Internal electrostatic confinement fusion ( 慣性静電閉じ込めによる核融合 ) 論文紹介 by 白鳥昂太郎

Paper

Institute Institute of Advanced Energy, Kyoto University Prof. Kiyoshi Yoshikawa's Research Group 京都大学エネルギー理工学研究所 エネルギー 生成研究部門 粒子エネルギー研究分野 吉川 潔 研究室 u.ac.jp/beam/index_j.html

Brief introduction of Internal electrostatic confinement fusion : IECF  IECF is the scheme of injecting the ions and electrons towards the spherical center, trapping both species in the electrostatic self-field and giving rise to fusion in the dense core. (Fusion mechanism is not completely understood.)  For effective production of neutron, multi-well potential is needed.  Energy of neutron d+d→ 3 He+n : 2.5 MeV d+t→ 4 He+n : 14.1 MeV (d+ 3 He→ 4 He+p : 14.7 MeV)

Background  The concept of IECF is conceived in 1950s.  The first purpose is to investigate the room temperature fusion system (for power source ?). →Not realistic … →Latest type, input 100W ⇔ Output by fusion 1μW But …  IECF is a good neutron source. → Investigation is continued.

The Machine Intensity of neutron d+d→ 3 He+n : 2.5 MeV → 5×10 6 n/s (High voltage and ion current are unknown)

Advantage of IECF compared with neutron source (example 252 Cf)  Mono-energetic spectrum  No decreasing by particle decay  Easy to operate  Able to use proton source (d+ 3 He→ 4 He+p : 14.7 MeV) Good application Energy spectrum of neutron from 252 Cf O.I. Batenkov et al., INDC(NDS)-146,(1983)

Purpose of this paper  To measure ion current dependency of neutron yield ( N ∝ I 2 ) for investigating IEFC mechanism  To explain mechanism by theoretical calculation for offering the technical advantages ↑  The structure of internal potential is unknown. → fusion mechanism  Information for developing the technical progress : To optimize high voltage, current and to develop cooling system →Technical advantages

Ion current dependency of neutron yield Calculation by multi-well potential: N ∝ I 2 (I=ion current) ⇔ Experimental result: scales linearly I  Limitation of high voltage and current are 70kV and 15 mA, respectively.  Not to exceed the threshold for multi-well potential Perveance : I(mA)/V 1.5 (kV) > 2.2 Re-experiment by sufficient condition by using pulse current  I 2 dependency over the threshold was confirmed.

Result of theoretical calculation To construct the program by multi- well potential and to simulate the dependency of ion current  N ∝ I 3 dependency exists in the high current region. →Increased ion current make multi-well potential unstable and this unstably increase the density of central region. ⇒ The experiment to confirm this dependency in the high current region should be performed.

Result of theoretical calculation To construct the program by multi- well potential and to simulate the dependency of ion current  N ∝ I 3 dependency exists in the high current region. →Increased ion current make multi-well potential unstable and this unstably increase the density of central region. ⇒ The experiment to confirm this dependency in the high current region should be performed.

Conclusion  The dependency of ion current (N ∝ I 2 ) by multi-well potential is confirmed.  There may be the dependency N ∝ I 3 in the high ion current region. → The experiment should be performed.

Progress after this experiment  Multi-well potential was first measured by the laser-induced fluorescence method.  To increase the nuetron intensity of D- D reaction → 2×10 8 n/s

Future plan  Improvement of ion source Glow discharge ＋ Magnetron ion source  Intensity of neutron will be increased by one-order (10 8 →10 9 n/s).

Application

Examples

Mine sweeper   Development with 7 organizations  They plan to operate this machine in Afghanistan.

Why neutron source ?  It is very difficult to distinguish mine from other metals by metal detector. → mine/metals = 1/1000 under the ground →The plastic and ceramic mine cannot be detected.  The composition of TNT is known. →By measuring γ ray from TNT reacted with neutron and back scattered neutron by proton in TNT, we will be able to distinguish mine from other metals.

What detect ?  γ ray from neutron capture : 1 H(n,γ), 14 N(n,γ)  Energy 1 H(n,γ) : 2.22 MeV 14 N(n,γ) : 10.8 MeV  CsI, NaI, BGO for detection  10.8 MeV → Detected by BGO multi compton gamma camera

BGO gamma compton camera  Expected performance (1m×1m field, 20cm depth, 30 g mine) ～ 10 6 n/cm 2 /s Efficiency 99.9% Miss identify 10 min

Other method 回転する鎖で地面をひたすら叩いて、 片っ端から爆発させる

Summary  Present performance of IECF : 2×10 8 n/s.  IECF will be able to be used for several applications by adjusting neutron intensity.  Mine sweeper with IECF is planned.