S11-1
Development on Disruption Research with the goal of DEMO Reactor Control
Explanation of Aim as Introduction
原型炉制御に向けたディスラプション研究の展開
趣旨説明	  はじめにMasatoshi Yagi
矢木	  雅敏Japan Atomic Energy Agency, Rokkasho Aomori 039-3212, Japan
日本原子力研究開発機構 〒039-3212	  青森県上北郡六ヶ所村尾駮表舘2-166
The aim of the symposium: ‘Development on disruption research with the goal of DEMO reactor control’
is briefly explained as an introduction. In the symposium, the current status and issues on disruption
research are overviewed in the experimental viewpoint. Subsequently, the issues that should be resolved on
DEMO reactor design are discussed. Following them, the domestic activity on theory and simulation
research aimed for the disruption control will be explained. The progress of simulation research on therunaway electrons and the integrated transport simulation of disruption control are presented. Finally, theurgent issues on the disruption research will be discussed and the related collaborations will be proposed in
the general discussion.

1. Introduction
The development of physical and technical basis
for the mitigation of disruption loads such as
electromagnetic and thermal ones has been the mostimportant challenges in ITER [1,2]. For this aim,
the predictive simulation of plasma operation
avoiding disruptions by integrated modeling, which
consists of tokamak equilibrium evolution, linear
and nonlinear stability analysis, and impurity
transport, has become an important topic. In
particular, for reactor-relevant regimes of multi-MA
plasma current, runaway electrons produced after a
rapid thermal quench are expected to cause asignificant damage on the PFCs (Plasma FacingComponent) and might give a limitation of their
lifetime. Therefore, the avoidance and mitigation of
runaway electrons has now been considered as oneof urgent tasks in ITPA TG. Nevertheless, atransient and complex behavior of tokamak
disruptions inhibits building up a solid basis for
runaway mitigation in ITER even though therunaway generation mechanism itself is describedbasically in a classical way of Coulomb andknock-on collisions, which appears in the textbook
of plasma physics.
In the domestic activity of plasma theory andsimulation research on burning plasmas physics,
BPSI (Burning Plasma Simulation Initiative) is themost active collaboration framework [3,4]. On thebasis of collaborations between universities, NIFS,JAEA, etc., BPSI aims at the prediction of burning
plasma behavior and the development of burncontrol method. Under this collaboration, physics
modeling framework as well as software andhardware has been developed. Furthermore,IFERC-CSC (International Fusion Energy ResearchCenter, Computer Simulation Center) offers
computer resource for fusion simulation research[5]. The objectives of CSC are to provide asupercomputer (named as HELIOS) and to exploit
high performance and large-scale simulations toanalyze experimental data on fusion plasmas, toprepare scenarios for ITER operation, to predict theperformance of the ITER, and to contribute to theDEMO design physics under the BA (BroaderApproach) activities [6]. Using these frameworks,disruption research on burning plasma is now goingon [7]. In the symposium, recent progress on
disruption research is reported.
The symposium will consist of 5 talks andgeneral discussion. The aim of the symposium isbriefly explained as an introduction. Then, thecurrent status and issues on disruption research areoverviewed in the view of present experiments.
Subsequently, the issues that should be resolved on
DEMO reactor design are discussed. Following that,theory and simulation researches on disruption
physics will be explained, which involves theprogress of simulation research on the runaway
electrons and the integrated transport simulations
for the disruption control. In the last part of thesymposium, the urgent issues on disruption research
are discussed, and the related collaborations will beproposed.
2. Disruption Physics
The disruption process is composed of several
related phenomena, such as (1) the thermal quenchdue to MHD instability, (2) runaway electron birth
due to induced loop voltage and (3) the termination

Disruption phase
Post-disruption phase
Runaway e generation phase㻹㻴㻰㻌㼕㼚㼟㼠㼍㼎㼕㼘㼕㼠㼥 㼞㼡㼚㼍㼣㼍㼥㻌㼑㻙㼓㼑㼚㼑㼞㼍㼠㼕㼛㼚㼀㼑㼙㼜㻚 ~20 keV㼚㼛㼞㼙㼍㼘㼐㼕㼟㼏㼔㼍㼞㼓㼑~1 keV㼠㼔㼑㼞㼙㼍㼘㻌㼝㼡㼑㼚㼏㼔㼏㼡㼞㼞㼑㼚㼠㻌㼝㼡㼑㼚㼏㼔~10 eVend㼢㼑㼞㼠㼕㼏㼍㼘㻌㼕㼚㼟㼠㼍㼎㼕㼘㼕㼠㼥㻴㼍㼘㼛㻌㼏㼡㼞㼞㼑㼚㼠Fig.1 Schematic view of whole life of a major disruption.

of runaway plasma due to the positional instability.
Figure 1 shows the schematic view of the whole lifeof disruption. Subsequent events during the wholetime of major disruptions might be categorized into
(1) disruption phase, (2) runaway electron
generation phase, and (3) post-disruption phase.
During a rapid thermal quench, the temperaturedrops from ~ 20 keV to ~ 10 eV, being dominatedby the balance between ohmic heating and impurity
radiation, and such a wide range of the temperature
variation must be included in the simulation.
Additionally, the time scale of disruption events
covers from Alfvénic time (~ 1 µs), transport time(~ the order of tens of ms), and the time constant forexternal circuit (~ seconds). It indicates that thedisruption is multi-scale and multi-physics
phenomena in their intrinsic properties and theintegrated simulation is indispensable to explore
their physics.
The multi-scale phenomena involved in therunaway electron physics is illustrated in Fig. 2,
which is characterized by the interplay between
MHD modes, runaway electrons, and induced loopvoltage. At the first point, MHD modes induce athermal quench, lead to the induced loop voltage tomaintain the plasma current, and finally yield thesignificant populations of runaways. In addition tosuch a classical picture of the runaway generation,
nonlinear behavior caused by the induced loop
voltage and runaway electrons through theavalanche process is recently clarified in the“marginal stability model” [8]. Also, once therunaway electrons are generated, they dominate theplasma current profile and closely connect to thelinear stability properties. The excitation of MHD
modes during the runaway generation phase has
intensely been studied in JT-60U and othertokamaks. Furthermore, in recent studies, the“actuator” such as massive gas injection has also
played a major role for the collisional dissipation ofrunaway electron beams, which is now considered

to be the most promising scheme in ITER. As awhole, the systems are thus become highly
nonlinear and are characterized by its transient andopen-system nature. To complete the picture ofmajor disruptions, it is also crucial to evaluate thewall damages by the vertical displacement event(VDE) and by Halo current [9].

Fig. 2 Concept of integrated simulation for disruption
phase and runaway electron generation phaseAcknowledgments
The author acknowledges Drs. A. Isayama(JAEA), R. Hiwatari (CRIEPI), A. Matsuyama(JAEA), A. Fukuyama (Kyoto Univ.) and N.
Nakajima (NIFS) for supporting the symposium.
This work was supported in part by Grants-in-Aid
for Scientific Research (23246163).
References[1] ITER Physics Expert Group on Disruptions, PlasmaControl, and MHD et al.: Nuclear Fusion 39, No.12(1999) 2321-2373.
[2] T. C. Hender et al.: Nuclear Fusion 47 (2007)
S128-S202.
[3] A. Fukuyama and M. Yagi: J. Plasma Fusion Res. 81(2005) 747-754 (in Japanese).
[4] http://bpsi.nucleng.kyoto-u.ac.jp/bpsi/en/[5] http://www.iferc.org/csc/csc.html[6] http://www.naka.jaea.go.jp/english/ba/index.html[7] http://kaken-yagi.jaea.go.jp/web_eg/index.html[8] B. N. Breizman, Nucl. Fusion 54 (2014) 072002.
[9] A. H. Boozer: Phys. Plasmas 19 (2012) 058101.