M. Ishikawa, Y. Kusama1, T. Nishitani1, M. Takechi1, K. Shinohara1, M, Baba, T, Itoga, M. Sasao, K. Nomu

ra, V. A. Krasilnikov2, Yu. Kashuck2 ,

Tohoku University, JAPAN1 Japan Atomic Energy Agency (JAEA), JAPAN

2TRINITI, Russia

10th Meeting of the ITPA Topical Group on DiagnosticsMoscow, 10 – 14, April, 2006

JT-60U

Fast Ion Measurements in JT-60U

JT-60U

- Introduction

- Diagnositcs for fast ion measruements

- Highlight Results and issues of fast ion measurements

- Development of Digital Signal Processor of neutron detectors using Flash ADC

- Summary

JT-60U

Contents of talk

JT-60U

AE experiments have been performed using Co-injected Negative-ion-based Neutral Beam (NNB) (ENNB : 340 ~ 400keV, PNNB :3 ~ 5MW) in several kinds of magnetic shear configurations

in Reversed shear (Weak Shear) plasma, • Reversed-Shear induced Alfvén Eigenmodes (RSAEs)　　 (Alfvén Cascades (ACs)), • Transition from RSAEs (ACs) to TAEs (M. Takechi, et al, POP 12(2005),082509 )

in Weak shear plasma with high h • Abrupt Large-amplitude Events (ALEs) (K. Shinohara, et al.,Nucl. Fusion 41(2001) p603)

As fast ion study in JT-60U, recently, Alfvén Eigenmodes (AEs) have been extensively studied.

Introduction

JT-60UFast Ion Measurements in JT-60U

Diagnostics for investigation of fast ion behavior • total neutron emission rate • neutron emission profile Stilbene neutron detector

• charge-exchange neutral particle flux Natural Diamond detector

Neutron ProfileMonitor

6 channel Neutron monitor

Neutral ParticleAnalyzer (NDD)

CX-Neutral Particle Analyzer

Highlight Results and issue offast ion measurements

JT-60U

1

10

100befor ALEafter ALE

ENNB

0

2

4

0 50 100 150 200 250 300 350 400energy [keV]

energy distribution of neutral particle

Only ions in limited energy are affected.=>Agrees with AE resonant condition

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1r/a

En

erg

etic

io

n p

rofi

le(1

018 m

-3)

before ALEafter ALE

<energetic ion profile>

ALEs expel a significant energetic ion population from core to the outer region (redistribution and loss )

-7

0

7

0 0.2 0.4 0.6 0.8 1

É¢S/S (%)

r/a

Averaged change rate of neutron emission profile measurement

Peripheral signals increase and center signals decrease

fast Ion Transport due to ALE in WS plasmas

(M. Ishikawa, et al. Nucl. Fus. 45 (2005) 1474)When bursting modes called Abrupt Large-amplitude Events (ALEs) were exited,

JT-60U

0

1

2

3

4total neutron

4 4.5 5 5.5 6 6.5 7time (s)

0

2

4

6

mode amplitude

180

100

120

140

160

N N B

JT-60U

Observation of two phases of AEs (RSAEs, TAEs) and w/o AEs

In (weak) reversed shear plasma, Reversed-Shear-induced AE (RSAE) and transition from RSAE to TAE was observed during NNBI. After that, mode was stabilized.

RSAETAE

• During RSAEs, TAEs (t ~ 4.5 – 5.5 s) An increase of total neutron emiss

ion rate (Sn) was suppressed

• After TAEs are stabilized (t ~ 5.5 s)

The rate of the increase of Sn is enhanced rapidly.

suggests confinement degradation of fast ions due to AEs

These instability behavior had been predicted by full wave code TASK WM [2].

Further, Task WM had predicted AE in transition phase is most unstable.

[2] A. Fukuyama et al, in proceeding of 6TH IAEA Technical Committee Meeting on Energetic Particles in Magnetic Confinement Systems (12~14 October 1999, Naka)

0

0.5

1

1.5

2

2.5

3

3.5

4 4.5 5 5.5 6 6.5 7

measuredcalculation

Neutron Emissionrate (10

15 s

-1)

Time (s)

RSAETAE

no-AE

Zeff ~ 2.4

Confinement degradation of fast ionsdue to AEs was observed

Measured neutron emission rate is smaller than calculated one (classical) during RSAE and TAE.

Neutron emission rate is calculated with OFMC (Orbit Following Monte Carlo) code assuming as follows

• Energetic ion profile in the calculation are classical• Neutron emission component is beam-thermal reaction

After TAE was destabilized, measured neutron rate is close to calculated one.

(beam-thermal neutron rate accounts for ~ 90% of total neutron rate)

Confinement degradation of fast ions was observed.It was found the reduction rate is largest in the transition phase

(Sn/Sn)Max ~ 45 %

JT-60U

0

1

2

3

4

total neutron

0

0.2

0.4

0.6

0.8

1

4 4.5 5 5.5 6 6.5 7

NEUT(12)

time (s)

neutron emission profilech.2 (r/a ~ 0.34)

180

100

120

140

160

N N B

JT-60UIssue of neutron profile measurements

Saturationof counts

Neutron emission profileChange in neutron signals during and after modes was observed.

RSAETAE

Our interest is how the fast ion profile change.

However, Neutron signal of some channels were saturated after the modes were stabilized

Issue

Maximum count rate of the present system is < ~ 1x105 cps. Dynamic range is narrow. (Statistics error is large)

Development of Digital Signal Processor

using Flash ADC and Stilbene Detector

JT-60U

JT-60U

JT-60U

Development of digital signal processor using Flash ADC

Anode signal(~400ns pulse) is directly fed to Flash ADC

Maximum count rate of Stilbene Neutron Detector : < ~ 105 counts/s Pulse Shape discrimination via an analog electric circuit

DC282 PC

MemoryADC Memory HDDAnode signal

n

γ

Flash ADC : Acqiris DC282 10bits, 8 G [samples/s]

Fast data acquisition system using Flash ADC

Objective : count rate > 106 counts/s

Optimization of integration time

and sampling time

neutrongamma

neutrongamma

1

τ2

JT-60U

Pulse Shape Discrimination by integrated charge with two different integration time

decrease number of sampling

Reduction of data amount

reduce discrimination time

Avoidance of Pile-up

Present condition of our system

Sampling time : 2nsIntegration time : 25ns(fast) 60ns (slow)

Flash-ADC PC

Stilbene

First measurement in JT-60U experimentJT-60U

The DSP system have been installed in understairs of JT-60U torus hall

The sight line passes through the center region of the plasma

Measurement of neutron signals was started and PSD was successfully performed.

00.5

11.5

22.5

33.5

4 5 6 7 8 9 10 11time (s)

analog0

0.2

0.4

0.6

0.8

1 DSP

E45844

JT-60USummary

Digital signal processor (DSP) using Flash ADC and Stilbene detector is developing in order to measure neutron signals with higher counting rate (> 106 counts/s)

The DSP system have been installed in understairs of JT-60U torus hall. Then, Measurements of neutron signals was started and PSD was successfully performed.

In JT-60U, AE experiments in ITER relevant domain have been extensively studied.

In order to investigate behavior of fast ions during AEs, • total neutron emission rate • neutron emission profile ( • charge-exchange neutral particle flux )have been measured.

Transport and confinement degradation of fast ions deu to AEs were observed.

Maximum counts rate of neutron profile measurements is < ~105 cps because of the analog PSD circuit.

JT-60UFuture Plan

DSP using Flash ADC and Stilbene detector

Optimization of method of PSD (integration time)

Development of software for PSD

Installation of the DSP to the present neutron emission profile monitor

Charge-exchange neutral particle flux with the NDD

Application of DSP system

[ Collaboration with TRINITI Lab.]

2345 q

min=2.8

0

200

400

600

800

0 0.2 0.4 0.6 0.8 1ρ

JT-60U

RSAE

2345 q

min=2.5

0 0.2 0.4 0.6 0.8 1ρ 0 0.2 0.4 0.6 0.8 1ρ

2345 q

min=2.3

• Case of reversed-shear configuration with qmin ~ 3.0 -> 2.0

TAE

Fre

que

ncy

qmin

3 2.5 2

(M. Takechi, et al, POP 12(2005),082509 )

Transition3.0 -> qmin -> 2.5 2.5 -> qmin -> 2.0

RSAEs (Alfvén cascades) and its transition to TAEs

JT-60U

the full wave code (TASK/WM) [1]- eigenfrequency, damping rate, eigenfunction

RSAE frequency changes rapidly as qmin changes.RSAE more unstable than TAE.AE in transition from RSAE to TAE is most unstable.

TASK/WM predicted AE transition from RSAE to TAE is most unstable

[1] A. Fukuyama et al, in proceeding of 6TH IAEA Technical Committee Meeting on Energetic Particles in Magnetic Confinement Systems (12~14 October 1999, Naka)

Eigenfrequency Damping rate

RSAE

RSAE

RSAE

RSAE

time

stable

AE instabilities in ITER relevant domain in terms of <βh> v.s. vb///vA are investigated in JT-60U by using N-NB of ~ 360keV vb// : parallel beam ion velocity vA : Alfven velocity

JT-60U

ρh / a is also comaprable,~ 0.05 for JT-60U and ~0.025 for ITER ρh : Hot ion Larmor radius a : Minor radius of plasma

Fast ion profile produced by NNB in JT-60U is more peaked than that of alpha particle in ITER

AE Experiments in ITER relevant domain