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RIS citation export for WEP103: A Plasma Attenuator for Soft X-Rays in LCLS-II

TY  - CONF
AU  - Fisher, A.S.
AU  - Benwell, A.L.
AU  - Feng, Y.
AU  - Jacobson, B.T.
ED  - Schaa, Volker R.W.
ED  - Decking, Winfried
ED  - Sinn, Harald
ED  - Geloni, Gianluca
ED  - Schreiber, Siegfried
ED  - Marx, Michaela
TI  - A Plasma Attenuator for Soft X-Rays in LCLS-II
J2  - Proc. of FEL2019, Hamburg, Germany, 26-30 August 2019
CY  - Hamburg, Germany
T2  - Free Electron Laser Conference
T3  - 39
LA  - english
AB  - 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.
PB  - JACoW Publishing
CP  - Geneva, Switzerland
SP  - 553
EP  - 555
KW  - plasma
KW  - electron
KW  - FEL
KW  - cavity
KW  - controls
DA  - 2019/11
PY  - 2019
SN  - 978-3-95450-210-3
DO  - doi:10.18429/JACoW-FEL2019-WEP103
UR  - http://jacow.org/fel2019/papers/wep103.pdf
ER  -