A. Ratti

A recirculating linac-based facility for ultrafast x-ray science

We present an updated design for a proposed source of ultra-fast synchrotron radiation pulses based on a recirculating superconducting linac, in particular the incorporation of EUV and soft x-ray production. The project has been named LUX - Linac-based Ultrafast X-ray facility. The source produces intense x-ray pulses with duration of 10-100 fs at a 10 kHz repetition rate, with synchronization of 10s fs, optimized for the study of ultra-fast dynamics. The photon range covers the EUV to hard x-ray spectrum by use of seeded harmonic generation in undulators, and a specialized technique for ultra-short-pulse photon production in the 1-10 keV range. High-brightness rf photocathodes produce electron bunches which are optimized either for coherent emission in free-electron lasers, or to provide a large x/y emittance ration and small vertical emittance which allows for manipulation to produce short-pulse hard x-rays. An injector linac accelerates the beam to 120 MeV, and is followed by four passes through a 600-720 MeV recirculating linac. We outline the major technical components of the proposed facility.

The SNS four-phase LEBT chopper

The Spallation Neutron Source front end incorporates a beam chopper in the LEBT that will remove a 295 ns section of beam at a 1.118 MHz rate (65% transmission) with less than 50 ns rise/falltime. The H/sup -/ beam pulse length is one ms at a 60-Hz rate (6% duty factor). The LEBT is all-electrostatic, and the chopper incorporates four 3-kV solid-state switches driving an einzel lens, split into quadrants, with a 4-phase chopping waveform. The suppressed beam is targeted on a four-segment Faraday cup which provides on-line intensity and steering diagnostics. Results of proton beam tests will be reported.

Ion-source and low-energy beam-transport issues with the front-end systems for the spallation neutron source

The front-end systems (FES) of the spallation neutron source project are being built by Berkeley Lab and will deliver a pulsed 40 mA H− ion beam at 2.5 MeV energy to the subsequent drift-tube linac. The FES accelerator components comprise a rf driven, volume-production, cesium-enhanced, multicusp ion source; an electrostatic low-energy beam transport (LEBT) that includes provisions for transverse focusing, steering, and beam chopping; a radio-frequency quadrupole accelerator; and a medium-energy beam transport line. The challenges for ion source and LEBT design are the generation of a plasma suitable for creating the required high H− ion density, lifetime of the rf antenna at 6% duty factor, removal of the parasitic electron population from the extracted negative ions, and emittance conservation. The article discusses these issues in detail and highlights key experimental results obtained so far.

The SNS RFQ prototype module

The RFQ included in the Front End injector for the Spallation Neutron Source (SNS) operates at 402.5 MHz, with a maximum H/sup -/ input current of 70 mA at a 6% duty factor. It is 3.72 m long and consists of four equally long modules. A brazed copper structure has been chosen due to the high power, high duty factor operation. The 1 MW peak r.f. power is coupled into the structure via eight ports, two per module. Quadrupole mode stabilization is obtained with a set of /spl pi/-mode stabilizing loops. The conceptual design has been completed, and a single, full size prototype RFQ module has been designed and is under construction to test the fabrication processes and r.f. performance. It will be operated at full r.f. power in order to test its cooling scheme, dual temperature water tuning, mode stabilization and beam acceptance. The detailed design, assembly processes, thermal analyses and a status report for the prototype module are presented.

High Speed Measurements of the LHC Luminosity Monitor

The LHC luminosity monitor is a gas ionization chamber designed to operate in the high radiation environment present in the TAN neutral absorbers at the LHC. One of the challenges is to measure the luminosity of individual bunch crossings with a minimum separation of 25 nsec. To test the time response and other aspects of a prototype chamber, we have performed a test using an x‐ray beam of 40–60 keV with pulse spacing of 26 nsec as an ionizing beam. The tests were made at BL 8.3.2 at the Advanced Light Source (ALS). This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DE‐AC02‐05CH11231.

The fabrication and initial testing of the SNS RFQ

The Lawrence Berkeley National Laboratory (LBNL) is designing and building the 2.5 MeV front end injector for the Spallation Neutron Source (SNS). This injector comprises an H/sup -/ ion source, a low energy beam transport line (LEBT), a radio-frequency quadrupole (RFQ) and a beam transport line designed to provide fast chopping of the beam. The RFQ is designed to accelerate the Hbeam from the energy of 65 keV to 2.5 MeV, while bunching it at 402.5 MHz. This high duty factor (6%) structure is made of a combination of Glidcop and OFE copper and is fully brazed. The RFQ is built in 4 modules, each approximately one meter long. This paper covers the mechanical fabrication details of the modules, three of which have been completed. While the modules are coming out of production, they are conditioned and tested to full power. This paper will also describe the results of the beam tests on the first module, including capture efficiency and transmission.

The luminosity monitoring system for the LHC: Modeling and test results

Simulation results of the Beam Rate of Neutrals (BRAN) luminosity detector for the CERN Large Hadron Collider are presented. The detectors are intended to measure the bunch-by-bunch relative luminosity at the ATLAS and CMS experiments. Building up from experimental results from test runs at the SPS, RHIC and ALS we extend the simulated setup to the TAN neutral absorbers located at 140 m at both sides the IP1 and IP5 interaction points. The expected signal amplitudes are calculated for pp-collisions energies between 450 GeV and 7 TeV using the Monte Carlo package FLUKA and its graphical user interface FLAIR.

High-Yield Neutron Source for Cargo Container Screening

A high-yield neutron source has been designed for the screening of sea-land cargo containers for shielded special nuclear materials (SNM). The accelerator-driven neutron source utilizes the D(d,n)3He reaction to produce a forward directed neutron beam. The key components of the neutron source are a high-current radio-frequency quadrupole (RFQ) accelerator and a high-power neutron production target. A thin entrance window has been designed that minimizes the energy loss of the deuteron beam and withstands the gas pressure. The source will be capable of delivering a neutron flux of up to 2 middot 107 n/(cm2middots) at a distance of 2.5 m from the target and will allow the comprehensive testing and demonstration of active neutron interrogation.

Fermi Timing and Synchronization System

The Fermi FEL will depend critically on precise timing of its RF, laser and diagnostic subsystems. The timing subsystem to coordinate these functions will need to reliably maintain sub-100fs synchronicity between distant points up to 300m apart in the Fermi facility. The technology to do this is not commercially available, and has not been experimentally demonstrated in a working facility. Therefore, new technology must be developed to meet these needs. Two approaches have been researched by different groups working with the Fermi staff. At MIT, a pulse transmission scheme has been developed for synchronization of RF and laser devices. And at LBL, a CW transmission scheme has been developed for RF and laser synchronization. These respective schemes have advantages and disadvantages that will become better understood in coming years. This document presents the work done by both teams, and suggests a possible system design which integrates them both. The integrated system design provides an example of how choices can be made between the different approaches without significantly changing the basic infrastructure of the system. Overall system issues common to any synchronization scheme are also discussed.

R&D Requirements, RF Gun Mode Studies, FEL-2 Steady-StateStudies, Preliminary FEL-1 Time-Dependent Studies, and Preliminary LayoutOption Investigation

This report constitutes the third deliverable of LBNLs contracted role in the FERMI {at} Elettra Technical Optimization study. It describes proposed R&D activities for the baseline design of the Technical Optimization Study, initial studies of the RF gun mode-coupling and potential effects on beam dynamics, steady-state studies of FEL-2 performance to 10 nm, preliminary studies of time-dependent FEL-1 performance using electron bunch distribution from the start-to-end studies, and a preliminary investigation of a configuration with FEL sinclined at a small angle from the line of the linac.