The DESY Gas Monitor Detector (GMD) at the SXR beamline at LCLS Stefan Moeller, LCLS Kai Tiedtke, Svea Kreis, Fini Jastrow, Andrei Sorokin (DESY) Michael Holmes, Tom Benson, Bill Schlotter (SXR/LCLS) Bruce Hill, Jen Loos (EPICS) Alex Wallace, Rick Maida, Ernesto Paiser (PLC)

SXR GMD DESY group provided detector, support and commissioning LCLS designed differential pumping, integration and controls Developed by PTB and DESY (both Germany) and Joffe Institute (Russia) Absolute intensity measurement (4-6%) Transparent, non-destructive Pulse by pulse measurement Energy range eV Wide dynamic Provides intensity measurement (absolute) of monochromatized beam after SXR monochromator. Designed to be portable (in principle)

GMD Schematic Differential pumping GMD chamber Gas Dellivery System (not shown)

GMD in SXR beamline

SXR Hutch Layout GMD Rack

Gas Monitor Detector Operating Principle -Atomic ionization of rare gases at low pressures (1E-5 to E-7Torr) -Charge detection of photo ions and – electrons (Faraday cups) -Open ion multiplier provides: -Pulse by Pulse Measurement -Mean charge -Purity of gas and radiation -Pulse mode is cross calibrated to average ion current - Electrons not being used presently

Electrons Ions FEL Beam Detection Electrodes Open Multipliers Pa GMD

GMD Equation Cross Section: Literature values measured Output Value Detector Acceptance Length Detection Efficiency Atomic Gas Density: n=p/kT Pressure: SRG Temperature: PT100 Number of Detected Ion/Electrons; Mean ion charge (ITOF spectra/literature) Ion current/pulses from Faraday cups (Keithley/Acqiris)

GMD Quantum Efficiency SXR photon energy range

SXR Gas Monitor Detector

Gas Dosing Controller: via Needle valve and Hot cathode gauge Flow is very stable: no PID loop control so far Spinning Rotor gauge provides: High precision pressure measurement

Kr, 548eV - - Average Ion current calibrated absolute (# of photons, pulse energy mJ (ave.) - Multiplier signals relative pulse by pulse Pulse signal Ion current signal (absolute)

Ion Current independent of Extraction Voltage Extraction voltage Ion current

GMD vs FEE Gas detector Ion signal ave FEE Gas detector (pulse)

GMD Sensitivity Ion current 2.67E-13A, Transmission: % 1.4% Dominated by 3 rd harmonic Further attenuation with slits: 0.1μJ level

Kr, 548eV various attenuation levels vs. Ion current signal. FEE ~0.25mJ Good response of GMD Average signal

Kr TOF spectrum 10/15/12

Averaged TOF Pulses (Butterworth filter) and average Ion current

Summary Desy GMD was installed in SXR beamline 10/2012 –Integrated with vacuum -, gas inlet – and controls system Good sensitivity over energy range of eV Robust differential pumping system allows absolute and relative pulse resolved intensity measurement in low charge mode (<10fs) with monochromatic beam TOF spectra allow mean charge measurement consistent with literature values Recently used for first user experiments at SXR – for normalizing signal in monochromatic mode

Future Plans and areas of collaboration Improve signal processing and calibration – relative single pulse signal –TOF pulse data vs ion signal –Continue with device characterization (SRG) Cross calibration with other devices: –calorimeter, foil, diode, FEE gas detector, ? –Transfer calibration to sample location (after KB system) –Monitor transmission of optical elements over time –Hard x-ray diagnostics LCLS II