UHDpulse -Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates is a recently started European Joint Research Project with the aim to develop and improve dosimetry standards for FLASH radiotherapy, very high energy electron (VHEE) radiotherapy and laser-driven medical accelerators. This paper gives a short overview about the current state of developments of radiotherapy with FLASH electrons and protons, very high energy electrons as well as laser-driven particles and the related challenges in dosimetry due to the ultra-high dose rate during the short radiation pulses. We summarize the objectives and plans of the UHDpulse project and present the 16 participating partners.

Abstract:The accurate measurement of the arrival time of a hard X-ray free electron laser (FEL) pulse with respect to a laser is of utmost importance for pump-probe experiments proposed or carried out at FEL facilities around the world. This manuscript presents the latest device to meet this challenge, a THz streak camera using Xe gas clusters, capable of pulse arrival time measurements with an estimated accuracy of several femtoseconds. An experiment performed at SACLA demonstrates the performance of the device at photon energies between 5 and 10 keV with variable photon beam parameters. © 2014 Optical Society of AmericaOCIS codes: (120.0120) Instrumentation, measurement, and metrology; (020.0020) Atomic and molecular physics; (140.2600) Free-electron lasers (FELs). Kumagai, "A compact X-ray free-electron laser emitting in the sub-angstrom region," Nat. Photonics 6(8), 540-544 (2012). 4. E. Allaria, C. Callegari, D. Cocco, W. M. Fawley, M. Kiskinova, C. Masciovecchio, and F. Parmigiani, "The FERMI@Elettra free-electron-laser source for coherent x-ray physics: photon properties, beam transport system and applications," New J. Phys. 12(7), 075002 (2010). 5. P. Oberta, U. Flechsig, and R. Abela, "The SwissFEL facility and its preliminary optics beamline layout," Proc. Krausz, "X-ray pulses approaching the attosecond frontier," Science 291(5510), 1923-1927 (2001). 18. M. Uiberacker, E. Goulielmakis, R. Kienberger, A. Baltuska, T. Westerwalbesloh, U. Keineberg, U. Heinzmann, M. Drescher, and F. Krausz, "Attosecond metrology with controlled light waveforms," Laser Phys. 15, 195-204 (2005). 19. B. L. Henke, E. M. Gullikson, and J. C. Davis, "X-ray interactions-photoabsorption, scattering, transmission, and reflection at E=50-30,000 eV, z=1-92," At. Data Nucl. Data Tables 54(2), 181-342 (1993). 20. D. Irimia, D. Dobrikov, R. Kortekaas, H. Voet, D. A. van den Ende, W. A. Groen, and M. H. M. Janssen, "A short pulse (7 micros FWHM) and high repetition rate (dc-5 kHz) cantilever piezovalve for pulsed atomic and molecular beams," Rev. Sci. Instrum. 80(11), 113303 (2009). 21. O. F. Hagena and W. Obert, "Cluster formation in expanding supersonic jets-effect of pressure, temperature, nozzle size, and test gas," J. References and links:

The SwissFEL Injector Test Facility operated at the Paul Scherrer Institute between 2010 and 2014, serving as a pilot plant and testbed for the development and realization of SwissFEL, the X-ray Free-Electron Laser facility under construction at the same institute. The test facility consisted of a laser-driven rf electron gun followed by an S-band booster linac, a magnetic bunch compression chicane and a diagnostic section including a transverse deflecting rf cavity. It delivered electron bunches of up to 200 pC charge and up to 250 MeV beam energy at a repetition rate of 10 Hz. The measurements performed at the test facility not only demonstrated the beam parameters required to drive the first stage of an FEL facility, but also led to significant advances in instrumentation technologies, beam characterization methods and the generation, transport and compression of ultra-low-emittance beams. We give a comprehensive overview of the commissioning experience of the principal subsystems and the beam physics measurements performed during the operation of the test facility, including the results of the test of an in-vacuum undulator prototype generating radiation in the vacuum ultraviolet and optical range.

Electro-optical detection of THz coherent synchrotron radiation is a nondestructive method for measuring subpicosecond electron bunches or subpicosecond substructures on otherwise longer electron bunches. With a new diagnostic setup at the Swiss Light Source, which combines an amplified Yb fiber laser and a suitable GaP crystal, we demonstrate sampling as well as spectrally resolved single-shot measurements of sliced electron bunches containing as little as a few pC of charge. The single-shot measurements not only allow for a precise electric field characterization but also for a detailed analysis of the timing jitter between the electron bunch and the synchronized Yb fiber laser. The measurements of subsequent turns in the storage ring show distinct deviations from the simulations and we find strong indications that this discrepancy is caused by radiation loss through coherent synchrotron radiation itself, which is not included in many of today's simulation codes.

Electro-optical detection has proven to be a valuable technique to study temporal profiles of THz pulses with pulse durations down to femtoseconds. As the Coulomb field around a relativistic electron bunch resembles the current profile, electro-optical detection can be exploited for non-invasive bunch length measurements at accelerators. We have developed a very compact and robust electro-optical detection system based on spectral decoding for single-shot longitudinal bunch profile monitoring at the European X-ray free electron laser (XFEL) for electron bunch lengths down to 200 fs (rms). Apart from the GaP crystal and the corresponding laser optics at the electron beamline, all components are housed in 19 " chassis for rack mount and remote operation inside the accelerator tunnel. An advanced laser synchronization scheme based on radio-frequency down-conversion has been developed for locking a custom-made Yb-fiber laser to the radio-frequency of the European XFEL accelerator. In order to cope with the high bunch repetition rate of the superconducting accelerator, a novel linear array detector has been employed for spectral measurements of the Yb-fiber laser pulses at frame rates of up to 2.26 MHz. In this paper, we describe all sub-systems of the electrooptical detection system as well as the measurement procedure in detail, and discuss first measurement results of longitudinal bunch profiles of around 400 fs (rms) with an arrival-time jitter of 35 fs (rms).

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The recent entry of X-ray free electron lasers (FELs) to all fields of physics has created an enormous need, both from scientists and operators, for better characterization of the beam created by these facilities. Of particular interest is the measurement of the arrival time of the FEL pulse relative to a laser pump, for pump-probe experiments, and the measurement of the FEL pulse length. This article describes a scheme that corrects one of the major sources of uncertainty in these types of measurements, namely the jitter in the arrival time of the FEL relative to an experimental laser beam. The setup presented here uses a combination of THz streak cameras and a spectral encoding setup to reduce the effect of an FEL's jitter, leaving the pulse length as the only variable that can affect the accuracy of the pulse length and arrival time measurement. A discussion of underlying principles is also provided.

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