BINP SB RAS, Novosibirsk
The first stage of Novosibirsk high power free electron laser (FEL) is in operation since 2003. Now the FEL provides average power up to 500 W in the wavelength range 120 - 240 micron. One orbit for 11-MeV energy with terahertz FEL lies in vertical plane. Other four orbits lie in the horizontal plane. The beam is directed to these orbits by switching on of two round magnets. In this case electrons pass four times through accelerating RF cavities, obtaining 40-MeV energy. Then, (at fourth orbit) the beam is used in FEL, and then is decelerated four times. At the second orbit (20 MeV) we have bypass with third FEL. When magnets of bypass are switched on, the beam passes through this FEL. The length of bypass is chosen to provide the delay, which necessary to have deceleration instead of acceleration at the third passage through accelerating cavities. Now two of four horizontal orbits are assembled and commissioned. The electron beam was accelerated twice and then decelerated down to low injection energy. Project average current 9 mA was achieved. First multi-orbit ERL operation was demonstrated successfully.
JLAB, Newport News, Virginia
Funding: Work supported by the US DOE Contract #DE-AC05-060R23177 and the Commonwealth of Virginia.
The characteristics of the system of “SF” Sextupoles for the infrared Free Electron Laser Upgrade at the Thomas Jefferson National Accelerator Facility (JLab) are described. These eleven sextupoles possess a large field integral (2.15 T/m) with ± 0.01% field quality over a 150 mm width within a very short effective length (150 mm pole length) and have field clamps for fast field roll-off. The field integrals reproduce extremely well with good absolute resolution (± 0.1%). The simple, two-dimensional shape pole tips (directly from the original 3-D RADIA magnetic model) of these “all ends” magnets include the correction for end fields. Magnetic measurements are compared to the model. The system’s hysteresis protocol and power supplies were also used for the measurement process to enhance reproducibility in service, a recent initiative at JLab. The intricacies of magnetic measurement using the JLab field probe based Stepper Stand are described. The challenges of developing the in-house design power supplies for these magnets, based on use of a low quality supply brought to 0.001% current regulation by a CAN-Bus control are described.
FEL/Duke University, Durham, North Carolina
PKU/IHIP, Beijing
Funding: This work was supported by US Air Force Office of Scientific Research medical FEL grant FA9550-04-01-0086.
The Madey theorem is a valuable research tool for studying Free-Electron Lasers (FELs). The theorem relates the shape of the on-axis spontaneous radiation spectrum of FEL wigglers to the FEL gain. The theorem predicts that degradation of the spontaneous spectrum, for example as a result of the increase of the electron beam energy spread, provides a direct measure of the reduction of the FEL gain. Extensive experiments have been performed to study the validity of the Madey theorem for a storage ring base optical klystron FEL. The experimental data show that the lasing wavelength of the FEL is very close to the maximum slope of spontaneous spectra as predicted by the Madey theorem with a relative wavelength discrepancy less than 0.2%. Further analysis is underway to understand this wavelength difference. In addition, we have performed direct measurements of the start up gain of the FEL and compared it with the changing slope of the spontaneous spectra. The preliminary results show a good agreement between the measured FEL gain and the prediction by Madey theorem.
ANL, Argonne
Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava
Funding: * Work at Argonne supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357.
Hall probe is the best way to do tuning and measurements of insertion devices. Horizontal Hall probe magnetic field measurements in the presence of a strong vertical magnetic field were tested in 1997. The next step of this investigation was reported at the 2004 FEL Conference. Hall probe horizontal field measurements in the presence of a vertical magnetic field are complicated due to the influence of the Planar Hall probe effect on the resulting Hall voltage. 2-axis Sentron Hall probe was used for the Linear Coherent Light Source devices. By positioning the Hall probe accurately in the vertical direction, the probe could be used for fast measurements and tuning of FEL devices. To eliminate the high sensitivity to the positioning of the probe, a new type of Hall probe, consisting of two sensors combined so as to cancel the influence of the PHE, was developed at the Institute of Electrical Engineering, Slovak Academy of Sciences. The results of tests done at the APS showed that it is not sensitive to vertical position and is 60 times less sensitive than a Bell probe to the angle between the Hall sensor current and the in-plane component of the field direction.
SLAC, Menlo Park, California
UCLA, Los Angeles, California
Funding: Work supported by U.S. DoE Grant No. DE-FG03-92ER40693.
The first successful attempt to generate ultrashort (1-10 picosecond) relativistic electron bunches characterized by a ramped current profile that rises linearly from head to tail and then falls sharply to zero was recently reported.* Bunches with this type of longitudinal shape may be applied to plasma-based accelerator schemes as an optimized drive beam, and to free electron lasers as a means of reducing asymmetry in microbunching due to slippage. We will review the technique used to generate these bunches, which utilizes a sextupole-corrected dogleg compressor to manipulate the longitudinal phase space of the beam, and examine its potential application in a realistic plasma wakefield accelerator scenario, the proposed FACET project at SLAC.
* R. J. England, J. B. Rosenzweig, G. Travish, Phys. Rev. Lett. 100, 214802 (2008).
MSL, Stockholm
DESY, Hamburg
The undulators of the European free-electron laser (XFEL) are 128 to 226 meters in length and divided into five meter long segments. Each segment ends with a quadrupole magnet to focus the electron beam and to maintain optimum spatial overlap between the electron and photon beams. At the Manne Siegbahn Laboratory a rotating coil instrument has been built to characterize these quadrupoles and to measure the position of the magnetic center. In combination with a coordinate measurement machine the magnetic center can be measured with respect to fiducials on the magnet. The aim is to measure the position of the magnetic center within 0.050 mm. In this work the experimental setup is presented together with fiducialization of test magnets.
DESY, Hamburg
Stockholm University, Stockholm
For the operation of the European X-Ray Free Electron Laser (XFEL), a system wide synchronous low-jitter clock and precise, adjustable triggers must be generated and distributed throughout the approximately 3.5 km long facility. They are needed by numerous diagnostics, controls, and experiments. Fast ADCs require the jitter of the distributed 1.3GHz clock to be in the order of a few pico seconds (RMS) and that it is synchronized to the accelerating RF. The phase of the 1.3GHz clock must therefore be adjustable at every endpoint. Due to cable lengths, and the temperature dependence of the propagation speed, temperature drifts are a serious issue. Therefore a complex monitoring and compensation mechanism has been developed to minimize these effects. Triggers must also be distributed throughout the system to synchronize different control or measurement tasks. The triggers must be adjustable in time in order to compensate for different cable lengths and should have a resolution of one ns but with ps stability. A prototype of this clock and trigger system has been developed and first measurements have shown, that the strong requirements can be fulfilled.