Non‐invasive online wavelength measurements at FLASH2 and present benchmark. (7th December 2017)

• Record Type: Journal Article
• Authors: Braune, Markus; Buck, Jens; Kuhlmann, Marion; Grunewald, Sören; Düsterer, Stefan; Viefhaus, Jens; Tiedtke, Kai
• Is Part Of: Journal of synchrotron radiation. Volume 25:Part 1(2018)
• Page Start: 3
• Page End: 15
• Publication Date: 2017-12-07
• Subjects: free‐electron laser -- soft X‐ray -- wavelength -- photoionization -- rare gases; Synchrotron radiation -- Periodicals; Free electron lasers -- Periodicals; 539.73505
• DOI: 10.1107/S1600577517013893
• Languages: English
• ISSNs: 0909-0495

Abstract

Abstract : The commissioning and the first year of operation of the online photoionization spectrometer OPIS at FLASH2 is reported. Abstract : At FLASH2, the free‐electron laser radiation wavelength is routinely measured by an online spectrometer based on photoionization of gas targets. Photoelectrons are detected with time‐of‐flight spectrometers and the wavelength is determined by means of well known binding energies of the target species. The wavelength measurement is non‐invasive and transparent with respect to running user experiments due to the low gas pressure applied. Sophisticated controls for setting the OPIS operation parameters have been created and integrated into the distributed object‐oriented control system at FLASH2. Raw and processed data can be stored on request in the FLASH data acquisition system for later correlation with data from user experiments or re‐analysis. In this paper, the commissioning of the instrument at FLASH2 and the challenges of space charge effects on wavelength determination are reported. Furthermore, strategies for fast data reduction and online data processing are presented.