8 th iaea technical meeting on energetic particles in magnetic confinement systems

8th IAEA Technical Meeting on Energetic Particles San Diego, CA, October 6 – 8, 2003

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8th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems

Summary of Experimental Papers


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Alpha ParticlesSource of instabilities.Energy source of self-sustainable burning plasma

Supra-thermal, run away electronsSource of dangers on disruption

Source of dangers Should be understood and controlledEnergy source Should be utilized most effectively


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-- 28 “Experimental” Papers --

11 Tokamak papers

8 Helical

1 Linear

7 Diagnostics

1 energetic electrons


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InstabilitiesOrbit Topology/alpha

channeling/Momentum injection/Diffusion Diagnostics

Supra-th.electrons

Tokamak Helical/L Tokamak Helical/L

Testa JET/ITER Sharapov JETSnipes C-ModFasoli JET/ITERShinoharaJT-60U/JFT2MWong DIII-D

Toi LHDIsobe CHSOsakabeLHD Zhao LAPD

ErikssonJET

WongDIIID

Murakami LHD

Ozaki LHDSaida LHDMatsushita

CHSOsakabe L

HDNotake LH

D

Darrow JET/ITER

Sasao ITER DarrowNSTXCecil

JET/ NSTX Roquemore

NSTXLu DIII-D

Gontcharov LHD

Osakabe LHD

PlysusninJET

Fredrickson NSTXGryaznevich MAST/STARTDarrow NSTXMedley NSTXHeidbrink NSTX/DIII-DMedley NSTX

understand use energy understand


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Understad Instabilities---Tokamak

Testa JET/ITER Active excitation/passive excitation

Damping Rate Study extended

PNBI Threshold for Excitation of n=5-8 TAEs Increases with Edge Magnetic

Shear

Mode Splitting and Lower Damping Rate for n=1 TAEs at PNBI>3MW , in L

ow magnetic shear.

nonlinear coupling of EPMs with MeV ions in advanced scenarios .

Error Field Affects Radial Profile of fFAST(E,r)•error field locks to q=2 surface distorting the magnetic topology:

–q=2 TAEs disappear completely–q=3 EAEs only marginally affected

•fast ions scattering: possible method to control peaking of FAST(r)?


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Damping Rate of n=0/1/2 AEs Increases with Edge Elongation and Triangularity

conventional tokamak scenario: monotonic q-profile agreement with theory: role of edge magnetic shear

Nucl. Fusion 41 (2001), 809


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Understad Instabilities---Tokamak

Testa JET/ITER Active excitation/passive excitation

PNBI Threshold for Excitation of n=5-8 TAEs Increases with Edge Magnetic

Shear

Mode Splitting and Lower Damping Rate for n=1 TAEs at PNBI>3MW , in L

ow magnetic shear.

nonlinear coupling of EPMs with MeV ions in advanced scenarios .

Error Field Affects Radial Profile of fFAST(E,r)•error field locks to q=2 surface distorting the magnetic topology:

–q=2 TAEs disappear completely–q=3 EAEs only marginally affected

•fast ions scattering: possible method to control peaking of FAST(r)?


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A.Fasoli

A new antenna system has been designed and is being constructed to excite MHD modes in the Alfvén range of frequencies, in the range n~5-15, which can be driven unstable by fusion generated alphas or other fast particles in large machines.


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Alfvén Eigen Modes Stability---Tokamak

Sharapov JET

Alfvén Cascades modes associated with qmin excited by fast ions.

Used successfully for monitoring the qmin(t) evolution

The temporal correlation between Alfvén grand-Cascades, ITB triggering eve

nts and integer values of qmin has been established for a wide range of pla

sma

conditions and pre-heating scenarios on JET


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Sharapov JET

A technique for obtaining ITBs in shear reversed plasmas by applying the m

ain

heating shortly before the AC time has been established on JET

A new way of detecting Alfvén Cascades with interferometry has been foun

d.

These measurements give a high-accuracy monitoring of qmi (t) and may lea

d to a systematic diagnosis of the transport properties of the layer surround

ing qmi


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Snipes C-Mod

Active and Passive Study has been carried out with a pair of active MHD antennas. Stable TAE resonances at q=1.5 are actively excited with a single high n antenna in both limited and diverted discharges in the range of toroidal fields and densities expected in ITER .

Software synchronous detection provides good fits to the stable TAE resonances on multiple pick-up coil signals with 0.5% < γ/ ω< 4%

Diverted discharges require an outer gap < 1 cm to see the resonance

Alfvén Cascades are observed in the current rise at low density with strong ICRF heating indicating slightly reversed shear with qmin= 3 Results agree well with MISHKA modeling of the Alfvén Cascades ･ Modes are also observed in the EAE frequency range ~ 1 MHz in relatively low density EDA H-modes rotating in the electron direction


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Alfvén Cascades in the Current Rise

Rapidly chirping Alfvén Cascades in the current rise with strong ICRF heating at low density indicate a reversed shear q profile and determine

the minimum q value at the minimum mode frequency


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Alfvén Eigen Modes Stability---TokamakShinohara JT-60U/JFT2M • Reversed-Shear-induced Alfvén Eigenmode (RSAE)

0

0.5

1

1.5

22.22.42.62.83q

min

E40739 E40743

E40744

Mag

net

ic F

luct

uat

ion

Time

[10-5

T]

Bt=3.7T, Ip=1.3MA for all shots

• To investigate dependence of mode amplitude on q-profile, NNB was injected into RS plasmas with various qmin

• n=1 mode amplitude has its maximum around qmi

n = 2.4 - 2.7


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(a)

234

0

5

10

0 0.5 1ρ

RSAE

0 0.5 1ρ 0 0.5 1ρ

TAE

qmin=2.5 qmin=2.3( )cqmin=2.8( )b ( )d

Fig. 3. K.Shinohara et.al.

• A gap is formed due to the reversed shear q-profile at the zero magnetic shear location and is not induced by toroidal coupling • AE was found around the upper and the lower boundary of the gap u

sing the calculation of TASK/WK code • RSAE and its transition to TAE is consistent with the observed upwa

rd and downward frequency sweeping and subsequent frequency saturation.

0

0.5

1

1.5

22.22.42.62.83q

min

E40739 E40743

E40744

Mag

net

ic F

luct

uat

ion

Time

[10-5

T]

Bt=3.7T, Ip=1.3MA for all shots


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Alfvén Eigen Modes Stability---TokamakShinohara JT-60U/JFT2M

• Escaping ion measurement in JFT-2M • Heat flux in Complex magnetic field produced by ferritic inserts

0

1

2

3

4

5

6

neut

ron

emis

sion

rat

e [1

013s-1

m-2]

E39672

4.35 4.4 4.45 4.5 4.55

ALE

0

1

2

B/B

[10-4 ]

~

Time [s]

n

1.1

1.2

1.3

S [1

015s-1 ]

(a)

(b)

(c)ch.1 r/a=0.21

ch.2 r/a=0.34

ch.3 r/a=0.48

ch.4 r/a=0.58

ch.5 r/a=0.75

ch.6 r/a=0.86

ch.6ch.5ch.4ch.3ch.2ch.1


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Alfvén Eigen Modes -- SphericalTokamaks

Fredrickson NSTXNeutral beam injection into the National Spherical Torus Experiment (NSTX) results in a broad spectrum of instabilities .The lowest frequency energetic ion driven modes have a bursting character with strong frequency chirpingas "fishbones".Mode activity in the frequency range of 80 to 150 kHz are classified as Toroidal Alfvén Eigenmodes (TAE). When the TAE exhibit bursting, they can cause substantial fast ion losses.In the frequency range from 0.5 MHz to over 3 MHz for CAE and in ST geometry

Belova NSTX Numerical Study on Compressional Alfvén Eigenmodes (CAEs) and Global Alfvén Eigenmodes (GAEs), which are driven unstable through the Doppler shifted cyclotron resonance with the beam ions [2]. The strong anisotropy in the fast-ion pitch-angle distribution provides the energy source for the instabilities.


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TAE bursts responsible for most of fast ion loss here

• Neutron drops ≈ 10-15 %.• Period is again ≈ 10 ms.• In steady-state, predicted

reduction in fast ion beta of 40 %.

• TAE have strong bursting character with multiple modes present.


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Fredrickson NSTX

In the frequency range from 0.5 MHz to over 3 MHz for CAE and in ST geometry

Belova NSTX Numerical Study on Compressional Alfvén Eigenmodes (CAEs) and Global Alfvén Eigenmodes (GAEs), which are driven unstable through the Doppler shifted cyclotron resonance with the beam ions [2]. The strong anisotropy in the fast-ion pitch-angle distribution provides the energy source for the instabilities.


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Darrow NSTXloss of 80 keV D beam ions .Comparison of the measurements and modeling. A detailed modelis being developed which compute the loss to a specified detector location, incorporating the measured plasma magnetic equilibrium, inferred beam deposition profile, and the range of orbits which enter the detector.

Medley NSTXHorizontally scanning Neutral Particle Analyzer(NPA) whose sightline views across the three co-injected neutral beams. For example, onset of an n = 2 mode leads to relatively slow decay of the energetic ion population (E ~ 5 - 100 keV) and consequently the neutron yield. The effect of reconnection events, sawteeth and bounce fishbones differs from that observed for MHD modes.


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Illustration of MHD-induced Ion Loss during H-mode BT = 4.8 kG, IP = 0.8 MA, Source A & B @ 90 keV, Low MCP Bias

• Following H-Mode onset at 230 ms, the NPA spectra show significant loss of energetic ions only for E>Eb/2.


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Gryaznevich MAST / START

Experimental study of Alfvénic instabilities in STs provides an opportunity to test theoretical models, which could then be applied to alpha-particle physics predictions in ITER and beyond. Several types of high frequency MHD activity that may be associated with toroidal Alfvén eigenmodes and energetic particle modes have been observed on START, MAST and NSTX in neutral beam heated discharges. Chirping down modes in STs were first observed on START. In contrast to START, chirping modes on MAST often exhibit a symmetric chirp up and down in frequency simultaneously. This behaviour can be described by the hole-clump model. MAST exhibits post-sawtooth humpbacked fishbones as well as conventional ones. EPD modes on MAST can trigger long-lasting tearing modes with NTM features. Results of the modelling (MISHKA and HAGIS codes) of the mode structure and frequency sweeping show good agreement with the experimental data and with theoretical predictions.


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Regime EPD modes observed impact on thermal plasma

impact on fast particles

low-(< 5%)

TAE, EAE;

multi-n chirping modes (up, down and both);

fishbones, n=1; ICE

not observed no correlation found on START and MAST up to date (but see NSTX)

higher-(5 - 15%)

chirping modes (down);

fishbones, n=1,2,3

small reversible loss of Wtot;

indirect effect through EPD-triggered long-lasting modes

correlated loss with chirping modes

high- (>15%)

not observed on START not observed on START

not observed on START

Impact of EPD MHD on START and MAST plasmasImpact of EPD MHD on START and MAST plasmas


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Heidbrink NSTX/DIII-D

The major radius dependence of Alfvén Eigen Modes stability is studeid by creating plasmas with similar minor radius, shape , magnetic field, density, Te, and beam population ( near tangential 80 keV deuterium injection) on both NSTX and DIIID. The major radius of NSTX is half of that of DIID.

The stability threshed for the TAW is similar in the devices.

The most unstable toroidal mode number n is larger in DIIID.


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K. ToiEnergetic-Ion Driven Alfvén Eigenmodes in Large Helical Device Plasmas with Three-Dimensional Structure and Their Impact on Energetic Ion Transport

3D-configuration: Non uniformity of the field strength on the magnetic surface in both poloidal & toroidal diections.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.2 0.4 0.6 0.8 1 1.2

0.0%-beta1.12%-beta1.61%-beta2.12%-beta2.66%-beta

Rotational Transform

ι/2π(=1/q)

ρ

q-profile: Negative shear configuration in the edge, and change to positive shear in the core with the increase in the toroidal beta.


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When the minimum ι(0) goes through 0.4, m~2,3/n=1 TAE is converted to m=3/n=1 GAE and m=2/n=1 mode.

m=2/n=1 mode will suffer from strong continuum damping, and it is consistent with exp. Results.

This phenomenon is similar to RS-TAEs in a RS-plasma of JT-60U.

Eigenmode transition from TAE to GAE during time evolution of ι-profile


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At low Bt<0.7T, coherent magnetic fluctuations less than 500 kHz in LHD are observed. Its frequency is about 8 times higher than TAE gap frequency.

They will be Helicity induced Alfven Eigenmode (HAE) whose frequency is by about Nq-times higher than TAE-frequency.

Observation of new AEs in 3D-configuration(Helicity-Induced Alfven Eigenmodes)

S. Yamaoto et al., to be publshed in PRL (2003)


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MHD induced loss of energetic particles are also observed in Helical Systems

Osakabe LHDIncrease and/or decrease of fast neutral flux being associated with the

MHD-bursts were observed for low magnetic field (Bt=0.5~1.2[T]) LHD standard configuration (Rax=3.6[m] and 3.75[m]), for co.-going particles, with dominant components of the MHD burst being assigned as TAE of n=2/m=3~4.

Isobe CHSEscaping fast ion probe is installed and observation shows that MHD acti

vity induces beam ion loss toward small R side.


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Evidence for the influence of fast ions on plasma rotation(L.-G. Eriksson)

• The absorption by fast resonating ions of toroidal momentum carried

by directed ICRF waves, and its subsequent transfer to the bulk

thermal plasma, is found to influence the toroidal plasma rotation

• Discharges with co (+90O antenna phasing) and counter (-90O) current

propagating waves have been compared.

• A reference discharge with about 30% of +90o ICRF power exchanged

for LH power was also performed, giving a lower stored energy and ion

pressure.


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Carbon rotation profiles measured with the charge exchange recombination spectroscopy using NBI blips (method described in Noterdaeme et al.1)

1J.M. Noterdaeme et al, Nuclear Fusion 2003

With LH

• The +90o discharge rotates more strongly in the centre than –90o, consistent with fast ion absorption of wave momentum.

• LH discharge shows the difference is not due to modified WDIA

or ion pressure.

(co-current wave momentum)

t=51 s


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Orbit Topology/alpha channeling/Momentum injection/Diffusion

Wong DIII-DAlpha channelling is demonstrated by experimental data from the DIII-D tokamak. 1. It is shown that spontaneous redistribution of energetic ions by the excited Alfven eigenmodes

can reduce the central magnetic shear and produce velocity shear at the same time - the two ingredients needed for ITB.

2. Quasi-steady-state ITB can be sustained in DIII-D when Alfven modes are excited. This experimental result demonstrates that the process envisioned in (1) can indeed occur.

3. This mechanism offers the possibility of having an ITB as a natural steady state of a burning plasma.

4. There may not be enough energetic alpha particles in the present ITER design to form an ITB, but it may be possible in a different design.

5. Partial effects, i.e., stabilization of part of the ITG turbulence, may be possible in ITER, and it can still be beneficial to plasma confinement.


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Orbit Topology/Ripples/Diffusion in Helical Systems

The ripple trapped energetic particle is one of important issues in the development of a reactor based on the helical system.

toroidal angle

Toroidalprojection(Boozer co.)

Toroidalprojection(Boozer co.)

B~cnst.

helically trapped

transition


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Murakami LHDRadial transport of energetic particles due to the ripple trapped particle.Complex behavior and radial transport of energetic ions duringNBI and ICRF heating using a global transport simulation code (GNET)Ozaki LHD Charge Exchange Neutral Particle Flux during Fueling Pellet Injection. The decay times depend on the particle energy.The radial information of the diffusion coefficient obtainedSaida LHDEffect of helical magnetic field ripples on energetic particle confinement was investigate. Matching of drift surfaces for trapped particles and Magnetic flux surfaces is important.Matsushita CHSDNB is scanned to see the confinement of energetic partilces.Notake LHDElectric Field effect on partilce orbit is studied.Resonant Loss-cone, cancellation of ExB drift and grad-B drift


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Zhao LAPDLiner basic plasma physics machine, 500 eV ions source.Plan for study of wave-particle resonance between a helium beam and Alfven waves.


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Diagnostics

M. Sasao Overview of Fusion Products Measurements of ITER1. 10 sub-systems are now on the planned for fusion product measurement o

n ITER.

2. Neutron emission rate (time response) measurement for burn control and MHD study will have the 1 MHz capability.

3. Neutron /Alpha birth profile can be obtained by 20 viewing chords and 7 viewing chords from the divertor. Deviation from the uniformity can be detected

4. Measurement of confined alpha particle distributions is a challenge. Several proposals are now under examination.

5. Escaping Alpha Diagnostics is a challenge. Several proposals are now under examination.


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Darrow JET/ITER Design of two lost alpha particle diagnostics for JETThey consist of a poloidal array of five sets of thin foil Faraday collectors, with good time resolution (1 kHz) A scintillator based probe located slightly below the midplane, the energy and pitch angle distribution resolutionThe two candidate scintillator materials, Y3Al5O12:Tb (P53) and Y2O3:Eu (P56), both are luminous to at least 400 C, Experience in operating both diagnostics in a high temperature and high radiation environment will be valuable in preparation for the design of similar diagnostics for ITER.

• Gyromotion of fast ions• Particle selection by slits• Light emission by scintillator


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Thin foil Faraday cups allow some energy resolution

• Detector composed of multiple thin metal foils

• Ion energy determines deposition depth

• Ion current measured for each foil individually

• Current vs depth gives energy distribution (E~30–50%)

Thin(2.5 m)Ni foils

Current flowto amplifiers

Pla

sma


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Cecil JET/ NSTX / DIII-DA new lost ion diagnostic on DIII-D and a redesigned probe on NSTX. The Faraday foil collectors New Results are shown.

RoquemoreNSTXThe neutron emission is seen to be very sensitive to fast-ion related phenomena such as MHD and internal reconnection events. A study presented being performed to evaluate the feasibility of installing aneutron profile monitor on NSTX to spatially resolve the fluctuations in the neutronsignal as well as provide information on fast ion transport and confinement. It is important to minimize Backscattering

Lu DIII-DMeasurement of re-neutralized beam ions for beam ion profile.

Gontcharov LHDThe multidirectional passive neutral particle analyzer has been applied to investigate the behavior of anisotropic distributions of suprathermal protonsLocal measurements of the plasma ion distribution function by detecting charge exchange neutrals from an impurity pellet ablation cloud.

Osakabe LHDBLIP experiment was performed with NPA to see the confinement of energetic partilces.New technics based on the Maximum Entropy and Maximum Likelihood Method(MEMLM).


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V.V. Plyusnin

Super-thermal and runaway electrons at reconnection events during JET disruptions. Study on major disruptions in JET spontaneous and intentional has been carried out to further understanding of the trends of disruption induced runaway process. Runaway electron parameters have been measured using the hard X-ray and neutron diagnostics. Soft X-ray inverse reconstruction and ECE measurements of the electron temperature profile have been used in order to investigate the effect of the magnetic field re-arrangement at disruptions on the runaway process. Soft X-ray inverse reconstruction of the magnetic field evolution at a reconnection event has shown that an axis-symmetric confining configuration has been created again in a very short time-scale (~200 microseconds) after reconnection providing confinement of the super-thermal or low energy runaway electrons generated at this event.


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Interaction between energetic ions and MHD perturbations are studied in major tokamaks, spherical tokamaks and LHD.

Progress in understanding and development of tools for understanding (codes, diagnostic) will be made by collaboration between different configurations.

8 th iaea technical meeting on energetic particles in magnetic confinement systems

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