The European XFEL will operate nominally at 17.5GeV in SP (short pulse) mode with 0.65ms long bunch train and 10Hz repetition rate. A possible upgrade of the linac to CW (continuous wave) or LP (long ...pulse) modes with a corresponding reduction of electron beam energy is under discussion for many years. Recent successes in the dedicated R&D program allow to forecast a technical feasibility of such an upgrade in the foreseeable future. One of the challenges is to provide sub-Ångström FEL operation in CW and LP modes. In this paper we perform a preliminary analysis of a possible operation of the European XFEL in the hard X-ray regime in CW and LP modes with electron energies of 7GeV and 10GeV, respectively. We consider lasing in the baseline XFEL undulator as well as in a new undulator with a reduced period. We show that, with reasonable requirements on electron beam quality, lasing on the fundamental will be possible in the sub-Ångström regime. As an option for generating brilliant photon beams at short wavelengths we also consider harmonic lasing that has recently attracted a significant attention.
We discuss the progress in the R&D program for a future upgrade of the European XFEL facility, namely for an operation in the continuous wave (cw) and long pulse (lp) modes, which will allow for ...significantly more flexibility in the electron and photon beam time structure. Results of cw/lp runs with preseries XFEL cryomodules and status of components needed for the new operation modes are presented here.
Lead photocathodes Smedley, J.; Rao, T.; Sekutowicz, J.
Physical review special topics. PRST-AB. Accelerators and beams,
01/2008, Letnik:
11, Številka:
1
Journal Article
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We present the results of our investigation of lead as a suitable photocathode material for superconducting rf injectors. Quantum efficiencies (QE) have been measured for a range of incident photon ...energies and compared to predictions from the three-step model of photoemission. A variety of cathode preparation methods have been used, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.
Photocathodes are a limiting factor for the next generation of ultrahigh brightness photoinjectors. We studied the behavior of a superconducting Pb cathode in the cryogenic environment of a ...superconducting rf gun cavity to measure the quantum efficiency, its spatial distribution, and the work function. We will also discuss how the cathode surface contaminants modify the performance of the photocathode as well as the gun cavity and we discuss the possibilities to remove these contaminants.
Superconducting TESLA cavities Aune, B.; Bandelmann, R.; Bloess, D. ...
Physical review special topics. PRST-AB. Accelerators and beams,
09/2000, Letnik:
3, Številka:
9
Journal Article
Recenzirano
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The conceptional design of the proposed linear electron-positron collider TESLA is based on 9-cell 1.3 GHz superconducting niobium cavities with an accelerating gradient of Eacc≥25MV/m at a quality ...factor Q0≥5×109 . The design goal for the cavities of the TESLA Test Facility (TTF) linac was set to the more moderate value of Eacc≥15MV/m . In a first series of 27 industrially produced TTF cavities the average gradient at Q0=5×109 was measured to be 20.1±6.2MV/m , excluding a few cavities suffering from serious fabrication or material defects. In the second production of 24 TTF cavities, additional quality control measures were introduced, in particular, an eddy-current scan to eliminate niobium sheets with foreign material inclusions and stringent prescriptions for carrying out the electron-beam welds. The average gradient of these cavities at Q0=5×109 amounts to 25.0±3.2MV/m with the exception of one cavity suffering from a weld defect. Hence only a moderate improvement in production and preparation techniques will be needed to meet the ambitious TESLA goal with an adequate safety margin. In this paper we present a detailed description of the design, fabrication, and preparation of the TESLA Test Facility cavities and their associated components and report on cavity performance in test cryostats and with electron beam in the TTF linac. The ongoing research and development towards higher gradients is briefly addressed.
Polish Free Electron Laser facility (PolFEL) will be the first free electron laser in Poland. The PolFEL superconducting linear electron accelerator will first consist of an electron gun and four ...RI-HZDR type cryomodules, each housing two 9-cell superconducting TESLA RF cavities. Such configuration allows the generation of a continuous wave and long pulse beam with 5-50 MeV of energy and a long pulse electron beam with energy up to 187 MeV and photon wavelength ranged from THz region down to 55 nm. In the second stage an extension is planned with two cryomodules, which allows to reach 300 MeV electron beam energy and extreme ultraviolet (EUV) range of electromagnetic radiation. RF cavities will be operated at 2.0 K (optionally 1.8 K). For a four cryomodule linac the static and dynamic loads are estimated to be 61 W and 240 W @ 2 K, respectively. One of the investigated option is that the cooling power will be generated by the TCF50 Linde helium plant. The helium plant has a liquefaction capacity of 6 g/s and 120 W at 4.5K of cooling power. During the beam-on operation mode of the linac, a shortage of cooling power will be compensated by liquid helium supplied from an external dewar, while the warm helium gas stream exceeding the liquefaction capacity will be collected in pressurized storage tanks. During the beam-off mode, the helium gas will be recovered from the storage tanks and re-liquefied to the external dewar. The other option is the installation of a dedicated cryoplant fully corresponding to the linac cryogenic requirements.
This paper reports on our efforts to develop a flangeable coaxial coupler for both higher order mode and fundamental coupling for nine-cell ILC-type cavities, which were designed in the early 1990’s ...for pulsed operation with a duty factor less than 1%. The design of the coupler has been done in such a way that the rf magnetic flux B at the flange connection was minimized and only a field of <5mT would be present for an operation at an accelerating field Eacc∼36MV/m (B∼150mT ) in the cavity. Even though we achieved reasonably high Q values at low field, the cavity/coupler combination was limited in the cw mode to only ∼7MV/m , where a thermally initiated degradation occurred. We believed that this limitation was caused by poor cooling of the shorting plate and inner tube in the coaxial coupler; therefore, we have improved the cooling conditions by initially drilling radial cooling channels every 30 degrees, then every 15 degrees into the shorting plate and eventually removing the “bridges” between the channels. This paper reports on our experiences with the modified coaxial coupler under cw and pulsed conditions.
The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many ...electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created.The first operation of the European X-ray free-electron laser facility accelerator based on superconducting technology is reported. The maximum electron energy is 17.5 GeV. A laser average power of 6 W is achieved at a photon energy of 9.3 keV.
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