ICRF heating:
    • Bt ~ 5.3 T, D(H) plasma  J antenna fast wave direct electron heating (no IC resonance), H-minority heating with D/E antennas.
    • Bt ~ 5.1 T, D(H) plasma with low 3He concentration  H-minority heating with D/E antennas and 3He-minority heating from J antenna.
    • Bt ~ 5.1 T, D(H) plasma with moderate 3He concentration  H-minority heating with D/E antennas and D(3He) mode conversion heating/current drive/flow drive from J antenna.
    • Bt ~ 3.3 T,  H-minority heating with J antenna and also 2nd harmonic deuteron heating.
  • Really recent data: No detailed analysis, but only preliminary intepretation.
fast wave electron heating
Fast Wave Electron Heating
  • J antenna at 50 MHz does not have an ion cyclotron resonance in normal Bt = 5.3 T D(H) plasmas.
  • Fast wave electron heating was observed in good confinement plasmas (relatively high β) pre-heated with minority heating.

Wplasma [kJ]

FWEH

Te [keV]

J (50 MHz) Power [MW]

D+E (80 MHz) Power [MW]

Data from 04/23

sawteeth period vs mccd
Sawteeth Period vs. MCCD

50 MHz, D(3He), Mode conversion near q = 1 surface

Co-Current CD, Average sawtooth 10 ms

Counter-Current CD, sawtooth 8 ms

Heating phase,

sawtooth 10 ms

Data from 04/22 and 04/25

D+E 1.7 MW D/E 1.7 MW and J 1.7 MW

strong rotation with small increase in w p
Strong Rotation with Small Increase in Wp

Strong co-Current rotation > 100 km/sec was observed with only 50 kJ increase in plasma energy in some mode conversion plasmas.

A factor of 2 more than normal intrinsic plasma rotation scaling

ΔV [km/sec] ~ 0.9* ΔW[kJ]/Ip[MA]

J antenna in mode conversion regime, while D and E in minority heating regime.

Toroidal rotation (km/s)

Stored energy (kJ)

J 50 MHz (MW)

D+E 80 MHz (MW)

First observed on 04/22/2008. Surprising result.

mode conversion flow drive
Mode Conversion Flow Drive

Toroidal rotation (km/s)

At the power level, J antenna in mode conversion regime generated about twice core rotation than D and E antenna in minority heating.

D+E

J-ant

Stored energy (kJ)

J 50 MHz (MW)

D+E 80 MHz (MW)

Data from 04/25

rotation velocity vs rf power
Rotation Velocity vs. RF power

Blue circles: Mode conversion flow scales with the RF power.

Black squares: Minority heating.

Data from 04/25 and 04/29

collaboration areas
Collaboration Areas
  • ICRF physics and technology
  • LHRF physics and technology
  • Diagnostics
  • MDS-plus
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