28pC10
ITERにおける損失アルファ粒子計測の課題 	 

Issues for lost alpha measurements on ITER	 
笹尾真実子1，岡本敦2，磯部光孝3，西浦正樹3
M. Sasao1, A. Okamoto1, M. Isobe3, M. Nishiura3
1

同志社大研究開発，2東北大院工，3核融合研
1
Office of R&D Promotion, Doshisha University, 2Graduate School of Engineering, Tohoku
University, 3National Institute for Fusion ScienceIntroduction
Alpha-particles produced by D-T reaction in afusion reactor transfer their energy to plasma(self-heating). However, some losses, not only
steady orbit losses, but also those coupled withvarious instabilities are anticipated. The loss ofalpha particles means deterioration of the heating
input power. Moreover, the loss localization may
cause serious damage of the first wall of reactor.
Deterioration of plasma performance due to theinflux of impurities sputtered by these high-energy
alpha particles striking the first wall would be also
serious problem. Upon these reasons, measurementof alpha-particle loss and study of loss mechanism
are required for machine protection and for
optimization of discharge scenarios on ITER.
Measurement Requirement
An “ideal” lost alpha diagnostic should provide
information on (1) loss distribution on the first wall,(2) Absolute values of lost alphas flux, or heat loadcaused by alpha-particle loss, (3) Time evolution ofalpha-particle loss (4) Energy and impinging angles
of lost alphas to identify the loss orbit. They should
be reliable and withstand severe conditions of ITER
environment (high neutron/gamma flux, hightemperature, strong magnetic field, etc.), and thediscrimination of alpha-particle loss from other ion
or electron load should be made.
Diagnostic Methodology
A number of measurement techniques have been
proposed for ITER[1]. As for the loss distribution
on the first wall, an infrared camera viewing issuggested, but it cannot discriminate alpha-particle
loss from other ion or electron load. Scintillator
probes [2,3], which have been applied on many
tokamaks and helical devices, faraday cups andbolometric detection using imaging foils [4] might
have a problem with signal to noise ratio, and thefragility under the circumstance of high neutron
flux and high temperature. The biggest problemof these probes is that they cannot be inserted close
to the detectable region that is closer to the plasmaboundary than the first wall (see Fig.1).
Possible Measurement Location
In ITER, alpha particles escaping drift downward,
and only small fraction may arrive onto theequatorial surface region. Possible measurement
locations are poison A and B in Fig. 1 but not nearequatorial but on the lower blanket module surface.
For those locations, only the infrared viewing, γ-ray
detection, and activation [5] are applicable. In therecent equatorial port design of ITER, the front
surface of a port plug is retracted by about 100 mm,
as shown in Fig. 1. The orbit calculation shows
the possibility of time-resolved measurement incase of 100 mm retraction [6]. The further work
starting from the location C, which is allocated in
EPP 8 of ITER is needed.

Fig. 1. Possible measurement locations in ITER for lostalpha diagnostic. Position A, and B should be on thelower blanket module surface.
References
1.
M. Sasao, et al. Fusion Science & Technology, Vol.
53, No. 2, p. 604-639 (2008)
2.
M. Isobe, et al., Nuclear Fusion, 46 (2006)
S918-S925.
3.
M. Nishiura, Review of Scientific Instruments, 81,10D313 (2010)
4.
E.A. Drapiko, Plasma and Fusion Research, 5(2010) S2096.
5.
G. Bonheure, et al., Review of Scientific
Instruments, 81, 10D331 (2010)
6.
A. Okamoto, et al.,, Review of Scientific
Instruments, 81 10D312 (2010).