1. 21th IAEA FEC
‘ th ~ 21th, Chengdu, China
E X / 6 - 2
Confinement Degradation of Energetic Ions due to Alfvén Eigenmodes in JT-60U Negative-Ion-Based Neutral Beam Injection Plasmas
Presented by
Masao Ishikawa (JAEA)
I will be talking about “Confinement Degradation of Energetic Ions due to Alfvén Eigenmodes in JT-60U Negative-Ion-Based Neutral Beam Injection Plasmas”
M. Ishikawa, M. Takechi , K. Shinohara, G. Matsunaga, Y. Kusama, V.A. Krasilnikov1, Yu. Kashuck1, M. Isobe2, T. Nishitani, A. Morioka, M. Sasao3, M. Baba3, JT-60 team
JAEA (Japan), 1 TRINITI (Russia), 2 NIFS (Japan), 3 Tohoku Univ. (Japan)

2. Table of Contents Introduction Alfvén eigenmodes experiments
• Background
• Previous results (large bh) and issues of
Alfvén eigenemodes study in JT-60U
Alfvén eigenmodes experiments
in weak shear plasmas
• Alfvén eigenmodes in weak shear plasma (moderate bh)
• Investigation of confinement degradation of energetic ions
Summary
In this presentation, first I am gonna talk about Introduction of our study.
I will then explain previous results and issues of Alfvén Eigenemodes Experiments in JT-60U.
Next, I will show you the experimental results of Alfvén Eigenemodes conducted in weak shear plasmas,
After I will explain the proferty of Alfvén Eigenemodes in weak shaea plasma, I will then report the result of investigation of confinement degradation of energetic ions due to AEs.
Finally I will make a brief summary.

3. Background
Burning plasmas are self-sustained by alpha-particle heating
However, a high alpha particle pressure gradient could destabilize
Alfvén eigenmodes (AEs)
Burning plasma
Loss of
α-particle
AEs induce
the enhanced transport of alpha-particles
from the core region
- A performance of a burning plasma
could be degraded
- First walls could be damaged by lost
alpha-particles
Fast α-particle
Shear Alfvén wave
Introduction
Burning plasmas are self sustained by alpha-particle heating
However, a high alpha particle pressure gradient could destabilize Alfven Eigenmode, AEs
Then, AE induce the enhance ment transport of alpha particles from the core region.
Due to such AE, A performance of a burning plasma could be degraded
Also, First walls could be damaged by lost alpha-particles
Therefore Understanding of the alpha particle transport in the presence of AEs is one of the urgent research issues for ITER
Excitation of AE
Understanding of the alpha particle transport in the presence of AEs is the important research issues for ITER

4. Previous results and issues of AE studies in JT-60U
In JT-60U, AE experiments have been performed utilizing
Co-injected Negative-ion-based Neutral Beam (NNB)
(ENNB : 340 ~ 400keV, PNNB :3 ~ 5MW)
in several kinds of magnetic shear plasma under combination with PNBs
In weak shear plasma with large h
• Bursting AEs called Abrupt Large amplitude Events (ALEs)
(h : energetic ion beta)
redistribution of energetic ions due to resonant interaction with AEs
M. Ishikawa, 20th. IAEA FEC in Portugal
New simulation result
G. Vlad, TH/P6-4 Fri, (this Conf.)
time scale : < 1 ms
ALE
amplitude : large
In JT-60U, in order to investigate energetic ion behavior due to AE,
AE experiments have been performed utilizing Negative-ion-based Neutral beam, NNB, in several kinds of magnetic shear plasma under combination with PNBs
We are carring out AE experiments in weak shear plasma extensively, because weak shear plasma is one of the steady state scenario in ITER experiments
In weak shear plasmas with large energetic ion beta,
Bursting AEs called Abrupt Large amplitude Events, ALE have been observed. The time scale of ALE is less than 1 millisecond and the amplitude is large.
For ALE, we have observed redistribution of energetic ions due to resonant interaction with AEs. Then, I reported this result last IAEA conference in Portugal.
In weak shear plasma with moderate energetic ion beta, we have observed AEs with moderate amplitude like this. This AE has frequency sweeping of the time scale of a few handred milliseconds, so called RSAE.
For this kind of AEs, We did not investigated energetic ion behavior yet, Recently, we have investigated energetic ion behavior during this kind of AEs. Here I will show the results
In weak shear plasma with moderate h
time scale : 100ms ~ 1 s
amplitude : moderate
We did not investigate energetic ion behavior
Investigation energetic ion behavior

5. Diagnostics for investigation of energetic ion transport
To investigate energetic ion behavior in the presence of AEs
radial profile
energy distribution
Neutron emission
profile measurement
CX neutral particle measurement
To investigate energetic ion behavior in the presence of AEs,
We investigate the radial profile of energetic ions.
In order to investigate radial profile of energetic ions, we measure neutron emission profiles. As shown here, we have 6 channel neutron emission profile measurement system., because beam thermal neutron is dominant component of the total neutron emission rate In AE experiment with NNB, we can infer change in the radial profile of energetic ions ,from change in the neutron emission profile.
Also, we investigate energy distribution of energetic ions by measuring charge exchange neutral particle. The neutral particles are measured with a natural diamond detector installed in the co direction port. Because energy distribution of neutral particles has information of energy distribution of energetic ions, we can investigate change in velocity space of energetic ions.
Neutral Particle
Analyzer (NDD)
Neutron Profile
Monitor
Energy distribution of neutral particles has information on energy distribution of energetic ions
Beam -Thermal neutron is dominant component of the total neutron rate

6. AEs in Weak Shear Plasma (moderate bh)
E MA/1.7T, ENNB~390 (keV)
(A)
n =1 modes with up-frequency sweeping are observed and its frequency saturates.
(A)
(B)
(B)
Only weak AEs are observed
qmn~ 1.5
transition
(2)
2 > qmn > 1.5
RSAE
(1)
qmn< 1.5
qmn= 1.4
TAE
(3)
qmn= 1.2
(4)
classical bb
weak AEs
I’ll show you typical results of AE experiment in weak shear plasma under moderate energetic ion beta.
This figure shows time trace of injection power of NNB, the minimum value of safety factor, qmin. NNB was turned off from 6.5s to 6.8s. These figure show the time trace of the frequency spectrum of the magnetic fluctuation. And, this figure shows the time trace of the amplitude of the magnetic fluctuation.
As you can see, in early NNB injection phase, we labeled A, n =1 modes with up frequency sweeping are observed and it frequency saturate. On the other hand, in the later NNB injection phase, we labeled, B, only weak AEs are observed, such AEs are not observed. Mode amplitude of this AEs are much smaller than such n = 1 AEs.
This evolution is explained as follows, corresponding to q minimum evolution.
These figure show continuum gap map at these time durations.
Namely this figure correspond to time duration of q minimum from 2 to 1.5.
In the time duration, RSAE frequency on the tip of lower continuum increase as q minimum decrease.
In this time duration of q minimum around 1.5, these continuum hit each other and then the TAE gap appear, RSAE transit to TAE, here, I call this phase as transition phase.
In this time duration of q minimum less than 1.5, frequency follow the evolution of TAE.
In later NNB injection phase, TAE are not excited. Probably this reason can be the energetic ion profile. This figure shows classical energetic ion beta profile calculated by Orbit following monte carlo code, OFMC. Amount and gradient of energetic ion beta, that is driving term of Alfven eigenmode, are small in TAE gap region like this.
We have investigated energetic ion confinement for this discharge.
Energetic ion confinement with AE can be investigated by compared with that in the later NNB injection phase
RSAE is global AEs localized near the zero magnetic shear region.

7. Confinement degradation of energetic ions due to n = 1 AEs
E MA/1.7T
To investigate energetic ion confinement, the total neutron rate (Sn) is calculated with the OFMC code
(A)
(B)
• Confinement of energetic ions is classical
(B) with only weak AEs
(A) with clear AEs
Measured Sn is smaller than calculated one
Time evolution of measured Sn agrees with calculated Sn
~ Classical confinement
Confinement degradation
DSn/Sn ~ 25 %
What you see here is time evolution of power of NNB and frequency spectrum, mode amplitude of magnetic fluctuation in the same discharge, I show the previous view graph.
This figure shows time trace of total neutron emission rate. Total neutron emission rate in the later NNB injection phase ia larger than that in early NNB injection phase even the injection power of NNB is lower by about 1 MW. This suggests confinement degradation of energetic ion due to these AE.
Then, to investigate of energetic ion confinement. Total neutron emission rate is calculated with Orbit Following Montecalro Code, OFMC code in JT-60U. In this calculation, it is assumed confinement of energetic ions is classical.
Red circles in this figure show calculated total neutron rate .
In the later NNB injection phase with only weak AE. The evolution of the measured Sn is almost consistent withthat of the calculated Sn.
This indicates confinement in this region is almost classical.
On the other hand, in early NNB injection phase with clear AEs, Measured Sn is smaller than calculated one.
This indicated energetic ion confinement is degraded due to these n = 1 AEs.
This figure shows reduction rate of measured Sn from the calculated one. The rediction rate is up to 25%. Horizontal axis in this figure is mode amplitude of the magnetic fluctuation and vertical axis is the reduction rate of the neutron emission rate. The reduction rate is large when mode amplitude is large.
Thus, confinement degradation of energetic ions due to these AE are observed quantitatively.
However, such total neutron rate is is a volume-integrated value, energetic ions transport in the plasma or lost is unknown.
Reduction rate in Sn increases when mode amplitude increases
DSn/Sn
Energetic ion transport ?

8. Energetic ion transport from the core region due to AEs
To investigate energetic ion transport, neutron emission profile was measured
Plasma configuration and sight lines
Calculated line integrated neutron profile with a transport code (TOPICS) is compared with the measurement.
(A)
(B)
(A) with AEs (t=6.4s)
(B) with weak AEs (t=7.8s)
Then, in order to investigate energetic ion transport during AEs, we measure neutron emission profile.
What you see here is frequency spectrum of magnetic fluctuation of same discharge and each signal of 6 channel of line integrated neutron emission rate. This figure shows plasma configuration and each sight line.the color in this figure correspond to color in this figure. Innermost channel is largest and outermost channel signal is smallest.
Here, in order to investigate of energetic ion transport during these AEs, we calculate line integrated neutron emission profile along each sight line with a transport code TOPICS and compared with the measurement at these point. In this calculation, classical confinement of energetic ions is assumed.
This figure is just a comparison of line integrated neutron emission profile between measurement and calculation. Horizontal axis in these figure is the innermost normalized minor radius each sight line passed through the plasma. As you can see, in the case of the later NNB injection phase, difference between measurement and calculation is small.
On the other hand, in the presence of clear AEs, measured neutron emission rate in the center region are smaller than calculation and outer region is larger.
This figure shows ratio of measurement to calculation. Less than 1 means measured neutron rate is smaller than calculation, namely smaller than classical value. In the center region with AE, measured neutron is much smaller than the classical value by 40 %
This result indicates energetic ions were transported from the core region to the outer region during AEs.
Energetic ion transport from the core region of the plasma

9. Local transport of energetic ions in the transition phase
In transition phase,
The innermost channel signal does not increase
qmin=1.5
The second channel signal increases rapidly
Further, we focus attention on change in neutron emission profile in the transition phase. What you see here is the same figure I show the previous viewgraph.
This broken line is time of q minimum is 1.5. In this region, TAE gap appear and mode transit to TAE.
Then, in this transition phase, increase of the innermost channel signal stopped like this. On the other hand, rate of increase of the second channel signal enhanced like this.
Then, in order to investigate energetic ion behavior in the transition phase, we calculate line integrated neutron emission rate with the topics code and compare with measurement.
First is in this point,,,,,,, . This figure shows the ratio of measured line integrated neutron emission profile to the calculation with TOPICS code. Horizontal line is innermost normalized minor radius each sight lin path though. Vertical axis is ratio of measurement to calculation. Value less than 1 means measurement is smaller than the classical value. At this point, the signals in the center region is smaller than the classical value. Further we compare at this point, as you can see, signal of inner most channel further decrease and second signal increase compared with this point.
Checking the alfven continuum, in the transition phase, TAE gap appear in the center region and q minimum and TAE gap both lie the round r/a < 0.3.
Then, this result suggest local transport of energetic ions in the center region due to AEs core localized.
qmin and q = 1.5 surface (TAE gap) both lie around r/a < 0.3
Local transport of energetic ions in the center region

10. Resonant interaction with AEs and eneregetic ions
Frequency (kHz)
100 50
5.5
6.0
7.0
6.5
5.0
8.0
time (s)
Neutral particle fluxes in limited energy range (50 ~ 300 keV) are enhanced.
Peak fraction of enhanced neutral particle flux is ~ 200 keV.
[ Resonance condition with the mode ]
( R. B. White et.al. Phys. Fluids 26 (1983) 2958 )
N= (f / fc) q - nq + m = integer
f = mode frequency ( kHz)
q = safety factor ( )
n, m = toroidal, poloidal mode number
Fc = troidal transition frequency of energetic ions
Resonant energy range => 140 ~ 280 keV
Let’s move to the next topic. Here I will show you the result of neutral particle measurement with natural diamond detector.
This figure is frequency spectrum and what you see here is energy distribution of charge exchange neutral particles. Red line is during AE, and blue line is in the later NNB injection phase. As you can see, due to AE, neutral particles in this energy range are enhanced. This figure shows energy dependence of enhancement factor due to AEs. Form this figure, neutral particle fluxes in limited energy range (50 ~ 300 keV) are enhanced.
Peak fraction of enhanced neutral particle flux is ~200 keV.
This equation shows resonance condition between energetic ions and mode. Substituting the experimental parameter, we can calculate the energy region satisfying resonant condition. From calculation, resonant energy range is obtained from 140 keV to 280 keV. As you can see, Changes in the energy distribution suggest the resonant interaction between energetic ions and modes. Further enhancement in such lower energy region. It is considered to be due to slowing down of transported energetic ions.
Changes in the energy distribution suggest the resonant interaction between energetic ions and modes

11. summary • AEs with frequency sweeping
in weak shear plasma with moderate h
• AEs with frequency sweeping
( time scale : 100ms ~ 1s, amplitude : moderate )
Energetic ion behavior is investigated with
• total neutron emission rate
• neutron emission profile
• charge exchange neutral particle flux
Confinement degradation of energetic ions are quantitatively observed.
Now, let me summarize my talk.
In our study, for AE with large frequency sweeping in weak shear plasma with moderated energetic ion beta, we investigate4 energetic ion behavior with total neutron emission rate
• neutron emission profile
• charge exchange neutral particle flux
As a result, Confinement degradation of energetic ions are quantitatively observed.
Neutron emission profile measurements indicate energetic ion transport from core region to outer region and local transport in the core region in the transition phase
Changes in neutral particle flux suggest the resonant interaction between energetic ions and modes.
Neutron emission profile measurements indicate energetic ion transport from core region to outer region and local transport in the core region in the transition phase.
Changes in neutral particle flux suggest the resonant interaction between energetic ions and modes.

12. Change in neutral particle flux suggests energetic ion transport from core to outer region
Neutral particle flux change after neutron emission rate changed
Time lag (t) ~ ms
time scale of transport and /or
slowing down
Energetic ions are neutralized through charge exchange reactions with D0 or C5+ in outer region of the plasma t
energetic ion transport from core region to outer region