- Email: [email protected]
Triton burnup measurements using scintillating fiber detectors on JT-60U
Fusion Engineering and Design 34-35 (1997) 563 566 ELSEVIER
Fusion Engineering and Design
Triton burnup measurements using scintillating fiber detectors on JT-60U T. Nishitani a, M. Isobe
b
G.A. W u r d e n c, R.E. Chrien ~, H. H a r a n o Y. K u s a m a a
d
K. Tobita a,
a Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, Ibaraki-Ken 311-01, Japan b Department of Fusion Science, Nagoya University, Nagoya 464-01, Japan ° Los Alamos National Laboratory, New Mexico 87545, USA d University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
Abstract
A new type of 14 MeV neutron detector, based on scintillating fibres, was developed for triton burnup measurements in JT-60U deuterium discharges. The detector consists of an array of scintillating fibres embedded in an aluminum matrix, coupled to a magnetic-resistant phototube with a high current output base, enabling count rates up to 100 MHz. The detector characteristics have been investigated using the Fusion Neutron Source (FNS) DT neutron generator. From the time-dependent measurement of 14 MeV neutron emission in neutral beam (NB) heated plasma discharges, the fast triton diffusivity has been evaluated to be 0.05-0.15 m 2 s-1. Loss of fast tritons caused by Toroidal Alfv6n Eignmode (TAE) instability was observed in the peripheral region of the plasma. © 1997 Elsevier Science S.A.
1. Introduction
Tritons of 1.0 MeV energy are produced in the d(d, p)t reaction at approximately the same rate as the 2.5 MeV neutrons from the d(d, n)3He reaction. The behavior of t MeV tritons is useful to predict the properties of D - T - p r o d u c e d 3.5 MeV alphas, because 1 MeV tritons and 3.5 MeV alphas have similar L a r m o r radii. As the 1 MeV triton slows down into the peak of the D T fusion reaction cross-section, it m a y undergo a D T fusion reaction, emitting a 14 MeV neutron which we then observe.
Time-resolved 14 MeV neutron measurements were made using a silicon diode in JET [1], T F T R [2] and JT-60U [3], or with NE213 scintillation detectors in JET [4]. However, the count rate of the silicon diode was limited to less than 100 kHz. Furthermore, the silicon diode is easily damaged by neutron irradiation ( ~ 10 la c m - 2 ) , which corresponds to the fluence at the detector for only 100 high-neutron-yield D D discharges. In this paper, triton burnup measurements with crude spatial resolution, but excellent time resolution, have been performed as part of a U S - J a p a n fusion collaboration.
0920-3796/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S0920-3796(96)00621-7
564
T. Nishitani et al./Fusion Engineering and Design 34 35 (1997) 563-566
2. Scintillating fiber detector system
101
Directional scintillating counters were built and studied by Chupp and Forrest [5] using plastic scintillating filaments in 1996. A new type of directional neutron detector has been developed for the 14 MeV neutron measurement [6] employing scintillating fibres (consisting of BCF-10 plastic scintillating filaments from Bicron, with optical cladding which acts as the light pipe). Because the maximum proton recoil range for a 14 MeV neutron is 2.2 mm in the plastic scintillator, we chose to use fibres with diameters that were smaller compared to the proton recoil range, i.e. either 1 or 0.5 mm diameter. Only the neutron incident along the axis of the fiber gives the highest energy deposition in the fibre, so this detector has an intrinsic directionality. Since one electron-folding length to scatter 14 MeV neutrons in the plastic scintillator is 10 cm, we chose a 10 cm fiber length. A total of 91 fibres (with 2.5 mm spacing) are embedded in a 10 cm long aluminum matrix, which stops the escaping recoil protons (from neutron interactions) and Compton electrons (produced by gammas) from crossing from one fiber to the next. The detector head is coupled to a magnetic-field-resistant phototube (Hananatsu R2490-05) with a high current-capable base. We utilize an active phototube base to supply linear high current output as needed (up t o 4 mA), which enables pulse counting without any amplifying electronics, resulting in counting rates of up to 100 MHz. The response functions of the detector for 14 MeV neutrons as a function of the incident angle were measured using the FNS D T neutron generator at JAERI Tokai, with a source strength of up to 1013 neutrons s 1, as shown in Fig. 1. The 'knee' feature from channels 300 to 800 is the most interesting part of the spectrum, and it changes with angle. The higher pulse height channel tail is not sensitive, and results from a design defect whereby recoil events nearest the P M T produce larger pulse heights, since the light from the events there is more effectively Collected by the P M T (because it does not have to be trapped in the fiber to reach the PMT). For pulse counting with a discrimination level of 300 mV, the direc-
10°
e, ~, x +
10-1 o (D
0 deg. 30 deg. 60 deg. 90 deg.
10-2 10-3 10-4 0
500
1000
Channel
1500
2000
Number
Fig. 1. Pulse height response functions for 14 MeV neutrons as a function of the incident angle, measured with a scintillating fiber 14 MeV detector using the FNS neutron generator at JAERI Tokai. tionality of the bare detector was evaluated to be _ 30 °, which is rather wide for the spatial resolution required next to the JT-60U. Consequently, the detector is mounted in a small collimator box, consisting of 40 x 61 x 61 cm 3 of 30% borated polyethylene, and the directionality is improved to _+ 7.5 °. Two sight lines have been installed near the midplane of the vessel, just outside the toroidal field coil position on the JT-60U as shown in Fig. 2. Another two sets will be added, and the precollimation will be improved as well, enabling simultaneous measurement of the 2.5 and 14 MeV neutron emission profiles. The scintillating fibre detector has been calibrated by the shot-integrated 14 MeV neutron
2.0
1.0
~0.0
-1.0
-2.0
2
3
4
R5(m)
6
7
8
Fig. 2, Poloidal cross-section of JT-60U, showing positions and sightlines of the scintillating fiber detectors. The spatial resolution is about a/2 at the plasma midplane.
T. Nishitani et al./ Fusion Engineering and Design 34-35 (1997) 563-566
~v~1.5 10 ~6
o
1
cm
5 10
"~ 1--
' I ....
I ....
.
.
25
.
2og 15~ 10 m
15
5 n r I ] I
010 o 10
.
14
I,,~E,#236'6~m~-]-'normaIized
f I~ " ~ .
her;' D=O.O0 m2/s
0
'I
10 13 x
*5 c
>
10 12
©
"~"
10 11 5
6
7 8 T i m e (s)
9
10
Fig. 3. Experimental and calculated 14 MeV neutron emissions after NB turn-off in a deuterium JT-60U plasma.
yield measured with the neutron activation technique using a pneumatic foil transfer system [7]. The foils are irradiated at 20 ~ 30 cm outside the plasma. Threshold reactions of 27Al(n, p), asSi(n, p) and 63Cu(n, 2n) were utilized for the 14 MeV neutron measurements. The counts from the scintillating fibre detector and the 14 MeV neutron yield measured with the neutron activation technique have shown linearity in the range of 14 MeV neutron yields of 1012-10 is per shot.
3. Evaluation of fast triton diffusivity Fig. 3 shows the typical waveforms of 14 MeV neutron emission in an N B - h e a t e d discharge. The peak 14 MeV neutron rate at the time of NB turn-off is as high as 0.6% of the total neutron emission. The shot-integrated triton burn up fraction is 0.55% in this discharge. We analyzed the time histories of the 14 MeV emission after turnoff of the 1.5-2 second NB injection pulse. The time-dependent 14 MeV neutron emissivity was simulated by a simple classical slowing-down model. The plasma was divided into 51 circular shells in the calculation. In each shell, the tritons were divided into 500 groups according to their birth time, with 10 ms time-bins. The number of tritons in a group is assumed to be proportional to the local 2.5 MeV neutron emissivity at the
565
birth-time of the tritons. The tritons were allowed to slow down in each shell according to the classical energy loss theory [8], The loss of confined tritons was then calculated assuming an exponential decay of the number of tritons with the form e - t/~, where t and ~ are the time since the birth and the confinement time of the tritons, respectively. The diffusivity of fast t r i t o n s , Dtriton, was estimated by matching the (confinement time ~ = a~/5.8 Dtriton), which reproduced the experimental triton burnup ratio. The time history of the 14 MeV neutron emission rate was calculated by using time-dependent data for the electron temperature profile from ECE measurements, the ion temperature profile from charge exchange recombination spectroscopy, and the electron density profile from the FIR and CO2 interferometers. In order to derive the deuteron density, we used the effective charge Zeff, from the visible bremsstrahlung measurement. The triton birth profile was then calculated using the 1.5D tokamak code TOPICS. Calculated 14 MeV neutron emissions are plotted in Fig. 3. In this case, a fast triton diffusivity, Dtriton , of 0.1 m 2 s - i gives good agreement with the experimental data. We applied similar analysis to other shots with different major radii. We found that Dtriton ranges between 0.05 and 0.15 m a s -1, and it increases with the plasma major radius where the toroidal ripple rate ranges from 0.4 to 2% at the edge, which suggests that Dtriton increases with the magnitude of the toroidal field ripple.
4. Triton burnup during TAE instability The Toroidal Alfv~n Eigenmode (TAE) instability has the potential to resonantly affect fast ions, and in particular, it can eject fast ions from the plasma. We investigated the triton burnup behavior in TAE modes excited by ion cyclotron range of frequency (ICRF) minority heating of hydrogen in the deuterium plasma. Fig. 4 shows the waveforms of the total neutron and 14 MeV neutron emission in a shot where tritons were first accumulated with 25 M W of NB heating for 1 s (from 5.5-6.5 s), and then the TAE mode was excited by 5 M W of I C R F after t = 7.1 s. The
566
T. Nishitani et al./Fusion Engineering and Design 34-35 (1997) 563 566 :~
#24739 (TS_I)10
,
.,
TAE
, , t , , , ~ ,[7,
Acknowledgements
~
n , , , n , , '-i
,:
-10 (kHz) 3 0 0
I t I / I •
,
I
,
(MW) 4
,
,
I L ~ I ~ I ~ I I !'t
I
,
i
r
I
i
i
~ " ~ . , ~ .
2
I I t I I L!
•
[Soft X - r a y
"-q ~ . ; - ~ ~
, f~-Plc
[
i
q
4 (A.U)
A.
3
The authors thank Y. Ikeda for the calibration of the FNS source and M. Hoek for his neutron cross-calibrations using the JT-60U foil activation system. This work was done as a part of the US-Japan fusion collaboration program in 1994 and 1995.
(1014 S-1 )1
References Total ne
(A.U)
r n n T I ~ , , , l , , , M e V neutron(center)i ~'
0 _ _ ~
(A.U)
3 2
1
14 MeV neutron (perpheral)--4~, ~
~
.14 MeV neutron
0,11
6.50
,
,
,
,
i
6.75
,
,
/~ I
,
,
n
r
r
f
i
7.00
. . . . . . . . . . 7.25 7.50
T I M E (S)
Fig. 4. Waveforms of TAE modes exited by the ICRF minority heating of hydrogen in the deuterium plasma. From the top, Mirnov coil signal, Mirnov frequency, ICRF power (Plc), soft X-ray intensity, total neutron emission, 14 MeV neutron emissions from center and peripheral regions, and the ratio of peripheral/central 14 MeV neutron emissions.
TAE frequency was 260 ,-~285 kHz, and increased with the decrease in the electron density. A sudden decrease in the intensity of the total neutron and the peripheral 14 MeV neutron emission intensity was observed after t = 7 . 3 s. However there was no significant change in the central 14 MeV neutron emission, which indicates that the TAE mode principally affected fast tritons in the plasma periphery. A possible explanation of the triton loss being delayed by 200 ms from the TAE onset is that the precessional drift frequency was resonated with the high n TAE modes [9] while the TAE frequency was changing due to decrease in the electron density.
[1] S. Conroy, O.N. Jarvis, G. Sadler and G. B. Huxtable, Time resolved measurements of triton burnup in JET plasmas, Nucl. Fusion, 28 (1988) 2127-2134. [2] C.W. Barnes, H. S, Bosch, E.B. Nieschmidt et al., Triton burnup studies on TFTR, Proc. 15th Euro. Conf. on Controlled Fusion and Plasma Heating, Dubrovnik, Vol. 1, European Physical Society, Geneva, 1988, pp. 87-90. [3] T. Nishitani, K. Tobita, K. Tani, et al., Beam-injected and fusion-produced particle studies in JT-60U, Plasma Physics and Controlled Nuclear Fusion Research 1992 Proc. 14th Int. Conf. Wtirzburg, Vol. 1, IAEA, Vienna, 1993, pp. 351-361. [4] F.B. Marcus, J.M. Adams, D.S. Bond, et al., Effects of sawtooth crashes on beam ions and fusion product tritons in JET, Nucl. Fusion, 34 (1994) 687-701. [5] E.L. Chupp and D.J. Forrest, A directional neutron detector for space research use, IEEE Trans. Nucl. Sci, NS-13 (1996) 468-477. [6] G.A. Wurden, R.E. Chrien, C.W. Barnes et al., Scintillating-fiber 14-MeV neutron detector on TFTR during DT operation, Rev. Sci. Instrum., 66 (1995) 901-903. [7] M. Hoek, T. Nishitani, Y. Ikelda and A. Morioka, Neutron yield measurements by use of foil activation at JT60U, Rev. Sci. Instrum,, 66 (1995) 885-887. [8] P. Batistoni and C.W. Barnes, Computation of classical triton burnup with high plasma temperature and current, Plasma Phys. Control. Fusion, 33 (1991) 1735-1756. [9] H. Kimura, M. Saigusa, S. Moriyama et al., Excitation of high n toroidicity-induced Alf6n eignmodes and associated plasma dynamical behaviour in the JT-60U ICRF experiments, Phys. Lett. A, 199 (1995) 86-92.
Fusion Engineering and Design
Triton burnup measurements using scintillating fiber detectors on JT-60U T. Nishitani a, M. Isobe
b
G.A. W u r d e n c, R.E. Chrien ~, H. H a r a n o Y. K u s a m a a
d
K. Tobita a,
a Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, Ibaraki-Ken 311-01, Japan b Department of Fusion Science, Nagoya University, Nagoya 464-01, Japan ° Los Alamos National Laboratory, New Mexico 87545, USA d University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
Abstract
A new type of 14 MeV neutron detector, based on scintillating fibres, was developed for triton burnup measurements in JT-60U deuterium discharges. The detector consists of an array of scintillating fibres embedded in an aluminum matrix, coupled to a magnetic-resistant phototube with a high current output base, enabling count rates up to 100 MHz. The detector characteristics have been investigated using the Fusion Neutron Source (FNS) DT neutron generator. From the time-dependent measurement of 14 MeV neutron emission in neutral beam (NB) heated plasma discharges, the fast triton diffusivity has been evaluated to be 0.05-0.15 m 2 s-1. Loss of fast tritons caused by Toroidal Alfv6n Eignmode (TAE) instability was observed in the peripheral region of the plasma. © 1997 Elsevier Science S.A.
1. Introduction
Tritons of 1.0 MeV energy are produced in the d(d, p)t reaction at approximately the same rate as the 2.5 MeV neutrons from the d(d, n)3He reaction. The behavior of t MeV tritons is useful to predict the properties of D - T - p r o d u c e d 3.5 MeV alphas, because 1 MeV tritons and 3.5 MeV alphas have similar L a r m o r radii. As the 1 MeV triton slows down into the peak of the D T fusion reaction cross-section, it m a y undergo a D T fusion reaction, emitting a 14 MeV neutron which we then observe.
Time-resolved 14 MeV neutron measurements were made using a silicon diode in JET [1], T F T R [2] and JT-60U [3], or with NE213 scintillation detectors in JET [4]. However, the count rate of the silicon diode was limited to less than 100 kHz. Furthermore, the silicon diode is easily damaged by neutron irradiation ( ~ 10 la c m - 2 ) , which corresponds to the fluence at the detector for only 100 high-neutron-yield D D discharges. In this paper, triton burnup measurements with crude spatial resolution, but excellent time resolution, have been performed as part of a U S - J a p a n fusion collaboration.
0920-3796/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S0920-3796(96)00621-7
564
T. Nishitani et al./Fusion Engineering and Design 34 35 (1997) 563-566
2. Scintillating fiber detector system
101
Directional scintillating counters were built and studied by Chupp and Forrest [5] using plastic scintillating filaments in 1996. A new type of directional neutron detector has been developed for the 14 MeV neutron measurement [6] employing scintillating fibres (consisting of BCF-10 plastic scintillating filaments from Bicron, with optical cladding which acts as the light pipe). Because the maximum proton recoil range for a 14 MeV neutron is 2.2 mm in the plastic scintillator, we chose to use fibres with diameters that were smaller compared to the proton recoil range, i.e. either 1 or 0.5 mm diameter. Only the neutron incident along the axis of the fiber gives the highest energy deposition in the fibre, so this detector has an intrinsic directionality. Since one electron-folding length to scatter 14 MeV neutrons in the plastic scintillator is 10 cm, we chose a 10 cm fiber length. A total of 91 fibres (with 2.5 mm spacing) are embedded in a 10 cm long aluminum matrix, which stops the escaping recoil protons (from neutron interactions) and Compton electrons (produced by gammas) from crossing from one fiber to the next. The detector head is coupled to a magnetic-field-resistant phototube (Hananatsu R2490-05) with a high current-capable base. We utilize an active phototube base to supply linear high current output as needed (up t o 4 mA), which enables pulse counting without any amplifying electronics, resulting in counting rates of up to 100 MHz. The response functions of the detector for 14 MeV neutrons as a function of the incident angle were measured using the FNS D T neutron generator at JAERI Tokai, with a source strength of up to 1013 neutrons s 1, as shown in Fig. 1. The 'knee' feature from channels 300 to 800 is the most interesting part of the spectrum, and it changes with angle. The higher pulse height channel tail is not sensitive, and results from a design defect whereby recoil events nearest the P M T produce larger pulse heights, since the light from the events there is more effectively Collected by the P M T (because it does not have to be trapped in the fiber to reach the PMT). For pulse counting with a discrimination level of 300 mV, the direc-
10°
e, ~, x +
10-1 o (D
0 deg. 30 deg. 60 deg. 90 deg.
10-2 10-3 10-4 0
500
1000
Channel
1500
2000
Number
Fig. 1. Pulse height response functions for 14 MeV neutrons as a function of the incident angle, measured with a scintillating fiber 14 MeV detector using the FNS neutron generator at JAERI Tokai. tionality of the bare detector was evaluated to be _ 30 °, which is rather wide for the spatial resolution required next to the JT-60U. Consequently, the detector is mounted in a small collimator box, consisting of 40 x 61 x 61 cm 3 of 30% borated polyethylene, and the directionality is improved to _+ 7.5 °. Two sight lines have been installed near the midplane of the vessel, just outside the toroidal field coil position on the JT-60U as shown in Fig. 2. Another two sets will be added, and the precollimation will be improved as well, enabling simultaneous measurement of the 2.5 and 14 MeV neutron emission profiles. The scintillating fibre detector has been calibrated by the shot-integrated 14 MeV neutron
2.0
1.0
~0.0
-1.0
-2.0
2
3
4
R5(m)
6
7
8
Fig. 2, Poloidal cross-section of JT-60U, showing positions and sightlines of the scintillating fiber detectors. The spatial resolution is about a/2 at the plasma midplane.
T. Nishitani et al./ Fusion Engineering and Design 34-35 (1997) 563-566
~v~1.5 10 ~6
o
1
cm
5 10
"~ 1--
' I ....
I ....
.
.
25
.
2og 15~ 10 m
15
5 n r I ] I
010 o 10
.
14
I,,~E,#236'6~m~-]-'normaIized
f I~ " ~ .
her;' D=O.O0 m2/s
0
'I
10 13 x
*5 c
>
10 12
©
"~"
10 11 5
6
7 8 T i m e (s)
9
10
Fig. 3. Experimental and calculated 14 MeV neutron emissions after NB turn-off in a deuterium JT-60U plasma.
yield measured with the neutron activation technique using a pneumatic foil transfer system [7]. The foils are irradiated at 20 ~ 30 cm outside the plasma. Threshold reactions of 27Al(n, p), asSi(n, p) and 63Cu(n, 2n) were utilized for the 14 MeV neutron measurements. The counts from the scintillating fibre detector and the 14 MeV neutron yield measured with the neutron activation technique have shown linearity in the range of 14 MeV neutron yields of 1012-10 is per shot.
3. Evaluation of fast triton diffusivity Fig. 3 shows the typical waveforms of 14 MeV neutron emission in an N B - h e a t e d discharge. The peak 14 MeV neutron rate at the time of NB turn-off is as high as 0.6% of the total neutron emission. The shot-integrated triton burn up fraction is 0.55% in this discharge. We analyzed the time histories of the 14 MeV emission after turnoff of the 1.5-2 second NB injection pulse. The time-dependent 14 MeV neutron emissivity was simulated by a simple classical slowing-down model. The plasma was divided into 51 circular shells in the calculation. In each shell, the tritons were divided into 500 groups according to their birth time, with 10 ms time-bins. The number of tritons in a group is assumed to be proportional to the local 2.5 MeV neutron emissivity at the
565
birth-time of the tritons. The tritons were allowed to slow down in each shell according to the classical energy loss theory [8], The loss of confined tritons was then calculated assuming an exponential decay of the number of tritons with the form e - t/~, where t and ~ are the time since the birth and the confinement time of the tritons, respectively. The diffusivity of fast t r i t o n s , Dtriton, was estimated by matching the (confinement time ~ = a~/5.8 Dtriton), which reproduced the experimental triton burnup ratio. The time history of the 14 MeV neutron emission rate was calculated by using time-dependent data for the electron temperature profile from ECE measurements, the ion temperature profile from charge exchange recombination spectroscopy, and the electron density profile from the FIR and CO2 interferometers. In order to derive the deuteron density, we used the effective charge Zeff, from the visible bremsstrahlung measurement. The triton birth profile was then calculated using the 1.5D tokamak code TOPICS. Calculated 14 MeV neutron emissions are plotted in Fig. 3. In this case, a fast triton diffusivity, Dtriton , of 0.1 m 2 s - i gives good agreement with the experimental data. We applied similar analysis to other shots with different major radii. We found that Dtriton ranges between 0.05 and 0.15 m a s -1, and it increases with the plasma major radius where the toroidal ripple rate ranges from 0.4 to 2% at the edge, which suggests that Dtriton increases with the magnitude of the toroidal field ripple.
4. Triton burnup during TAE instability The Toroidal Alfv~n Eigenmode (TAE) instability has the potential to resonantly affect fast ions, and in particular, it can eject fast ions from the plasma. We investigated the triton burnup behavior in TAE modes excited by ion cyclotron range of frequency (ICRF) minority heating of hydrogen in the deuterium plasma. Fig. 4 shows the waveforms of the total neutron and 14 MeV neutron emission in a shot where tritons were first accumulated with 25 M W of NB heating for 1 s (from 5.5-6.5 s), and then the TAE mode was excited by 5 M W of I C R F after t = 7.1 s. The
566
T. Nishitani et al./Fusion Engineering and Design 34-35 (1997) 563 566 :~
#24739 (TS_I)10
,
.,
TAE
, , t , , , ~ ,[7,
Acknowledgements
~
n , , , n , , '-i
,:
-10 (kHz) 3 0 0
I t I / I •
,
I
,
(MW) 4
,
,
I L ~ I ~ I ~ I I !'t
I
,
i
r
I
i
i
~ " ~ . , ~ .
2
I I t I I L!
•
[Soft X - r a y
"-q ~ . ; - ~ ~
, f~-Plc
[
i
q
4 (A.U)
A.
3
The authors thank Y. Ikeda for the calibration of the FNS source and M. Hoek for his neutron cross-calibrations using the JT-60U foil activation system. This work was done as a part of the US-Japan fusion collaboration program in 1994 and 1995.
(1014 S-1 )1
References Total ne
(A.U)
r n n T I ~ , , , l , , , M e V neutron(center)i ~'
0 _ _ ~
(A.U)
3 2
1
14 MeV neutron (perpheral)--4~, ~
~
.14 MeV neutron
0,11
6.50
,
,
,
,
i
6.75
,
,
/~ I
,
,
n
r
r
f
i
7.00
. . . . . . . . . . 7.25 7.50
T I M E (S)
Fig. 4. Waveforms of TAE modes exited by the ICRF minority heating of hydrogen in the deuterium plasma. From the top, Mirnov coil signal, Mirnov frequency, ICRF power (Plc), soft X-ray intensity, total neutron emission, 14 MeV neutron emissions from center and peripheral regions, and the ratio of peripheral/central 14 MeV neutron emissions.
TAE frequency was 260 ,-~285 kHz, and increased with the decrease in the electron density. A sudden decrease in the intensity of the total neutron and the peripheral 14 MeV neutron emission intensity was observed after t = 7 . 3 s. However there was no significant change in the central 14 MeV neutron emission, which indicates that the TAE mode principally affected fast tritons in the plasma periphery. A possible explanation of the triton loss being delayed by 200 ms from the TAE onset is that the precessional drift frequency was resonated with the high n TAE modes [9] while the TAE frequency was changing due to decrease in the electron density.
[1] S. Conroy, O.N. Jarvis, G. Sadler and G. B. Huxtable, Time resolved measurements of triton burnup in JET plasmas, Nucl. Fusion, 28 (1988) 2127-2134. [2] C.W. Barnes, H. S, Bosch, E.B. Nieschmidt et al., Triton burnup studies on TFTR, Proc. 15th Euro. Conf. on Controlled Fusion and Plasma Heating, Dubrovnik, Vol. 1, European Physical Society, Geneva, 1988, pp. 87-90. [3] T. Nishitani, K. Tobita, K. Tani, et al., Beam-injected and fusion-produced particle studies in JT-60U, Plasma Physics and Controlled Nuclear Fusion Research 1992 Proc. 14th Int. Conf. Wtirzburg, Vol. 1, IAEA, Vienna, 1993, pp. 351-361. [4] F.B. Marcus, J.M. Adams, D.S. Bond, et al., Effects of sawtooth crashes on beam ions and fusion product tritons in JET, Nucl. Fusion, 34 (1994) 687-701. [5] E.L. Chupp and D.J. Forrest, A directional neutron detector for space research use, IEEE Trans. Nucl. Sci, NS-13 (1996) 468-477. [6] G.A. Wurden, R.E. Chrien, C.W. Barnes et al., Scintillating-fiber 14-MeV neutron detector on TFTR during DT operation, Rev. Sci. Instrum., 66 (1995) 901-903. [7] M. Hoek, T. Nishitani, Y. Ikelda and A. Morioka, Neutron yield measurements by use of foil activation at JT60U, Rev. Sci. Instrum,, 66 (1995) 885-887. [8] P. Batistoni and C.W. Barnes, Computation of classical triton burnup with high plasma temperature and current, Plasma Phys. Control. Fusion, 33 (1991) 1735-1756. [9] H. Kimura, M. Saigusa, S. Moriyama et al., Excitation of high n toroidicity-induced Alf6n eignmodes and associated plasma dynamical behaviour in the JT-60U ICRF experiments, Phys. Lett. A, 199 (1995) 86-92.