The design and results of an upgraded cyclotron center region in which a mirror field type inflector was replaced by a spiral inflector is described. The main goals of the design were to facilitate injection at higher energies in order to improve transmission efficiency and to reduce down-time due to the need of replacing mirror inflector wires which rapidly break when exposed to high beam currents. The design was based on a detailed model of the spiral inflector and matching center region electrodes using AMaze, a 3D finite element suite of codes. The spiral inflector was used to extract a 2.0 pμA 250 MeV Ca beam from the cyclotron thus meeting design goals. Furthermore, the inflector was utilized during an eight week experiment without any issues delivering around 1 pμA Ca as requested by the users.

The VENUS ion source functions as a research and development tool in the ECR community as well as an injector for LBNL’s 88-Inch cyclotron. In order to meet the needs of both the ECR community and users at the 88Inch cyclotron, technology such as ovens and a sputter probe have been developed for introducing metals into the plasma. Using a modified high temperature oven, VENUS has produced 450eμA of 238U and 400eμA of 238U, twice the required Uranium beam current needed for FRIB. In addition, after upgrading its high voltage capabilities VENUS produced 11emA of 4He, a capability that remains unparalleled by other ECR ion sources. In addition to its recent record high intensities VENUS is also being developed to deliver low intensity, ultra high charge state ions for the cocktails beams, where many species are produced simultaneously for use by the BASE Facility. 124Xe is now in regular production for the 16MeV/u cocktail, and development of 209Bi for the 10MeV/u cocktail is in progress and has been accelerated through the 88-Inch cyclotron. This paper presents the latest work towards integrating the VENUS ion source into our research and operational goals. INTRODUCTION During the last two years a lot of effort has gone into the integration of VENUS into the operation of the 88Inch cyclotron as well as a continued effort to use it to push the limits of ECR’s. To meet the needs of the 88Inch cyclotron users VENUS should provide intense medium charge state beams for studies involving lowcross section reactions as well as several low intensity medium and high charge state ions simultaneously for the cocktails. A low temperature oven has been developed and work with the high temperature oven continues for the production of intense metal ion beams. To produce a variety of low intensity beams development of a sputter probe has begun and initial results are presented. In order to continue to explore the limits of ECR ion production capability we continue to work to make improvements. In this paper we discuss improvements in the VENUS high voltage capability as well as potential improvements to be made in the VENUS plasma chamber. The mechanical layout and specifics of the VENUS ECR ion source have been discussed at length previously and as such will not be done so here [1,2]. Table 1 provides key specifics. Table 1: Key Parameters of the VENUS ECR Ion Source VENUS Key Parameters Values Maximum 18GHz/28GHz Power 2,000W/10,000W Maximum INJ/ /EXT Fields 4.0T/3.0T Maximum RADIAL Field at wall 2.2T

The complex 3-D magnetic field structure of the 88-Inch Cyclotron combined with the large number of tuning parameters such as trim coils, valley coils, the main field itself and the injection/extraction components makes it challenging to tune the Cyclotron. Furthermore, beam diagnostic devices to help tuning were limited to a stationary Faraday cup at the exit of the machine and a so-called Dee-probe which allowed for beam current measurements as a function of the turn radius. Motivated to improve the transmission of the Cyclotron due to misalignment of the ion beam in the center region and insufficient beam diagnostics, we have developed an optical beam viewer which we can move radially in and out of the machine. It allows us to image the beam cross section and its axial position with high spatial resolution as a function of radius. In this paper, we describe the mechanical development of the device which consists of a KBr scintillator disc, a fiber bundle and a digital camera and we present data from its initial commissioning.

A number of superconducting electron cyclotron resonance (ECR) ion sources use gyrotrons at either 24 or 28 GHz for ECR heating. In these systems, the microwave power is launched into the plasma using the TE01 circular waveguide mode. This is fundamentally different and may be less efficient than the typical rectangular, linearly polarized TE10 mode used for launching waves at lower frequencies. To improve the 28 GHz microwave coupling in VENUS, a TE01-HE11 mode conversion system has been built to test launching HE11 microwave power into the plasma chamber. The HE11 mode is a quasi-Gaussian, linearly polarized mode, which should couple strongly to the plasma electrons. The mode conversion is done in two steps. First, a 0.66 m long "snake" converts the TE01 mode to the TE11 mode. Second, a corrugated circular waveguide excites the HE11 mode, which is launched directly into the plasma chamber. The design concept draws on the development of similar devices used in tokamaks and stellerators. The first tests of the new coupling system are described below.

The stability of ion beams extracted from ECR ion sources has been studied with the VENUS ion source at LBNL and the 14 GHz A-ECR at JYFL. Oscillations of the beam current in kHz range are characterized with the Discrete Fourier transform. The effect of the ion source tuning parameters on the frequency and amplitude of the oscillations of various charge states is discussed. It was found that double frequency heating affects the oscillation frequency, the biased disc can be used to mitigate their amplitude, increasing B-minimum results to pronounced instabilities and operating the ion source with significantly higher mirror ratio than suggested by ECRIS scaling laws yields the most stable ion beams. It is argued that the observed beam current fluctuations are correlated with plasma processes.

Recently the Versatile ECR for NUclear Science (VENUS) ion source was engaged in a 60-day long campaign to deliver high intensity (48)Ca(11+) beam to the 88-Inch Cyclotron. As the first long term use of VENUS for multi-week heavy-element research, new methods were developed to maximize oven to target efficiency. First, the tuning parameters of VENUS for injection into the cyclotron proved to be very different than those used to tune VENUS for maximum beam output of the desired charge state immediately following its bending magnet. Second, helium with no oxygen support gas was used to maximize the efficiency. The performance of VENUS and its low temperature oven used to produce the stable requested 75 eμA of (48)Ca(11+) beam current was impressive. The consumption of (48)Ca in VENUS using the low temperature oven was checked roughly weekly, and was found to be on average 0.27 mg/h with an ionization efficiency into the 11+ charge state of 5.0%. No degradation in performance was noted over time. In addition, with the successful operation of VENUS the 88-Inch cyclotron was able to extract a record 2 pμA of (48)Ca(11+), with a VENUS output beam current of 219 eμA. The paper describes the characteristics of the VENUS tune used for maximum transport efficiency into the cyclotron as well as ongoing efforts to improve the transport efficiency from VENUS into the cyclotron. In addition, we briefly present details regarding the recent successful repair of the cryostat vacuum system.

The 28 GHz Ion Source VENUS (versatile ECR for nuclear science) is back in operation after the superconducting sextupole leads were repaired and a fourth cryocooler was added. VENUS serves as an R&D device to explore the limits of electron cyclotron resonance source performance at 28 GHz with its 10 kW gryotron and optimum magnetic fields and as an ion source to increase the capabilities of the 88-Inch Cyclotron both for nuclear physics research and applications. The development and testing of ovens and sputtering techniques cover a wide range of applications. Recent experiments on bismuth demonstrated stable operation at 300 eμA of Bi31+, which is in the intensity range of interest for high performance heavy-ion drivers such as FRIB (Facility for Rare Isotope Beams). In addition, the space radiation effects testing program at the cyclotron relies on the production of a cocktail beam with many species produced simultaneously in the ion source and this can be done with a combination of gases, sputter probes, and an oven. These capabilities are being developed with VENUS by adding a low temperature oven, sputter probes, as well as studying the RF coupling into the source.

This work presents the latest results of an ongoing effort to simulate the extraction from ECR ion sources and the Low Energy Beam Transport (LEBT). Its aim is to help understand the influence of parameters like initial ion distributions at the extraction aperture, ion temperatures and beam neutralization on the quality of the beam and to provide a design-tool for extractionand transport-systems. Simulations of multispecies beams (Uranium of charge state 15+ to 42+ and Oxygen) extracted from the VENUS ECR ion source are presented and compared to experimentally obtained emittance values.

Electron Cyclotron Resonance (ECR) ion sources are essential components of heavy-ion accelerators due to their ability to produce the wide range of ions required by these facilities. The ever-increasing intensity demands have led to remarkable performance improvements of ECR injector systems mainly due to advances in magnet technology as well as an improved understanding of the ECR ion source plasma physics. At the same time, enhanced diagnostics and simulation capabilities have improved the understanding of the injector beam transport properties. However, the initial ion beam distribution at the extraction aperture is still a subject of research. Due to the magnetic confinement necessary to sustain the ECR plasma, the ion density distribution across the extraction aperture is inhomogeneous and charge state dependent. In addition, the ion beam is extracted from a region of high axial magnetic field, which adds a rotational component to the beam, which leads to emittance growth. This paper will focus on the beam properties of ions extracted from ECR ion sources and diagnostics efforts at LBNL to develop a consistent modeling tool for the design of an optimized beam transport system for ECR ion sources.

This paper describes the recent development and commissioning of a pepper-pot emittance meter at the Lawrence Berkeley National Laboratory (LBNL). It is based on a potassium bromide (KBr) scintillator screen in combination with a charged coupled device camera. Pepper-pot scanners record the full four-dimensional transverse phase space emittances which are particularly interesting for electron cyclotron resonance ion sources. The strengths and limitations of evaluating emittances using optical pepper-pot scanners are described and systematic errors induced by the optical data acquisition system will be presented. Light yield tests of KBr exposed to different ion species and first emittance measurement data using ion beams extracted from the 6.4 GHz LBNL electron cyclotron resonance ion source are presented and discussed.

Two Electron Cyclotron Resonance (ECR) ion sources are currently available to inject beams into the 88-Inch Cyclotron at Lawrence Berkeley National Lab (LBNL). Ion beam emittances for various ion species of both sources were measured using a recently commissioned pepper-pot emittance scanner[1] and are discussed in this paper. Pepper-pot scanners[1,2,3] are capable of extracting the full four-dimensional transverse phase space of the beam, allowing for the calculation of the cross coupled emittances xy' and yx'. This is especially of interest for ECR ion sources, where asymmetric beams are extracted in the presence of a strong solenoidal field. The axial field adds a rotational momentum to the extracted beam resulting in a transverse emittance growth, which depends on the magnetic stiffness of the extracted species. In this paper, the pepper-pot software is described and emittance data from both LBNL ECR sources are presented and compared. The data confirm a strong mass dependence of the normalized emittance for ions with the same mass-tocharge-state ratio, as previously also observed by other groups. This dependence indicates different particle distributions at the extraction aperture for different ion species.

Two Electron Cyclotron Resonance (ECR) ion sources are currently available to inject beams into the 88-Inch Cyclotron at Lawrence Berkeley National Lab (LBNL). Ion beam emittances for various ion species of both sources were measured using a recently commissioned pepper-pot emittance scanner[1] and are discussed in this paper. Pepper-pot scanners[1,2,3] are capable of extracting the full four-dimensional transverse phase space of the beam, allowing for the calculation of the cross coupled emittances xy' and yx'. This is especially of interest for ECR ion sources, where asymmetric beams are extracted in the presence of a strong solenoidal field. The axial field adds a rotational momentum to the extracted beam resulting in a transverse emittance growth, which depends on the magnetic stiffness of the extracted species. In this paper, the pepper-pot software is described and emittance data from both LBNL ECR sources are presented and compared. The data confirm a strong mass dependence of the normalized emittance for ions with the same mass-tocharge-state ratio, as previously also observed by other groups. This dependence indicates different particle distributions at the extraction aperture for different ion species.

The versatility of ECR (Electron Cyclotron Resonance) ion sources makes them the injector of choice for many heavy ion accelerators. However, the design of the LEBT (Low Energy Beam Transport) systems for these devices is challenging, because it has to be matched for a wide variety of ions. In addition, due to the magnetic confinement fields, the ion density distribution across the extraction aperture is inhomogeneous and charge state dependent. In addition, the ion beam is extracted from a region of high axial magnetic field, which adds a rotational component to the beam. In this paper the development of a simulation model (in particular the initial conditions at the extraction aperture) for ECR ion source beams is described. Extraction from the plasma and transport through the beam line are then simulated with the particle-in-cell code WARP. Simulations of the multispecies beam containing Uranium ions of charge state 18+ to 42+ and oxygen ions extracted from the VENUS ECR ion source are presented and compared to experimentally obtained emittance values.

A dedicated effort to accurately simulate beam extraction and transport from the superconducting electron cyclotron resonance (ECR) ion source VENUS (Versatile ECR for NUclear Science) using particle-in-cell methods has been underway at Lawrence Berkeley National Laboratory (LBNL). The wide range of beam diagnostics used along the VENUS transport system has been essential in benchmarking simulation against experiment. Measurements with some of these devices are presented and are compared with simulation.