• S. Mickat, W.A. Barth, L.A. Dahl, M. Kaiser
  GSI, Darmstadt
• K. Aulenbacher
  IKP, Mainz
• M. Busch, F.D. Dziuba, H. Podlech, U. Ratzinger
  IAP, Frankfurt am Main
• T. Weilbach
  HIM, Mainz

GSI applied for a new superconducting (sc) cw-LINAC in parallel to the existing UNILAC. Such a machine is highly desirable with respect to the progress in the field of Superheavy Elements (SHE) for example. The UNILAC at GSI is limited in providing a proper beam for SHE and in fulfilling the requirements for FAIR simultaneously. A sc CH-structure is the key component of the proposed efficient and compact linac. In first vertical rf-tests at the Institute of Applied Physics (IAP) maximum gradients up to 7 MV/m were achieved. The cavities for the cw-LINAC should be operated at 217 MHz providing gradients of about 5.1 MV/m at a total length of minimum 0.6 m . In a first step a prototype of such a sc cw-LINAC as a demonstrator is financed by the Helmholtz Institute Mainz (HIM). The demonstrator is the first section of the proposed cw-LINAC consisting of a sc CH-cavity embedded by two sc solenoids. The aim is a full performance test of the demonstrator with beam at the GSI high charge injector (HLI) in 2013. Presently the tendering of the solenoids, the cavity, the cryostat and the rf-amplifier is in preparation.

• H. Podlech, M. Amberg, M. Busch, F.D. Dziuba, U. Ratzinger, R. Tiede
  IAP, Frankfurt am Main
• W.A. Barth, S. Mickat
  GSI, Darmstadt

The search for Super-Heavy Elements (SHE) is one of the frontiers in nuclear physics. By trend the production cross sections decrease significantly for larger proton numbers and heavier nuclei, respectively. To limit the required beam time it is necessary to use the highest available intensity. This prefers cw operation and the use of superconducting cavities. A cw operated superconducting linac using CH-cavities at GSI has been designed. As front end the existing 10⁸ MHz High Charge Injector (HLI) will be used which is presently being upgraded for cw operation. The superconducting part of the linac covers the energy between 1.4 AMeV and 7.5 AMeV. It consists of 9 multi-cell CH-cavities operated at 217 MHz. Each cavity is optimized for a specific particle velocity but without beta profile. Above 3.5 AMeV the linac is fully energy variable. The first superconducting CH-cavity is already under construction and will be tested with beam delivered by the HLI. The talk covers the development of the prototypes and the overall design including beam dynamics issues.

• D. Noll, L.P. Chau, M. Droba, O. Meusel, H. Podlech, U. Ratzinger
  IAP, Frankfurt am Main

The Frankfurt Neutron Source (FRANZ) currently under construction at IAP (Goethe University of Frankfurt) is designed to produce short neutron pulses at high intensity and repetition rates up to 250 kHz [*]. To achieve a bunch length of one nanosecond despite the high space charge forces, a bunch compressor of the Mobley type [**] using four dipole magnets and two rebunchers has been developed [***] to merge 9 linac bunches into the final focus. The first rebuncher cavity, a λ/4 resonator operating at 87.5 MHz, has to feature nine beam paths due to the multi-trajectory system. Additionally the gaps have to be displaced relatively to each other in a way that all bunches arrive at the correct rf phase. The second rebunching cavity will provide final focusing as well as an energy variation of ±0.2 MeV in front of the target and will be operating at 175 MHz. This paper presents the design of these novel cavities as well as the simulated beam dynamic properties.

* Meusel et al., LINAC 2006
** Mobley, Phys. Rev. 88(2), 360-361 (1951)
*** Chau et al, LINAC 2010

• F.D. Dziuba, M. Busch, H. Klein, H. Podlech, U. Ratzinger, C. Zhang
  IAP, Frankfurt am Main

Recent international cw operated high-current applications with ambitious requirements regarding beam power and quality ask for new linear accelerator developments. In this context the CH-structure (Crossbar-H-mode) has been developed at the Institute for Applied Physics (IAP) of Frankfurt University. It is a multi-cell drift tube cavity for the low and medium energy range operated in the H21-mode and can be used for superconducting as well as for room temperature applications. Because of the large energy gain per cavity, which leads to high real estate gradients, the CH-cavity is an excellent candidate for the efficient acceleration in high power proton and ion accelerators with fixed velocity profiles. One possible application for this kind of cavity is the EUROpean research programme for the TRANSmutation (EUROTRANS) of high level nuclear waste in an accelerator driven system (ADS), which requires an efficient high-current cw-linac (600 MeV, 4 mA, protons, 352 MHz). The paper describes the status of the CH-cavity development and the actual beam dynamics results for the reference design of the 17 MeV EUROTRANS injector.