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Fast Ion Measurements in JT-60U

Fast Ion Measurements in JT-60U. JT-60U. JT-60U. 10th Meeting of the ITPA Topical Group on Diagnostics Moscow, 10 – 14, April, 2006.

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Fast Ion Measurements in JT-60U

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  1. Fast Ion Measurements in JT-60U JT-60U JT-60U 10th Meeting of the ITPA Topical Group on Diagnostics Moscow, 10 – 14, April, 2006 M. Ishikawa, Y. Kusama1, T. Nishitani1, M. Takechi1, K. Shinohara1, M, Baba, T, Itoga, M. Sasao, K. Nomura, V. A. Krasilnikov2, Yu. Kashuck2 , Tohoku University, JAPAN 1 Japan Atomic Energy Agency (JAEA), JAPAN 2TRINITI, Russia

  2. Contents of talk 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

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

  4. Fast Ion Measurements in JT-60U JT-60U Neutral Particle Analyzer (NDD) 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 6 channel Neutron monitor CX-Neutral Particle Analyzer Neutron Profile Monitor

  5. Highlight Results and issue offast ionmeasurements JT-60U

  6. JT-60U before ALE after ALE Energetic ion profile (1018 m-3) r/a fast Ion Transport due to ALE in WS plasmas When bursting modes called Abrupt Large-amplitude Events (ALEs) were exited, (M. Ishikawa, et al. Nucl. Fus. 45 (2005) 1474) Peripheral signals increase and center signals decrease Averaged change rate of neutron emission profile measurement Only ions in limited energy are affected. =>Agrees with AE resonant condition <energetic ion profile> energy distribution of neutral particle ALEs expel a significant energetic ion population from core to the outer region (redistribution and loss )

  7. Observation of two phases of AEs (RSAEs, TAEs) and w/o AEs JT-60U 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. • During RSAEs, TAEs (t ~ 4.5 – 5.5 s) An increase of total neutron emission rate (Sn) was suppressed TAE RSAE • 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)

  8. JT-60U Zeff ~ 2.4 no-AE TAE RSAE Confinement degradation of fast ionsdue to AEs was observed 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 (beam-thermal neutron rate accounts for ~ 90%of total neutron rate) Measured neutron emission rate is smaller than calculated one (classical) during RSAE and TAE. After TAE was destabilized, measured neutron rate is close to calculated one. Confinement degradation of fast ions was observed. It was found the reduction rate is largest in the transition phase (Sn/Sn)Max ~ 45 %

  9. JT-60U Issue of neutron profile measurements Our interest is how the fast ion profile change. Neutron emission profile TAE Change in neutron signals during and after modes was observed. RSAE However,Neutron signal of some channels were saturated after the modes were stabilized Issue Saturation of counts Maximum count rate of the present system is < ~ 1x105 cps. Dynamic range is narrow. (Statistics error is large)

  10. Development of Digital Signal Processorusing Flash ADC and Stilbene Detector JT-60U JT-60U

  11. Fast data acquisition system using Flash ADC JT-60U n γ PC DC282 Anode signal HDD ADC Memory Memory Maximum count rate of Stilbene Neutron Detector : < ~ 105 counts/s Pulse Shape discrimination via an analog electric circuit Development of digital signal processor using Flash ADC Objective : count rate > 106 counts/s Anode signal(~400ns pulse) is directly fed to Flash ADC Flash ADC : Acqiris DC282 10bits, 8 G [samples/s]

  12. Pulse Shape Discrimination by integrated charge with two different integration time JT-60U neutron gamma 1 τ2 Optimization of integration time and sampling time Reduction of data amount decrease number of sampling Avoidance of Pile-up reduce discrimination time Present condition of our system Sampling time : 2ns Integration time : 25ns(fast) 60ns (slow)

  13. First measurement in JT-60U experiment JT-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. Stilbene PC Flash-ADC

  14. Summary JT-60U 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. 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.

  15. Future Plan JT-60U 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.]

  16. JT-60U RSAEs (Alfvén cascades) and its transition to TAEs (M. Takechi, et al, POP 12(2005),082509 ) • Case of reversed-shear configuration with qmin ~ 3.0 -> 2.0 Transition 2.5 -> qmin -> 2.0 3.0 -> qmin -> 2.5 TAE RSAE Frequency qmin 2.5 3 2

  17. JT-60U Damping rate Eigenfrequency RSAE RSAE RSAE RSAE TASK/WM predicted AE transition from RSAE to TAE is most unstable 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. stable time [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)

  18. JT-60U AE Experiments in ITER relevant domain AE instabilities in ITERrelevant domain in termsof <βh> v.s. vb///vA areinvestigated in JT-60U byusing N-NB of ~ 360keV vb// : parallel beam ion velocity vA : Alfven velocity h/ a is also comaprable,~ 0.05 for JT-60U and ~0.025for ITER h : 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

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