Injector: What is needed to improve the beam quality? From TTF I to TTF II to XFEL Klaus Floettmann, Frascati ‘03

PITZ Results I: high duty cycle operation 40 MV/m at the cathode (~ 3 MW), 10 Hz, 900 µs duty cylcle: 0.9 %, average rf power: 27 kW no rf trips !! (results limited by conditioning time)

PITZ Results I: high duty cycle operation 10 Hz, 2.2 MW 800 μs 500 μs 200 μs On a variation of the average rf power the temperature distribution of the gun body has to adjust itself. This leads to 5-10 min of increased refl. power. In Zeuthen we operate without refl. power interlock and with waveguides filled with SF6. How to operate at TTF II?

PITZ Results II: beam dynamics issues For the optimal performance a laser with homogeneous transverse and flat-top longitudinal profile is required Recent streak camera measurement at MBI, - FWHM = 21ps - rise/fall time ≥ 4ps

PITZ Results II: beam dynamics issues The first step on the way to a long, flat-top laser pulse which short rise/fall time is a short laser pulse. strong space charge effects at the cathode transmission difficult due to new solenoid position

PITZ Results II: beam dynamics issues Energy and Energy spread measurements (0.5-1nC)

PITZ Results II: beam dynamics issues measured transverse emittances of 3-4 mrad mm in accordance to expectation for the short laser pulse detailed simulations are in progress

A0 Results: dark current Measurements by W. Hartung et. al. The dark current spike at very low gradient is caused by multipacting in the gun. Multipacting, dark current and quantum efficiency depend on solenoid field configuration.

PITZ Results III: dark current Indication of contribution of secondary emission to the dark current of Cs2Te Cathode. Simulations are on the way.

TTF II: Schematic layout of Injector III ~38

TTF II, what is required We need a long flat-top laser pulse, upgrade of the laser is planned, developments are on the way, but we don’t know what we will have when we start the commissioning of the TTF II injector. We will start without the 3rd harmonic cavity we need to be prepared for different parameter sets

TTF II, operation w.o. 3rd harmonic example of velocity bunching: bunch length, peak current and transverse emittance vs. phase of the first cavity in the module

TTF II: Injector performance

TTF II: known unknowns At some occasions irregular beam spots have been observed behind ACC1 during TTF I operation. Maybe caused by coupler kicks? No clear experimental evidence, also not supported by simulations. Only foreseen remedy: Steeres and BPM´s to control position and angle of incoming beam.

XFEL, what is different to TTF II higher gradient in the gun assumed (60 MV/m at the cathode), solenoid even further downstream, increased length between gun and module. more space between elements in the bunch compressor region. total length of the injector: 45 m.