BERLinPro - A COMPACT DEMONSTRATOR ERL FOR HIGH CURRENT AND LOW EMITTANCE BEAMS A. Jankowiak * , M. Abo-Bakr, W. Anders, T. Kamps, J. Knobloch, B. Kuske, O. Kugeler, A. Matveenko, A. Meseck, A. Neumann, T. Quast, J. Rudolph Helmholtz-Zentrum Berlin f¨ ur Materialien und Energie (HZB), Berlin, Germany Abstract The HZB (previously BESSY) was the first institution in Germany to build and operate a dedicated synchrotron light source (BESSY I). About 10 years ago BESSY II, a third generation synchrotron light source, was commis- sioned and is very successfully running since that time. Due to its expertise in development and operation of ac- celerator facilities HZB is ideally suited to realize new ac- celerator concepts. Therefore HZB is proposing to build a demonstrator ERL facility (BERLinPro) that will real- ize high current and low emittance operation at 100 MeV. BERLinPro is intented to bring ERL technology to matu- rity. This paper presents an overview of the project and the key components of the facility. GOALS OF THE BERLinPro: ADDRESSING THE CHALLENGES OF ERLS ERL specific issues revolve primarily around the fact that an ultra-low-emittance beam must be generated at storage-ring-level currents that then is accelerated to full energy without emittance dilution. It must also be demon- strated that efficient energy recovery is possible, even when the beam’s energy spread is increased. Nearly all com- ponents along the linac are impacted by these unique op- erating conditions. While not all aspects can be cov- ered exhaustively, the following are key areas which the BERLinPro program will concentrate on. CW SRF Cavity System The high average current in an ERL requires a CW ma- chine operation. Together with the need for a high gradi- ent in the RF cavities superconducting accelerating tech- nology is a key aspect for ERLs. The basic superconduct- ing linac technology has been developed and demonstrated with great success in facilities such as FLASH, which uses pulsed TESLA technology [1]. For several years, exten- sive studies at HZB/BESSY with HoBiCaT [2] have al- ready served to adapt this to CW operation [3]. Other insti- tutes, such as Cornell University, FZ Dresden-Rossendorf and Daresbury Laboratory have also been modifying vari- ous aspects of TESLA technology for CW linacs. It will therefore also provide the baseline for BERLinPro. Electron source A variable ERL source must be able to provide an average current of order 100 mA, with ap- proximately 50-100 pC bunch charge at a GHz repetition * contact: Andreas.Jankowiak@helmholtz-berlin.de rate and a normalized emittance better than 1 mm mrad. SRF photoinjectors have the greatest potential and flexi- bility, as they are able to operate at 100% duty factor and can generate significantly higher fields than (CW-operated) normal conducting RF and DC systems. One of the primary goals of the BERLinPro facility will therefore be to demon- strate that a high brightness, high-average-power electron beam can be generated and maintained by a photo-driven SRF gun. Main challenges are the cathode system and its implementation in the gun cavity, cathode lifetime and han- dling and the achievement of highest accelerating fields by employing appropriate treatment techniques. Injection System The injection linac is a short accel- eration section that boosts the beam energy from the gun to approximately 5-10 MeV. This beam energy is not re- covered. Consequently, the booster module must provide the full beam power (500-1000 kW at 100 mA), placing stringent boundary conditions on the SRF hardware and the beam dynamics. The voltage provided by each cavity is limited by the average RF power that can be coupled to the beam, rather than the achievable peak field. Thus suit- able high-average-power RF sources must be developed as well as an RF input coupler system capable to handle the large thermal loading, operating with more than 100 kW RF power per cavity. SRF Main Linac The SRF main linac does not only accelerate the electrons but also decelerates them after ”us- age” for energy recovery, so that the effective beam loading is negligible. Common to the booster, the cavities must handle a large current. For ps long bunches higher order mode (HOM) power in the order of 100 W/m can be generated, with a frequency spectrum out into the 100 GHz range. Optimiz- ing the cavity shape and number of cells is an important method to reduce the HOM power in the first place. The remaining HOM power must be extracted with specialized HOM absorbers in the cryostat, guaranteeing the efficient power extraction with minimum beam disruption. The main linac of an X-ray ERL represents by far the dominant cryogenic load and hence is a significant cost driver both in terms of capital investment and operating costs. For the feasibility of future ERL facilities, it must be demonstrated that lowest-loss (high Q-factor) cavities can be produced and operated over the long term in an ERL system. Beam Dynamics One of the ERL’s advantages is the fact that emittance and bunch length do not arise from an equilibrium condi- tion like in storage rings but are defined by the source and Proceedings of Linear Accelerator Conference LINAC2010, Tsukuba, Japan TUP007 01 Electron Accelerators and Applications 1B Energy Recovery Linacs 407