@misc{oai:ir.soken.ac.jp:00000508,
 author = {宮沢, 順一 and ミヤザワ, ジュンイチ and MIYAZAWA, Junichi},
 month = {2016-02-17, 2016-02-17},
 note = {Establishment of a fueling method in hot and large plasmas is one of the important issues to realize the fusion rector.  An ideal fueling system for the steady-state fusion reactor should be as simple as the gas puffing, simultaneously achieving high fueling efficiency as the ice-pellet injection.  Furthermore, the fueling method that can improve the confinement property of the main plasma is favorable.  In this thesis, two fueling methods in the Large Helical Device (LHD) are studied.  One is the gas puffing, which is the most basic fueling method, and another is the Compact Toroid (CT) infection, which is the most advanced fueling method.  For reliable density control by gas puffing, it is important to understand the response of the plasma density to the gas puff flux.  The fueling efficiency of gas puffing in LHD has not been known, while it has been estimated as 〜10 % in diverted tokamaks.  Determination of the fueling efficiency is often complicated and one should carefully consider the particle balance.  Investigation of the confinement improvement is one of the important themes of the fusion plasma experiment.  Making use of the flexibility of gas puffing that the working gas can be changed from hydrogen to other high-Z gasses, it is possible to change the plasma property.  The confinement improvement due to the high-Z gas puffing has been reported from tokamaks as known as the radiative improved mode.  The high-Z gas puff experiment can be more easily carried out in currentless LHD plasmas, since there is no concern about the dangerous current disruption.  In the meanwhile, gas puffing is not capable of the direct fueling into the hot plasma core, which is thought to be favorable for the fusion reactor.  One of the possible methods is the CT injection, where a high-density magnetized plasmoid is accelerated and injected into the target plasma.  CT injection has been carted out in small/medium tokamaks.  However, it has not been obvious if this can be applied to the large helical plasmas.  Technically, the critical pass of CT injection in LHD lies in the long-distance transfer of CT.  The distance from LHD port to plasma center is about 4 m.  Since such a long distance transfer has not been reported, it is necessary to carry out the experiment for proof.<br />　In this thesis, the fueling efficiency of gas puffing in LHD has been estimated for the first time.  The 'effective' fueling efficiency of hydrogen gas puffing ranges from 10 to 50 %, in LID.  Here, the effective fueling efficiency is defined as the time derivative of the total number of electrons divided by the electron flux supplied by gas puffing.  The particle balance analysis reveals that the recycling flux increases during the gas puffing and causes the high effective fueling efficiency.  At the limit of small recycling flux, the effective fueling efficiency decreases to 〜10 %, which can be taken as the 'real' fueling efficiency of gas puffing in LHD.  In the helium gas puff discharge, where the recycling flux is large, the effective fueling efficiency is larger than the hydrogen gas puffing and approaches 100 %.  This can be related to the large recycling coefficient of more than 0.95.<br />　Two representative examples of the high-Z gas puff experiment in LHD are also presented.  The particle confinement was improved in the high-density pellet shot after the methane mixed hydrogen gas puff discharges.  Only four discharges introducing 〜20 Pa･m3 of methane caused the reduction of the radiation loss and the level of metal impurities as expected as the real time carbonization effect.  Decay rate of the electron density was mitigated in the pellet shot after methane discharges.  Transport analysis shows 60 % reduction in the particle transport coefficient at the half of the averaged minor radius.  In the neon gas puff experiment, reduced ton number density resulted in the higher ton temperature than that obtained in hydrogen plasmas.  The electron energy confinement of neon plasmas is highlighted and revealed to be similar to that of hydrogen plasmas.  In both cases, the global electron energy confinement strongly depends on the electron gyro-radius.  A new scaling law that describes the global electron energy confinement of hydrogen and neon plasmas in LHD has been derived.<br />　The possibility of CT injection experiment on LHD has been researched based on the CT orbit calculation and the development of a CT injector named SPICA (SPherornak Injector using Conical Accelerator).  CT trajectories in the helical magnetic field were calculated and the possibility of central fueling was confirmed with a model CT of 0.2 m diameter, 10 22 m-3 electron density, and 300 km/s initial velocity, in the case of CT injection into LHD magnetic field of 1.5 T.  A CT of spheromak-type magnetic configuration can be formed using co-axial plasma gun.  Optimization of the CT injector for LHD has been canted out and a conical electrode for CT compression is adopted in the design.  Point-model of CT acceleration in a co-axial electrode was solved to optimize the electrode geometry and the power supplies.  Based on the results, SPICA was developed and the CT acceleration experiments have been canted out.  SPICA is the largest CT injector in the world, which alms at fueling.  In the experiment, high speed CT of over 200 km/s was obtained.  It was also demonstrated that the CT could be transferred more than 3.6 m after the acceleration.  These results indicate that SPICA has enough performance to carry out the CT infection experiment on LHD.<br />　The basic objective of this thesis is to extend our knowledge on the fueling and the related physics problems.  Although the knowledge obtained here is limited it will be available for understanding the fueling physics.  In the investigation of other fueling methods, such as the pellet injection, and the neutral beam injection, the information presented in this thesis will give the basis for comparison.  Even for the complementary study of tokamak plasmas with helical plasmas, the results of this thesis can afford the basic database., 総研大乙第125号},
 title = {Study of Fueling on the Large Helical Device by Gas Puffing and Compact Toroid Injection},
 year = {}
}