Knobloch J.

Paper	Title	Page
MO301	Review of SRF linac-based FELs
	J. Knobloch BESSY
	In the last two decades the reliability of superconducting RF has been amply demonstrated in many machines. Initially this was primarily in the domain of particle, nuclear and ion physics (KEK, HERA, LEP, CEBAF, ALPI etc).However the expansion into the light-source regime is now fully underway,including 3rd generation storage rings such as Diamond, Soleil and the Taiwan Light Source. Not surprising, more recent 4th generation linac-based light sources (FELs) are also turning to SRF for the driver linac. Existing machines include the JLab FEL, ELBE, and the JAEA-FEL with many new ones being planned (e.g., BESSY FEL, Wisconsin FEL, 4GLS, Arc-en-Ciel). This report provides an overview of a few of these superconducting FELs and discusses some of the challenges and resulting solutions for the linac technology.
	Slides(PDF)
TUP40	CW Operation of Superconducting TESLA Cavities	222
	W. Anders, J. Knobloch, O. Kugeler, A. Neumann BESSY
	Several recently proposed superconducting linacs are designed to operate in CW mode. The TELSA technology, which they are based upon, was originally developed for pulsed mode. In order to demonstrate the feasibility of CW mode with TESLA technology, BESSY has built the HoBiCaT test facility [1]. The main issues of CW operation were examined and solutions are shown on the following topics: Limits of heat conduction in the Helium vessel, gas dynamics in the two phase line, layout of a CW cryo module, heating of HOM couplers, CW operation of the main RF coupler, choice of helium bath temperature, pressure stability of the helium bath and microphonics and their compensation.
WE201	Microphonics in CW tesla cavities and their compensation with fast tuners	377
	A. Neumann, W. Anders, J. Knobloch, O. Kugeler BESSY
	Superconducting linac cavities of single pass Free Electron Lasers or Energy Recovery Facilities have a very low or near zero beamloading and are thus operated at a high quality factor with a narrow RF resonance, respectively. Following the phase and amplitude stability of the RF field is very easily degraded by any kind of mechanical detuning. InCWoperation microphonics is the main error source for cavity detuning. To achieve high field stabilities in the regime of 0.02 degree in phase and 1e-3 down to 1e-4 in amplitude a fast tuning system is mandatory to compensate the detuning. In this paper the microphonics detuning measured at HoBiCaT will be shown and analyzed with respect to a detuning controller application. The controller design is given by a combination of a feedback and adaptive feedforward approach based on fast piezo tuners implemented in the Saclay coarse tuner designs. It will be shown, that at 1.8 K and loaded quality factors between 3e7-1e8 a compensation of a least a factor of two up to seven is achievable.
	Slides(PDF)
WEP56	Cavity and linac RF and detuning control simulations	627
	A. Neumann, J. Knobloch BESSY
	Single pass free electron lasers, such as the planned BESSY-FEL, require a very stable beam with a bunch-tobunch time jitter of less than 50 fs and a relative energy jitter below 1e-3. Regarding the low beamloading the 144 cavities of the superconducting linac will be operated in CW at a high loaded quality factor of 3e^7. To understand the achievable stability of the beam and the budget of the individual error sources for the cavity field stability a single cavity simulation tool has been developed. It includes the cavity field envelope model, an LLRF feedback system model and further on mechanical transfer functions, tuner characteristics, the fast piezo control system, microphonics and other noise sources measured or developed at HoBi- CaT. Incorporating realistic beam parameters due the acceleration process in the photoinjector and the first booster cavity allows to model the resultant energy and time jitter of the beam at the end of the linac entering the undulator section of the FEL. Furthermore the model has been used to find optimum operation parameters for the cavity and controller.
WEP58	Investigation of passive stabilization- and different tuning systems for TESLA cavities with respect to CW operation	637
	O. Kugeler, A. Neumann, J. Knobloch, W. Anders Bessy
	BESSY has planned a free-electron-laser that will be operated with TESLA type cavities at high Q-values in CW mode. These operating parameters imply a low cavity bandwidth and thus a high sensitivity towards ponderomotive oscillations, in particular microphonics. In the Ho- BiCaT facility, located at BESSY, we have tested various tuning systems (Saclay I, Saclay II) and compared their usability for CW operation. Furthermore, the impact of "Rossendorf"-type stabilization fixtures on the mechanical properties was investigated.