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The Σp scattering experiment has just been started at J-PARC this year (2018). We made ”Σ beam factory” a reality where a beam with an intensity of more than 5 × 105 Σ− beam per day could be produced by using 20 M/spill π− beam. The CATCH system, which is a dedicated system to detect recoil proton from the Σp scattering, operated stably under the high counting rate, and its successful operation was confirmed by identifying the pp scattering events in J-PARC. In the June beam time, the production run of the Σ− p scattering was carried out for 2 days, which was just 10% of the requested beam time. The remaining beam time of the Σ− p channel and the Σ+ p channel will take place in the spring of 2019. [ABSTRACT FROM AUTHOR]

In order to evaluate deposition of cesium (Cs) in the plasma grid (PG) and investigate the origin of the gradual degradation of the negative ion current in a 100 s long pulsed operation in the JT-60SA negative ion source, Cs behavior in the source is model. To do this, Cs adsorption/desorption coefficient with a wide range of temperature is experimentally measured by a surface ionization detector and a quartz crystal microbalance. As a result, both of the adsorption and desorption are drastically varied at temperature range from room temperature to 100 °C. Based on these data, the model calculates the amounts of the Cs mass in the chamber wall and PG. The calculation result shows that, in the operation, an increase of temperature in the chamber wall (Twall) causes the evaporation of the huge amount of Cs in it. This leads to over pilling-up of Cs in the PG and the slight degradation of the negative ion production. Therefore, it is found that the constant temperature operation is needed to sustain the thickness of the Cs monolayer in the PG, and the Twall is desired to be less than 60 °C to suppress the evaporation of Cs in the chamber wall. According to this model, it is showed that there are many combinations of the temperatures to achieve it with low Cs consumption. [ABSTRACT FROM AUTHOR]

A thermal beam emittance measurement method is developed specifically to measure high power density beams for the ITER neutral beam injection system (NBI)’s. A one-dimensional carbon-fiber composite (CFC) target is utilized to withstand the high current densities of the negative hydrogen beam making the beam emittance measurement possible. Schemes for the emittance measurement were discussed since beam instabilities are present in various stages of the beam phase. The allowable time for the measurement will be less than 2 seconds and it’s necessary to monitor the CFC temperature to not exceed 2000°C. The proposed measurement scheme to minimize beam instabilities is through the constant operation of the arc discharge and pulsed beam extraction. Mechanical structures are also being designed for rapid measurements to select different phases of the beam and for implementing the measurement system to long pulse beam operation. [ABSTRACT FROM AUTHOR]

A high power density and a long pulse negative ion beam accelerator has been developed in QST to realize the ITER neutral beam accelerator. A main target was the H- ion beam acceleration up to 1 MeV with 200 A/m² for 60 s. After the achievement of 1 MeV at a short pulse, the pulse length has been gradually extended by modifications of grid configurations to suppress grid heat loads due to negative ions and electrons. However, the beam energy was limited up to 0.7 MeV at 60 s operation. One issue was an unstable negative ion production for a long time due to arcing and excess temperature rise of a plasma grid for optimum negative ion production. To suppress arcing, a cathode filament shape was modified. The plasma grid was modified to have a large heat capacitance in order to suppress temperature rise for 60 s operation at high discharge power required for 1 MeV operation. Another issue is to optimize beam optics more precisely. Fine tuning of the 1st acceleration stage was carried to improve beam optics for high current density beam. With these modifications, high power density beam acceleration of 0.97 MeV, 190 A/m² has been achieved for 60 s. This is the first long pulse acceleration of ITER class high power density beam. [ABSTRACT FROM AUTHOR]

The optics design of the multi-beamlet negative ion accelerator for MITICA has been verified by means of specific experiments in the NITS test facility at the QST lab, employing a scaled-down configuration having the same features as the accelerator of MITICA and ITER HNB. The experiments confirmed the validity of the accelerator design. However it was found that, in the presence of transverse magnetic field in the ion extraction stage, the ion beamlet deflection in numerical simulations was somehow underestimated with respect to the beamlet deflection inferred from thermal images of a CFC target exposed to the negative ion beam. A detailed benchmark, using also another (completely independent) numerical model of the accelerator, has allowed the identification of possible origins of the differences. [ABSTRACT FROM AUTHOR]