The Bucharest FN Tandem Accelerator was put in operation in 1973 and upgraded a first time in 1983 to 9 MV. In the period 2006-2009 a second program of the tandem upgrade was performed aiming to transform this accelerator in a modern and versatile facility for atomic and nuclear physics studies as well as for different applications using accelerated ion beams. The upgrade was achieved by replacing the main components of the tandem by new ones and by adding new components. The old HVEC belt of the Van de Graaff generator was replaced by a “pelletron” system, the old inclined field stainless steel electrodes accelerator tubes were replaced by titanium spiral field tubes, the old HICONEX 834 sputter negative ion source was replaced by a new SNICS II sputter source and all old electronic equipment including RMN and Hall probe gauss meters as well as low voltage and high voltage power supplies for the magnets, lenses and ion sources were replaced by new ones. The new equipment added to the tandem consists of a helium negative ion source, a new injector based on a multi-cathode ion source 40 MC-SNICS II for AMS applications, a new GVM, a new pulsing system in the millisecond range and a new chopper and bunching system for pulsing the ion beam in the nanosecond range. Now the tandem is currently operated in very stable conditions up to 9 MV on a basis of about 4000 hours/year accelerating a broad range of ion species.

The Bucharest FN tandem accelerator, installed in 1973 and upgraded in 1983 to 9 MV, has been used for atomic and nuclear physics studies as well as for different applications using accelerated ion beams. In the last three years a program of modernization of the tandem accelerator including the replacement of the old accelerator equipment by new ones, installation of a pelletron system for the Van de Graaff generator and installation of new negative ion injectors was undertaken. In parallel a development of the tandem accelerator was started. In 2009, a beam pulsing system in the nanosecond range is scheduled to be installed. All these works aimed to transform the tandem accelerator in a reliable and efficient tool for research and applications are presented. The main lines of the research program at the Bucharest tandem accelerator are shortly presented too.

Two RF cavities will be installed in the High-Energy Storage Ring (HESR) of the future International Facility for Antiproton and Ion Research (FAIR) in Darmstadt. One “large” cavity will be used for beam acceleration, deceleration and for bunch rotation. Additionally a barrier bucket (BB) with h=1..5 will be formed by this “large” cavity to combine the decelerated bunch with a new injected RESR bunch in the high luminosity mode (HL). During the experiment a “small” cavity will provide a low noise barrier-bucket signal. Both prototype cavities are manufactured and first RF-measurements were carried out at COSY. The recent results are presented here.

We describe the integration of a broadband cavity based on the material VitroPerm into COSY [1]. The electrical characteristics of the 12 cores arranged in two half-cavities allow the application of a fundamental from 400 kHz to 1.6 MHz together with 2 higher harmonics. The second harmonic can be driven at up to 50 % amplitude, the third or fourth harmonic at 20% amplitude of the fundamental. The impedance is a function of the magnetic material and also of the cooling medium. We measure the impedance with tap water, low conductivity water and Fluorinert FC_77. Like colleagues from KEK [2] we obtained at least 400 Ω . The acceleration voltage requirements of COSY allow beam tests with this cavity by semiconductor amplifiers in the kW power range. We plan an upgrade to a tube amplifier with 50 kW RF power, to compare different schemes of γ-transition crossing.

We describe the integration of a broadband cavity based on the material VitroPerm into COSY (1). The electrical characteristics of the 12 cores arranged in two half-cavities allow the application of a fundamental from 400 kHz to 1.6 MHz together with 2 higher harmonics. The second harmonic can be driven at up to 50 % amplitude, the third or fourth harmonic at 20% amplitude of the fundamental. The impedance is a function of the magnetic material and also of the cooling medium. We measure the impedance with tap water, low conductivity water and Fluorinert FC_77. Like colleagues from KEK (2) we obtained at least 400 Ω . The acceleration voltage requirements of COSY allow beam tests with this cavity by semiconductor amplifiers in the kW power range. We plan an upgrade to a tube amplifier with 50 kW RF power, to compare different schemes of γ-transition crossing.

At the Max-Planck-Institut fur Kernphysik in Heidelberg the first phase of the High Current Injector was successfully finished. The Linac, consisting of a high current source for singly charged ions, two RFQs and eight 7-gap-resonators demonstrated its performance with an accelerated He-beam (1.85 MeV/u, Q/A=1/4) and an Oxygen-beam (0.5 MeV/u, Q/A=1/9). For Coulomb explosion imaging experiments at the storage ring we were able to produce and deliver sev- eral different light molecules, singly charged, with intensi- ties about 10 A. In a second phase an ECR source will be added to provide the full spectrum of also highly charged ions up to uranium. To increase the intensity of various kinds of ions for the Hei- delberg Heavy Ion Storage Ring TSR a High Current Injec- tor was developed and built. In its first phase the new in- jector consists of a commercial CHORDIS ion source (1), two RFQs (2) and eight 7-gap resonators (3) for the vari- ability of the end energy for Q/A 9. The CHORDIS is optimized for mainly singly charged ions. To provide also highly charged heavy ions an ECR-source, which is under installation at a test bench, will deliver the full spectrum of highly charged heavy ions in a second phase. Figure 1 shows the layout of the injector. The accelerator is in- stalled parallel to the Tandem and beams are injected di- rectly into the postaccelerator. In the second phase strip- ping will be used behind the last seven gap resonator and the proper charge state will be selected by an achromatic separator consisting of four 60 -magnets. Like the existing post accelerator the new injector operates at 108.48 MHz. The ion velocity of =v/c=6% after the High Current injec- tor is well adapted to the post accelerator and final energies higher than 5 MeV/u will be achieved for all ion species in a pulsed mode operation with up to 25% duty cycle.

The new High Current Injector at the Max-Planck-Institut fur Kernphysik in Heidelberg provides ion beams with in- tensities up to several mA. Compared to the old injector that implies an increase of the ion current by two orders of magnitude. As a consequence, the diagnostic systems employed on the old part of the facility are not applicable anymore. It was hence necessary to develop a beam diag- nostics that can be used under the conditions of the High Current Injector. On this purpose a profile grid system for profile and position measurements of beams with interme- diate currents ( 10 A, DC) was set up. This part of the work mainly concerned the development of a new readout electronics matching to the personal computer control. For higher ion currents a beam profile monitor based on the projection of the residual gas particles ionized by the inter- action with the beam was developed. Calculations and sim- ulations of the projection process showed that the imaging defect of this device, estimated to be 170 m, is small compared to the intrinsic resolution of the detector in use, which amounts to 800 m. The profile measurements suc- cessfully carried out during beam times proved the func- tionality of the new diagnostic devices.

At the Max-Planck-Institut fur Kernphysik in Heidelberg the first phase of the High Current Injector was successfully finished. The Linac, consisting of a high current source for singly charged ions, two RFQs and eight 7-gap-resonators demonstrated its performance with an accelerated He-beam (1.85 MeV/u, Q/A=1/4) and an Oxygen-beam (0.5 MeV/u, Q/A=1/9). For Coulomb explosion imaging experiments at the storage ring we were able to produce and deliver sev- eral different light molecules, singly charged, with intensi- ties about 10 A. In a second phase an ECR source will be added to provide the full spectrum of also highly charged ions up to uranium. To increase the intensity of various kinds of ions for the Hei- delberg Heavy Ion Storage Ring TSR a High Current Injec- tor was developed and built. In its first phase the new in- jector consists of a commercial CHORDIS ion source (1), two RFQs (2) and eight 7-gap resonators (3) for the vari- ability of the end energy for Q/A 9. The CHORDIS is optimized for mainly singly charged ions. To provide also highly charged heavy ions an ECR-source, which is under installation at a test bench, will deliver the full spectrum of highly charged heavy ions in a second phase. Figure 1 shows the layout of the injector. The accelerator is in- stalled parallel to the Tandem and beams are injected di- rectly into the postaccelerator. In the second phase strip- ping will be used behind the last seven gap resonator and the proper charge state will be selected by an achromatic separator consisting of four 60 -magnets. Like the existing post accelerator the new injector operates at 108.48 MHz. The ion velocity of =v/c=6% after the High Current injec- tor is well adapted to the post accelerator and final energies higher than 5 MeV/u will be achieved for all ion species in a pulsed mode operation with up to 25% duty cycle.

At the MPI fur Kernphysik, a new type of accelerator is under construction which consists of a CHORDIS ion source [1], two RFQ and eight 7-gap resonators [2]. The High Current Injector will deliver 1-3 orders of magnitude higher intensities in comparison to the existing tandem-postaccelerator combination. The RFQ is designed to accelerate ions with a minimum charge to mass ratio of q/m = 1:9 up to an energy of 0.478 MeV/u. Both resonators operate at a frequency of 108.48 MHz with a pulsed power of 90 kW (25% duty factor (DF)). By means of an optimizing algorithm, it was possible to lower the electrode voltage of the RFQ-accelerator from 71 kV to 60 kV maintaining a slightly reduced final energy and a particle transmission of about 80% with ion currents of 10 mA [3]. A new electrode profile was developed in order to combine sufficient cooling with good mechanical stability. Moreover the fabrication process of the RFQ-stems and the electrodes were simplified and optimized. Both resonators are tuned and tested with low level measurements and under high power with a H-2(+)-ion beam. (C) 1998 Elsevier Science B.V.

Many experiments at the Test Storage Ring TSR are limited by weak ion beam intensities [1], delivered from a tandem-postaccelerator combination. A new high current injector, consisting of a CRORDIS ion source, 2 RFQ and 8 seven-gap resonators, will deliver 1-3 orders of magnitude higher intensities of singly charged ions. The final energy of 1.8 MeV/u is well adapted to the acceptance of the postaccelerator. By adding an ECR-source in a second phase the system will be able to deliver heavy ion beams up to uranium with energies above the coulomb barrier of the heaviest elements. The CHORDIS is already operating in cw-mode, in sputter mode the pulsed intensity has still to be optimized. By means of an optimizing algorithm it was possible to; lower the electrode voltage of the RFQ-accelerator from 71 kV to 60 kV maintaining a particle transmission of about 80% with ion currents of 10 mA. All of the 8 seven-gap resonators have been power tested successfully and performed as expected. This paper describes the status of the project.

A novel acceleration system for the (simultaneous) application of higher or multiple-harmonics in proton or heavy-ion synchrotrons has been developed for various uses, e.g. the passage of the transition point, applying stochastic cooling on a bunched beam, or for other longitudinal beam manipulations as bunch stretching or compression. The system consists of a coaxial cavity filled with the ferritic amorphous metal VITROVAC of VAC, Hanau, in lieu of the conventional ceramic materials. In its current configuration, it can support a frequency range of 0.2-8 MHz. Amplifier modules for both 10 and 50 kW are available to produce gap voltages in the kV-range. By means of digital synthesis techniques, virtually arbitrary voltage waveforms with harmonic admixtures up to fourth order can routinely be generated at the cavity gap. As illuminating examples we, achieved at high precision a flat-top wave form suitable, e.g. for the transition crossing, a linearized force law at the center of the bucket, and a fourth-order flattened bucket for bunched-beam cooling. The compact cavity system should be well suited for any synchrotron operating in this frequency range. Actual installation of such a system is projected for the medium energy device COSY Julich, and the therapy-oriented ring TERA.

A novel digital RF-noise generator was used to excite the COSY-beam longitudinally at a certain harmonic of the revolution frequency. Rectangular shaped noise spectra with bandwidths of the order of 10 kHz and frequency resolution of about 6 Hz were used. Beam distributions were measured during shaping and after switching off the noise source in dependence of bandwidth and amplitude of the RF-noise

The ferrite loaded, tunable reentrant-coaxial symmetric (2×λ/4) accelerator cavity for the cooler synchrotron COSY is of the SATURNE type. For h=1, frequencies range from 450 kHz at injection to a maximum of 1.6 MHz, with a maximum rf power level of 50 kW. We have determined the cavity circuit properties both at low signal levels with standard rf test equipment, and at operation conditions, depending on frequency and power level. Moreover, the acceleration system was tested for its suitability to pass through gamma transition. For this end, a sudden phase jump of 180° was imposed at the input of the amplifier chain by means of the digital frequency synthesizer developed for COSY. At higher frequencies, a loss of Q was observed, partly aiding the transition crossing speed. Finally, a simple replacement circuit, incorporating the measured quantities, is used to model the cavity

A newly designed radio frequency cavity was used at the storage ring TSR in Heidelberg to accelerate stored 12C6+ (E0=73.3 MeV) beams. It was possible to accelerate about 90% of the stored particles by more than a factor of three in kinetic energy (Efin ≈240 MeV). A new operating mode of the machine close to the transition energy was also investigated. Up to 10 μA 12 C6+ and protons could be stored, however the beams were susceptive to longitudinal instabilities. For 21 MeV protons (γ=1.02) a γtr parameter of 1.04 could be reached. A new method to produce a beam of polarized ions, based on spin selective attenuation by a polarized atomic hydrogen target was successfully proved with 23 MeV protons. To minimize losses of the beam particles the TSR was operated in the low-beta mode. After one hour a beam polarisation of 0.014 was achieved

A high current injector for the heavy ion storage ring TSR in Heidelberg is under construction. As a part of the injector eight seven-gap resonators with high shunt impedance are being developed. These resonators (ƒ0 = 108.48 MHz) are designed for the synchronous velocities of βs = 3.7, 4.5, 5.1 and 5.7%. Low power models with scaling factors of 1:2.5 were built in order to study the characteristics of these new resonators. Following low level measurements to optimize the voltage distribution and eigenfrequency, a first power resonator was built and successfully tested at 80 kW (duty cycle of 25%). At this power, the resonator generated a maximum voltage (summation of all gap amplitude voltages) of 1.75 MV. This paper describes the design of the resonators and gives some details of the measurements.

The existing accelerator facility at the Max-Planck-Institute in Heidelberg consists of a 12 MV tandem Van de Graaff accelerator, a post-accelerator and a heavy ion cooler storage ring TSR. Many experiments at the TSR, especially laser cooling, are limited by the low current delivered by the MP tandem. A new injector consisting of a high current source, two RFQs and eight seven-gap resonators will increase the currents for singly charged ions by up to three orders of magnitude. In a second phase, an ECR source for highly charged ions will be added and the high current injector will be used in combination with the Heidelberg heavy ion post-accelerator. This new system will deliver beams up to uranium with energies above the Coulomb barrier of the heaviest elements. In this paper the design and the status of the project are presented.