[en] The factors that affect the voltage at which vacuum gaps break down are analyzed. Based on the literature and some simplifying assumptions, a functional dependence is hypothesized. The hypothesis is related to a proposed experiment using radio-frequency power to generate the breakdown voltage

[en] Energy spectroscopy measurements of x-rays from rf structures at high power provide an independent method of finding accelerating-gap voltages in the multiple-cell accelerating structures. An x-ray detector is used to measure the energy of the emitted x-rays; and the high-energy endpoint of the energy spectrum histogram corresponds with the peak-gap voltage in the rf structure. The x-ray measurements are used to provide a calibration relating peak-gap voltage to rf structure field sampling probes. The analyzed x-ray data has been compared to theoretical SUPERFISH and MAFIA3D predictions and to beam-dynamics data for the multiple-cell structures. Information about this diagnostic technique and its value for verifying accelerator modeling codes is presented

[en] Exploiting the potential efficiency gain of a normal conducting rf accelerator operated at cryogenic temperatures requires careful preparation of the rf conducting surface. Experimental apparatus has been assembled to study the surface conductivity to rf currents at 425 MHz and 850 MHz through a temperature range from room temperature to 14 K. The apparatus is built around an open-ended coaxial cavity with the cavity tubular ends below the cutoff frequency at resonance. The center conductor in the coaxial cavity is the test sample, and the use of a dielectric stand-off for the center conductor precludes the need for an rf contact joint and facilitates sample changes. The rf testing is conducted under vacuum with low-power rf. A CTI-Cryogenics cryopump coldhead is used for cryogenic temperature cycling of the test cavity. A detailed description of the apparatus and measurement procedures are presented

[en] The Ground Test Accelerator (GTA) has the objective of verifying much of the technology (physics and engineering) required for producing high-brightness, high-current H^- beams. GTA commissioning is staged to verify the beam dynamics design of each major accelerator component as it is brought on-line. The commissioning stages are the 35 keV H^- injector, the 2.5 MeV Radio Frequency Quadrupole (RFQ), the Intertank Matching Section (IMS), the 3.2 MeV first 2βγ Drift Tube Linac (DTL-1) module, the 8.7 MeV 2βγ DTL (modules 1--5), and the 24 MeV GTA; all 10 DTL modules. Commissioning results from the IMS beam experiments will be presented

[en] The Ground Test Accelerator (GTA) has the objective of verifying much of the technology (physics and engineering) required for producing high-brightness, high-current H^- beams. GTA commissioning is staged to verify the beam dynamics design of each major accelerator component as it is brought on-line. The commissioning stages are the 35-KeV H^- injector, the 2.5-MeV radio-frequency quadrupole (RFQ); the intertank matching section (IMS), the 3.2-MeV first 2-βλ drift-tube linac (DTL-1) module, the 8.7-MeV 2-βλ DTL (modules 1-5), and the 24-MeV GTA (all 10 DTL modules). Commissioning results from the IMS beam experiments are presented. (Author) 10 refs., 6 figs

[en] The Ground Test Accelerator (GTA) has the objective of verifying much of the technology (physics and engineering) required for producing high-brightness, high-current H^- beams. GTA commissioning is staged to verify the beam dynamics design of each major accelerator component as it is brought on line. The commissioning stages are the 35-keV H^- injector, the 2.5-MeV radio-frequency quadrupole (RFQ), the intertank matching section (IMS), the 3.2-MeV first 2-βλ drift tube linac (DTL-1) module, the 8.7-MeV 2-βλDTL (modules 1-5), and the 24-MeV GTA (all 10 DTL modules). Commissioning results from the RFQ beam experiments are presented along with comparisons with simulations. (Author) 8 refs., 9 figs

[en] The Ground Test Accelerator (GTA) is being used to resolve the physics and engineering issues related to accelerating, focusing, and steering a high-brightness, high-current H^- beam and then neutralizing it. The goal is to produce a 24 MeV, 50 mA device with a 2% duty factor. Specific features of the GTA -- injector, beam optics, rf linac structures, diagnostics, control and rf power systems are described. The first four steps in commissioning have been completed. The RFQ predicted and measured performances are in good agreement; however, the transmission is lower than specifications. Input emittance is larger than design specifications and increases the effects of image charge and multipoles. Displacement of steering magnets in either the horizontal or vertical plane caused beam displacements in both planes. It is suspected that quadrupole rotation is the cause of the coupled motion. 9 figs., 5 tabs., 11 refs

[en] The Ground Test Accelerator (GTA) is supported by the Strategic Defense command as part of their Neutral Particle Beam (NPB) program. Neutral particles have the advantage that in space they are unaffected by the earth's magnetic field and travel in straight lines unless they enter the earth's atmosphere and become charged by stripping. Heavy particles are difficult to stop and can probe the interior of space vehicles; hence, NPB can function as a discriminator between warheads and decoys. We are using GTA to resolve the physics and engineering issues related to accelerating, focusing, and steering a high-brightness, high-current H^- beam and then neutralizing it. Our immediate goal is to produce a 24-MeV, 50mA device with a 2% duty factor