Charge to the Committee
The RF Technical Review for the Linac Coherent Light Source (LCLS) Injector will be held at Stanford Linear Accelerator Center (SLAC) on November 3, 2004. The reviewers will be given the LCLS injector performance requirements, and are asked to critically assess the RF, thermal and mechanical designs for the gun and first accelerator section which are proposed to meet these requirements. Presentations will cover beam dynamics and the dual feed and racetrack designs for the gun and L0-1 accelerator section. Thermal management and RF mode issues for the gun will also be presented. Specific technical issues include the elimination of dipole and quadrupole field distortions with dual feed couplers and racetrack shaped coupler cells, thermal distortion of the gun when operated at 120 Hz, and the excitation of the 0-mode and its effect in the gun during the RF transient. Specifically we ask the committee to recommend whether or not the 0-pi mode separation should be increased. Manufacturing, RF testing and tuning procedures will also be discussed.
The committee is requested to:
1. Identify and quantify technical issues related to the Injector RF design
2. Determine if the design will meet LCLS requirements
3. Identify any technical issues not already included in design
4. Determine if design, RF tuning and construction plans are reasonable
5. Make comments and suggestions for improving the RF design
A written report of the committee’s comments and recommendations is requested.
General Description of the LCLS Injector
The last kilometer of the SLAC 3-km linac will be used to provide a 10-15 GeV beam for the LCLS. A new off-axis injector will be built at Sector 20 in an existing vault. The injector utilizes an S-band rf gun with a metal photocathode. The laser for exciting the cathode will be in a laser room which will be inside an existing building above the vault. Additional information on LCLS can be found at the LCLS web site:
The goal of the LCLS injector is to produce an electron beam bright enough to saturate the SASE x-ray fel within a 120 meter undulator. The injector parameters needed to achieve this are given in Table I.
Table I. Parameter goals of the LCLS injector
The injector consists of an RF photocathode gun and two s-band SLAC-sections to give a total beam energy of 135 MeV, as shown in the figure below. The photocathode gun produces electrons using a drive laser located in a room located directly above the gun. In order to achieve the challenging parameters given in Table I, the injector has been designed to include features not found in other injectors.These include:
- Cathode load lock and a cathode lab located near the injector.
- Rf gun with dual rf feeds to minimize field asymmetry.
- High-resolution energy diagnostics between the gun and the first linac section.
- Dual rf feeds on the first accelerator section to eliminate time-dependent rf kicks.
- Transverse rf deflecting cavity for direct measurement of the longitudinal phase space and slice emittance.
- Electro-optical bunch shape diagnostics.
- High-resolution spectrometer for measuring beam properties at 135 MeV.
- A ‘laser heater’ is included to allow a controlled increase in the uncorrelated energy to suppress coherent synchrotron radiation and longitudinal space charge instabilities.
Presentations will be posted at the web site here below by
See also the two technical notes on the RF system for the LCLS injector related to the LCLS injector RF systems:
The LCLS Injector at Sector 20