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Oscillation of emittance and Twiss parameters in the negative ion (H−) beam from the J-PARC 2MHz RF ion source is measured by application of a double-slit emittance monitor located at the RFQ entrance. The emittance monitor is equipped with a newly-developed 60 MS/s data acquisition system, so that beam current oscillations at a few MHz can be observed with enough time resolution. From the measurement, it is shown that the beam phase space consists of: (1) a Direct Current component in the beam core; (2) a 2 MHz oscillating component which takes place in the diverging halo; (3) a doubled RF frequency (4 MHz) oscillation which faintly exists in the beam halo. The major component is the 2 MHz component, which resultantly decides the beam emittance oscillation frequency. A typical value of the beam emittance in the present experiment is 0.33 π mm-mrad, while the amplitude of the 2 MHz oscillation is around 0.04 π mm-mrad. The results indicate that the high-frequency oscillation component occupying about ten-percent of the beam from the RF source travels a few meters passing through a magnetic lens focusing system. [ABSTRACT FROM AUTHOR]

Operation of a cesiated RF-driven negative hydrogen ion source was initiated in September 2014 in response to the requirements of beam current upgrade in J-PARC linac. Delivery of the required beam current from the ion source to the J-PARC accelerators has been successfully performed. In 2016-2017 campaign, continuous operation of the ion source for 1,845 hours (RUN#75 from April to July 2017) was achieved with beam current, RF pulse width and repetition of 45 mA, 0.8 ms and 25 Hz, respectively. We present the operation status of the ion source and a high current H- beam with 70 mA extracted from the ion source for further high-power upgrade in J-PARC accelerators. [ABSTRACT FROM AUTHOR]

In order to satisfy the Japan Proton Accelerator Research Complex (J-PARC) second stage requirements of an H ion beam of 60mA within normalized emittances of 1.5mm·mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500 s25Hz) and a life-time of longer than 1month, the J-PARC cesiated RF-driven H ion source was developed by using an internal-antenna developed at the Spallation Neutron Source (SNS). The transverse emittances of the source were measured with various conditions to find out the optimum operation conditions minimizing the horizontal and vertical rms normalized emittances. The transverse emittances were most effectively reduced by operating the source with the plasma electrode temperature lower than 70C. The optimum value of the cesium (Cs) density around the beam hole of the plasma electrode seems to be proportional to the plasma electrode temperature. The fine control of the Cs density is indispensable, since the emittances seem to increase proportionally to the excessiveness of the Cs density. Furthermore, the source should be operated with the Cs density beyond a threshold value, since the plasma meniscus shape and the ellipse parameters of the transverse emittances seem to be changed step-function-likely on the threshold Cs value. [ABSTRACT FROM AUTHOR]

In order to satisfy the Japan Proton Accelerator Research Complex (J-PARC) 2nd stage requirements of an H- ion beam current of 60mA within normalized emittances of 1.5πmm·mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500μs×25Hz) and a life-time of more than 50days, a cesiated RF-driven H- ion source using a internal-antenna developed at the Spallation Neutron Source (SNS) was developed. As similar as the SNS ion source, the 60kW pulsed 2MHz-RF and 200W CW 30MHz-RF systems are used in order to produce pulsed high-temperature 2MHz-RF plasma and CW low-temperature 30MHz-RF plasma. Each matching network for each system is composed of two vacuum variable condensers (VVCs). In order to supply pulsed 60kW-2MHz-RF power from the power supply (PS) on the ground level, a one-turn isolation transformer using FINEMET cores is installed between the PS and the J-PARC ion source. By comprehending the matching networks with the LTspice IV simulations and high- and low- power experiments and setting the parameters properly, the pulsed 2MHz-RF power up to 46 kW is successfully input to the hydrogen plasma without any misfire and with almost no reflected power. [ABSTRACT FROM AUTHOR]

In order to satisfy the Japan Proton Accelerator Research Complex (J-PARC) 2nd stage requirements of an H- ion beam current of 60mA within normalized emittances of 1.5πmm·mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500μs×25Hz) and a life-time of more than 50days, a cesiated RF-driven H- ion source using a internal-antenna developed at the Spallation Neutron Source (SNS) was developed. The horizontal and vertical emittances were measured by using two double (W) slit emittance monitors for several different conditions. Although the measured normalized rms emittances are more than 1.4-times larger than those of a J-PARC H- ion source driven with two tungsten (W) filaments probably due to the RF field around extraction gap, the J-PARC 2nd stage requirement of the 60mA beam within 1.5πmm·mrad was satisfied if a beam more than 66mA were extracted. [ABSTRACT FROM AUTHOR]

In order to satisfy the Japan Proton Accelerator Research Complex (J-PARC) 2nd stage requirements of an H- ion beam current of 60mA within normalized emittances of 1.5πmm·mrad both horizontally and vertically, a flat top beam duty factor of 1.25% (500μs×25Hz) and a life-time of more than 50days, a cesiated RF-driven H- ion source using a internal-antenna developed at the Spallation Neutron Source (SNS) was developed. The J-PARC RF-driven ion source was manufactured by modifying the J-PARC cesiated H- ion source driven with two tungsten (W) filaments, which successfully produced a 76.2mA H- ion beam current but had an insufficient life time of about 500hours. It successfully produced a 77.5mA H- ion beam with a flat top duty factor of 2% (800μs×25Hz) whose 87.7% (68.0mA) and 89.1% (69.1mA) are within horizontal and vertical 1.5πmm·mrad emittances, respectively. It also had successfully produced more than 66mA (more than 60mA within 1.5πmm·mrad emittances both horizontally and vertically) H- ion beam continuously over 100hours. [ABSTRACT FROM AUTHOR]

A cesium (Cs)-seeded RF-driven H- ion source using an internal-antenna is under development for the Japan Proton Accelerator Research Complex (J-PARC). The J-PARC second-stage requirements are an H- ion beam current of 60 mA within normalized emittances of 1.5 πmm·mrad both horizontally and vertically and a flat top beam duty factor of 1.25% (500 μs × 25 Hz). An H- ion beam current of 77.5 mA with a flat top duty factor of 2% (800 μs × 25 Hz), whose approximately 90% (corresponding to approximately 70 mA) of each emittance is within 1.5 πmm·mrad, is successfully extracted from it. The experimental results of axial magnetic field (AMF) optimization with an axial magnetic field correction (AMFC) coil, which significantly enhances the H- ion beam current by 10% typically, are presented in this paper. Although it is reported that the plasma density and the beam current are enhanced by an AMF of more than 160 G in an RF-driven H- ion source of Tohoku University, the physical phenomenon seems to be different form the J-PARC source beam enhancement, since there is the optimal field strength of much lower value (approximately 60 G) in the J-PARC source. [ABSTRACT FROM AUTHOR]