Low energy beam transport for facility for rare isotope beams driver linear particle accelerator

The driver linac for the facility for rare isotope beams (FRIB) will provide a wide range of primary ion beams for nuclear physics research. The linac will be capable of accelerating a uranium beam to an energy of up to 200 Mev∕u and delivering it to a fragmentation target with a maximum power of 400 kW. Stable ion beams will be produced by a high performance electron cyclotron resonance ion source operating at 28 GHz. The ion source will be located on a high voltage platform to reach an initial beam energy of 12 keV∕u. After extraction, the ion beam will be transported vertically down to the linac tunnel in a low energy beam transport (LEBT) system and injected into a radio frequency quadrupole (RFQ) operating at a frequency of 80.5 MHz. To meet the beam power requirements, simultaneous acceleration of two-charge states will be used for heavier ions (≥Xe). This paper presents the layout of the FRIB LEBT and the beam dynamics in the LEBT. In particular, simulation and design of the beam line section before charge state selection will be detailed. The need to use an achromatic design for the charge state selection system and the advantage of an ion beam collimation system to limit the emittance of the beam injected into the RFQ will be discussed in this paper.     

H- beam transport experiments in a solenoid low energy beam transport

The Front End Test Stand (FETS) is located at Rutherford Appleton Laboratory and aims for a high current, fast chopped 3 MeV H(-) ion beam suitable for future high power proton accelerators like ISIS upgrade. The main components of the front end are the Penning ion source, a low energy beam transport line, an radio-frequency quadrupole (RFQ) and a medium energy beam transport (MEBT) providing also a chopper section and rebuncher. FETS is in the stage of commissioning its low energy beam transport (LEBT) line consisting of three solenoids. The LEBT has to transport an H(-) high current beam (up to 60 mA) at 65 keV. This is the injection energy of the beam into the RFQ. The main diagnostics are slit-slit emittance scanners for each transversal plane. For optimizing the matching to the RFQ, experiments have been performed with a variety of solenoid settings to better understand the actual beam transport. Occasionally, source parameters such as extractor slit width and beam energy were varied as well. The paper also discusses simulations based on these measurements.     

Deuteron injector for Peking University Neutron Imaging Facility project

The deuteron injector developed for the PKUNIFTY (Peking University Neutron Imaging Facility) has been installed and commissioned at Peking University (PKU). The injector system must transfer 50 keV 50 mA of D(+) ion beam to the entrance of the 2 MeV radio frequency quadrupole (RFQ) with 10% duty factor (1 ms, 100 Hz). A compact 2.45 GHz permanent magnet electron cyclotron resonance (PMECR) ion source and a 1.36 m long low energy beam transport (LEBT) line using two solenoids was developed as the deuteron injector. A φ5 mm four-quadrant diaphragm was used to simulate the entrance of RFQ electrodes. The beam parameters are measured after this core with an emittance measurement unit (EMU) and a bending magnet for ion fraction analysis at the end of injector. During the commissioning, 77 mA of total deuteron beam was extracted from PMECR and 56 mA of pure D(+) beam that passed through the φ5 mm four-quadrant diaphragm was obtained at the position of RFQ entrance with the measured normalized rms emittance 0.12-0.16π?mm?mrad. Ion species analysis results show that the deuteron fraction is as high as 99.5%. All of the parameters satisfy PKUNIFTY's requirements. In this paper, we will describe the deuteron injector design and report the commissioning results as well as the initial operation.     

Initial commissioning results with the NSCL Electron Beam Ion Trap

The ReA reaccelerator is being added to the National Superconducting Cyclotron Laboratory (NSCL) fragmentation facility in order to provide exotic rare-isotope beams, not available at the Isotope Separation On-Line facilities, in the several-MeV/u energy range. The first stage of the NSCL reaccelerator complex, consisting of an EBIT charge breeder, a room-temperature radiofrequency quadrupole (RFQ) accelerator, and superconducting linear accelerator modules, has been completed and is being put into operation. Commissioning of the EBIT has started by extracting charge-bred residual gas ions, ions created from a Ne gas jet directed across the EBIT's electron beam and ions captured from an external test ion source. Charge-bred ions from the Ne gas jet have been extracted as a pulse and accelerated through the RFQ and the two cryomodules.     

A study of H+ production using metal hydride and other compounds by means of laser ion source

A laser ion source can provide wide variety of ion beams from solid target materials, however, it has been difficult to create proton beam efficiently. We examined capability of proton production using beeswax, polyethylene, and metal hydrides (MgH(2) and ZrH(2)) as target materials. The results showed that beeswax and polyethylene could not be used to produce protons because these targets are transparent to the laser wavelength of 1064 nm. On the other hand, the metal hydrides could supply protons. Although the obtained particle numbers of protons were less than those of the metal ions, the metal hydrides could be used as a target for proton laser ion source.     

MeV negative ion source from ultra-intense laser-matter interaction

Experimental demonstration of negative ion acceleration to MeV energies from sub-micron size droplets of water spray irradiated by ultra-intense laser pulses is presented. Thanks to the specific target configuration and laser parameters, more than 10(9) negative ions per steradian solid angle in 5% energy bandwidth are accelerated in a stable and reliable manner. To our knowledge, by virtue of the ultra-short duration of the emission, this is by far the brightest negative ion source reported. The data also indicate the existence of beams of neutrals with at least similar numbers and energies.     

Laser ion source with a double pulse laser system

To extend an ion beam pulse of a laser ion source, multiple laser shots could be used. To check the feasibility of this idea, we tested double laser irradiations on an iron target. When the interval of the two laser shots is longer than 10 μs, the obtained ion current profile was expressed as a sum of two individual expanded laser plasmas. However, if the interval is too close, a current reduction was observed. This technique can be effectively applied to low charge state ion production.     

Ion optics of RHIC electron beam ion source

RHIC electron beam ion source has been commissioned to operate as a versatile ion source on RHIC injection facility supplying ion species from He to Au for Booster. Except for light gaseous elements RHIC EBIS employs ion injection from several external primary ion sources. With electrostatic optics fast switching from one ion species to another can be done on a pulse to pulse mode. The design of an ion optical structure and the results of simulations for different ion species are presented. In the choice of optical elements special attention was paid to spherical aberrations for high-current space charge dominated ion beams. The combination of a gridded lens and a magnet lens in LEBT provides flexibility of optical control for a wide range of ion species to satisfy acceptance parameters of RFQ. The results of ion transmission measurements are presented.     

Proton emission from a laser ion source

At intensities of the order of 10(10) W∕cm(2), ns pulsed lasers can be employed to ablate solid bulk targets in order to produce high emission of ions at different charge state and kinetic energy. A special interest is devoted to the production of protons with controllable energy and current from a roto-translating target irradiated in repetition rate at 1-10 Hz by a Nd:Yag pulsed laser beam. Different hydrogenated targets based on polymers and hydrates were irradiated in high vacuum. Special nanostrucutres can be embedded in the polymers in order to modify the laser absorption properties and the amount of protons to be accelerated in the plasma. For example, carbon nanotubes may increase the laser absorption and the hydrogen absorption to generate high proton yields from the plasma. Metallic nanostrucutres may increase the electron density of the plasma and the kinetic energy of the accelerated protons. Ion collectors, ion energy analyzer, and mass spectrometers, used in time-of-flight configuration, were employed to characterize the ion beam properties. A comparison with traditional proton ion source is presented and discussed.     

Li+ ion emission from a hot-plate alumina-silicate source stimulated by flash heating with an infrared laser

The Neutralized Drift Compression Experiment-II accelerator under construction at Lawrence Berkeley National Laboratory has been designed to employ a lithium-doped alumino-silicate (Al-Si) hot-plate surface-ionization ion source. In order to achieve the design 1 mA∕cm(2) current density, the emitter must be constantly kept at a high temperature, leading to the accelerated loss of Li material as ions or neutrals. As a result, the estimated lifetime of the source is 50 h. This lifetime can be extended if the source is kept at low temperature during standby, and pulse heated to the high temperature during the ion extraction phase only. A pulsed heating technique based on an infrared laser (CO(2) gas discharge, λ = 10.6 μm) is described in this paper. The feasibility of ion current emission stimulated by flash heating with an infrared (IR) laser was demonstrated. High repeatability of the laser-stimulated ion current was observed, creating an opportunity for modulation and gating of the ion current with a laser pulse. It was found that with the available low power (≈115 W∕cm(2)) IR laser, current densities as high as 0.8 mA∕cm(2) could be achieved with a 2.8 mm diameter source. Various approaches for scaling to a larger (10 cm diameter) source and the application of short pulse, high power lasers are discussed. The results and conclusions of this paper may apply to various species of hot-plate ion sources.     

Proton emission from thin hydrogenated targets irradiated by laser pulses at 10(16) W∕cm2

The iodine laser at PALS Laboratory in Prague, operating at 1315 nm fundamental harmonics and at 300 ps FWHM pulse length, is employed to irradiate thin hydrogenated targets placed in vacuum at intensities on the order of 10(16) W∕cm(2). The laser-generated plasma is investigated in terms of proton and ion emission in the forward and backward directions. The time-of-flight technique, using ion collectors and semiconductor detectors, is used to measure the ion currents and the corresponding velocities and energies. Thomson parabola spectrometer is employed to separate the contribution of the ion emission from single laser shots. A particular attention is given to the proton production in terms of the maximum energy, emission yield, and angular distribution as a function of the laser energy, focal position, target thickness, and composition. Metallic and polymeric targets allow to generate protons with large energy range and different yield, depending on the laser, target composition, and target geometry properties.     

Fast ion beam-plasma interaction system

A device has been constructed for the study of the interaction between a fast ion beam and a target plasma of separately controllable parameters. The beam of either hydrogen or helium ions has an energy of 1-4 keV and a total current of 0.5-2 A. The beam energy and beam current can be varied separately. The ion source plasma is created by a pulsed (0.2-10-ms pulse length) discharge in neutral gas at up to 3 x 10(-3) Torr. The neutrals are pulsed into the source chamber, allowing the neutral pressure in the target region to remain less than 5 x 10(-5) Torr at a 2-Hz repetition rate. The creation of the source plasma can be described by a simple set of equations which predict optimum source design parameters. The target plasma is also produced by a pulsed discharge. Between the target and source chambers the beam is neutralized by electrons drawn from a set of hot filaments. Currently under study is an unstable wave in a field-free plasma excited when the beam velocity is nearly equal to the target electron thermal velocity (v(beam) approximately 3.5 x 10(7) cm/s, Te = 0.5 eV).     

Measurement of axial neutral density profiles in a microwave discharge ion thruster by laser absorption spectroscopy with optical fiber probes

In order to reveal the physical processes taking place within the "μ10" microwave discharge ion thruster, internal plasma diagnosis is indispensable. However, the ability of metallic probes to access microwave plasmas biased at a high voltage is limited from the standpoints of the disturbance created in the electric field and electrical isolation. In this study, the axial density profiles of excited neutral xenon were successfully measured under ion beam acceleration by using a novel laser absorption spectroscopy system. The target of the measurement was metastable Xe I 5p(5)((2)P(0) (3/2))6s[3/2](0) (2) which absorbed a wavelength of 823.16 nm. Signals from laser absorption spectroscopy that swept a single-mode optical fiber probe along the line of sight were differentiated and converted into axial number densities of the metastable neutral particles in the plasma source. These measurements revealed a 10(18) m(-3) order of metastable neutral particles situated in the waveguide, which caused two different modes during the operation of the μ10 thruster. This paper reports a novel spectroscopic measurement system with axial resolution for microwave plasma sources utilizing optical fiber probes.     

Resonant holography of plasma flow phenomena

A dye laser, tuned near the Ba II ion resonance line at 4554 A and used as a light source for a holographic interferometer, allows ion densities as low as 5 x 10(13) cm(-3) to be measured in flowing barium plasmas.     

A Laser-Plasma Ion Source with Normal Light Incidence on the Target Surface

A laser ion source with the beam focused along the normal to the target surface was designed and produced. Tests of this system performed in comparison with the conventional for laser sources laser-beam injection and focusing at an angle of 45° have shown that the fraction of multiply charged high-energy ions significantly increases in such a design of the source.     

Time-resolved momentum imaging system for molecular dynamics studies using a tabletop ultrafast extreme-ultraviolet light source

We describe a momentum imaging setup for direct time-resolved studies of ionization-induced molecular dynamics. This system uses a tabletop ultrafast extreme-ultraviolet (EUV) light source based on high harmonic upconversion of a femtosecond laser. The high photon energy (around 42 eV) allows access to inner-valence states of a variety of small molecules via single photon excitation, while the sub--10-fs pulse duration makes it possible to follow the resulting dynamics in real time. To obtain a complete picture of molecular dynamics following EUV induced photofragmentation, we apply the versatile cold target recoil ion momentum spectroscopy reaction microscope technique, which makes use of coincident three-dimensional momentum imaging of fragments resulting from photoexcitation. This system is capable of pump-probe spectroscopy by using a combination of EUV and IR laser pulses with either beam as a pump or probe pulse. We report several experiments performed using this system.     

A subnanosecond pulsed ion source for micrometer focused ion beams

A new, compact design of an ion source delivers nanosecond pulsed ion beams with low emittance, which can be focused to micrometer size. By using a high-power, 25 fs laser pulse focused into a gas region of 10(-6) mbar, ions at very low temperatures are produced in the small laser focal volume of 5 mum diameter by 20 mum length through multiphoton ionization. These ions are created in a cold environment, not in a hot plasma, and, since the ionization process itself does not significantly heat them, have as a result essentially room temperature. The generated ion pulse, up to several thousand ions per pulse, is extracted from the source volume with ion optical elements that have been carefully designed by simulation calculations. Externally triggered, its subnanosecond duration and even smaller time jitter allow it to be superimposed with other pulsed particle or laser beams. It therefore can be combined with any type of collision experiment where the size and the time structure of the projectile beam crucially affect the achievable experimental resolution.     

Efficient Kalpha x-ray source from submillijoule femtosecond laser pulses operated at kilohertz repetition rate

We report an efficient Cu K(alpha) x-ray source produced by focusing submillijoule, 120 fs Ti:sapphire laser pulses on a solid copper target to a spot diameter of few microns. The experimental results show strong emission of K(alpha) x-rays from solid targets from microplasmas created by p-polarized 0.2-0.3 mJ laser pulses at 1 kHz repetition rate. We have demonstrated K(alpha) x-ray point source emission rates of 6.7 x 10(9) photonss into 2 pi sr at 1 kHz repetition rate. The source has an x-ray conversion efficiency into Cu K(alpha) line emission of 3.2 x 10(-5). The source has a measured size of approximately 8 microm. Such a high repetition rate K(alpha) x-ray source can be very useful for time resolved x-ray diffraction and radiographic applications.