In this paper we review the present picture of km halo in proton linacs. Space-charge forces acting in mismatched beams have been identified as a major cause of beam-halo. We present a definition of halo based on a ratio of moments of the distribution of the beam coordinates. We find from our initial studies that for halo detined in this way, a beam can have rms emittance growth without halo growth, but halo growth is always accompanied by rms emittance growth. We describe the beam-halo experiment that is in preparation at Los Alamos, which will address questions about the beam profiles, maximum particle amplitudes, and rms emittance growth associated with the halo.

/pdf/beam-halo-in-proton-linac-beams-2k8gh43t6t.pdf

Beam Halo in Proton Linac Beams

The Low-Energy Demonstration Accelerator (LEDA) radio-frequency quadrupole (RFQ) is a 100% duty factor (CW) linac that delivers >100 mA of H beam at 6.7 MeV. The 8-m-long, 350-MHz RFQ structure accelerates a dc, 75-keV, 110-mA H beam from the LEDA injector with >90% transmission. LEDA [1,2] consists of a 75-keV proton injector, 6.7-MeV, 350-MHz CW RFQ with associated high-power and low-level rf systems, a short high-energy beam transport (HEBT) and high-power (670-kW CW) beam stop. The beam emittance is inferred from wire scanner measurements of the beam profile at a single location in the HEBT. The beam profile is measured as a function of the magnetic field gradient in one of the HEBT quadrupoles. As the gradient is changed the spot size passes through a transverse waist. Measurements are presented for peak currents between 25 and 100 mA.

/pdf/beam-emittance-measurements-for-the-low-energy-demonstration-3ufmw3fmy3.pdf

Beam emittance measurements for the low-energy demonstration accelerator (LEDA) radio-frequency quadrupole (RFQ)

The LEDA facility has been used to characterize the pulsed- and cw-beam performance of a 6.7-MeV, 100-mA radio frequency quadrupole (RFQ). Diagnostic instrumentation, primarily located in a short beam transport downstream of the RFQ, allowed facility commissioners and operators to measure and monitor the RFQ's accelerated and total beam transmission, beam loss, bunched beam current, beam energy and output phase, and beam position. Transverse beam profile measurements are acquired under both low and high duty- factor pulsed beam conditions using a slow wire scanner and a camera that images beam-induced fluorescence. The wire scanner is also used to acquire transverse beam emittance information using a technique known as a "quad scan". This paper reviews the measurement performance and discusses some of the resulting data.

/pdf/beam-diagnostic-instrumentation-for-the-low-energy-1w093hozqj.pdf

Beam diagnostic instrumentation for the low-energy demonstration accelerator (leda): commissioning and operational experience

Quadruple scans were used to characterize the LEDA RFQ beam. Experimental data were fit to computer simulation models for the rms beam size. The codes were found to be inadequate in accurately reproducing details of the wire scanner data. When this discrepancy is resolved, we plan to fit using all the data in wire scanner profiles, not just the rms value.

/pdf/determining-phase-space-properties-of-the-leda-rfq-output-41h0oj4zzo.pdf

Determining Phase-Space Properties of the LEDA RFQ Output Beam

The Low Energy Demonstration Accelerator (LEDA), located at Los Alamos National Laboratory, utilizes a slow wire scanner to measure beam profiles. The beam energy is 6.7 MeV and the peak current is 100 mA. This wire scanner profile measurement is located in the High Energy Beam Transport (HEBT) section of the LEDA beam line. This section of beam line is used to expand the proton beam coming out of the LEDA Radio Frequency Quadrupole (RFQ) prior to impacting the beam-stop. The purpose of the scanner is to provide horizontal and vertical beam profiles. The wires or fibers are a Silicon Carbide (SiC) material, and are attached to an actuator driven by a stepping motor. The actuator drives the fibers through the beam in incremental steps. At each step, the amount of secondary electrons generated by the interactions of the proton beam and the wire are measured. From these incremental measurements the beam profile is constructed. This paper will discuss the operation of the scanner, two of the experiments conducted to understand the capability of the SiC wire to survive and some of the different uses of the beam profile data acquired during the ongoing commissioning of LEDA.

/pdf/slow-wire-scanner-beam-profile-measurement-for-leda-47z5t7vr4u.pdf

Slow wire scanner beam profile measurement for LEDA

The Low Energy Demonstration Accelerator (LEDA) facility has been used to characterize the pulsed- and cw-beam performance of a 6.7 MeV, 100 mA radio frequency quadrupole (RFQ). Diagnostic instrumentation, primarily located in a short beam transport downstream of the RFQ, allow facility commissioners and operators to measure and monitor the RFQ’s accelerated and total beam transmission, beam loss, bunched beam current, beam energy and output phase, and beam position. Transverse beam profile measurements are acquired under both low and high duty-factor pulsed beam conditions using a slow wire scanner and a camera that images beam-induced fluorescence. The wire scanner is also used to acquire transverse beam emittance information using a technique known as a “quad scan”. This paper reviews the measurement performance and discusses the resulting data.

/pdf/leda-beam-diagnostics-instrumentation-measurement-49kvflw6l6.pdf

LEDA beam diagnostics instrumentation: Measurement comparisons and operational experience

Measurement of high-power proton beam-halo formation is the ongoing scientific experiment for the Low Energy Demonstration Accelerator (LEDA) facility. To attain this measurement goal, a 52-magnet beam line containing several types of beam diagnostic instrumentation is being installed. The Experimental Physics and Industrial Control System (EPICS) and commercial software applications are presently being integrated to provide a real-time, synchronous data acquisition and control system. This system is comprised of magnet control, vacuum control, motor control, data acquisition, and data analysis. Unique requirements led to the development and integration of customized software and hardware. EPICS real-time databases, Interactive Data Language (IDL) programs, LabVIEW Virtual Instruments (VI), and State Notation Language (SNL) sequences are hosted on VXI, PC, and UNIX-based platforms which interact using the EPICS Channel Access (CA) communication protocol. Acquisition and control hardware technology ranges from DSP-based diagnostic instrumentation to the PLC-controlled vacuum system. This paper describes the control system hardware and software design, and implementation.

M. Pieck

Papers

LEDA beam diagnostics instrumentation: Measurement comparisons and operational experience

Control System for the LEDA 6.7-MeV Proton Beam Halo Experiment