
Staff List
Name 
: 
Yasuhiro IDOMURA 
Title 
: 
Principal Researcher 
Address 
: 
515 Kashiwanoha, Kashiwashi, Chiba 2778587, JAPAN 
Research Title
Study of ion turbulent transport and profile formations using global gyrokinetic fullf Vlasov simulation

Abstract 

A global gyrokinetic toroidal fullf five dimensional Vlasov simulation GT5D is extended including sources and collisions. Long time tokamak microturbulence simulations in open system tokamak plasmas are enabled for the first time based on a fullf gyrokinetic approach with selfconsistent evolutions of turbulent transport and equilibrium profiles. The neoclassical physics is implemented using the linear FokkerPlanck collision operator, and the equilibrium radial electric field E_{r} is determined selfconsistently by evolving equilibrium profiles. In ion temperature gradient driven turbulence simulations in a normal shear tokamak with onaxis heating, key features of ion turbulent transport are clarified. It is found that stiff ion temperature T_{i} profiles are sustained with globally constant L_{ti}T_{i}/T_{i}' near a critical value, and a significant part of the heat flux is carried by avalanches with 1/f type spectra, which suggest a selforganized criticality. The E_{r} shear strongly affects the directions of avalanche propagation and the momentum flux. Nondiffusive momentum transport due to the E_{r} shear stress is observed and a nonzero (intrinsic) toroidal rotation is formed without momentum input near the axis. 

Spatiotemporal evolutions of (a) ion heat diffusivity χ_{i},(b) T_{i} gradient R_{0}/L_{ti}, (c) E_{r} shear, and (d) parallel flows U_{//} observed in source driven ITG turbulence simulations. 

Reference 

[1] "Study of ion turbulent transport and profile formations using
global gyrokinetic fullf Vlasov simulation", Y. Idomura, S. Tokuda, N. Aiba, and H. Urano, Nucl. Fusion 49, 65029 (2009).
[2] "Conservative Global Gyrokinetic Toroidal Fullf 5D Vlasov Simulation", Y. Idomura, S. Tokuda, N. Aiba, and H. Urano, 22nd IAEA Fusion Energy Conference, Geneva, Switzerland, 2008 (International Atomic Energy Agency, Vienna, 2008), IAEACN165/TH/82 (oral).

Conservative Global Gyrokinetic Toroidal Fullf Five Dimensional Vlasov Simulation

Abstract 

A new conservative global gyrokinetic toroidal fullf five
dimensional Vlasov simulation (GT5D) is developed using a novel
nondissipative conservative finite difference scheme. The
scheme guarantees numerical stability by satisfying relevant first
principles in the modern gyrokinetic theory, and enables robust
and accurate simulations of tokamak microturbulence. GT5D is
verified through comparisons of zonal flow damping tests, linear
analyses of ion temperature gradient driven (ITG) modes, and
nonlinear ITG turbulence simulations against a global gyrokinetic
toroidal δf particle code. In the comparison, global solutions of
the ITG turbulence are identified quantitatively by using two
gyrokinetic codes based on particle and mesh approaches. 


A typical eigenfunction of the ion temperature gradient driven mode in a ITER like configuration of JT60SA.


Reference 

[1] "Conservative Global Gyrokinetic Toroidal Fullf Five Dimensional Vlasov Simulation", Y. Idomura, M. Ida, T. Kano, N. Aiba, and S. Tokuda, Comput. Phys. Commun. 179, 391403 (2008)

Conservative Gyrokinetic Fullf Vlasov Simulation

Abstract 

A new conservative gyrokinetic fullf Vlasov code is developed
using a finite difference operator which conserves both the L1
and L2 norms. The growth of numerical oscillations is suppressed
by conserving the L2 norm, and the code is numerically stable
and robust in a long time simulation. In the slab ion temperature
gradient driven (ITG) turbulence simulation, the energy
conservation and the entropy balance relation are confirmed, and
solutions are benchmarked against a conventional δf particleincell
(PIC) code. The results show that the exact particle number
conservation and the good energy conservation in the
conservative Vlasov simulation are advantageous for a long time
microturbulence simulation. In the comparison, physical and
numerical effects of the v_{//} nonlinearity are clarified for the Vlasov
and PIC simulations. 

Comparisons of time histories of the total, field, and kinetic
energy in long time ITG turbulence simulations using (a) Vlasov
and (b) PIC codes. The total energy conservation is dramatically
improved in a new conservative Vlasov code. 

Reference 

[1] "New conservative gyrokinetic fullf Vlasov code and its
comparison to gyrokinetic δf particleincell code", Y. Idomura, M.
Ida, S. Tokuda, and L. Villard, J. Comput. Phys. 226, 244262 (2007).
[2] "Conservative gyrokinetic Vlasov simulation", Y. Idomura, M.
Ida, and S. Tokuda, Commun. Nonlinear Sci. Numer. Simul. 13, 227233 (2007).

Selforganization in Electron Temperature Gradient Driven Turbulence

Abstract 

Based on first principle gyrokinetic calculations, a zonal flow
generation mechanism in the slab electron temperature gradient
driven (ETG) turbulence with weak magnetic shear is identified as
selforganization via the turbulent spectral cascade in the two
dimensional rotating fluid turbulence. The inverse energy
cascade and the scaling of a zonal flow wavenumber, which is
consistent with the Rhines scale length, are confirmed. An impact
of the scaling, which depends on the density gradient, on the
turbulent structure and transport is demonstrated for the slab
ETG turbulence. 

Selforganized structures of the ETG turbulence (b) with and (a)
without the diamagnetic plasma rotation or the density gradient. 

Reference 

[1] "Selforganization in electron temperature gradient driven
turbulence", Y. Idomura, Phys. Plasmas. 13, 080701 (2006).

Global Gyrokinetic Simulations of Toroidal Electron Temperature Gradient Driven Turbulence

Abstract 

Using a gyrokinetic toroidal particle code with global profile
effects, the toroidal electron temperature gradient driven (ETG)
turbulence in positive and reversed shear tokamaks is studied. In
the simulation, initial saturation levels of the ETG mode are
consistent with the mixing length theory, which shows a Bohm
(gyroBohm) like ρ^{*}scaling for a ballooning type (slab like) ETG
mode in a positive (reversed) shear configuration, where ρ^{*} is the
electron Larmor radius ρ_{te} divided by the minor radius a. In a
realistic small ρ^{*} positive shear configuration, the ETG mode has
a higher saturation level than the large ρ^{*} positive shear
configuration and the reversed shear configuration. In the
nonlinear turbulent state, the ETG turbulence in the positive and
reversed shear configurations shows quite different structure
formations. In the positive shear configuration, the ETG
turbulence is dominated by streamers which have a ballooning
type structure, and the electron temperature T_{e} profile is quickly
relaxed by enhanced heat transport in a turbulent time scale. In
the reversed shear configuration, quasisteady zonal flows are
produced in the negative shear region, while the positive shear
region is characterized by streamers. Accordingly, the electron
thermal diffusivity χ_{e} has a gap structure across the qmin surface,
and the T_{e} gradient is sustained above the critical value for a long
time. The results suggest a stiffness of the T_{e} profile in positive
shear tokamaks and a possibility of the T_{e} transport barrier in
reversed shear tokamaks. 

Zonal flows and streamers observed in grobal ETG turbulence simulations of reversed shear tokamaks. 

Reference 

[1] "Global profile effects and structure formations in toroidal electron
temperature gradient driven turbulence", Y. Idomura, S. Tokuda, and Y.
Kishimoto, Nucl. Fusion 45, 15711581 (2005).
[2] "Global Gyrokinetic Simulations of Toroidal Electron Temperature
Gradient Driven Mode in Reversed Shear Tokamaks",
Y. Idomura, S. Tokuda, and Y. Kishimoto, 20th IAEA Fusion Energy
Conference, Vilamoura, Portugal, 2004 (International Atomic Energy Agency,
Vienna, 2004), IAEACN116/TH/81 (oral).

Gyrokinetic Simulations of Tokamak Microturbulence including Kinetic Electron Effects

Abstract 

A gyrokinetic toroidal particle code for a 3dimensional nonlinear turbulence simulation (GT3D) has been developed to study the ion temperature gradient driventrapped electron mode (ITGTEM) turbulence in tokamak plasmas. From linear zonal flow damping tests and nonlinear ITG simulations, it is shown that a new method based on a canonical Maxwellian distribution is essential to simulate correct zonal flow dynamics in tokamaks. Recently, GT3D has been extended including kinetic trapped electrons. A computational cost of ITGTEM calculations are drastically reduced by using a new bounceaveraged kinetic trapped electron model. A short wavelength unstable region of the ITGTEM is calculated using a gyrokinetic field solver with a Pade approximation. From preliminary linear ITGTEM calculations, the validity of these calculation models are confirmed. 

Growth rate of ITGTEM calculated using driftkinetic, and
bounceaveraged electron models. 

Reference 

[1] "Gyrokinetic simulations of tokamak microturbulence
including kinetic electron effects", Y. Idomura, S. Tokuda, and Y.
Kishimoto, J. Fusion Plasma Res. SERIES Vol.6, 1722 (2004).

Global Gyrokinetic Simulation of Ion Temperature Gradient Driven Turbulence with Canonical Maxwellian Distribution

Abstract 

A new gyrokinetic toroidal particle code has been developed to
study the ion temperature gradient (ITG) driven turbulence in
reactor relevant tokamak parameters. We use a new method
based on a canonical Maxwellian distribution F_{CM}(P_{φ}, ε, μ), which is defined by three constants of motion in the axisymmetric toroidal
systemthe canonical angular momentum P_{φ}, the energy ε, and
the magnetic moment μ. A quasiballooning representation
enables linear and nonlinear highm,n global calculations to be
carried out, with a good numerical convergence. Conservation
properties are improved by using optimized particle loading.
From comprehensive linear global analyses over a wide range of
unstable toroidal mode numbers (n=0~100) in large tokamak
parameters (a/ρ_{ti}=320~460), it is found that the reversed shear
configuration produces an effective stabilizing effect on the ITG
mode in the q_{min} region through global effects. In the nonlinear
simulation, it is found that the new method based on F_{CM} can
simulate a zonal flow damping correctly; and spurious zonal flow
oscillations, which are observed in a conventional method based
on a local Maxwellian distribution F_{LM}(Ψ, ε, μ), do not appear in the nonlinear regime.


(a) ITG turbulence simulations and (b) Zonal flow damping tests
using local and Canonical Maxwellian distributions. 

Reference 

[1] "Global gyrokinetic simulation of ion temperature gradient driven
turbulence in plasmas with canonical Maxwellian distribution", Y. Idomura,
S. Tokuda, and Y. Kishimoto, Nucl. Fusion 43, 234243 (2003).
[2] "Gyrokinetic global analysis of ion temperature gradient driven mode in
reversed shear tokamaks", Y. Idomura, S. Tokuda and Y. Kishimoto, 19th
IAEA Fusion Energy Conference, Lyon, France, 2002 (International Atomic
Energy Agency, Vienna, 2002), p. IAEACN94/TH/P108 (poster).

Development of Large Scale Fusion Plasma Simulation and Storage Grid on JAERI Origin3800 System

Abstract 

Under the Numerical EXperiment of Tokamak (NEXT) research
project, various fluid, particle, and hybrid codes have been
developed. These codes require a computational environment
which consists of high performance processors, high speed
storage system, and high speed parallelized visualization system.
In this paper, the performance of the JAERI Origin3800 system is
examined from a point of view of these requests. In the
performance tests, it is shown that the representative particle and
fluid codes operate with 15~40% of processing efficiency up to
512 processors. A storage area network (SAN) provides high
speed parallel data transfer. A parallel visualization system
enables order of magnitude faster visualization of a large scale
simulation data compared with the previous graphic workstations.
Accordingly, an extremely advanced simulation environment is
realized on the JAERI Origin3800 system. Recently, development
of a storage grid is underway in order to improve a computational
environment of remote users. The storage grid is constructed by
a combination of SAN and a wavelength division multiplexer
(WDM). The preliminary tests show that compared with the
existing data transfer methods, it enables dramatically high speed
data transfer ~100 Gbps over a wide area network. 



Reference 

[1] "Development of large scale fusion plasma simulation and
Storage Grid on JAERI Origin3800 system", Y. Idomura, M.
Adachi, K. Gorai, Y. Suzuki, and X. Wang, J. Plasma Fusion Res.
79, 172187 (2003).

Slablike ion temperature gradient driven mode in reversed shear tokamaks

Abstract 

The ion temperature gradient driven (ITG) mode in reversed shear
tokamaks is analysed using a gyrokinetic toroidal particle code. It
is found that the ITG mode in the reversed shear configuration
shows a coupled mode structure between the slab and toroidal
ITG modes. Especially in the q_{min}region, a slablike feature due to the reversed shear slab ITG mode becomes strong. This coupled
eigenmode structure is changed from a slab mode to a toroidal
mode depending on η_{i} =L_{n}/L_{ti} and L_{ti}. Results show that in reversed
shear tokamaks the ITG mode is determined from a competition
between the slab and toroidal ITG modes.


Poloidal harmonics structures of toroidal ITG modes in (a) normal
and (b) reversed shear tokamaks. 

Reference 

[1] "Slablike ion temperature gradient driven mode in reversed
shear tokamaks", Y. Idomura, S. Tokuda, and Y. Kishimoto, New J.
Phys. 4, 101.1101.13 (2002).

Gyrokinetic theory of drift waves in negative shear tokamaks

Abstract 

Linear and nonlinear properties of slab drift waves in the
negative sheared slab configuration modelling of the q_{min} surface
region in negative shear tokamaks are studied, where q_{min} is the
minimum value of the safety factor q. Linear calculations show
that both the slab ion temperature gradient (ITG) driven mode and
the slab electron temperature gradient (ETG) driven mode
become strongly unstable around the q_{min} surface. Nonlinear
simulations are performed for ETG turbulence, which evolves on
a much faster timescale than ITG turbulence. It is found that
quasisteady E_{r}×B zonal fows are generated by an inverse wave
energy cascade process. Linear stability analyses of the
electrostatic KelvinHelmholtz (KH) mode show that the quasisteady
E_{r}×B zonal flow profile is closely related to the q profile or
to the magnetic shear, which has a stabilizing effect on the KH
mode. It is shown that the microscopic quasisteady E_{r}×B zonal
fows arising from ETG turbulence have a strong stabilizing effect
on the slab ITG mode.


(a) real frequency and (b) growth rate of slab ITG modes
suppressed by microscopic ETG zonal flows with a flow
amplitude v_{0}.


Reference 

[1] "Gyrokinetic theory of drift waves in negative shear tokamaks",
Y. Idomura, S. Tokuda, Y. Kishimoto, and M. Wakatani, Nuclear
Fusion 41, 437445 (2001).
[2] "Gyrokinetic theory of drift waves in negative shear tokamaks",
Y. Idomura, S. Tokuda, Y. Kishimoto, and M. Wakatani, 18th IAEA
Fusion Energy Conference, Sorrento, Italy, 2000 (International
Atomic Energy Agency, Vienna, 2000), IAEACN77/TH2/6 (oral).

Stability of E×B zonal flow in electron temperature gradient driven turbulence

Abstract 

The electron temperature gradient driven turbulence in a slab
configuration modeling the negative shear tokamak is studied
using a gyrokinetic finite element particleincell code. It is found
that quasisteady E_{r}×B zonal flows are generated in finite magnetic
shear regions in both sides of the q_{min}surface, where the electron
thermal transport is reduced substantially compared with the qminsurface
region. Stability analyses of the electrostatic Kelvinç•„
Helmholtz (KH) mode show that the quasisteady E_{r}×B zonal flow
pattern is closely related to the q profile or the magnetic shear,
which has a stabilizing effect on the KH mode. By changing the q
profile to reduce the magnetic shear, the KH mode becomes
unstable for the quasisteady E_{r}×B zonal flow, and the E_{r}×B zonal
flows disappear in the weak magnetic shear region. Numerical
results show a possibility of controlling E_{r}×B zonal flows with the
magnetic shear, which depends on the stability of the KH mode.


Time histories of ETG turbulence showing selforganization of zonal flows.


Reference 

[1] "Stability of E×B zonal flow in electron temperature gradient
driven turbulence", Y. Idomura, S. Tokuda, and M. Wakatani, Phys.
Plasmas 7, 35513566 (2000).

Gyrokinetic eigenmode analysis of slab ITG and ETG modes in negative shear tokamaks

Abstract 

With a gyrokinetic integral eigenvalue code, it is shown that both
the slab ion temperature gradient (ITG) mode and the slab
electron temperature gradient (ETG) mode have three types of
branches in the negative shear configuration: a single moderational
surface mode, a double moderational surface mode, and
a nonresonant mode. For typical fusion plasma parameters
satisfying λ_{De}^{2} >> ρ_{te}^{2}, a Webertype differential eigenmode equation
of the ETG mode becomes essentially different from that of the
ITG mode, because of the Debye shielding effect, where λ_{De} is the
Debye length and ρ_{te} is the electron Larmor radius. A scale length
of the ETG modes is characterized by λ_{De}, and different types of
analytic solutions are obtained for the ETG modes. From a
comparison of the transport coefficient based on the mixing
length theory, it is shown that in the negative shear configuration,
the slab ETG mode gives an order of magnitude larger transport
coefficient compared with an estimate for the conventional
normalsheared slab ETG mode.


Multiscale spectra of ITG and ETG modes in normal shear and reversed shear configurations.


Reference 

[1] "Gyrokinetic theory of slab electron temperature gradient
mode in negative shear tokamaks", Y. Idomura, S. Tokuda, and M.
Wakatani, Phys. Plasmas 7, 24562468 (2000).
[2] "Gyrokinetic theory of slab ion temperature gradient mode in
negative shear tokamaks", Y. Idomura, S. Tokuda, and M.
Wakatani, Phys. Plasmas 6, 46584671 (1999).

