The next generation, superconducting electron cyclotron resonance (ECR) ion source VENUS (versatile ECR ion source for nuclear science) started operation with 28 GHz microwave heating in 2004. Since then it has produced world record ion beam intensities. For example, 2850 e microA of O(6+), 200 e microA of U(33+) or U(34+), and in respect to high charge state ions, 1 e microA of Ar(18+), 270 e microA of Ar(16+), 28 e microA of Xe(35+), and 4.9 e microA of U(47+) have been produced. A brief overview of the latest developments leading to these record intensities is given and the production of high intensity uranium beams is discussed in more detail.

Next-generation heavy ion beam accelerators require a great variety of high charge state ions with an order of magnitude higher beam intensity than is currently routinely available. Driven by this increasing demand for high performance ECR ion sources and enabled by advances in superconducting magnet technology, third generation superconducting (SC) ECR ion sources have been developed world-wide. The superconducting VENUS ECR ion source at the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory is the first ECR ion source designed for optimum operation at 28 GHz. Since it started operation in 2002 many world record ion beam intensities have been produced. VENUS has pioneered the field of high field SC ECR ion sources, and many of the design features and lessons learned during the VENUS commissioning phase have been incorporated in current 28 GHz ECR ion source projects such as GYROSERSE and SC-ECRIS. This paper will highlight recent progress on the VENUS ECR ion source for medium and high charge state production. In addition, it will discuss perspectives and main technical challenges of building 4th generation superconducting ECR ion sources using microwave heating frequencies of 56 GHz.

A radial sputter probe has been developed for the AECR-U as an additional method of producing metal ion beams. Negative voltage is applied to the probe to incite collisions with target atoms, thereby sputtering material into the plasma. The sputter probe is positioned through one of the 6 radial access slots between the permanent hexapole structure of the AECR-U. The probe position can be varied with respect to the inner edge of the hexapole magnet structure. Charge state distributions and peak beam intensities at bias voltages up to -5kV were obtained for gold samples at varying distances of the probe with respect to the plasma. For high charge states production the radial position with respect to the plasma was more sensitive than for the medium and lower charge states. For high charge state ion production the probe was optimized at a distance of 0.6cm inside the chamber wall (4.1cm from the center of the chamber). Stable beams with peak intensities of up to 28e mu A of AU(24+) and 1.42e mu A of Au41+ have been produced using the sputter probe technique. In addition, a solid state circuit under development by Scientific Solutions, Inc which provides a bandwidth up to 100MHz was used to drive the 14GHz klystron amplifier for the LBNL AECR-U ion source. Various broadband and discrete heating modes were tested and the results for high charge state ion production were compared with single frequency heating.

The next generation, superconducting ECR ion source VENUS (Versatile ECR ion source for NUclear Science) has operated with 28 GHz since 2004, and has produced world record ion beam intensities. The VENUS project is focused on two main objectives. First, for the 88-Inch Cyclotron, VENUS will serve as the third injector source boosting both the energy and intensity of beams available from the facility. Secondly, VENUS also serves as the prototype injector source for a high intensity heavy ion beam driver linac for a next generation radioactive ion beam facility, where the goal is to produce intense beams of medium to low charge states ions such as 240 eµA of Xe20+ or 250 eµA of U28+ to 34+. These high intensity ion beam requirements present a challenge for the beam transport system since the total currents extracted from the ECR ion source reach several mA. Therefore in parallel to ion beam developments, we are also enhancing our ion beam diagnostics devices and are conducting an extensive ion beam simulation effort to improve the understanding of the ion beam transport from the VENUS ECR ion source. The paper will give an overview of recent experiments with the VENUS ECR ion source. Since the last ECR ion source workshop in Berkeley in 2004, we have installed a new plasma chamber, which includes x-ray shielding. This enables us to operate the source reliably at high power 28 GHz operation. With this new chamber several high intensity beams (such as 2.4 mA of O6+, 600eµA of O7+, 1mA of Ar9+, etc.) have been produced. In addition, we have started the development of high intensity uranium beams. For example, 200 eµA of U33+and U34+ have been produced so far. In respect to high charge state ions, 1 eµA of Ar18+, 133 eµA of Ar16+, and 4.9 eµA of U47+ have been measured. In addition, ion beam profile measurements are presented with, and without the sextupole magnetic field energized. These experimental results are being compared with simulations using the WARP code.

The 4.5 MeV/nucleon heavy ion cocktail at the 88-Inch Cyclotron has been expanded by incorporating beams from solid material to fill in the linear energy transfer curve. This supercocktail is available by special request and is useful when only normal incidence between the beam and the device under test is possible or desirable.

VENUS (Versatile ECR ion source for NUclear Science) is a next generation superconducting ECR ion source, designed to produce high current, high charge state ions for the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory. VENUS also serves as the prototype ion source for the RIA (rare isotope accelerator) front end. The goal of the VENUS ECR ion source project as the RIA R&D injector is the production of 200eμA of U30+, a high current medium charge state beam. On the other hand, as an injector ion source for the 88-Inch Cyclotron the design objective is the production of 5eμA of U48+, a low current, very high charge state beam. To achieve those ambitious goals, the VENUS ECR ion source has been designed for optimum operation at 28GHz. The nominal design fields of the axial magnets are 4T at injection and 3T at extraction; the nominal radial design field strength at the plasma chamber wall is 2T, making VENUS currently the world’s most powerful ECR plasma confinement structure. Recently, the six year project has made significant progress. In June 2002, the first plasma was ignited at 18GHz. During 2003, the VENUS ECR ion source was commissioned at 18GHz, while preparations for 28GHz operation were being conducted. In May 2004 28GHz microwave power has been coupled into the VENUS ECR ion source for the first time. Preliminary performance-tests with oxygen, xenon and bismuth at 18GHz and 28GHz have shown promising results. Intensities close to or exceeding the RIA requirements have been produced for those few test beams. The paper will briefly describe the design of the VENUS source and its beam analyzing system. Results at 18GHz and 28GHz including first emittance measurements will be described.

Commissioning of the superconducting ECR ion source, VENUS, at 28 GHz began in May 2004. In its first four months of operation at this frequency, it has produced a number of intense heavy ion high charge state beams such as 320 eA of Xe 20+ and 240 eA of both Bi25+ and Bi29+. The intensities of these beams meet or exceed the requirements for the RIA driver linac ion source. Emittance measurements on bismuth also fall within the acceptance for the proposed accelerator. VENUS has also produced very high charge states beams including 11 eA of Bi 43+ and 1 eA of Bi 49+ that can be used for the 88-Inch Cyclotron. In the paper, we describe the performance of VENUS at 18 and 28 GHz, the design and operation of the 28 GHz gyrotron, measurements of the bremstrahlung heating of the cryogenic system and plans for further development.