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Negative halogen ions have recently been proposed as a possible alternative to positive ions for heavy-ion fusion drivers because electron accumulation would not be a problem in the accelerator, and if desired, the beams could be photodetached to neutrals (Nucl. Instr. and Meth. A 464 (2001) 315; Fusion Sci. Technol. 43 (2003) 191; Laser Part. Beams 21 (2003) 545). To test the ability to make suitable quality beams, an experiment was conducted at Lawrence Berkeley National Laboratory using chlorine in an RF-driven ion source. Without introducing any cesium (which is required to enhance negative ion production in hydrogen ion sources) a negative chlorine current density of 45 mA/cm 2 was obtained under the same conditions that gave 57 mA/cm 2 of positive chlorine, suggesting the presence of nearly as many negative ions as positive ions in the plasma near the extraction plane. The negative-ion spectrum was 99.5% atomic chlorine ions, with only 0.5% molecular chlorine, and essentially no impurities. Although this experiment did not incorporate the type of electron suppression technology that is used in negative hydrogen beam extraction, the ratio of co-extracted electrons to Cl − was as low as 7 to 1, many times lower than the ratio of their mobilities, suggesting that few electrons are present in the near-extractor plasma. This, along with the near-equivalence of the positive- and negative-ion currents, suggests that the plasma in this region was mostly an ion–ion plasma. The negative chlorine current density was relatively insensitive to pressure, and scaled linearly with RF power. If this linear scaling continues to hold at higher RF powers, it should permit current densities of 100 mA/cm 2 , sufficient for present heavy-ion fusion injector concepts. The effective ion temperatures of the positive and negative ions appeared to be similar and relatively low for a plasma source.

Radio frequency driven multicusp source was set up to run chlorine plasma and the source performance was compared between positive and negative chlorine ion production. A maximum Cl− current density of 45 mA/cm2 was achieved at 2.2 kW of rf power with electron to negative ion ratio of 7 and positive to negative ion ratio of 1.3. 99.8% of the total negative chlorine beam was atomic Cl−. To produce negative boron ions for semiconductor manufacturing applications, a noncesiated, sputtering-type surface production ion source was constructed. An external rf antenna geometry and large LaB6 converter were implemented in the source design. Maximum B2− ion current density of 1 mA/cm2 was achieved at 800 W of rf power and −600 V converter voltage. Total B2− ion current was 1.8 mA.

Use of high mass atomic neutral beams produced from negative ions as drivers for inertial confinement fusion has been suggested recently. Best candidates for the negative ions would be bromine and iodine with sufficiently high mass and electron affinity. These materials require a heated vapor ion source. Chlorine was selected for initial testing because it has similar electron affinity to those of bromine and iodine, and is available in gaseous form. An experiment was set up by the Plasma and Ion Source Technology Group in Lawrence Berkeley National Laboratory to measure achievable current densities and other beam parameters by using a rf driven multicusp ion source [K. N. Leung, Rev. Sci. Instrum. 65, 1165 (1994); Q. Ji et al., Rev. Sci. Instrum. 73, 822 (2002)]. Current density of 45 mA/cm2 was achieved with 99.5% of the beam as atomic negative chlorine at 2.2 kW of rf power. An electron to negative ion ratio as low as 7 to 1 was observed, while the ratio of positive and negative chlorine ion currents w...

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{sup 2} of 99.5% atomic negative Cl with an e/Cl{sup -} ratio as low as 7:1 and good emittance.

Negative halogen ions have recently been proposed as a possible alternative to positive ions for heavy ion fusion drivers because electron accumulation would not be a problem in the accelerator, and if desired, the beams could be photodetached to neutrals [1,2,3]. To test the ability to make suitable quality beams, an experiment was conducted at Lawrence Berkeley National Laboratory using chlorine in an RF-driven ion source. Without introducing any cesium (which is required to enhance negative ion production in hydrogen ion sources) a negative chlorine current density of 45 mA/cm{sup 2} was obtained under the same conditions that gave 57 mA/cm{sup 2} of positive chlorine, suggesting the presence of nearly as many negative ions as positive ions in the plasma near the extraction plane. The negative ion spectrum was 99.5% atomic chlorine ions, with only 0.5% molecular chlorine, and essentially no impurities. Although this experiment did not incorporate the type of electron suppression technology that is used in negative hydrogen beam extraction, the ratio of co-extracted electrons to Cl{sup -} was as low as 7 to 1, many times lower than the ratio of their mobilities, suggesting that few electrons are present in the near-extractor plasma. This, along with the near-equivalence of the positive and negative ion currents, suggests that the plasma in this region was mostly an ion-ion plasma. The negative chlorine current density was relatively insensitive to pressure, and scaled linearly with RF power. If this linear scaling continues to hold at higher RF powers, it should permit current densities of 100 mA/cm{sup 2}, sufficient for present heavy ion fusion injector concepts. The effective ion temperatures of the positive and negative ions appeared to be similar and relatively low for a plasma source.

Proton beams are needed in neutral-beam injection for diagnostic development of an internal magnetic field measurement. High proton fraction, low axial energy spread, current density in excess of 30 mA/cm2, and a parallel ion beam with cw operation are the requirements for the ion source/extraction system. A multicusp-type ion source with an external rf antenna was constructed at Lawrence Berkeley National Laboratory. A proton fraction of 85% and proton current density of 32 mA/cm2 were achieved at 1.8 kW of rf power. Plasma parameters were measured with a rf compensated Langmuir probe.

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 photo-detached to neutrals if desired. Initial experiments using chlorine produced a current density of 45 mA/cm{sup 2} of 99.5% atomic negative Cl with an e/Cl- ratio as low as 7:1 and good emittance.

Fast deuterium (D+) and tritium (T+) ion beam pulses are needed in some neutron-based imaging systems. A compact, integrated fast ion beam extraction and chopping system has been developed and tested at the Lawrence Berkeley National Laboratory for these applications, and beam pulses with 15ns full width at half maximum have been achieved. Computer simulations together with experimental tests indicate that even faster pulses are achievable by shortening the chopper voltage rise time. This chopper arrangement will be implemented in a coaxial neutron generator, in which a small point-like neutron source is created by multiple 120keV D+ ion beams hitting a titanium target at the center of the source.