SLAC, Menlo Park, California
The LCLC RF gun requires a water cooling thermal system to tune the resonance frequency of the cavity to 2856.03MHz. The RF system operates in pulsed mode with bursts of 2.5usec at a repetition rate of 30-120Hz. The thermal system operates in combination with the low-level RF system to set the operation point of the cavity. The Low-Level RF system controls the magnitude and phase of the cavity voltage and define slow signals to the thermal system. The thermal system operates by pre-heating / pre-cooling the water and mixing both channels to achieve the optimal temperature to control the cavity resonant frequency. The tune control of the RF gun include two systems with different dynamics. The dynamics of the thermal system is slow while the RF system is fast. Additionally, different actuators in the system present limits that introduce non-linearities to be taking into account during the start up process . Combining these characteristics, a controller is designed for the resulting hybrid system that allows convergence in large for all the operation conditions and achieve the performance in the magnitude and phase of the cavity voltage required around the operation point.
SLAC, Menlo Park, California
DESY, Hamburg
LBNL, Berkeley, California
The Linac Coherent Light Source (LCLS) is a SASE x-ray free-electron laser project presently under construction at SLAC. The injector section from RF photocathode gun through the first bunch compressor chicane was installed during the Fall of 2006. The first bunch compressor chicane is located at 250 MeV and nominally compresses a 1-nC electron bunch from an rms length of about 1 mm to 0.2 mm. The degree of compression is highly adjustable using RF phasing and also chicane magnetic field variations. Transverse phase space and bunch length diagnostics are located immediately after the chicane. We present measurements and simulations of the longitudinal and transverse phase space after the chicane in various beam conditions, including extreme compression where coherent radiation effects are expected to be striking.
SLAC, Menlo Park, California
DESY, Hamburg
The Linac Coherent Light Source (LCLS) is a SASE x-ray Free-Electron Laser (FEL) project presently under construction at SLAC. The injector section, from drive-laser and RF photocathode gun through the first bunch compressor chicane, was installed during the Fall of 2006. Initial system commissioning with an electron beam takes place in the Spring and Summer of 2007. The second phase of construction, including the second bunch compressor and the FEL undulator, will begin later, in the Fall of 2007. We report here on experience gained during the first phase of machine commissioning, including RF photocathode gun, linac booster section, energy spectrometers, S-band and X-band RF systems, the first bunch compressor stage, and the various beam diagnostics.
SLAC, Menlo Park, California
LBNL, Berkeley, California
The Linac Coherent Light Source at SLAC will be the brightest X-ray laser in the world when it comes on line. In order to achieve the brightness a 100fS length electron bunch is passed through an undulator. To creat the 100fS bunch, a 10pS electron bunch, created from a photo cathode in an RF gun, is run off crest on the RF to set up a position to energy correlation. The bunch is then compressed chicanes. The stability of the RF system is critical in setting up the position to energy correlation. Specifications derived from simulations require the RF system to be stable to below 100fS in several critical injector stations and the last kilometer of linac. The SLAC linac RF system is being upgraded to meet these requirements.
SLAC, Menlo Park, California
DESY, Hamburg
Fermilab, Batavia, Illinois
CEA, Gif-sur-Yvette
It is well known that an electron beam excites Higher Order Modes (HOMs) as it passes through an accelerating cavity~[panofsky68]. The properties of the excited signal depend not only on the cavity geometry, but on the charge and trajectory of the beam. It is, therefore, possible to use these signals as a monitor of the beam's position. Electronics were installed on all forty cavities present in the FLASH~[flashref] linac in DESY. These electronics filter out a mode known to have a strong dependence on the beam's position, and mix this down to a frequency suitable for digitisation. An analysis technique based on Singular Value Decomposition (SVD) was developed to calculate the beam's trajectory from the output of the electronics. The entire system has been integrated into the FLASH control system.
SLAC, Menlo Park, California
DESY, Hamburg
Fermilab, Batavia, Illinois
UMAN, Manchester
Higher Order Modes (HOMs) excited by the passage of the beam through an accelerating cavity depend on the properties of both the cavity and the beam. It is possible, therefore, to draw conclusions on the inner geometry of the cavities based on observations of the properties of the HOM spectrum. A data acquisition system based on two 20 GS/s, 6 GHz scopes has been set up at the FLASH facility, DESY, in order to measure a significant fraction of the HOM spectrum predicted to be generated by the TESLA cavities used for the acceleration of its beam. The HOMs from a particular cavity at FLASH were measured under a range of known beam conditions. The dipole modes have been identified in the data. 3D simulations of different manufacturing errors have been made, and it has been shown that these simulations can predict the measured modes.
LLNL, Livermore, California
Royal Holloway, University of London, Surrey
SLAC, Menlo Park, California
KEK, Ibaraki
UCB, Berkeley, California
LBNL, Berkeley, California
UCL, London
Cornell University, Department of Physics, Ithaca, New York
Fermilab, Batavia, Illinois
University of Cambridge, Cambridge
DESY, Hamburg
SLAC, Menlo Park, California
The ultra-short bunches of the electron beam for LCLS are generated in two 4-dipole bunch compressors located at energies of 250 MeV and 4.3 GeV. Although an absolute measurement of the bunch length can be done by using a transverse deflecting cavity in an interceptive mode, a non-interceptive single shot method is needed as a relative measurement of the bunch length used in the continuous feedback for beam energy and peak current. We report on the design and implementation of two monitors measuring the integrated power of coherent edge radiation from the last dipole in each chicane. The first monitor is installed in early 2007 and we compare its performance with the transverse cavity measurement and other techniques.
SLAC, Menlo Park, California
OXFORDphysics, Oxford, Oxon
Fermilab, Batavia, Illinois
LLNL, Livermore, California
We report on measurements of picosecond bunch lengths and the energy-z correlation of the bunch with a high energy electron test beam to the A-line and End Station A (ESA) facilities at SLAC. The bunch length and the energy-z correlation of the bunch are measured at the end of the linac using a synchrotron light monitor diagnostic at a high dispersion point in the A-line and a transverse RF deflecting cavity at the end of the linac. Measurements of the bunch length in ESA were made using high frequency diodes (up to 100 GHz) and pyroelectric detectors at a ceramic gap in the beamline. Modelling of the beam's longitudinal phase space through the linac and A-line to ESA is done using the 2-dimensional tracking program LiTrack, and LiTrack simulation results are compared with data. High frequency diode and pyroelectric detectors are planned to be used as part of a bunch length feedback system for the LCLS FEL at SLAC. The LCLS also plans precise bunch length and energy-z correlation measurements using transverse RF deflecting cavities.