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Design, development, manufacturing, and test activities of the RF power system (RFPS) for Linear IFMIF Prototype Accelerator (LIPAc) were completed in Europe. Installation and commissioning activities were carried out at the International Fusion Materials Irradiation Facility-Engineering Validation and Engineering Design Activities (IFMIF/EVEDA) site in Rokkasho, Japan. Challenging IFMIF requirements led to a number of innovations during design and development. Commissioning required a major effort on calibration and fine setting and led to development of new functionalities. The RFPS was validated under full power and 125-mA deuteron beam loading conditions, in the radio frequency quadrupole (RFQ), demonstrating good performance. This article is an overview about how technical challenges impacted the prototype RFPS design and its functional evolution during commissioning, cavity conditioning, and beam operation of the RFQ.

量研では、全8機のITERジャイロトロン実機の製作を完了し、5機の性能試験を実施し、出力1MW/効率50％/300秒発振の高繰り返し運転を90%以上の運転信頼度で成功させている。また、ITERの幅広い運転領域に対応するために複数周波数ジャイロトロンの開発研究も進めている。開発試験では、狙い通りに170GHzと137GHz発振では1MW/300秒、104GHz発振では0.9MW/300秒という単一ジャイロトロンによる3周波数での高出力連続運転を成功させた。, 核融合エネルギー連合講演会

ITERをはじめとする大型トカマク装置で運用される1MW級電子サイクロトロン加熱電流駆動システムでは、あらゆる磁場配位に対して入射モード(O/X)を制御する目的で低損失のマイターベンド型偏波器が用いられる。本研究では、偏波器の応答関数を抽出し、偏波器を擁する伝送路から真空容器への出力偏波の計算手法を確立した。実際の伝送系を用いて検証を実施した結果、計算と実測偏波の差は十分小さく、モード純度98.5%以上を達成できることが分かった。本手法はITER水平ランチャー内部の可動ミラーの反射角を考慮した偏波計算にも適用できる。, 第14回核融合エネルギー連合講演会

JT-60SAの初期研究フェーズで用いられるECH/CD装置（138GHz/110GHz/82GHz）について伝送路のレイアウト設計と評価を行った。新たに設計したレイアウトでの伝送効率を評価するために、これまで考慮されてこなかった、伝送路を構成する導波管の接合部におけるミスアライメントによる傾きや、伝搬するミリ波の偏波角も考慮した、従来よりも現実に即した伝送損失の計算を行ってきた。今回、本計算の妥当性を評価するため、既存の伝送路を使用して、伝送効率を測定し、計算値と比較した。その結果、計算結果が実験結果とよく一致し、計算が現実の伝送効率をよく表すことが明らかとなった。新レイアウトの伝送効率は本計算によると、入射ポートまでの距離の長い系統で84%、より短距離の系統では87%（いずれも110GHz）であり、目標値である伝送効率80%以上を見込めるレイアウトとなっていることが分かった。また、本伝送路では2台の偏波器を用いた偏波制御を行うが、伝送路上に配置する偏波器の位置に依存して3周波数の一部に生成できない偏波が存在する。そこで、新レイアウト上での偏波器の位置に対する出力可能な偏波状態を総当たりで計算し、プラズマ実験で必要となる偏波状態と比較、その差が最小となる偏波器の最適な位置を求めた。これにより、新レイアウトにおいて3周波数いずれもプラズマ入射時のモード純度99%以上が達成可能な偏波器の配置に成功した。, 第14回核融合エネルギー連合講演会

同軸RFカップラ（175 MHz、, 日本原子力学会 2022年春の年会

The eight-chain RF system and radio frequency quadrupole (RFQ) linac were successfully integrated at the facility of the Linear IFMIF Prototype Accelerator (LIPAc). We achieved an unprecedented high current deuteron beam up to 55 mA in pulse operation ( $300~\mu \text{s}$ , 1 Hz). The keys of the success were (1) understanding reflected power from RFQ to RF system, (2) tuning each RF chain individually, (3) intensive RF conditioning for holding the stable RF power in the RFQ, and (4) optimizing the beam loading compensation control. Interestingly, the reflection at the breakdown in RF conditioning was higher than an estimation and reached up to 600 kW so far. In order to avoid damage on tetrodes by the high reflection, the impedance of each circulator was accurately adjusted.

JT-60SAの統合コミッショニング期において使用される二系統のECRF装置について、ジャイロトロンを用いた高パワーでの伝送効率の評価を行った。また、通常のコンディショニングに使用しているジャイロトロン近傍のダミーロード位置、および伝送効率測定に使用しているランチャー直近の二カ所に加え、MOU出口と伝送路上二カ所の計五カ所においても仮設の短パルスダミーロードを用いてパワー測定を行った。本会議ではパワー測定および伝送路中の各要素における損失評価の結果について報告する。, 第38回 プラズマ・核融合学会年会

量研は、ITER国内機関として8機のジャイロトロンを調達する。ITERジャイロトロンは、2016年より製作を開始して、2021年5月に8機目が完了した。これらのジャイロトロンは、量研のテストスタンドにて性能確認試験を順次実施しており、周波数170GHz/出力1MW/効率50％/運転信頼度90%/5kHz出力変調といった試験要件に対して、既に4機が完遂し、現在5機目が試験中である。一方、ITER機構からの研究要請により170GHz/104GHzの2周波数ジャイロトロンの設計開発も行ってきた。現在、2周波数ジャイロトロン試作機を製作中であり、10月から実証試験を開始する計画である。, 第38回 プラズマ・核融合学会 年会

The 1st proton beam acceleration of the Linear IFMIF Prototype Accelerator (LIPAc) through its novel RFQ was succeeded on 13th June 2018. Addition to plenty of beam diagnostics equipped in the beam line, we prepared some radiation detectors placed around the accelerator in order to acquire supplemental information of the beam, as an indirect measurement. In the first day of the beam injection to the RFQ, the gamma-rays corresponding to certain excited states of Al of the low power beam dump were successfully detected by a LaBr3(Ce) scintillation detector. Some neutrons, which would originate from the interaction of protons with Cu somewhere, were also observed. These results proved that the beam was certain-ly accelerated up to about 2.5 MeV, and provided us a definitive confidence that the RFQ was working appro-priately from the very beginning of the commissioning. Also, the comparison of the radiation yields with the RFQ transmission provided additional information on the beam energy distribution.

The IFMIF accelerator facility consists of 2 identical linacs, each accelerating a 125 mA CW deuteron beam up to the energy of 40 MeV. In order to reach these unprecedented performances, the Linear IFMIF Prototype Accelerator (LIPAc) is under installation and commissioning at the International Fusion Energy Research Centre (IFERC) in Rokkasho, Japan, in the framework of the IFMIF/EVEDA project, which is part of the Broader Approach (BA) agreement between Japan and EU. The accelerator is designed to validate components up to 125 mA CW deuteron beam at 9 MeV. The accelerator components of LIPAc have been designed and manufactured mainly by European Institutes. The injector and superconducting linac, RFQ, MEBT, Diagnostics Plate, HEBT and beam dump have been developed respectively by CEA-Saclay, INFN-Legnaro and CIEMAT-Madrid and were delivered to Rokkasho between 2013 and 2016. The commissioning of the injector with beam started in November 2014. This paper dealt with the experimental data obtained with the beam diagnostics of the injector. The electrical measurements of the beam intensity on the beam stopper were compared with calorimetric measurements. The beam profiles measured with a CCD camera and a custom image-intensified CID camera are also addressed. The analysis of beam emittance and ion species fractions from data obtained with an Allison scanner is described and the results of species fraction measurements are compared with those obtained by using a deported spectrometer. Finally, the analysis of beam space potential from data obtained with a 4-Grid analyser is presented.

In many tokamak devices in the world, electron cyclotron wave heating plays an important role in plasma control, and polarization control by polarizers is essential to select an appropriate injection mode. Generally, a polarizer internally decomposes the input electric field into two orthogonal components (fast polarization and slow polarization) and generates a phase difference between those components to produce a polarization different from the input. Therefore, the response of a polarizer is characterized by two parameters: the angle at which the electric field is decomposed and the generated phase difference. In Stokes space, each polarization is represented as a vector, and it is known that a rotation operator represents the response of a polarizer. In this presentation, we propose the new method to determine polarizers' response parameters by converting the input and output polarizations into Stokes vectors to identify the rotation operators from a necessary and sufficient dataset. In the conventional method, the measured electric field components are analyzed in real space, and the equation for determining the response parameters of the polarizer tends to be complicated. However, by considering the polarizer's response geometrically in Stokes space, the response parameters can be determined more prospectively. In order to confirm the analysis method, a polarization measurement were carried out using a horn antenna detector and two polarizers for 110/138 GHz transmission lines. The method to determine the response parameters of one polarizer and to simultaneously determine the response parameters of two polarizers were verified. In both cases, it was confirmed that the output polarizations calculated from the determined response parameters agreed with the measured polarizations with a purity of more than 99%., Korea-Japan Workshop on Physics and Technology of Heating and Current Drive

現在JT-60SAのECRF設備のコミッショニングが進められている。今回統合コミッショニング期において使用される二系統のECRF設備について、伝送路の損失と伝送効率を評価するための熱量測定を行った。計測の結果、小口径導波管を用いている1号機では60%の、大口径導波管を用いている2号機では三周波数いずれに対しても81-85%の伝送効率を得た。本会議では熱力測定および伝送路中の各要素における損失評価の結果と、現在までに進められているECRF設備のコミッショニングの進捗について報告する。, Korea-Japan Workshop on Physics and Technology of Heating and Current Drive

International audience; Design, development, manufacturing, and test activities of the RF power system (RFPS) for Linear IFMIF Prototype Accelerator (LIPAc) were completed in Europe. Installation and commissioning activities were carried out at the International Fusion Materials Irradiation Facility-Engineering Validation and Engineering Design Activities (IFMIF/EVEDA) site in Rokkasho, Japan. Challenging IFMIF requirements led to a number of innovations during design and development. Commissioning required a major effort on calibration and fine setting and led to development of new functionalities. The RFPS was validated under full power and 125-mA deuteron beam loading conditions, in the radio frequency quadrupole (RFQ), demonstrating good performance. This article is an overview about how technical challenges impacted the prototype RFPS design and its functional evolution during commissioning, cavity conditioning, and beam operation of the RFQ.

ITERにおける電子加熱/電流駆動(ECH/ECCD)用の水平ポートランチャーは量研機構により調達される予定であり、2021年の最終設計レビューに向けて設計が進められている。これに対して量研機構では昨年度、ITER機構が指定する導波管の配置に準拠すると同時に加熱/電流駆動特性の要求値を満足させるための光学設計を最終化させることに成功した。本報告では、トカマク配位安定化のための電流分布制御に関する計算の進捗を含む、水平ランチャーの現設計から想定されるプラズマの加熱/電流駆動特性を報告した。, 第37回 プラズマ・核融合学会 年会

In summer 2019 the IFMIF/EVEDA Radio Frequency Quadrupole (RFQ) accelerated its nominal 125 mA deu-teron (D+) beam current up to 5 MeV, with 90% transmis-sion for pulses of 1 ms at 1Hz. The Linear IFMIF Prototype Accelerator (LIPAc) is a high intensity D+ linear accelera-tor; it is the demonstrator of the International Fusion Ma-terial Irradiation Facility (IFMIF). In particular the RFQ is the longest and most powerful ever operated. An intense campaign of measurements has been performed in Rok-kasho to characterize several performances of this complex machine: transmission, emittances, energy spectrum and beam loading. The history and the results of the commis-sioning until this important project milestone are here de-scribed. An overview of the foreseen activities to be carried out to reach the CW operation is also presented, 11th international particle Accelerator conference (IPAC'20)

The design of the LIPAc RF Power System main components will be presented in this contribution, including the RF modules, the SSPA (Solid State Power Amplifier) for the re-buncher cavities, the HVPS (High Voltage Power Supply) for the final amplifiers anodes and the RF water cooling system. Additionally, the main difficulties encountered during the first months of the RFPS commissioning and operation will be described, together with the applied improvements., 31st Symposium on Fusion Technology (SOFT2020)

The eight-chain RF system and radio frequency quadrupole (RFQ) linac were successfully integrated at the facility of the Linear IFMIF Prototype Accelerator (LIPAc). We achieved an unprecedented high current deuteron beam up to 55 mA in pulse operation (300 μs, 1 Hz). The keys of the success were (1) understanding reflected power from RFQ to RF system, (2) tuning each RF chain individually, (3) intensive RF conditioning for holding the stable RF power in the RFQ, and (4) optimizing the beam loading compensation control. Interestingly, the reflection at the breakdown in RF conditioning was higher than an estimation and reached up to 600 kW so far. In order to avoid damage on tetrodes by the high reflection, the impedance of each circulator was accurately adjusted.

In this study a hybrid simulation environment to investigate the lower-hybrid-wave-driven tokamak plasmas is presented, and its application to the spherical tokamak TST-2 is described. These plasma are formed and driven by radio-frequency waves without the use of the central solenoid, and are characterized by low density and low magnetic field. A hybrid simulation environment which is divided into two groups, one using magneto-hydrodynamic (MHD) as well as particle-in-cell (PIC) approaches, and the second group using ray-tracing and Fokker–Planck solvers, is applied to describe the behavior of energetic electrons, bulk plasma, wave propagation, and the wave-particle interaction. Both groups of solvers can be coupled via the energetic-particle velocity distribution function and the equilibrium conditions of magnetic field, pressure, and density profiles to obtain a self-consistent solution. First results show the impact of a self-consistent equilibrium on ray trajectories and current density profiles. Therefore, new insights in lower-hybrid-wave-driven plasmas of TST-2 can be obtained using the proposed hybrid simulation environment.

The Radio Frequency Quadrupole (RFQ) linac and 1.6 MW RF power system of the Linear IFMIF Prototype Accelerator (LIPAc) facility in the International Fusion Energy Research Center (IFERC) in Rokkasho (Japan) has been installed and conditioned. During the assembly and tuning process, the RFQ cavity was protected with a temporary tent from the potential deterioration of performance caused by dust. The vacuum in the cavity was improved through the 100 °C baking process of the cavity. The high power test of the 175 MHz RF systems up to 200 kW in CW for each of the eight RF chains was performed for checking its stable output reproducibility in Japan, before connecting 9–3/16 inch coaxial transmission lines from the RF chains to the RF input couplers of the cavity. It was confirmed that the eight RF chains provided the balanced RF power to the single RFQ cavity in-phase using a feedback loop and a synchronization system. The peak power in the cavity achieved 150 kW in the pulsed mode, which corresponds approximately to the required electric field to accelerate proton beam. Such RF conditioning process is ongoing to achieve 600 kW approximately required for deuteron beam commissioning planned in 2018.

The construction of the Linear IFMIF Prototype Accelerator (LIPAc) is in progress in order to demonstrate the feasibility of the low energy section of an IFMIF deuteron accelerator up to 9 MeV with a beam current of 125 mA in CW. The next milestone of the project is the so-called Phase-B beam commissioning, and one of the missions is to demonstrate the acceleration of the proton beam up to 2.5 MeV or the deuteron beam up to 5.0 MeV in pulsed mode with a low duty cycle of 0.1% through RFQ. Most of the components and subsystems necessary for Phase-B were delivered by 2016 under the responsibility of Fusion for Energy (F4E) as in-kind contributions of several European institutes, namely CEA (France), CIEMAT (Spain), INFN (Italy), and SCK-CEN (Belgium), and QST is in charge of the installation of the delivered equipment. The installation and check-out of the RFQ subsystem and the RF power system was completed by July 2017, and the RF conditioning of the RFQ cavity started. Also, the installation and the check-out of the important sub-systems for Phase-B, namely MEBT and beam diagnostics, have been completed. Keywords: IFMIF, LIPAc, RFQ, Accelerator, Deuteron, Neutron source

The validation of the Linear IFMIF Prototype Accelerator (LIPAc) is being conducted in Rokkasho Fusion Institute of QST, Aomori, Japan. The beam commissioning of the novel LIPAc RFQ has been progressing significantly, and the acceleration of the world highest current deuteron beam of 125 mA to 5 MeV (1 ms, 1 Hz pulsed beam) was achieved for the 1st time in July 2019. This study is devoted to evaluating the amount of beam loss during the high current acceleration phase by measuring the neutron produced by the interaction of the beam with accelerator components so as to verify the accelerator design. The foil activation method and the 3He neutron probes were utilized. It turned out that there was no significant trace of unexpected beam loss at the high energy section of the RFQ and the Medium Energy Beam Transport (MEBT) section.The measurement using the 3He neutron probes provided an evidence that the beam loss was well controlled in the RFQ cavity as designed. This study concludes that the LIPAc RFQ as well as MEBT is working well as predicted by the design calculation, and its concept is successful.

Based on the latest optical design of ITER ECH&CD equatorial launcher, the power absorption at the plasma breakdown is evaluated with considering reflections by the 3-dimensional first wall structure. The beam diffusion is simulated by a bunch of spreading rays and the reflections on the first wall are analyzed for each ray. The power absorption is evaluated by the optical thickness when the rays pass across the resonant surface. The frequency of EC wave is 170 GHz and the density of concern is from 2.5 × 10 15 m − 3 . As a result, at least 2 MW is absorbed out of 6.7 MW injection from the Top row in the case of fundamental O-mode injection even at the breakdown. In the case of 2nd harmonic X-mode injection, the total absorbing power is 200 kW at the electron density of 10 18 m − 3 and the electron temperature of 5 eV, which is proportional to the electron density and the electron temperature. It is found that a certain injection angle should be excluded in order to prevent intense stray RF injection up to 4 MW propagating toward specific ports within a few reflections.

For the development of the International Fusion Materials Irradiation Facility (IFMIF) aiming at material tests for fusion power plants, the construction of the Linear IFMIF Prototype Accelerator (LIPAc) has been conducted at Rokkasho, Japan under the Broader Approach Agreement. The commissioning of LIPAc has been progressing significantly. The world most powerful RFQ successfully accelerated proton beam of 58 mA, and an important project milestone of the acceleration of deuteron beam to 5 MeV with the beam current of 125 mA in pulse mode was successfully achieved. The result proves the validity of the present RFQ design. The adjustment and tuning of the RF power system and the injector for enabling an operation at maximum performances played an important role in achieving this result. For the next step, the preparation of the high duty cycle operation of RFQ is underway. The installation of the HEBT (High Energy Beam Transport line) and the beam dump accepting 1 MW, CW beam, has been completed and a new beam transport line is under manufacturing. Also the assembly of the Superconducting RF (SRF) linac to accelerate the beam up to 9 MeV started in a clean room in Rokkasho., The 14th International Symposium on Fusion Nuclear Technology

The Linear IFMIF (International Fusion Materials Irradiation Facility) Prototype Accelerator (LIPAc) is a 9 MeV, 125 mA, continuous wave (CW) deuteron accelerator aimed to validate the technology for the IFMIF accelerators. The construction of LIPAc, which is currently the most powerful deuteron accelerator in the world, has been carried out under the Broader Approach (BA) Agreement between EU and Japan, and it is located at Rokkasho (Japan). CIEMAT is one of the five European Institutions that has participated in the design, manufacturing and commissioning/operation of the main accelerator components, among them, the Radio Frequency Power System (RFPS). The RFPS contains all the equipment necessary to generate the required RF power to feed the LIPAc cavities. These cavities demand eighteen RF power chains at 175 MHz being distributed as follows: eight 200 kW tetrode-based chains for the Radiofrequency Quadrupole (RFQ), two 16 kW solid-state chains for the re-buncher cavities, and eight 105 kW tetrode-based chains for the Superconducting RF Linac Half-Wave Resonators. The design of the RFPS main components is presented in this paper, including the tetrode-based chains, the Solid-State Power Amplifier (SSPA) for the re-buncher cavities, the High Voltage Power Supplies (HVPSs) for the final amplifiers anodes and the RF water cooling system. Additionally, the main difficulties encountered during the first months of the RFPS commissioning and operation will be described, together with the applied improvements.

For the development of the International Fusion Materials Irradiation Facility (IFMIF) aiming at material tests for fusion power plants, the construction of the Linear IFMIF Prototype Accelerator (LIPAc) has been conducted at Rokkasho, Japan under the Broader Approach Agreement. The commissioning of LIPAc has been progressing significantly. The world most powerful RFQ successfully accelerated proton beam of 58 mA, and an important project milestone of the acceleration of deuteron beam to 5 MeV with the beam current of 125 mA in pulse mode was successfully achieved. The result proves the validity of the present RFQ design. The adjustment and tuning of the RF power system and the injector for enabling an operation at maximum performances played an important role in achieving this result. For the next step, the preparation of the high duty cycle operation of RFQ is underway. The installation of the HEBT (High Energy Beam Transport line) and the beam dump accepting 1 MW, CW beam, has been completed and a new beam transport line is under manufacturing. Also the assembly of the Superconducting RF (SRF) linac to accelerate the beam up to 9 MeV started in a clean room in Rokkasho.

For the development of the International Fusion Materials Irradiation Facility (IFMIF) aiming at material tests for fusion power plants, the construction of the Linear IFMIF Prototype Accelerator (LIPAc) has been conducted at Rokkasho, Japan under the Broader Approach Agreement. The commissioning of LIPAc has been progressing significantly. The world most powerful RFQ successfully accelerated proton beam of 58 mA, and an important project milestone of the acceleration of deuteron beam to 5 MeV with the beam current of 125 mA in pulse mode was successfully achieved. The result proves the validity of the present RFQ design. The adjustment and tuning of the RF power system and the injector for enabling an operation at maximum performances played an important role in achieving this result. For the next step, the preparation of the high duty cycle operation of RFQ is underway. The installation of the HEBT (High Energy Beam Transport line) and the beam dump accepting 1 MW, CW beam, has been completed and a new beam transport line is under manufacturing. Also the assembly of the Superconducting RF (SRF) linac to accelerate the beam up to 9 MeV started in a clean room in Rokkasho.

Background Cerebral hemangioblastomas are benign tumors with abundant blood flow that occur mainly in the posterior fossa. Tumor removal en bloc is important in surgical treatment because of the risk of bleeding; however, it is actually rather difficult in practice. Therefore, we propose a surgical strategy for visualizing hypervascular tumors of the posterior fossa utilizing indocyanine green (ICG). Case description Case 1 involved a 48-year-old male with a history of von Hippel-Lindau (VHL) disease. Magnetic resonance imaging (MRI) revealed a solid tumor measuring 3.0 cm in diameter in the right cerebellopontine angle. We performed surgery because the tumor was pressing against the brainstem. Surgery was performed via the posterior subtemporal transtentorial approach in order to visualize the feeding artery and draining vein intraoperatively. The vessels were confirmed by ICG and the tumor was removed en bloc. Case 2 involved a 30-year-old woman. Signs of increased intracranial pressure were noted, and an MRI revealed a solid tumor 3.5 cm in diameter in the left cerebellar hemisphere. Surgery was performed via the midline suboccipital approach. Similarly, we confirmed the vessels using ICG and the tumor was removed en bloc. Conclusions For hypervascular tumors of the posterior fossa, preoperative image assessment is important. Furthermore, the use of ICG during surgery is advantageous for surgical strategies where the feeding arteries and draining veins exist superficially in the operative field and are therefore easier to remove en bloc.

The goal of LIPAc (Linear IFMIF Prototype Accelerator) is to achieve a 125 mA, 9 MeV, CW (continuous wave, i.e. 100% duty cycle) deuteron beam with an average beam power of 1.125 MW. In the beam current measurement, it is considered that calorimetric measurement is advantageous for high current and CW operations since it is not subject to secondary electrons, etc. In calorimetric measurements, it is necessary to measure the temperature rise of the cooling water as accurately as possible. We applied this method to LIPAc proton beams at the Beam Stop unit. In order to check the reliability, we inserted a heater in the cooling loop as a heat source and obtained correlation between the applied and measured power, which was found to be 1.0. Moreover, using this heater, accuracy of this measurement with respect to the flow rate of the cooling water was investigated. Due to heat transfer and the fluctuations of water temperature, etc., there is a range of flow rates in which the measurement error can be minimized with our calorimetric measurement system.

Removal of the central solenoid is essential to realize an economical spherical tokamak fusion reactor, but non-inductive plasma start-up is a challenge. On the TST-2 spherical tokamak, non-inductive plasma start-up using lower-hybrid (LH) waves has been investigated. Using the capacitively-coupled combline (CCC) antenna installed at the outboard midplane, fully non-inductive plasma current ramp-up up to a quarter of that of the typical Ohmic discharges has been achieved. Although it was desirable to keep the density low during the plasma current ramp-up to avoid the LH density limit, it was recognized that there was a maximum current density that could be carried by a given electron density. Since the density needed to increase as the plasma current was ramped-up, the achievable plasma current was limited by the maximum operational toroidal field of TST-2. The top-launch CCC antenna was installed to access higher density with up-shift of the parallel index of refraction. Numerical analysis of LH current drive with the outboard-launch and top-launch antennas was performed and the results were qualitatively consistent with the experimental observations.

During the EVEDA (engineering validation and engineering design activities) phase of the International Fusion Materials Irradiation Facility (IFMIF) project, a 125 mA/9 MeV linear prototype accelerator (LIPAc) has to be built, tested and operated in Rokkasho-mura (Japan). Involved in this project for several years, CEA-Saclay designed the injector of this accelerator which is composed of an electron cyclotron resonance ion source, delivering a 140 mA deuteron beam at 100 keV, and a low energy beam transport (LEBT) line to match the beam for the injection into the radio-frequency quadrupole. In this paper, the components of the LIPAc injector are described. The commissioning of the ion source and LEBT with beam started in November 2014. The different phases of the commissioning are explained and some noticeable experimental results obtained with a beam at 100 keV are presented.

In TST-2 Ohmic discharges, local current is measured using a Rogowski probe by changing the angle between the local magnetic field and the direction of the hole of the Rogowski probe. The angular dependence shows a peak when the direction of the hole is almost parallel to the local magnetic field. The obtained width of the peak was broader than that of the theoretical curve expected from the probe geometry. In order to explain this disagreement, we consider the effect of sheath in the vicinity of the Rogowski probe. A sheath model was constructed and electron orbits were numerically calculated. From the calculation, it was found that the electron orbit is affected by E × B drift due to the sheath electric field. Such orbit causes the broadening of the peak in the angular dependence and the dependence agrees with the experimental results. The dependence of the broadening on various plasma parameters was studied numerically and explained qualitatively by a simplified analytical model.

Recent lower hybrid (LH) current drive experiments on Alcator C-Mod have motivated measurement of the parallel wavenumber of LH waves with an aim to understand the significance of the k|| up-shift mechanisms such as scattering by turbulence or parametric decay instabilities. To this end, a new diagnostic system is under development, consisting of two rows of three RF magnetic loop probes (one row sensitive to B||, the other row B⊥) and three Langmuir probes. These will be mounted on a radially movable probe system on the low field side of the tokamak, which is magnetically mapped to the LH launcher but toroidally separated by about 110 deg from the launcher. This location is expected to be ideal for detecting the parallel wavenumber spectrum of the pump and sideband LH waves up to n|| of 6.5. The use of the loop probes will help unambiguously resolve the polarization of these waves. These loop probes have been developed under the collaboration with the University of Tokyo, and vacuum-compatible versions h...

AC Ohmic coil operation experiments with frequencies up to 10 kHz were performed on the TST-2 spherical tokamak device, and the pre-ionization process was studied in detail. The minimum loop voltage for pre-ionization was 0.4 V, which corresponds to 0.5 V ${\rm m}^{-1}$ at the inboard limiter. Dependences of growth rate and saturation level of the process on various parameters were obtained, and they are compared with a time-dependent 0-dimensional model based on Townsend avalanche and loss along field lines. Most of the dependences are reproduced qualitatively by the model, and quantitative differences are within a factor of several. However, the external vertical field dependence of the appearance time, which is defined as the time to observe a plasma, and the isotope effect cannot be reproduced by the model. An ambipolar diffusion state which is predicted theoretically but mitigated experimentally is discussed. It was found that secondary electron emission at the limiter surfaces is a candidate mechanism to mitigate the state.