No abstract

Negative halogen ion beams have recently been proposed as heavy ion fusion drivers. They would avoid the problem of electron accumulation in positive ion beams, and could be efficiently photodetached to neutrals if desired [1]. Initial experiments using chlorine produced a current density of 45 mA/cm 2 of 99.5% atomic negative Cl with an e/Cl -ratio as low as 7:1 and good emittance.

High-intensity fast white neutron pulses are needed for pulsed fast neutron transmission spectroscopy ͑PFNTS͒. A compact tritium-tritium fusion reaction neutron generator with an integrated ion beam chopping system has been designed, simulated, and tested for PFNTS. The design consists of a toroidal plasma chamber with 20 extraction slits, concentric cylindrical electrodes, chopper plates, and a central titanium-coated beam target. The total ion beam current is 1 A. The beam chopping is done at 30 keV energy with a parallel-plate deflector integrated with an Einzel lens. Beam pulses with 5 ns width can be achieved with a 15 ns rise/fall time ±1500 V sweep on the chopper plates. The neutrons are produced at 120 keV energy. A three-dimensional simulation code based on Vlasov iteration was developed for simulating the ion optics of this system. The results with this code were found to be consistent with other simulation codes. So far we have measured 50 ns ion beam pulses from the system.

While a 20 mA dc H− source system at 25–30 keV beam energy has been developed at TRIUMF several years ago, another recent demand on the system is to provide a 4 to 5 mA H− at the 4–6 keV energy range. We found that at this low energy range, the existing source/extraction system can only give ∼1 mA with poor emittance due to strong space-charge effect. Fortunately, a very special source/extraction mechanism together with the use of neutralization was discovered and developed to overcome this difficulty. Up to 4 mA with a normalized rms emittance of 0.15 π mm mr has been achieved at 6 keV. This performance finds its usefulness for injection systems where lower beam energy and higher beam intensity are required. A copy of the TRIUMF system was constructed and successfully tested in the summer of 2000 for the “H− Acceleration Project” for the K130 cyclotron at Jyväskylä University, Finland.

Proton beams are needed in neutral beam injection for fusion research conducted at Princeton Plasma Physics Laboratory (PPPL). High proton fraction, low axial energy spread, current density in excess of 30 mA/cm 2 and a parallel ion beam are the requirements for the ion source/extraction system. A multicusptype ion source with an external RF antenna was constructed at Lawrence Berkeley National Laboratory (LBNL). Proton fraction of 85 % and proton current density of 32 mA/cm 2 was achieved at 1.8 kW of RF power. Plasma parameters were measured with an RF compensated Langmuir probe.