Fyzika tokamaků1: Úvod, opakování1 Tokamak Physics Jan Mlynář 8. Heating and current drive Neutral beam heating and current drive,... to be continued

Fyzika tokamaků 1: Úvod, opakování 1

Tokamak PhysicsJan Mlynář

8. Heating and current drive

Neutral beam heating and current drive, ... to be continued

Neutral Beam Injection: principle

Ion source

Neutral

beam

Electricity -> other form(kinetic energy of particles)

Transport to plasma (outside part)

Neutraliser

Magnetic

filter

Beam duct

(inside part)

Accellerator

Ionisation Thermalisation

NBI Principle, in more detail

I E Day

Size matters – ITER beamline vs Torus

I E Day

power and pulse length for ITER

0

5

10

15

20

0 1000 2000 3000 4000 5000

pulse length (s)

po

wer

/be

amlin

e (M

W)

I E Day

Evolution from Present Status - ITER

Tokamak Physics 6

Neutral beam heating

8: Heating and current drive

= 2.9.1017

Tokamak Physics 7



Tokamak Physics 8



Tokamak Physics 9

Beam slowing


Tokamak Physics 10

Distribution function


Tokamak Physics 11

Beam current drive


Wave heating

Electricity -> other form(electromagnetic oscillations)

Transport to plasma (outside part)transmission linesantenna

(inside part)waves

Thermalisation

Antenna

Wave to particles

Resonance zone

R

Classification of waves

• phase velocity

– fast

– slow

• direction of propagation

– k parallel to B0: according to polarisation

(with respect to B0, in other fields of science –e.g. optics- wrt propagation direction)

• right -> direction of rotation of electrons

• left -> direction of rotation of ions

– k perpendicular to B0

• ordinary: E1 // B0

• extraordinary: E1 perp to B0

Tokamak Physics 14

Wave Heating


Review of Plasma Waves

Tokamak Physics 15

Wave Heating


Dielectric Tensor

Tokamak Physics 16

Wave Heating


Classification of waves

Tokamak Physics 17

Wave Heating


Resonances, Cut-offs

Tokamak Physics 18

Wave Heating


Resonances, Cut-offs

Tokamak Physics 19

Wave Heating


Energy flow

Tokamak Physics 20

Wave Heating: Ray tracing


Tokamak Physics 21



ASDEX-U

Tokamak Physics 22



Mode conversion

Boundary conditions

Tokamak Physics 23

Wave Heating: CMA diagram


In each region, the topological form of thephase velocity remain unchanged. Fast wave is outside (the wave front in vacuumwhich would always be a circle) slow wave is inside.E.g. in the top left region (high B, low n) the X/L wave is slow, the O/R wave is fast(X and O have k || B, L and R have k ┴ B)

Tokamak Physics 24

Ion Cyclotron Heating


ii

eB

m fast wave ~ tens of MHz

Plasma edge cutoff below 18 32 10 mn

heatingon harmonic frequencies

on minorities (e.g. on H in D plasmas)

Resonant layer is vertical at 1

TB R

Heating on harmonics vL

energies often higher than Ec

relaxation is mostly due to heating of electrons

Tokamak Physics 25



Tokamak Physics 26



Heating on minorities:

Decreases with increasing concentration, however,

new “ion-ion” hybrid resonance emerges.

May result in IBW (Ion Bernstein Wave)

can drive electrons

Disadvantage: strongly sensitive on minority concentration

ICRHadvantages: Economic, powerful, important ion heating

disadvantages: high E, problems with reflected power (ELMs),

(“coupling of waves to plasma”, in particular

problems with ELMs), non-directional.

Plasma edge – evanescent region (cutoff below )

i.e. “waves tunnels through”

The antenna produces a wide spectrum

wide spectrum of fast electrons due to

the Landau damping current drive

Tokamak Physics 27

Lower Hybrid Resonance


Slow wave at a small angle to B ~ GHz long path to the resonant region Landau damping along the path turns out

to be more important than LH itself

18 310 mn

k

Reminder: The current drive would not exist if

distribution of velocities of plasma particles were

flat. However, Maxwellian distribution is not flat,

which means wave can locally flatten the

distribution in the direction of the wave

propagation.

Tokamak Physics 28

Lower Hybrid Resonance


Mode converter

Equally split the RF power in 3 in the poloidal direction

1 input & 3 outputs WR-229 Conversion efficiency: 98.65 % Return Loss: -20.5dB

J. Hilairet

i

a ca

r mf

c ar ed h

i

a ca

r mf

c ar ed h

LH - Wave Propagation

Depends onne and B

Antenna structure

Tokamak Physics 31

Electron Cyclotron Resonance


~ 28 [T] GHz (~ mm)B

Advantages : no evanescent region

highly directional

highest achievable power density

Disadvantages: acts only on electrons

expensive

new technology (less reliable)

Highly directional profile controle.g. suppression of NTMs (mg. islands)

Tokamak Physics 32



Tokamak Physics 33



Tokamak Physics 34



Current Drive (ECCD)

Other applications of ECR:

3

1~

v

1) Fisch – Boozer

directional increase of decreases

2) Ohkawa

increase of pushes passing particles

into the trapped region (opposite direction to the Fisch - Boozer)

lower momentum loss

v

v

- plasma heating- current profile control for advanced regimes- transport studies via modulated ECRH- plasma start-up assistance - wall conditioning (ITER)

Tokamak Physics 35

Bulk and Tail Current Drive


Tokamak Physics 36

ITER ECR system


24 x 1 MW, 170 GHz gyrotrons

3 x 1 MW, 120 GHz gyrotrons for SUA

wave guide switch to …

equatorial or upper launcher

Tokamak Physics 37

ITER ECR Upper Port


• 3 ports with 8 beams in two rows• Main function: NTM (and sawtooth) control• Front steering

– In vertical direction to scan radial deposition

– Well focussed for optimised localization at q=3/2 and 2

Documents

Fyzika tokamaků1: Úvod, opakování1 Tokamak Physics Jan Mlynář 8. Heating and current drive Neutral beam heating and current drive,... to be continued