The influence of wakefields on superconducting TESLA-cavities in FEL-operation

Due to the additional need of very short bunches for the FEL operation with the TESLA-machine strong wakefield effects are expected. One third of the total wakefield energy per bunch is radiated into the frequency region above the energy gap of Cooper pairs in superconducting niobium. The energy of the cooper pairs in superconducting niobium at 2 K corresponds to a frequency of 700 GHz. An analytical and experimental estimation for the overall energy loss of the FEL bunch above energy gap is presented. The analytical method is based on a study from R. B. Palmer [1]. The results of the wakefield estimations are used to calculate possible quality factor reduction of the TESLA cavities during FEL operation. Results are presented

Performance of a First-Level Muon Trigger with High Momentum Resolution Based on the ATLAS MDT Chambers for HL-LHC

Highly selective first-level triggers are essential to exploit the full physics potential of the ATLAS experiment at High-Luminosity LHC (HL-LHC). The concept for a new muon trigger stage using the precision monitored drift tube (MDT) chambers to significantly improve the selectivity of the first-level muon trigger is presented. It is based on fast track reconstruction in all three layers of the existing MDT chambers, made possible by an extension of the first-level trigger latency to six microseconds and a new MDT read-out electronics required for the higher overall trigger rates at the HL-LHC. Data from $pp$-collisions at $\sqrt{s} = 8\,\mathrm{TeV}$ is used to study the minimal muon transverse momentum resolution that can be obtained using the MDT precision chambers, and to estimate the resolution and efficiency of the MDT-based trigger. A resolution of better than $4.1\%$ is found in all sectors under study. With this resolution, a first-level trigger with a threshold of $18\,\mathrm{GeV}$ becomes fully efficient for muons with a transverse momentum above $24\,\mathrm{GeV}$ in the barrel, and above $20\,\mathrm{GeV}$ in the end-cap region.Comment: 6 pages, 11 figures; conference proceedings for IEEE NSS & MIC conference, San Diego, 201

Energy Propagation through the TESLA Channel: Measurements with Two Waveguides Modes

A new method for the determination of S-matrices of devices in multimoded waveguides and first experimental experiences are presented. The theoretical foundations are given. The scattering matrix of a TESLA copper cavity at a frequency above the cut-off of the second waveguide mode has been measured

The design of the HOM-damping cells for the S-band linear collider

Damping cells for the higher order modes are necessary for the S-band linear collider to minimize BBU (Beam-Break-Up). The construction of the damper cells has to take into account the different field geometries of the higher order modes. So two different types of dampers have been designed: a wall slotted an an iris slotted cell. In order to optimize the two types of damping cells with respect to damping strength, impedance matching between coupling system and waveguide dampers and between damping cell and undamped cells and the tuning system, damping cells of both types have been built and examinated

The effect of a single HOM-damper cell within a channel of undamped cells

The effect of a single HOM-damper cell within a channel of undamped cells is described theoretically using an equivalent circuit model. From this a simple equation can be derived which relates the Q-value of the single damping-cell, the bandwidth of the passband under consideration, and the additional phase shift which is introduced by the damper cell to provide energy flow into the damper cell. This equation immediately shows the limitations of such single cell damping systems. Comparisons with experimental results are shown

Kilohertz laser ablation for doping helium nanodroplets

A new setup for doping helium nanodroplets by means of laser ablation at kilohertz repetition rate is presented. The doping process is characterized and two distinct regimes of laser ablation are identified. The setup is shown to be efficient and stable enough to be used for spectroscopy, as demonstrated on beam-depletion spectra of lithium atoms attached to helium nanodroplets. For the first time, helium droplets are doped with high temperature refractory materials such as titanium and tantalum. Doping with the non-volatile DNA basis Guanine is found to be efficient and a number of oligomers are detected