Development and test results of the low-energy demonstration accelerator (LEDA) proton injector on a 1.25 MeV cw radio frequency quadrupole

The low-energy demonstration accelerator (LEDA) 75-keV proton injector is being developed for tests of high-current (100-mA) cw linacs. The injector comprises a microwave proton source and a space-charge neutralized magnetic low-energy beam-transport system (LEBT). The LEDA injector has been configured to provide flexible 50-keV beam matching into a cw 1.25-MeV radio-frequency quadrupole (RFQ) brought from Chalk River Laboratories (CRL). The LEBT has two solenoid focus magnets separated by 117 cm. Between the solenoids are two steering magnets and diagnostic stations for measuring the beam current, profile, and position. The ion-source extraction system was modified to a 50-keV triode to test the injector/RFQ system. Beam-matching tests showed that injector-RFQ transmission is 90% for 50-mA RFQ current. At the RFQ design current of 75 mA the beam transmission decreased to 80--85%. Optimized injector tuning led to 100-mA beam accelerated through the RFQ

A dc proton injector for use in high-current cw linacs

A 75-keV dc and pulsed-mode proton injector is being developed for beam testing of a 100-mA, 6.7-MeV cw radio frequency quadrupole (RFQ) at Los Alamos. A microwave proton source operating at 2.45 GHz produces 130-mA hydrogen-ion beam currents with > 85% proton fraction, yielding the 110-mA proton current required at the RFQ injection point. Doppler-shift spectroscopy confirms previously measured proton fractions. The discharge may be pulsed by current modulation of the magnetron power supply. A 1-MHz coherent oscillation observed in the extracted ion beam was eliminated by selecting proper magnetron operation. Transport and matching of the proton beam to the RFQ is accomplished by a two-solenoid, beam space-charge neutralized low-energy beam transport (LEBT) system. The injector was temporarily reconfigured to operate at 50 keV for injector matching studies into a 1.25 MeV cw RFQ. A maximum current of 100-mA has been accelerated through the RFQ in cw mode

Accelerator drift-tube braze-joint failures in the PIGMI APF cavity

During the assembly of the Alternating Phase Focusing cavity for the PIGMI Prototype proton accelerator, recurring failures of drift-tube braze joints occurred. In the fabrication technique, a torch braze was used to attach the stems to both the drift-tube body and the stem termination; all materials used were stainless steel. The assemblies were copper plated, using bright-acid-leveling copper plating. Some braze joints, although satisfactorily tension-tested before plating, later failed at a relatively low loading. A detailed investigation of one drift tube indicated that residual copper-plating solution in the cooling passages acted to dissolve the braze solution over a period of weeks, leading to an eventual joint failure

Mechanical design of RFQ resonator cavities in the 400-MHz frequency range

Many RFQ resonator-cavity design concepts have been proposed in the 400-MHz frequency range. Los Alamos has been evaluating RFQ resonator-cavity designs that provide acceptable combinations of necessary mechanical features, easy tunability and long-term stability. Four RFQ resonator test cavities have been fabricated to test rf joints between the RFQ vanes and the resonator cavity. Two of these joints (the C-seal and the rf clamp-joint) allow vane movement for tuning. These test data, and the design of the present generation of RFQ resonator cavities, are presented

Radio-frequency-quadrupole linac in a heavy ion fusion driver system

A new type of linear accelerator, the radio-frequency quadrupole (RFQ) linac, is being developed for the acceleration of low-velocity ions. The RFQ accelerator can be adapted to any high-current applications. A recent experimental test carried out at the Los Alamos Scienific Laboratory (LASL) has demonstrated the outstandig properties of RFQ systems. The test linac accepts a 30-mA proton beam of 100-keV energy and focuses, bunches, and accelerates the beam to an energy to 640 keV. This ia done in a length of 1.1 m, with a transmission efficiency of 87% and with a radial emittance growth of less than 60%. The proven capability of the RFQ linac, when extended to heavy ion acceleration, should provide an ideal technique for use in the low-velocity portion of a heavy-ion linac for inertial-confinement fusion. A specific concept for such an RFQ-based system is described

Brazing techniques for side-coupled electron accelerator structures

The collaboration between the Los Alamos National Laboratory and the National Bureau of Standards (NBS), started in 1979, has led to the development of an advanced c-w microtron accelerator design. The four 2380-MHz NBS accelerating structures, containing a total of 184 accelerating cavities, have been fabricated and delivered. New fabrication methods, coupled with refinements of hydrogen-furnace brazing techniques described in this paper, allow efficient production of side-coupled structures. Success with the NBS RTM led to Los Alamos efforts on similar 2450-MHz accelerators for the microtron accelerator operated by the Nuclear Physics Department of the University of Illinois. Two accelerators (each with 17 cavities) have been fabricated; in 1986, a 45-cavity accelerator is being fabricated by private industry with some assistance from Los Alamos. Further private industry experience and refinement of the described fabrication techniques may allow future accelerators of this type to be completely fabricated by private industry

Development of a 130-mA, 75-kV high voltage column for high-intensity dc proton injectors

A reliable high-voltage (HV) column has been developed for dc proton injectors with applications to high-intensity cw linacs. The HV column is coupled with a microwave-driven plasma generator to produce a 75-keV, 110-mA dc proton beam. Typical proton fraction from this source is 85--90%, requiring the HV column and accelerating electrodes to operate with a 130-mA hydrogen-ion beam current. A glow-discharge, which was caused by the ion source axial magnetic field, was initially observed in the HV column. This problem was solved by scaling the electron production processes, the magnetic field, and the HV column pressure into a favorable regime. A subsequent 168 hour reliability run on the 75-keV injector showed that the ion source (plasma generator and HV column) has >98% beam availability