High Intensity Heavy Ion Beams Research Articles

Sputtering of targets in high-intensity heavy-ion beam experiments

Based on available models and experimental data, the sputtering of target atoms in long-term experiments with intense heavy ion (HI) beams has been considered. The experiments on the synthesis of superheavy nuclei (SHN), which are carried out in laboratories around the world, are examples of such experiments encountering the target atoms sputtering in specific conditions. Rotating wheels with a relatively large target annulus area are used in these experiments to reduce the temperature and radiation loads on the target. Large areas of rotating targets allow one to reduce the sputtering yields of target atoms significantly. The question arises about the reliability of these yields in experiments on the synthesis of SHN with Z>118. These nuclei can be produced with extremely low cross sections, requiring HI beam doses exceeding 10 20 particles passed through the target to observe several decay events of the thus synthesized SHN. Estimates based on approximations and simulations considered in this work are presented and compared with some data on actinide target sputtering obtained in experiments performed on the synthesis of SHN.

Performance of prototype dual gain multilayer thick gas electron multiplier with high-intensity heavy-ion beam injections in low-pressure hydrogen gas

Abstract A prototype Dual Gain Multilayer Thick Gas Electron Multiplier (DG-M-THGEM) with an active area of 10 cm × 10 cm was manufactured aiming at the production of a large-volume active-target time projection chamber which can work under the condition of high-intensity heavy-ion beam injections. The DG-M-THGEM has an alternating structure of electrodes and insulators. Effective gas gains of two regions, which are called beam and recoil regions, are separately controlled. Performance of the prototype DG-M-THGEM in hydrogen gas at a pressure of 40 kPa was evaluated. Irradiating a 132Xe beam, an effective gas gain lower than 100 with a charge resolution of 3% was achieved in the beam region while an effective gas gain of 2000 was maintained in the recoil region. Position distributions of measured charges along the beam axis were investigated in order to evaluate gain uniformity in the high-intensity beam injection. The gain shift was estimated by simulations considering space charges in the drift region. The gain shift was suppressed within 3% even at the beam intensity of 2.5 × 106 particles per second.

Nitrogen gas scintillation counter for high-intensity heavy ion beams with negligible radiation damage

We developed an N2 gas scintillation counter as a time-of-flight counter for particle identification of radioactive isotope beams. Radiation damage, which often becomes a problem for high-intensity heavy ion beams, can be prevented by a continuous flow of N2 gas. The scintillator, with a volume of 60 mm × 60 mm × 100 mm, was filled with N2 gas at a pressure of approximately 100 kPa. Photons were detected using photomultiplier tubes attached to both sides of the vessel. The main emission wavelength of photons produced in the detector was 300–400 nm. Performance tests confirmed that the detector had sufficient detection efficiency, intrinsic time resolution, and short decay time. Additionally, the detector was demonstrated to be effective for particle identification.

Longitudinal Beam Dynamics for the Heavy-Ion Synchrotron Booster Ring at HIAF

To accelerate high-intensity heavy-ion beams to high energy in the booster ring (BRing) at the High-Intensity Heavy-Ion Accelerator Facility (HIAF) project, we take the typical reference particle 238U35+, which can be accelerated from an injection energy of 17 MeV/u to the maximal extraction energy of 830 MeV/u, as an example to study the basic processes of longitudinal beam dynamics, including beam capture, acceleration, and bunch merging. The voltage amplitude, the synchronous phase, and the frequency program of the RF system during the operational cycle were given, and the beam properties such as bunch length, momentum spread, longitudinal beam emittance, and beam loss were derived, firstly. Then, the beam properties under different voltage amplitude and synchronous phase errors were also studied, and the results were compared with the cases without any errors. Next, the beam properties with the injection energy fluctuation were also studied. The tolerances of the RF errors and injection energy fluctuation were dictated based on the CISP simulations. Finally, the effect of space charge at the low injection energy with different beam intensities on longitudinal emittance and beam loss was evaluated.

LINAC developments for heavy ion operation at GSI and FAIR

The first cavity of a standalone superconducting (sc) continuous wave (cw) heavy ion Linac as a demonstration of the capability of 217 MHz multi gap Crossbar H-mode structures (CH) has been already commissioned at high acceleration gain. The worldwide first beam test with a superconducting multi gap CH-cavity was a milestone of the R&D work of HIM and GSI in collaboration with Goethe University Frankfurt (GUF) in preparation of the sc cw heavy ion Linac project, substituting GSI-UNILAC as a heavy ion high duty factor Linac. Recently the first two of four fully equipped cw-Linac cryomodules are in procurement. To meet the future FAIR science requirements higher beam intensity has to be achieved in the present GSI-accelerator complex. In the last years ion source developments, in particular for the high current Vacuum Arc Ion Sources (VARIS), were concentrated on heavy elements, as Bi and Pb, aiming for stable routine ion source operation at a sufficient rep. rate and high production efficiency. Stripping is a key technology for all heavy ion accelerators. After upgrade of the supersonic N2-gas jet implementation of high current foil stripping, recently a new H2gas cell, using a pulsed gas regime synchronized with arrival of the beam pulse has been developed. An enhanced stripper gas density as well as a simultaneously reduced gas load results in an increased stripping efficiency, while the beam emittance remains the same. A new record beam intensity (11.1 emA) for238U28+beams at 1.4 MeV/u has been achieved, applying the pulsed high density H2-stripper target to a high intensity238U4+beam from the VARIS ion source. Further ion source developments have been accomplished recently providing for sufficient heavy ion beam intensities at the High Current Injector Linac. A machine investigation program has been performed in 2020. The focus was to optimize the entire FAIR injector chain for high intensity heavy ion beam after the successful implementation of different upgrade measures. Besides a dedicated operation mode applying UNILAC, as a heavy ion Linac, at a synchronous phase significantly lower than 30 degrees for high intensity proton beam, could be established. Thus, UNILAC is able to deliver a sufficient proton beam intensity for the FAIR commissioning phase, when the FAIR-proton Linac is not yet available.

The Compressed Baryonic Matter Experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at FAIR aims to study the area of the QCD phase diagram at high net baryon densities and moderate temperatures using heavy-ion collisions. The FAIR accelerator will provide high-intensity heavy-ion beams up to Au ions in the beam momentum range 3.5A-12A GeV/c per nucleon. In order to achieve it's physics goals and to perform multi-differential measurements of rare probes such as multistrange hadrons or hypernuclei, CBM plans to operate at unprecedented peak interaction rates of up to 10 MHz.Following an introduction into the physics program of the CBM, recent developments related to the preparation of the experiment, physics performance studies, and detector components tests within the so-called FAIR PHASE-0 program are discussed. In particular, the status of the mCBM project at GSI, which operated with high-intensity beams for the first time last year and combines various CBM detector subsystems with a common data acquisition system (DAQ), are presented.

High-energy-density physics based on HIAF

High-energy-density physics (HEDP) deals with the study of matter under extreme conditions with an energy density higher than 1011 J/m3, corresponding to a pressure of 100 GPa. Such matter exists in abundance in deep interiors of the planets and stars. It also exists for a short duration during nuclear explosion and the loading of high-power-pulsed machines. HEDP is the international frontier of national security, astrophysics and fusion science, and it is also one of the main scientific goals of the high-power laser-facilities, Z-machines and heavy-ion-accelerators. Herein, the HEDP research based on High Intensity heavy-ion Accelerator Facility (HIAF), which is the “12th Five-Year Plan” national major science and technology infrastructure, will be introduced. The HIAF is advocated to provide the world with a heavy-ion beam with utmost high power. The energy and power of one beam pulse is about 100 J and several TW, respectively. With such a high-power heavy-ion beam, heating a solid-state lead sample, for example, could generate homogenous high-energy-density matter with a spatial scale from mm to cm and a temperature of 10 eV, near-solid density, and energy density of 1013 J/m3. Thus, through the HIAF, the generation, properties and evolution of high-energy-density matter can be investigated. This paper also reports the state of the art in the field of HEDP based on HIAF, including the generation and development of high-energy-density matter driven by a high-intensity heavy-ion beam, micro mechanism of interaction between the ion beam and dense matter or plasma, and key diagnostics of the high-energy-density matter driven by a hevy-ion beam.

Development of four-beam IH-RFQ linear accelerator

It is difficult to accelerate a high intensity heavy ion beam because the upper limit of the beam current in an RFQ (Radio Frequency Quadrupole) linac depends on the applied voltage at the RFQ electrode and the strength of the space charge effect. A multi-beam RFQ linac, with multiple beam-channels accelerating several beams in parallel in one cavity, and utilizing multiple beams to decrease the space charge effect can be used to achieve a higher beam current. In order to demonstrate that a four-beam IH-RFQ (Interdigital H-type RFQ) linear accelerator is suitable for high-intensity, heavy ion beam acceleration, we have developed a four-beam prototype.A four-beam IH-RFQ cavity was fabricated according to design parameters obtained from our previous detailed simulations. Low-power RF property measurements of the fabricated four-beam IH-RFQ cavity were carried out with a network analyzer. After the low-power RF property measurements, we performed a high-power test and an acceleration test.

Laser ablation plasma with solenoid field confinement.

A Laser Ion Source (LIS) can produce high charge state and high intensity ion beams (∼emA), especially, refractory metallic ion beams, which makes it a promising candidate as an ion source for heavy ion cancer therapy facilities and future accelerator complexes, where pulsed high intensity and high charged heavy ion beams are required. However, it is difficult for the LIS to obtain a long pulse width while ensuring high current intensity, thus limiting the application of the LIS. To solve the conflict, magnetic fields are proposed to confine the expansion of the laser produced plasma. With a solenoid along the normal direction to the target surface, the lateral adiabatic expansion of the laser ablation plasma is suppressed which extends the pulse width of the ion beam effectively. The characteristics of laser ablation plasma with solenoid field confinement will be presented and discussed in this paper.

Charge stripping at high energy heavy ion Linacs

For each heavy-ion accelerator facility charge stripping is a key technology – the stripping charge state, its efficiency to produce ions in the selected charge state, and the beam quality after stripping substantially determine the entire accelerator performance. Modern heavy ion accelerator facilities such as the future Facility for Antiproton and Ion Research (FAIR) at GSI, Darmstadt, Germany provide for high-intensity heavy-ion beams beyond 200 MeV/u. Heavy ions generated in an ion source at comparatively low charge states are pre-accelerated in a Linac to a few MeV/u, after charge stripping the average charge state is increased and one (or several) ion charge states are selected for further acceleration. This enables more efficient acceleration up to the final beam energy, compared to acceleration of ions with a low charge state. C-foil stripping allows for highest mean charge state and best stripping efficiency into the desired charge state. Therefore minimum acceleration voltage could be expected utilizing C-foil stripping. Due to the high power deposited by the ions in the stripping media and radiation damages if solids are used, self-recovering stripper media must be used in any case. First layout scenarios for a 200 MeV/u heavy ion Linac considering efficient heavy ion stripping will be presented.

Development of a laser ion source for production of high-intensity heavy-ion beams

A laser ion source has been developed as a high-intensity source for the ion implanter and the single pulsed beam of the azimuthally varying field cyclotron at TIARA. Highly charged beams of C5+ and C6+ ions and low-charged beams of heavy ions such as C, Al, Ti, Cu, Au, and Pt are required for the single-pulse acceleration in the cyclotron and for the ion implanter, respectively. In the vacuum chamber of the ion source, a target holder on a three-dimensional linear-motion stage provides a fresh surface for each laser shot. A large-sized target with a maximum size of 300mm×135mm is mounted on the holder for long-term operation. The ion current (ion charge flux) in the laser-produced plasma is measured by a Faraday cup and time-of-flight spectra of each charge state are measured using a 90° cylindrical electrostatic analyzer just behind the Faraday cup. Carbon-plasma-generation experiments indicate that the source produces intense high- and low-charged pulsed ion beams. At a laser energy of 483mJ (2.3×1013W/cm2), average C6+ current of 13mA and average C5+ current of 23mA were obtained over the required time duration for single-pulse acceleration in the cyclotron (49ns for C6+ and 80ns for C5+). Furthermore, at 45mJ (2.1×1012W/cm2), an average C2+ current of 1.6mA over 0.88μs is obtained.

Design of four-beam IH-RFQ linear accelerator

The multi-beam acceleration method is an acceleration technique for low-energy high-intensity heavy ion beams, which involves accelerating multiple beams to decrease space charge effects, and then integrating these beams by a beam funneling system. At the Tokyo Institute of Technology a two beam IH-RFQ linear accelerator was developed using a two beam laser ion source with direct plasma injection scheme. This system accelerated a carbon ion beam with a current of 108mA (54mA/channel×2) from 5 up to 60keV/u.In order to demonstrate that a four-beam IH-RFQ linear accelerator is suitable for high-intensity heavy ion beam acceleration, we have been developing a four-beam prototype. A four-beam IH-RFQ linear accelerator consists of sixteen RFQ electrodes (4×4 set) with stem electrodes installed alternately on the upper and lower ridge electrodes.As a part of this development, we have designed a four-beam IH-RFQ linear accelerator using three dimensional electromagnetic simulation software and beam tracking simulation software. From these simulation results, we have designed the stem electrodes, the center plate and the side shells by evaluating the RF properties such as the resonance frequency, the power loss and the electric strength distribution between the RFQ electrodes.

Studies of high density baryon matter with high intensity heavy-ion beams at J-PARC

In J-PARC heavy-ion project, we aim at studies of QCD phase structures and hadron properties in high baryon density close to the neutron star core. We have developed a heavy-ion acceleration scheme with a new linac and a new booster with existing two synchrotrons with the goal beam rate of about 1011 Hz. We have also designed a large acceptance spectrometer based on a toroidal magnet. We have evaluated the spectrometer performance, and demonstrated reconstructing dielectron and dimuon spectra with full detector simulations. Finally, we designed a hypernuclear spectrometer which can utilize the full intensity ion beams.

High power acceleration of an HSC type injector for cancer therapy**Supported by National Natural Science Foundation of China and One Hundred Person Project of CAS

A hybrid single cavity (HSC) linac, which is formed by combining a radio frequency quadrupole (RFQ) and a drift tube (DT) structure into one interdigital-H (IH) cavity, is fabricated and assembled as a proof of principle injector for cancer therapy synchrotron, based on the culmination of several years of research. The HSC linac adopts a direct plasma injection scheme (DPIS), which can inject a high intensity heavy ion beam produced by a laser ion source (LIS). The input beam current of the HSC is designed to be 20 mA C6+ ions. According to numerical simulations, the HSC linac can accelerate a 6-mA C6+beam, which meets the requirement of the needed particle number for cancer therapy (108–9 ions/pulse). The HSC injector with the DPIS method makes the existing multi-turn injection system and stripping system unnecessary, and can also bring down the size of the beam pipe in existing synchrotron magnets, which could reduce the whole cost of synchrotron. The radio frequency (rf) measurements show excellent rf properties for the resonator, with a measured Q equal to 91% of the simulated value. A C6+ ion beam extracted from the LIS was used for the HSC commissioning. In beam testing, we found the measured beam parameters agreed with simulations. More details of the measurements and the results of the high power test are reported in this paper.

Electron cooling system in the booster synchrotron of the HIAF project

The High Intensity heavy ion Accelerator Facility (HIAF) is a new accelerator complex under design at the Institute of Modern Physics (IMP). The facility is aiming at the production of high intensity heavy ion beams for a wide range of experiments in high energy density physics, nuclear physics, atomic physics and other applications. It consists of a superconducting electron-cyclotron-resonance ion source and an intense proton ion source, a linear accelerator, a 34Tm booster synchrotron ring, a 43Tm multifunction compression synchrotron ring, a 13Tm high precision spectrometer ring and several experimental terminals. A magnetized electron cooling device is supposed to be used in the booster ring for decreasing the transverse emittance of injected beams. The conceptual design and main parameters of this cooler are presented in this paper.

Electron stripping of Bi ions using a modified 1.4 MeV/u gas stripper with pulsed gas injection

The GSI UNILAC will serve as an injector system for the future Facility for Antiproton and Ion Research (FAIR) facility. To meet the high demands for high-intensity heavy-ion beams, an upgrade of the existing 1.4 MeV/u gas stripper is envisaged with the aim of increasing the stripping efficiency for the required charge state. For this, an increase of the stripping gas density is pursued. Since FAIR will use pulsed beams with a very small duty cycle, a new stripper setup with a pulsed gas injection was implemented to minimize the gas load and thereby enables an increase of the gas pressure. The setup was tested using a bismuth ion beam with a nitrogen gas target. The performance is compared with that of the existing nitrogen gas-jet stripper. The charge stripping of bismuth ions into the same average charge state (26+) was achieved.

A mask for high-intensity heavy-ion beams in the MAYA active target

The use of high-intensity and/or heavy-ion beams in active targets and time-projection chambers is often limited by the strong ionization produced by the beam. Besides the difficulties associated with the saturation of the detector and electronics, beam-related signals may hide the physical events of interest or reduce the detector performance. In addition, space-charge effects may deteriorate the homogeneity of the electric drift field and distort the subsequent reconstruction of particle trajectories. In anticipation of future projects involving such conditions, a dedicated beam mask has been developed and tested in the MAYA active target. Experimental results with a 136Xe beam are presented.

A new compact structure for a high intensity low-energy heavy-ion accelerator

A new compact accelerating structure named Hybrid RFQ is proposed to accelerate a high-intensity low-energy heavy ion beam in HISCL (High Intensive heavy ion SuperConducting Linear accelerator), which is an injector of HIAF (Heavy Ion Advanced Research Facility). It is combined by an alternative series of acceleration gaps and RFQ sections. The proposed structure has a high accelerating ability compared with a conventional RFQ and is more compact than traditional DTLs. A Hybrid RFQ is designed to accelerate 238U34+ from 0.38 MeV/u to 1.33 MeV/u. The operation frequency is described to be 81.25 MHz at CW (continuous wave) mode. The design beam current is 1.0 mA. The results of beam dynamics and RF simulation of the Hybrid RFQ show that the structure has a good performance at the energy range for ion acceleration. The emittance growth is less than 5% in both directions and the RF power is less than 150 kW. In this paper, the results of beam dynamics and RF simulation of the Hybrid RFQ are presented.

Iron beam acceleration using direct plasma injection scheme

A new set of vanes of radio frequency quadrupole (RFQ) accelerator was commissioned using highly charged iron beam. To supply high intensity heavy ion beams to the RFQ, direct plasma injection scheme (DPIS) with a confinement solenoid was adopted. One of the difficulties to utilize the combination of DPIS and a solenoid field is a complexity of electro magnetic field at the beam extraction region, since biasing high static electric field for ion extraction, RFQ focusing field, and the solenoid magnetic field fill the same space simultaneously. To mitigate the complexity, a newly designed magnetic field clamps were used. The intense iron beam was observed with bunched structure and the total accelerated current reached 2.5 nC.

Production of beams from solid materials at Center for Nuclear Study electron cyclotron resonance ion source

Two methods for the feed of vapor from solid materials in the Center for Nuclear Study ECR ion source are described. A rod placed near the wall of the plasma chamber, operating up to a melting point of 2600 °C, has been used for CaO, SiO2, and FeO. An oven with a number of openings, operating up to 800 °C, has been used for P2O5, Li, and S. Typical ion beam intensities of (7)Li(2+), (6)Li(3+), (40)Ca(12+), and (56)Fe(15+) are achieved 280, 75, 28, and 7 eμA, respectively. High intensity heavy ion beams are stably supplied into the azimuthally varying field cyclotron.