Study of current fluctuations for cw Penning SPS with hollow cathode drive was done. The noiseproof measurements of negative ion beam current, current in extracted electrode circuit, discharge current and voltage were carried out by the low-inductive probes in wide frequency range. Spectrum and intensity of fluctuations at various operation modes, parameters and electrode geometry were recorded for two versions of cw Penning SPS. H-beam current and the extracted electrode circuit current had the level of ripples higher, than the ripples in discharge current and voltage signals. Frequency spectrum of beam and discharge fluctuations displayed stable peaks. The main peak had location in the range 0.1 divided by 1.5 MHz and FWHM of about 0.1 MHz. For the basic operational mode the main peak in frequency spectrum was in the range 0.3-0.4 MHz. The fluctuations of current in extracted electrode circuit and in accelerated electrode circuit had the similar structure and correlated with beam current fluctuations. The obtained data show that plasma density oscillations are responsible for the beam current fluctuations. The 0.1 divided by 1.5 MHz fluctuations of plasma density could be produced by oscillations of cathode emissivity and of discharge current distribution between the specific cathode regions.

Status of direct current hydrogen negative-ion source development for tandem accelerator is described. The electrodes enforcing its water cooling and introducing of the electrons’ interception permitted to increase the source discharge power and to obtain regularly the H−-ion beam with energy >25kV and current up to 15mA.

УСКОРИТЕЛЬ-ТАНДЕМ С ВАКУУМНОЙ ИЗОЛЯЦИЕЙ КАК ОСНОВА МЕДИЦИНСКОГО КОМПЛЕКСА ДЛЯ ЛЕЧЕНИЯ ЗЛОКАЧЕСТВЕННЫХ ОПУХОЛЕЙ МЕТОДОМ БОРНЕЙТРОНОЗАХВАТНОЙ ТЕРАПИИ И ТАМОЖЕННОГО КОМПЛЕКСА ДЛЯ ДИСТАНЦИОННОГО ОБНАРУЖЕНИЯ ВЗРЫВЧАТЫХ ВЕЩЕСТВВ статье описана конструкция и области применения оригинального протонного ускорителя с вакуумной изо

Status of dc H- ion source development for tandem accelerator of boron capture neutron therapy is described. Upgrade and study of the Penning surface-plasma source with hollow cathodes was continued. Results of source optimization, of ion optic computer simulation, and of emittance measurement are presented. The upgraded source delivers dc H- beam with energy 25 W, current 8 mA, 1rms emittance E-X similar to 0.2 pi mm(.)mrad, E-Y similar to 0.3 pi mm(.)mrad at discharge power <= 0.5 kW.

This symposium addresses all aspects of H- and D- sources, the formation of negative hydrogen and deuterium beams from these sources, and their beam transport properties. The discussion includes both the latest theoretical and experimental work in these areas. The negative ion sources are multicusp, Penning, magnetron, rf (1-13 MHz), surface converter, microwave/ECR (GHz frequency), and polarized source types. Experimental work also includes beam chopping, space-charge lenses, optimized negative ion extraction systems, and beam diagnostics. The negative ion production mechanisms are volume (pure hydrogen or deuterium discharge) and surface production using cesium or other alkali metal to catalyze negative ion production. Theoretical analyses include plasma chemistry, particle-in-cell modeling, and H-/D- extraction physics simulations. The main applications for H- sources are in high-energy neutral beam injectors for fusion reactors and H- sources for charge exchange injection into synchrotrons or spallation neutron source storage rings.

Compact cesiated hollow cathodes (CHC) has been developed and studied in two large multicusp H− ion sources at NIFS, aiming the long lifetime cathodes for plasma production in the neutral beam injectors. Results on hollow cathodes and power supplies improvement are described. Basic characteristics of multicusp source discharge, driven by several CHCs were studied. Key issues about simultaneous CHCs operation in high current discharge mode are discussed. Each of advanced CHC delivered stable and quiet income with current up to 70A for 5sec to multicusp source discharge. The hollow cathode operation with no Cs feed was obtained by using 30%Xe+70%H2 gas mixture.

A compact cw hydrogen negative ion source having reliable operation and a simplified maintenance is developed at Budker Institute of Nuclear Physics for a tandem accelerator of boron capture neutron therapy installation. The source uses a Penning discharge with a hydrogen and cesium feed through the hollows in the cathodes. Discharge voltage is about 60–80 V, current 9 A, hydrogen pressure 4–5 Pa, magnetic field 0.05–0.1 T, and cesium seed <1 mg/h. Negative ions are mainly produced on the cesiated anode surface due to conversion of hydrogen atoms. An optimal anode temperature is 250–350 °C. Negative ion beam current is directly proportional to the discharge current and to the emission hole area. A triode system for the beam extraction and acceleration system is used. The flux of accompanying extracted electrons was decreased by filtering in the transverse magnetic field. This electron flux was intercepted to the special electrode, biased at 4 kV potential with respect to the anode. Source stable cw operation for several hour runs was multiply tested. A H− ion beam with current up to 8 mA, beam energy 23 keV was produced regularly. Negative ion current of heavy impurities had a value of about 3% of the total beam current. Beam normalized emittance is about 0.3 π mm mrad and emission current density −0.1 A/cm2. A built-in cathode heater provides the operation quick start.

Large current and high current density deuterium negative ion sources are investigated on the MANTIS test bed with the objective of producing several amperes of D− beams, at an accelerated current density in the range 10–20 mA/cm2, for possible application in future neutral beam injectors, e.g. ITER. As a first step, the DRAGON source, which was built by Culham Laboratory was tested on the MANTIS test bed in order to test this large source using only ‘‘pure volume’’ production of negative ions. The accelerated negative ion current is found to be a strong function of the source operating pressure and the arc power, and a significant isotopic effect is observed. The maximum accelerated currents are 1.3 A of H− (3.3 mA/cm2) and 0.5 A (1.3 mA/cm2) at 110 kW of arc power. Cesium injection from a non conventional dispenser together with an improved extraction system, have significantly improved the D‐current. A maximum of 14 mA/cm2 of D−1 are accelerated at 30 kV, which corresponds potentially, to more than 5 A for a full aperture extraction with an arc power of 140 kW (2250 A of arc current).

Neutral beam injection (NBI) is one of the candidates for plasma heating and current drive in the new generation of large magnetic fusion devices (ITER). In order to produce the required deuterium atom beams with energies of 1 MeV and powers of tens of MW, negative D− ion beams are required. For this purpose, multiampere D− beam production and 1 MeV electrostatic acceleration is being studied at Cadarache. The SINGAP experiment, a 1 MeV 0.1 A D− multisecond beam accelerator facility, has recently started operation. It is equipped with a Pagoda ion source, a multiaperture 60 keV preaccelerator and a 1 MV 120 mA power supply. The particular feature of SINGAP is that the postaccelerator merges the 60 keV beamlets, aiming at accelerating the whole beam to 1 MeV in a single gap. The 1 MV level was obtained in less than 2 weeks, the accumulated voltage on-time of being ∼22 min. A second test bed MANTIS, is devoted to the development of multiampere D− sources. It is capable of driving discharges with current up to 2500 A at arc voltages up to 150 V. A large multicusp source has been tested in pure volume and cesiated operation. With cesium seeding, an accelerated D− beam current density of up to 5.2 mA/cm2 (2 A of D−) was obtained. A modification of the extractor is underway in order to improve this performance. A 3D Monte Carlo code has been developed to simulate the negative ion transport in magnetized plasma sources and optimize magnetic field configuration of the large area D− sources.

A compact, safe system for directed cesium deposition into large volume sources is described. It consists of a small oven mounted on a feedthrough, which permits one to rotate and move the oven across the discharge chamber length or to remove it from the vacuum box to reload the oven. Special industrial pellets containing the cesium compound (30% of cesium chromate +70% titanium) were used for a pure cesium release. The pellets are insensitive to pollution by air and can provide the cesium release during several cycles of heating and cooling in long-term experiments. There was no ‘‘poisoning’’ impurities degassing (oxygen, water) during the standard oven operation. The Cs system was reliably operated for cesium deposition in multiampere negative-ion source experiments.

Experimental data on the enhancement of D− (H−) negative ion production due to cesium injection into a large volume multiampere negative ion source (MANTIS) are described. The directed deposition of small cesium amounts (5–100 mg) from a compact, movable oven, placed into the central part of a MANTIS gas-discharge box was used. A calorimetrically measured D− beam with an intensity up to 1.6 A and an extracted current density up to 4.2 mA/cm2 (beam energy 25 kV) was obtained. Exactly 30 mg of cesium provides at least one month of source operation (1000 pulses with a discharge pulse duration of 4 s). The effect of cesium on NI enhancement was immediately displayed after the distributed Cs deposition, but it needed some ‘‘conditioning’’ of cesium by tens of discharge pulses (or by several hours ‘‘pause’’) in the case of a localized Cs deposition. No degradation of extraction-acceleration voltage holding on within the tested range of cesium injection was observed.

Up to energies of 140 keV neutral beam injection (NBI) based on positive ions has proven to be a reliable and flexible plasma heating method and has provided major contributions to most of the important experiments on virtually all large tokamaks around the world. As a candidate for additional heating and current drive on next step fusion machines (ITER) it is hoped that NBI can be equally successful. The ITER NBI parameters of 1 MeV 50 MW D0 demand primary D- beams with current densities of at least 15 mA/cm2. Although considerable progress has been made in the area of negative ion production and acceleration the high demands still require substantial and urgent development

Negative ion sources and the mechanisms for negative ion production are reviewed. Several classes of sources with surface origin of negative ions are examined in detail: surface-plasma sources where ion production occurs on the electrode in contact with the plasma, and ''pure surface'' sources where ion production occurs due to conversion or desorption processes. Negative ion production by backscattering, impact desorption, and electron-and photo-stimulated desorption are discussed. The experimental efficiencies of intense surface negative ion production realized on electrodes contacted with hydrogen-cesium or pure hydrogen gas-discharge plasma are compared. Recent modifications of surface-plasma sources developed for accelerator and fusion applications are reviewed in detail.

It is found that the escape of Cs from a discharge chamber occurs mainly at the end of the discharge pulse.(AIP)