The University of Sarajevo Physics Department, in collaboration with CERN’s Accelerator Beam Physics group, proposes a compact linear accelerator design for applied physics research spanning from beam dynamics studies to material surface analysis. The Sarajevo Ion Accelerator (SARAI) consists of an electron cyclotron resonance ion source, a low energy beam transport line (LEBT) and a radiofrequency quadrupole (RFQ). The ion source can produce an array of ions extracted with 30 kV. This study presents an iterative parameter optimization method that suggests two LEBT optics: one for beam diagnostics and another for compact beam matching to the RFQ acceptance. The RFQ discussed here is a 750 MHz, 2.5 MeV/u RFQ, used for medical applications. SARAI RFQ aims at 0.5 - 2 MeV/u. A novel RFQ technology allows a significant reduction in footprint. This paper further discusses plans for source commissioning and potential research applications.

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.

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.

A hollow electron beam has been proposed as an active control tool to remove the beam halo from high-energy, high-current hadron or ion machines (such as the High-Luminosity Large Hadron Collider). To study the halo removal rate and assess the effect on the ion beam core, one of the two electron lenses in the Relativistic Heavy Ion Collider was changed from a Gaussian beam profile to a hollow profile. We describe the design and verification of the hollow electron beam parameters as well as the methods to minimize the hollow beam profile distortions, which can result in an ion beam emittance increase. The hollow beam alignment with the ion beam by using a backscattered electron detector has been demonstrated. Furthermore, experiments were carried out to explore the efficiency of the halo removal by scanning the current and inner radius of the hollow electron beam, which is pulsed either every turn or every nth turn. The effects of the hollow electron beam on the ion beam emittance and luminosity were also assessed experimentally by scanning the inner radius of the electron beam.

In this paper 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. This paper is a highly condensed version of an exhaustive report on the topic [1], which we would like to refer to for further details.

We report high steady-state nuclear polarization of 1 torr He-3 gas nuclei via metastability exchange optical pumping at magnetic fields above 2T. The introduction of highly polarized He-3 gas into Brookhaven's Electron Beam Ion Source would enable a new, polarized He-3 ion source for use at the Relativistic Heavy Ion Collider and a future Electron-Ion Collider facility. By adapting recent developments in high field metastability exchange optical pumping for higher pressure gas, we have successfully polarized 1 torr 3 He sealed cells in the EBIS solenoid. Through careful manipulation of the RF discharge parameters, polarizations above 80% were attained at 2, 3 and 4 T, with 89% being reached at 3 T with a 664 s relaxation time.

This paper describes a method for reducing the energy of the cyclotron motion for charged particles in coherent beams using a nonadiabatic magnetic field. For the purpose of reducing the cyclotron motion, a local magnetic field reduction of the main guiding field should be situated in the region of the descending phase of the beam oscillation. The required local magnetic field depression can be produced with a soft iron ring or with a magnet coil. The nonadiabatic element can be positioned on the descending part of any period of the beam oscillation where the beam still remains sufficiently coherent. The effect of reducing the cyclotron motion with such nonadiabatic magnetic field is independent of the electric field of the cathode-anode gap and seems to be a universal method for the cyclotron motion control in coherent beams. Therefore, it can be used for reducing the cyclotron motion of electron beams produced with different kinds of guns with different perveances and sizes. For instance, the method is capable of creating ripple-free, laminar beams even for magneto-immersed guns positioned in a magnetic field of only a few hundred Gs and with a cathode emission current density exceeding 30 A/cm(2). It can also be applied for guns producing tubular beams, as demonstrated by our simulations. The results of computer simulations are presented, which demonstrate the capability of effective cyclotron motion control with nonadiabatic magnetic field.

A pepperpot emittance meter was used to measure the transverse emittance of multiply charged beams from REXEBIS, an Electron Beam Ion Source (EBIS) used for charge breeding of radioactive ion beams. The emittance meter is equipped with a Micro Channel Plate (MCP), a phosphor screen and a CCD camera for detection of the ion signal. The pulsed beam structure of low duty cycle imposes challenging constraints on the detector settings. In this article we give a careful analysis of the optimal operating parameters of the pepperpot emittance meter for ion beams of varying intensities. Emittance values for mass-separated and non-separated beams for different operating modes of the EBIS are presented. Furthermore we report on aberrations created in our injection∕extraction system.

There are many applications of electron beams in accelerator facilities: for electron coolers, electron lenses, and electron beam ion sources (EBIS) to mention a few. Most of these applications require magnetic compression of the electron beam to reduce the beam radius with the goal of either matching the circulating ion beam (electron lenses and electron coolers) or increasing the ionization capability for the production of highly charged ions (EBIS). The magnetic compression of the electron beam comes at a cost of increasing share of the transverse component of energy and therefore increased angles of the electron trajectories to the longitudinal axis. Considering the effect of the magnetic mirror, it is highly desirable to produce a laminar electron beam in the electron gun. The analysis of electron guns with different configurations is given in this paper with emphasis on generating laminar electron beams.

The capability of accelerating a polarized $^3$He ion beam in RHIC would demonstrate an effective polarized neutron beam for the study of new high-energy QCD studies of nucleon structure. This development would be particularly beneficial for the future plans of an Electron Ion Collider (EIC), which could use a polarized $^3$He ion beam to probe the spin structure of the neutron. The proposed polarized $^3$He ion source is based on the Electron Beam Ion Source (EBIS) currently in operation at Brookhaven National Laboratory (BNL). $^3$He gas would be polarized within the 5 T field of the EBIS solenoid via Metastability Exchange Optical Pumping (MEOP) and then pulsed into the EBIS vacuum and drift tube system where the $^3$He will be ionized by the 10 Amp electron beam. The goal of the polarized $^3$He ion source is to achieve $2.5 \times 10^{11}$ $^3$He$^{++}$/pulse at 70\% polarization. An upgrade of the EBIS is currently underway at BNL. The EBIS capability to produce polarized $^{3}$He$^{++}$ is being developed through a collaboration between BNL and MIT.

MEDeGUN [1] is an electron gun to be used in an Electron Beam Ion Source (EBIS) designed to serve as C6+ source for LINAC-based 2nd generation hadron therapy facilities [2]. The latter require short pulses of at least 1*10(8) particles at a repetition rate of 40t) Hz, which exceeds the possibilities of currently used electron cyclotron resonance ion sources (ECRIS) and EBISes. The design of MEDeGUN is based on a combination of electrostatic and magnetic compression, which is commonly referred to as Brillouin gun. As previous devices have shown, it is difficult to achieve the design goals in this configuration due to the high sensitivity of the electron beam to any field imperfection. Therefore, the number of interfaces between the cathode, Wehnelt and anode electrodes have been reduced to only two in our design. In spring 2017, the MEDeGUN assembly was installed at the TwinEBIS test bench at CERN 131. We have since then propagated an electron beam of more than 1 A at 10 keV electron energy through the 2T solenoid with losses of less than 1 mA. We will here present the conunissioning results and discuss them with respect to the design goals.

To investigate the influence of the dip in magnetic field between the two superconducting solenoids in the design of the BNL ExtendedEBIS, we calculated electron and ion trajectories with space charge effect of the electron beam, but neglecting the space charge of the ions. The results showed that the area of the phase space plots of the ions is conserved because of the helical pitch of radial oscillations is short compared with the scale length for changes of the axial magnetic and electric field. Consequently, the ion trajectories will not be greatly affected after passing through the dip in magnetic field.

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 C 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.

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 C 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.

A low energy beamline has been designed for the TwinEBIS setup. The beamline will be used to transport ions extracted from the electron beam ion source into an accelerating radio frequency quadrupole or into secondary devices, like a time of flight-mass spectrometer, attached to the beamline via a fast three way 20̂ ion switchyard. Optional injection of ions from an external source into the electron beam ion source is foreseen. In this article the general layout of the beamline is presented and supported with simulations of the ion-optical matching. Furthermore, the switchyard and gridded electrostatic lenses, chosen as the main focusing elements, have been simulated to assess their impact on the beam quality and the dynamics of secondary electrons emitted by the gridded lenses. In addition, the beamline includes general diagnostic devices, including a bidirectional pepperpot beam profiler. An overview of the diagnostic elements is given.

Two electron lenses (e-lenses) have been in operation during the 2015 RHIC physics run as part of a head-on beam-beam compensation scheme. While the RHIC lattice was chosen to reduce the beam-beam-induced resonance-driving terms, the electron lenses reduced the beam-beam-induced tune spread. This has been demonstrated for the first time. The beam-beam compensation scheme allows for higher beam-beam parameters and therefore higher intensities and luminosity. In this paper, we detail the design considerations and verification of the electron beam parameters of the RHIC e-lenses. Longitudinal and transverse alignments with ion beams and the transverse beam transfer function measurement with head-on electron-proton beam are presented.

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.

A head-on beam-beam compensation scheme was implemented for operation in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory [Phys. Rev. Lett. 115, 264801 (2015)]. The compensation consists of electron lenses for the reduction of the beam-beam induced tune spread, and a lattice for the minimization of beam-beam generated resonance driving terms. We describe the implementations of the lattice and electron lenses, and report on measurements of lattice properties and the effect of the electron lenses on the hadron beam.