V. Yuan

Commissioning of the first drift tube linac module in the Ground Test Accelerator

The Ground Test Accelerator (GTA) has the objective of verifying much of the technology required for producing high-brightness, high-current H/sup -/ beams. GTA commissioning is staged to verify the beam-dynamics design of each major accelerator component as it is brought online. The major components are the 35-keV H/sup -/ injector, the 2.5-MeV radiofrequency quadrupole (RFQ), the intertank matching section (IMS), the 3.2 MeV first 2/spl betaspl lambda/ drift tube linac (DTL-1) module, and the 24-MeV GTA with 10 DTL modules. Results from the DTL-1 beam experiments will be presented.<<ETX>>

Unexpected matching insensitivity in DTL of GTA accelerator

The intertank matching section (IMS) of the Ground Test Accelerator (GTA) contains four variable-field quadrupoles (VFQs) and is designed to match beam exiting the radio-frequency quadrupole to the first tank of the Drift-Tube Linac (DTL-1). By varying the VFQ field strengths to create a range of beam mismatches at the entrance to DTL-1, one can test the sensitivity of the DTL-1 output beam to variations in the DTL-1 input beam. Experimental studies made during commissioning of the GTA indicate an unexpected result: the beam exiting DTL-1 shows little variation for a range of mismatches produced at the entrance. Results of the experiment and simulation studies are presented.

Phase-scan analysis results for the first drift tube linac module in the Ground Test Accelerator: data reproducibility and comparison to simulations

The Ground Test Accelerator (GTA) had the objective of producing a high-brightness, high-current H/sup -/ beam. The major accelerator components were a 35 keV injector, a Radio Frequency Quadrupole, an intertank matching section, and a drift tube linac (DTL), consisting of 10 modules. This paper discusses the phase-scan technique which was used to experimentally determine the rf operating parameters for the commissioning and routine operation of the first DTL module.

Characterization of a ramped gradient DTL: experiment and theory

An experimental demonstration confirming the beam dynamics of a ramped-gradient drift-tube linac (RGDTL) was performed at Los Alamos National Laboratory. The RGDTL was designed to meet the requirements of maximum beam acceleration, minimum longitudinal and transverse emittance growth, and acceptable wall power loss. At low beam energies, transverse-magnet focusing is weak and the RF defocusing must be minimized. As the beam energy increases, stronger RF defocusing can be tolerated and the RF electric field gradient can increase. A detailed comparison of theory and experiment was carried out. Experimental data and theory were in good agreement.<<ETX>>

Measurement of longitudinal emittance growth using a laser-induced neutralization method

A laser-induced neutralization technique called LINDA (Laser-Induced Neutral Diagnostic Approach) has been used to study the longitudinal emittance of the 5-MeV H/sup -/ beam exiting the drift-tube linac of the Los Alamos Accelerator Test Stand. By using multiple laser intersection points, longitudinal emittance growths over drift distances of 23.6 and 30.6 cm were measured. Subsequently, a beam transport line, which consisted of one arm of a beam funnel, was substituted for the drift space. Measurements show that the elements of the funnel constrain emittance growth while the H/sup -/ beam is contained within these transport elements.<<ETX>>

H - beam characterization using laser-induced neutralization

The capabilities of the laser-induced neutralization technique, LINDA, as a diagnostic go beyond its primary function of quantitatively determining emittance sizes. It is also valuable for its capability to characterize, both quantitatively and qualitatively, the performance and match of linear accelerator (linac) components. The authors present LINDA experimental results that show how the output beam of a radio-frequency quadrupole (RFQ) and drift-tube linac (DTL) combination changes with the variation of RFQ-DTL relative phase and of DTL cavity power. Results showing the effect of a longitudinal buncher on beam emittance are also presented.<<ETX>>