Conceptual design report on a charge breeder for HIE-ISOLDE

In this conceptual design report the possible options for an upgrade of the REX/HIE-ISOLDE charge breeder are discussed. The performance requirements imposed by standard HIE-ISOLDE physics as well as injection into a possible future TSR@ISOLDE are discussed, and thereafter translated into machine parameters. Experimental results from tests of a high-current and high-density electron gun performed at Brookhaven National Laboratory are presented, and alternative gun designs are discussed. Finally, a cost estimate is given together with possible beneficiaries of the on-going R&D, and potential collaboration partners are identified

High Performance Charge Breeder for HIE-ISOLDE and TSR@ISOLDE Applications

We report on the development of the HEC2 (High Energy Compression and Current) charge breeder, a possible high performance successor to REXEBIS at ISOLDE. The new breeder would match the performance of the HIE-ISOLDE linac upgrade and make full use of the possible installation of a storage ring at ISOLDE (the TSR@ISOLDE initiative [1]). Dictated by ion beam acceptance and capacity requirements, the breeder features a 2-3.5 A electron beam. In many cases very high charge states, including bare ions up to Z=70 and Li/Na-like up to Z=92 could be requested for experiments in the storage ring, therefore, electron beam energies up to 150 keV are required. The electron-beam current density needed for producing ions with such high charge states at an injection rate into TSR of 0.5-1 Hz is between 10 and 20 kA/cm2, which agrees with the current density needed to produce A/q<4.5 ions for the HIE-ISOLDE linac with a maximum repetition rate of 100 Hz. The first operation of a prototype electron gun with a pulsed electron beam of 1.5 A and 30 keV was demonstrated in a joint experiment with BNL [2]. In addition, we report on further development aiming to achieve CW operation of an electron beam having a geometrical transverse ion-acceptance matching the injection of 1+ ions (11.5 {\mu}m), and an emittance/energy spread of the extracted ion beam matching the downstream mass separator and RFQ (0.08 {\mu}m normalized / +/- 1% ).Comment: 9 pages, 8 figures, EBIST14 conference pape

Beam Simulations of a Gridded Lens for the Low-Energy Beam Transport of the Carbon RFQ

The Low-Energy Beam Transport (LEBT) section is the part of the injector which transports the beam from the source to the Radio Frequency Quadrupole (RFQ). Its main purpose is to match the beam to the acceptance of the RFQ. The electrostatic gridded lens is an alternative to the more commonly used Einzel-lens or solenoid. It is especially well suited in the scope of designing a LEBT for the carbon RFQ as it only minimally increases the transverse beam emittance. This note presents the design of the gridded lens for the carbon RFQ LEBT and the crosscheck of the beam dynamics results with two independent particle tracking codes. In addition, a sensitivity study to explore the flexibility and demonstrate the capabilities of the gridded lens is performed

Electron gun producing beams with controllable current density

The existing Brillouin-type electron gun at the TwinEBIS test bench is, according to Herrmann theory, capable of producing an electron beam with a current density of 3850 A/cm$^{2}$ in the 2 T solenoid. To control the electron beam current density and the magnetic flux inside the beam, the existing electron gun - now using purely electrostatic focusing - can be modified by permitting magnetic flux to reach the cathode. In such a configuration, the stabilizing magnetic flux inside the electron beam can be controlled by changing the current in the magnet coil surrounding the cathode. The radial oscillations of the electron beam, resulting from the increased magnetic field on the cathode, can be significantly reduced by employing a non-adiabatic magnetic field near the electron gun. This method has been recently developed and successfully used at REXEBIS at CERN. We present the computer simulations of such electro-optical system

Summary of charge breeding investigations for a future 11^{11}C treatment facility

In this report we discuss the possibilities of using a charge breeding scheme based on an Electron Beam Ion Source for beam preparation of a radioactive 11C beam for hadron therapy. Test measurements under extreme operating conditions were conducted at the REX-ISOLDE facility to explore the limitations of the charge breeder for high-intensity, low-repetition-rate, molecular CO+ beams. Based on our findings, we discuss different possible scenarios of coupling a charge breeder with either a medical synchrotron or linear accelerator

Parametric study of a high current–density EBIS Charge Breeder regarding Two Stream plasma Instability (TSI)

In this paper we report on our results from the design study of an advanced Electron Beam Ion Source (EBIS) based Charge Breeder (ECB). The ECB should fulfill the requirements of the HIE-ISOLDE upgrade, and if possible be adapted for ion injection into TSR@ISOLDE, as well as serve as an early prototype of a future EURISOL ECB. Fulfilling the HIE-ISOLDE/TSR@ISOLDE specifications requires simultaneous increase in electron beam energy, current and current density in order to provide the requested beams with proper charge state, high intensity and with a specified pulse repetition rate. We have carried out a study on the technical requirements of the ECB. The obtained parameters were optimized to comply with technical limitations arising from the electron beam technology and plasma physics in an EC

Simulation and design of an electron beam ion source charge breeder for the californium rare isotope breeder upgrade

An electron beam ion source (EBIS) will be constructed and used to charge breed ions from the californium rare isotope breeder upgrade (CARIBU) for postacceleration into the Argonne tandem linear accelerator system (ATLAS). Simulations of the EBIS charge breeder performance and the related ion transport systems are reported. Propagation of the electron beam through the EBIS was verified, and the anticipated incident power density within the electron collector was identified. The full normalized acceptance of the charge breeder with a 2 A electron beam, 0.024π  mm mrad for nominal operating parameters, was determined by simulating ion injection into the EBIS. The optics of the ion transport lines were carefully optimized to achieve well-matched ion injection, to minimize emittance growth of the injected and extracted ion beams, and to enable adequate testing of the charge bred ions prior to installation in ATLAS

Nonadiabatic electron gun at an electron beam ion source: Commissioning results and charge breeding investigations

The electron gun of the REXEBIS charge breeder at the REX/HIE-ISOLDE facility at CERN has been upgraded from a standard magneto-immersed type to a gun using a nonadiabatic magnetic element. The results from the cathode emission and electron beam propagation tests are presented, as well as the charge breeding efficiency for the new design. Complete mass-scans of the extracted beam have been performed from which the level of cathode-originating contaminations could be established, as well as partial pressures of the most abundant residual gases in the ion trapping region. Furthermore, optimal breeding times for a broad range of elements and charge states, either introduced as a gas or externally injected as singly charged ions into the trapping region, are given for different electron currents. From these values, effective electron current densities have been derived. Finally, the axial ion energy distributions of various elements and charge states were also measured, and the derived ion temperatures were correlated with the ion and electron beam overlap factors. This paper was published in PHYSICAL REVIEW ACCELERATORS AND BEAMS 25, 013402 (2022), DOI: 10.1103/PhysRevAccelBeams.25.01340