| Paper | Title | Other Keywords | Page |
|---|---|---|---|
| WEP103 | A Plasma Attenuator for Soft X-Rays in LCLS-II | electron, FEL, cavity, controls | 553 |
|
|||
| Attenuation of X-ray FEL beams is often required to avoid damaging optics and detectors during alignment, and to study fluence-dependent effects. Soft X-rays are commonly attenuated by photoabsorption in a gas such as argon. However, absorbing a mJ pulse along a meter creates a pressure wave that drives gas away from the X-ray propagation axis, until equilibrium recovers in ~1 ms. This timescale matched the 120-Hz pulse spacing of LCLS, but at the high repetition rate (up to 1 MHz) and power (up to 200 W) of LCLS-II, the attenuation of subsequent pulses is reduced. Simulations demonstrate hysteresis and erratic attenuation from gas-density depletion. Instead, we propose to replace the gas column with an argon plasma in a TM010 RF cavity. The density profile then is largely set by the RF mode. X-ray absorption becomes a perturbation compared to the energy in the plasma. An LCLS-II solid-state RF amplifier, generating up to 4 kW at 1.3 GHz, can provide the drive, and the FPGA-based low-level RF controller can be programmed to track tuning with plasma density. Several diagnostics are planned to monitor plasma properties over a fill-pressure range of 10 to 1000 Pa. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP103 | ||
| About • | paper received ※ 16 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019 | ||
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | ||
| THP048 | Progress Towards Laser Plasma Electron Based Free Electron Laser on COXINEL | laser, electron, undulator, FEL | 684 |
|
|||
|
Laser plasma acceleration (LPA) with up to several GeV beam in very short distance appears very promising. The Free Electron Laser (FEL), though very challenging, can be viewed as a qualifying application of these new emerging LPAs. The energy spread and divergence, larger than from conventional accelerators used for FEL, have to be manipulated to fulfil the FEL requirements. On the test experiment COXINEL (ERC340015), the beam is controlled in a manipulation [1,2] line, using permanent magnet quadrupoles of variable strength [3] for emittance handing and a decompression chicane equipped with a slit for the energy selection, enabling FEL amplification for baseline reference parameters [2]. The electron position and dispersion are independently adjusted [4]. The measured spontaneous emission radiated by a 2 m long 18 mm period cryo-ready undulator exhibits the typical undulator spatio-spectral pattern, in agreement with the modelling of the electron beam travelling along the line and of the afferent photon generation. The wavelength is easily tuned with undulator gap variation. A wavelength stability of 2.6% is achieved. The undulator linewidth can be controlled.
[1] A. Loulergue et al., New J. Phys. 17 023028 (2015) [2] M. E. Couprie et al., PPCF 58, 3 (2016) [3] F. Marteau et al., APL 111, 253503 (2017) [4] T. André et al., Nature Comm. 1334 (2018) |
|||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP048 | ||
| About • | paper received ※ 13 August 2019 paper accepted ※ 16 September 2019 issue date ※ 05 November 2019 | ||
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | ||