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Justifications for the measurement requirements related to fast ions in ITER ( action item 11a253)

Justifications for the measurement requirements related to fast ions in ITER ( action item 11a253). Francesco Paolo Orsitto ENEA C R Frascati. Contributions. Reference : F P Orsitto, J-M Noterdaeme,A E Costley, A J H Donne’ – IAEA FEC 2006 IT/P1-27. Introduction.

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Justifications for the measurement requirements related to fast ions in ITER ( action item 11a253)

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  1. Justifications for the measurement requirements related to fast ions in ITER( action item 11a253) Francesco Paolo Orsitto ENEA C R Frascati 12th ITPA Princeton 26-30march2007

  2. Contributions • Reference : • F P Orsitto, J-M Noterdaeme,A E Costley, A J H Donne’ – IAEA FEC 2006 IT/P1-27 12th ITPA Princeton 26-30march2007

  3. Introduction • Recent experiments on JET and JT60U have underlined the need to look into the parameter measurement requirements for fast particles on ITER: • in particular the documented interaction of fast ions with AE and fishbones on JET and JT60U ( in particular the short time scales) • In general the need to detect all the fast ions ( He4,p,T,He3) present in the plasma is proposed Because all of them can interact with AE, and this interaction could lead to a deterioration of confinement of fast ions and loss of efficiency of plasma heating. • The electron distribution function is important as well to be detected and characterized: the deviation of electron d.f. from maxwellian play a central role in the Electron Cyclotron Heating and CD, and in the measurements of electron temperature. 12th ITPA Princeton 26-30march2007

  4. JT-60U In weak shear plasma with moderate h time scale : 100ms ~ 1 s amplitude : moderate results of AE studies in JT-60U In JT-60U, AE experimentshave been performed utilizing Co-injectedNegative-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) time scale : < 1 ms amplitude : large 12th ITPA Princeton 26-30march2007

  5. Local transport of energetic ionsfor weak shear plasmas(Ishikawa IAEA 2006, EX/6-2) qmin and q = 1.5 surface (TAE gap) both lie around r/a < 0.3 Local transport of energetic ions in the center region In transition phase, The innermost channel signal does not increase The second channel signal increases rapidly qmin=1.5 12th ITPA Princeton 26-30march2007

  6. outline • Short Review of proposed new technical specs for fast particles • Justification and discussion of the new requirements on measurements • Analysis of the present status of the diagnostic systems proposed for ITER • Conclusions and summary of R&D needed 12th ITPA Princeton 26-30march2007

  7. Introduction to classification of ITER diagnostics and Review of ‘old’ technical specs for fast particles 12th ITPA Princeton 26-30march2007

  8. ‘old’ technical specs for fast particles • Alpha and He3 must be detected • Spatial resolution =a/10=20cm • Time resolution = 100ms • Accuracy 10-30% Level 1 technical specs (september 2006): in blue the new tech specs 12th ITPA Princeton 26-30march2007

  9. Discussion of new technical specifications 12th ITPA Princeton 26-30march2007

  10. Tech Specs:physics basis Above a critical bfast (beta of fast particles), Alfvén cascades can be excited in a reversed shear discharge, giving rise to a spatial redistribution of fast particles over the minor radius in a time scale of tF ~ 100-300 tA ~ 100-300 ms (tA = Alfvén time = R0/VA ~1ms for a DT (50%/50%) in a ITER rev Shear scenario, R0= major radius, VA = Alfvén velocity=B/(4pni mi)). Indeed such a spatial redistribution on time scales, similar to that calculated by theory, has been reported by JT-60U. (Shinohara NF2001, Ishikawa NF2005, Fogaccia et al EPS2006 Roma, G Vlad et al IAEA FEC2006) 12th ITPA Princeton 26-30march2007

  11. Relevant Time scales • i) time scale related to the saturated non-linear interactions of energetic particles and Alfvén modes tF ~ 100-300 tA; • ii) slowing down time of the fast ions tsd ~0.2-0.5s; • iii) confinement time tE~ 4s ; • iv) resistive relaxation time : tR~ 200-300s. 12th ITPA Princeton 26-30march2007

  12. Relevant spatial scales The relevant spatial scales in general are: i) Larmor radius rfast ~ 0.2-7 cm; ii) Neoclassical Tearing Mode (NTM) island width ≥ ion Larmor radius; iii) Internal Transport Barrier(ITB) width with spatial scale of the order of the pressure gradient; iv) H-mode pedestal width ~ ion Larmor radius; v) turbulence correlation length ~ ion/electron Larmor radius; the scaling of the confinement in H mode depends upon the Larmor radius. 12th ITPA Princeton 26-30march2007

  13. Fast particle energy spectrum • For slowing down distributions the energy range of fast ions is determined by the critical energy (E*) ,for energies E~E* , 50% of energy of fast ions goes directly the electrons and 50% to ions . • E*(He3)~14Te, E*(D)=18Te,E*(H)=30Te, depending on the ion mass. • For ITER(Te=20keV) the energy range important for the transfer of energy to electrons is : • E*He3> 280keV,E*(D)>360keV,E*(H)>600keV 12th ITPA Princeton 26-30march2007

  14. Range of Larmor radius and slowing down time of fast ions 12th ITPA Princeton 26-30march2007

  15. Tech specs • the measurement requirements for fast particles could be proposed: • i) spatial resolution ~ a/20 (10 cm on ITER) close to a Larmor radius; • ii) time resolution (minimum) ~ 100 tA (~ 100 ms for ITER); • iii) density range of fast ions: the density of minority ions could be 4-10% of the plasma density 12th ITPA Princeton 26-30march2007

  16. ‘New’ requirements on measurements for fast particles (*) (*)He0 neutralization proposed by M Sasao for alpha particle meas. 12th ITPA Princeton 26-30march2007

  17. Present motivations in Level1 12th ITPA Princeton 26-30march2007

  18. measurement of fast ion energy ( Motivations I: physics basis) The measurement of the energy spectrum of fast particles is a fundamental quantitywhich enters the dynamics of transfer of energy between fast particles and bulk plasma. The details of the distribution are important also in the context of the impact of evaluating the effect of various instabilities like Alfven Modes and fishbones on the confinement of fast ions and the efficiency of the transfer of energy to bulk plasma. Not only the alpha particles and He3 ions are to be measured , but also protons, tritium and deuterium fast particlesbecause they can interact with MHD modes, and participate to the global energy balance. 12th ITPA Princeton 26-30march2007

  19. Measurement of fast ion energy and spatial distr function( Motivations II: spatial resolution) • In general Not the same specs or measurement requirements for all ion species are needed , but the requirement shown in the table are minimal for all of them • Spatial resolution- in particular : if the gyroradius is the fundamental quantity which determines the spatial resolution then a resolution of a/20 is a conservative evaluation( corresponding to alpha particles larmor radius) , (but a/30 could be more suitable, taking into account the gyroradius of all the fast ions). • Category :The measurements are all in the category 1b or 2 12th ITPA Princeton 26-30march2007

  20. Measurement of fast ion energy and spatial distr. function( Motivations III: time resolution) • Time resolution: It would be ideal having time resolution of 100tA which is the time scale of interaction with AE , but • 1/10 of the slowing down time (~100ms) could be enough taking into account the difficulties of the diagnostics. 12th ITPA Princeton 26-30march2007

  21. Measurement of fast ion energy and spatial distr function( Motivations IV: energy spectrum and density) • The energy spectrum to be measured is • 0.1 < E < 3.5MeV • For ITER(Te=20keV) the energy range important for the transfer of energy to electrons (Critical Energy) is : • E*He3> 280keV,E*(D)>360keV,E*(H)>600keV • Density range of fast ions: the density of minority ions could be 4-10% of the plasma density 12th ITPA Princeton 26-30march2007

  22. 12th ITPA Princeton 26-30march2007

  23. Diag for confined fast ions 1.g-ray spectr.: it detects 1<E<5MeV, ( Be and C impurities are used) R&D needed to demonstrate the feasibility(rejection of n backgr by LiH absorbers) in ITER . and new reactions must be explored for the detection of low energy ions. 2.CTS: nominally meets req.s; R&D needed to test the ITER concept in a real experiment; accuracy difficult to achieve in practice at the requested time resolution. 3.CXRS: spatial resolution and accuracy not achievable for r<0.3. 4.NPA : no spatial resolution.energy and time resolution achievable. In The range of energy of fast particles 0.1<E<1000keV in practice no proven technique exists which meet all the requirements 12th ITPA Princeton 26-30march2007

  24. Dia for fast particles: g ray spectroscopy 1. it detects 1<E<5MeV, 2.Alphas are detected using Be as impurity: 9Be(a,ng)12C(Eg=4.44MeV) 3.Deuterons are detected using 12C(d,ng)13C(Eg=3.1MeV) 4. He3 are detected using 12C(He3,ng)14N(Eg=2.31MeV,5.1MeV) 5.R&D needed to demonstrate the feasibility in ITER : rejection of n backgr by LiH absorbers 6.In practice ( looking to JET experience) the required accuracy is difficult to achieve ; The integration time needed is in the range of 100ms: so definitely the gamma ray spectroscopy Could see the slowing down of fast ions , but not the fast spatial redistribution due to the interaction with the Alfven modes. 7. 12th ITPA Princeton 26-30march2007

  25. Collective Thomson Scattering • The CTS proposed uses a gyrotron at 60GHz , applying the principle that using a source at a frequency below the first harmonic of ECE is beneficial to lower the plasma background temperature. The system proposed has the capability of measuring ions with velocity parallel and perpendicular to the magnetic field. • The spatial resolution is 20cm ( i.e. a/10) and the time resolution is 100ms, with an accuracy of 20%. • The energy spectrum to be measured has been specified (0.1-3.5MeV) . • The main difficulty of CTS is that in principle it cannot distinguish between ions with the same Z/M. CTS: nominally meets req.s; R&D needed to test the ITER concept in a real experiment; accuracy difficult to achieve in practice at the requested time resolution. Presently CTS experiments on FTU and ASDEX 12th ITPA Princeton 26-30march2007

  26. CTS sources 12th ITPA Princeton 26-30march2007

  27. Present motivations in Level 1 12th ITPA Princeton 26-30march2007

  28. measurement of fast particle losses( motivations I: physics basis) • The measurement of fast particle losses have important implication on the machine safety (because the fast particle lost could damage the wall), for the measurement of the effects of MHD instabilities on the confinement of fast ions. • The losses of particles have a strong impact on the global confinement properties of the discharges as it has been demonstrated in series of experiments related with the variation of the ripple losses on JET , and JT60U. • Classification : the diagnostic of fast particle losses is important for safety of the machine - it must be put in the diag set 1a for machine control and safety 12th ITPA Princeton 26-30march2007

  29. Measurement of fast particle losses( motivations II: space , time resolution and energy spectrum) • Spatial resolution : the system could be built as an array of detectors covering some poloidal region, so the poloidal angle could be specified . The proposed poloidal distance is a/20. • Time resolution is enough to detect fast events.Whether the time resolution of 0.1-0.5ms is achievable:it depends on the sensors.With scintillator probes this could be easily achievable • The energy spectrum depends on the resolution of the measured gyroradius r~(E)1/2 / B: ra~70mm for 3.5MeV alpha part., a resolution of 10% in ra , means 20%in energy. In JET for example a 15% resolution on gyroradius can be achieved, with the scintillator probe. 12th ITPA Princeton 26-30march2007

  30. 12th ITPA Princeton 26-30march2007

  31. Diagnostics • Faraday Cups (FC) and Scintillator probes(SP) were already tested on JET and TFTR. • The JET FC system measures the poloidal distribution of lost fast ions with a course energy resolution. Alpha particles in the range of 1-3 MeV can be detected with an energy resolution of the order of 10-15% . • The SP measures the gyroradius and pitch angle of a fast particle, the accuracy of measurement of gyroradius is 15%, while that of the pitch angle is 5%, the time resolution is 0.1ms. • systems as scintillators and Faraday-cups are subject to failure in the high radiation fields at ITER. • Preliminary analysis lead to consider other systems like ceramic scintillators and infrared multifoil thermal detectors 12th ITPA Princeton 26-30march2007

  32. Infrared viewing bolometers (IRVBs) with absorber foils of varying thickness to measure the intensity and energy distribution of escaping a-particles have been successfully tested at JT-60U [[i]]. The first images from these bolometers are reasonably consistent with images obtained with resistive bolometers. The IRVBs can operate in a reactor environment and prospects for their utilization in ITER are optimistic. [i] B. Peterson, presented at the 11th Meeting of the ITPA Topical Group on Diagnostics, Sendai, 2006. Infrared viewing bolometers 12th ITPA Princeton 26-30march2007

  33. Level 1 requirements on neutron 12th ITPA Princeton 26-30march2007

  34. measurement of neutron distribution and spectrum ( motivations I) • the spatial resolution of a/20 (10cm) is achievable with the present camera(s), in particular if a vertical camera is included.( preliminary study by L Petrizzi and B Esposito) • the time resolution of 0.1-0.5ms is achievable with the presently available ( still under test) electronics which is able to discriminate the neutron from gammas. • are the specs achievable also for neutron energy spectrum measurements?: • the compact neutron spectrometers based on scintillators likely not • CVD can achieve the time resolution required. 12th ITPA Princeton 26-30march2007

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  36. Conclusion and R&D • New technical specs are derived from physics of alfven wave interaction and the necessity of measuring all the fast ions. • Intensive R&D is needed to demonstrate the feasibility of • g ray spectroscopy, • Collective Thomson Scattering , • neutron fast electronics, • neutron compact spectrometers, • CXRS • Escaping fast ions sensors : multifoil bolometers , • Diagnostics capability for fast ions with energy in the range between 0.1Mev and 0.6 MeV and lost fast particle diagnostics needs urgently to be improved 12th ITPA Princeton 26-30march2007

  37. Slides for discussion 12th ITPA Princeton 26-30march2007

  38. Typical data on distribution functions on fast ions in ITER 12th ITPA Princeton 26-30march2007

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  40. 12th ITPA Princeton 26-30march2007

  41. Heating systems in ITER 12th ITPA Princeton 26-30march2007

  42. Neutronics for ITER • A study has been done about the possibility for the ITER neutron camera to meet the requirements ( L Petrizzi SOFT sept2006 and B Esposito ), the code used has been prepared for the task EFDA EFDA/04-1209 for RNC • Parameters assumed : • DT full power (scenario 2), • diameter of collimators 2 cm in-vessel and 1 cm ex-vessel (corrisponding to 1-2 MHz max , count rate sostainible by the detectors), • 0.1 ms time resolution • Detector efficiency 1%. 12th ITPA Princeton 26-30march2007

  43. Neutronics for ITER • The code used for the design of the ITER RNC has produced the Abel inverted neutron emissivity , assuming the equilibrium of ITER, the emissivity constant on the magnetic surfaces and the actual configuration of the line of sights of ITER RNC. For the case of 0.1ms time resolution. • The reconstructed emissivity for 0.1ms time resolution is divided To that in normal conditions ( 10ms) , and this ratio is determined versus the flux coordinate. • It is detected that the accuracy on the emissivity is inside 20%. 12th ITPA Princeton 26-30march2007

  44. The reconstructed emissivity for 0.1ms time resolution is divided To that in normal conditions ( 10ms) , and this ratio is determined versus the flux coordinate. 12th ITPA Princeton 26-30march2007

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