JACoW logo

Joint Accelerator Conferences Website

The Joint Accelerator Conferences Website (JACoW) is an international collaboration that publishes the proceedings of accelerator conferences held around the world.

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

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  - 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  -