Beam Bunch Research Articles

Shielded button electrodes for time-resolved measurements of electron cloud buildup

We report on the design, deployment and signal analysis for shielded button electrodes sensitive to electron cloud buildup at the Cornell Electron Storage Ring. These simple detectors, derived from a beam-position monitor electrode design, have provided detailed information on the physical processes underlying the local production and the lifetime of electron densities in the storage ring. Digitizing oscilloscopes are used to record electron fluxes incident on the vacuum chamber wall in 1024 time steps of 100ps or more. The fine time steps provide a detailed characterization of the cloud, allowing the independent estimation of processes contributing on differing time scales and providing sensitivity to the characteristic kinetic energies of the electrons making up the cloud. By varying the spacing and population of electron and positron beam bunches, we map the time development of the various cloud production and re-absorption processes. The excellent reproducibility of the measurements also permits the measurement of long-term conditioning of vacuum chamber surfaces.

Controllability of intense-laser ion acceleration

AbstractAn ion beam has the unique feature of being able to deposit its main energy inside a human body to kill cancer cells or inside material. However, conventional ion accelerators tend to be huge in size and cost. In this paper, a future intense-laser ion accelerator is discussed to make the laser-based ion accelerator compact and controllable. The issues in the laser ion accelerator include the energy efficiency from the laser to the ions, the ion beam collimation, the ion energy spectrum control, the ion beam bunching, and the ion particle energy control. In the study, each component is designed to control the ion beam quality by particle simulations. The energy efficiency from the laser to ions is improved by using a solid target with a fine sub-wavelength structure or a near-critical-density gas plasma. The ion beam collimation is performed by holes behind the solid target or a multi-layered solid target. The control of the ion energy spectrum and the ion particle energy, and the ion beam bunching are successfully realized by a multi-stage laser–target interaction.

Electron gun jitter effects on beam bunching

For routine operation of Beijing Electron Positron Collider II (BEPCII) linac, many factors may affect the beam bunching process directly or indirectly. We present the measurements and analyses of the gun timing jitter, gun high voltage jitter, and beam energy at the exit of the standard acceleration section of the linac quantitatively. Almost 80 mV and more than 200 ps of gun high voltage and time jitters have ever been measured, respectively. It was analyzed that the gun timing jitter produced severe effects on beam energy than the gun high voltage jitter, if the timing jitter exceeded 100 ps which eventually deteriorates both the beam performance and the injection rate to the storage ring.

TURN-BY-TURN BEAM EXTRACTION DURING ACCELERATION IN A SYNCHROTRON

A synchrotron to accelerate protons or carbon ions for medical applications is being designed at Brookhaven National Laboratory (BNL). Single beam bunches with maximum beam energy of 1.18 GeV and 400 MeV/u for protons and carbon ions respectively will be extracted from the synchrotron at 15 Hz. For protons, the maximum required energy for irradiating a tumor is ∼206 MeV. A pencil-like proton beam containing ∼5.4×107 p/bunch delivers a therapeutic dose of 2.5 Gy in ∼1.5 minutes to treat a tumor of 1 liter volume. It will take ∼80 minutes with bunches containing 4.5×104 ions/bunch to deliver the same dose of 2.5 Gy with a 400 MeV/u pencil-like carbon beam. This extended treatment time when using carbon ions is not acceptable. In addition, the synchrotron cannot be controlled with a beam bunch containing such a low number of carbon ions. To overcome these two problems of the extended treatment time and the low bunch intensity required for the treatment when carbon ions are used, we have devised a method to “peel” the required 4.5×104 carbon-ions/bunch from the accelerating carbon beam bunch containing ∼108 ions/bunch and deliver them to the tumor on a “turn-by-turn” basis. Unlike other methods of beam extraction from a synchrotron, such as resonance extraction, this method does not allow for any beam losses during the extraction and the carbon beam can be peeled off in less than 15 ms during the acceleration or deceleration cycle of the synchrotron. Thus, this turn-by-turn beam extraction method provides beam with variable energy and precisely controlled beam current during the 30 ms acceleration or deceleration time.

First results from the CRIS experiment

The ability to study rare isotopes with techniques such as mass spectrometry and laser spectroscopy is often prevented by low production rates and large isobaric contamination. This has necessitated the development of novel beam cleaning techniques that can efficiently isolate the isotope of interest. The Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE, achieves this by resonantly ionizing a bunched atom beam in a region of ultra high vacuum. This method is motivated by the need to measure the hyperfine structure and isotope shift at the extremes of isospin where typical production rates drop to 1 atom/s. The technique also offers the ability to purify an ion beam and even select long-lived isomeric states (> 1 ms) from the ground state, which can be subsequently studied by decay spectroscopy or mass spectrometry experiments. This paper will report on the successful commissioning of the CRIS beam line and the recent laser spectroscopy results and laser assisted nuclear decay spectroscopy on the neutron deficient francium isotopes.

Upgrade of a kicker control system for the HIRFL

A kicker system plays an important role in beam extraction and injection for a ring-like accelerator. The kicker system in the Heavy Ion Research Facility in Lanzhou (HIRFL) is used for beam extraction and injection between two cooling storage rings (CSRs). The system consists of two parts: one part is used for beam extraction from the CSR/main (CSRm), and the other is used for beam injection into the CSR/experimental (CSRe). To meet the requirements of special physics experiments, we upgraded the kicker control system. In this upgraded system, the position of the beam bunches can be determined by measuring the phase of the radio frequency (RF) signal in real time because each beam bunch is synchronized with the RF signal. The digital timing control and delay regulatory function, which are based on a new design using ARM+DSP+FPGA technology, achieved a precision of 2.5ns, which is a significant improvement over old system's precision of 5ns. In addition, this system exhibits a better anti-interference capability. Moreover, the efficiency of beam extraction can be enhanced, and the accuracy of the reference voltage setting can reach as low as 0.1%, compared to 2% for the old system.

Measurements of aperture and beam lifetime using movable beam scrapers in Indus-2 electron storage ring

In this paper, the measurements of vertical and horizontal aperture which are available for stable beam motion in Indus-2 at beam energy 2.5 GeV using movable beam scrapers are presented. These beam scrapers are installed in one of the long straight sections in the ring. With the movement of beam scrapers towards the beam centre, the beam lifetime is measured. The beam lifetime data obtained from the movement of vertical and horizontal beam scrapers are analyzed. The contribution of beam loss due to beam-gas scattering (vacuum lifetime) and electron-electron scattering within a beam bunch (Touschek lifetime) is separated from the measured beam lifetime at different positions of the beam scrapers. Vertical and horizontal beam sizes at scrapers location are estimated from the scraper movement towards the beam centre in quantum lifetime limit and their values closely agree with measured value obtained using X-ray diagnostic beamline.

Transformer ratio studies for single bunch plasma wakefield acceleration

In Plasma Wakefield Acceleration (PWFA) plasma oscillations are driven by ultra relativistic electron beams. The ratio of the maximum accelerating field behind the driving beam (bunch) and the maximum decelerating field inside the driving beam (bunch) is defined as Transformer Ratio, a key parameter that determines the energy gain in particle acceleration. We investigate the transformer ratio for different shapes of a single driving bunch. One dimensional, fluid, relativistic, cold plasma equations have been numerically solved. A complete map of the transformer ratio is obtained by varying: bunch shape, bunch length and density ratio. It is found that the transformer ratio critically depends on the bunch shape and on the density ratio. Moreover both in the linear as well as in the non-linear regime the theoretical limit of 2 for the transformer ratio of a single symmetric bunch can be exceeded using asymmetric bunches in the linear regime as well as symmetric bunches in nonlinear regime.

Beam ion instability: Measurement, analysis, and simulation

A weak vertical coupled-bunch instability with oscillation amplitude of the order of a few $\ensuremath{\mu}\mathrm{m}$ has been observed in SPEAR3 at nominal vacuum pressure. The instability becomes stronger with increasing neutral gas pressure as observed by turning off vacuum pumps, and becomes weaker when the vertical beam emittance is increased. These observations indicate that the vertical beam motion is driven by ions trapped in the periodic potential of the electron beam. In this paper we present a series of comprehensive beam measurements, impedance-based stability analysis, and numerical simulations of beam-ion interactions in SPEAR3. The effects of vacuum pressure, gas species, beam current, bunch fill pattern, chromaticity, and vertical beam emittance are investigated.

Double negative-metamaterial based Terahertz radiation excited by a sheet beam bunch

We describe a new method to generate enhanced terahertz (THz) surface wave (SW) via its coupling with reversed Cherenkov radiation (RCR), excited by a sheet beam bunch which travels in a vacuum above an isotropic double negative metamaterial (DNM). The physical mechanism for the enhancement is that the DNM can support a RCR which can resonantly interact with a sheet electron beam bunch, resulting in an enhanced SW due to its coupling with the enhanced RCR. Numerical results show strong enhancement effect for the SW and RCR in the THz band. This enhanced THz radiation has potential applications to high-power THz radiation sources and Cherenkov detectors which require large signals.

Online monitoring of beam phase and intensity using lock-in amplifiers

We have developed a monitoring system dedicated for heavy-ion cyclotrons that incorporates lock-in amplifiers (LIAs) that can measure the beam phase of signals from phase probe with an amplitude of a few hundred nanovolts. We have compared the performance of the LIA system with that of a conventional system that incorporates oscilloscopes (OSCs). It was confirmed that the LIA system has a much higher precision than the OSC system by the measurement with a wide dynamic range of beam current. Isochronism measurements for a ring cyclotron with a low velocity gain (1.5) were made using both systems and excellent agreement was found between them. However there was a discrepancy between the beam phase measurements using the OSC system and the LIA system, for the case of a ring cyclotron with a high velocity gain of 4.0. It turned out due to a large radial variation of the phase width of circulating beam bunch according to a radial distribution of the acceleration voltage. It was also confirmed that the cable dispersion disturbs the beam-phase measurement using OSC system.

A possible scheme of electron beam bunching in laser plasma accelerators

A possible scheme for increasing the injection efficiency in laser plasma accelerators is proposed. It allows an improvement of both the number of captured electrons and the energy spread. The operation in linear regime is discussed. The plasma channel is divided into two stages: the modulating stage with a variable plasma density for pre-bunching the beam and the accelerating stage with a constant plasma density. The variation of the plasma density in the bunching stage and the matching between the stages are discussed.

Numerical modeling of multi-GeV laser wakefield electron acceleration inside a dielectric capillary tube

Numerical modeling of laser wakefield electron acceleration inside a gas filled dielectric capillary tube is presented. Guiding of a short pulse laser inside a dielectric capillary tube over a long distance (∼1 m) and acceleration of an externally injected electron bunch to ultra-relativistic energies (∼5-10 GeV) are demonstrated in the quasi-linear regime of laser wakefield acceleration. Two dimensional axisymmetric simulations were performed with the code WAKE-EP (Extended Performances), which allows computationally efficient simulations of such long scale plasma. The code is an upgrade of the quasi-static particle code, WAKE [P. Mora and T. M. Antonsen, Jr., Phys. Plasmas 4, 217 (1997)], to simulate the acceleration of an externally injected electron bunch (including beam loading effect) and propagation of the laser beam inside a dielectric capillary. The influence of the transverse electric field of the plasma wake on the radial loss of the accelerated electrons to the dielectric wall is investigated. The stable acceleration of electrons to multi-GeV energy with a non-resonant laser pulse with a large spot-size is demonstrated.

Effect of nonlinear radiofrequency electromagnetic fields on theemittance of bunched beams

Gap transformations are frequently used in ion Linac codes, to efficientlydescribe the particle dynamics. Using similar approach, we analyze theuniformly bunched beam passing through an axis-symmetric radiofrequency (RF)cavity. The method can be used for other distributions as well using asimilar six dimensional analysis. The effect of non-linear RF field inradial and axial directions in an RF cavity and the finite phase width ofthe bunch, on the transverse and longitudinal emittance growth have beenstudied. The expressions obtained have been verified for the two types ofcavity cells namely the zero mode DTL and pi mode CCL type used frequentlyin ion linacs. The results are seen to be valid for the entire maximum phaseacceptance up to 360 degrees. Simulations with the equivalent beams ofnon-uniform distributions namely Waterbag and Gaussian show that atsynchronous phases closer to the wave crest, the results give a goodapproximation of emittance growth in both planes for non-uniform beams.

A measurement of the energy and timing resolution of the GlueX Forward Calorimeter using an electron beam

The performance of the GlueX Forward Calorimeter was studied using a small version of the detector and a variable energy electron beam derived from the Hall B tagger at Jefferson Lab. For electron energies from 110MeV to 260MeV, which are near the lower-limits of the design sensitivity, the fractional energy resolution was measured to range from 20% to 14%, which meets the design goals. The use of custom 250MHz flash ADCs for readout allowed precise measurements of signal arrival times. The detector achieved timing resolutions of 0.38ns for a single 100mV pulse, which will allow timing discrimination of photon beam bunches and out-of-time background during the operation of the GlueX detector.

Laser ion acceleration toward future ion beam cancer therapy - Numerical simulation study -.

Ion beam has been used in cancer treatment, and has a unique preferable feature to deposit its main energy inside a human body so that cancer cell could be killed by the ion beam. However, conventional ion accelerator tends to be huge in its size and its cost. In this paper a future intense-laser ion accelerator is proposed to make the ion accelerator compact. An intense femtosecond pulsed laser was employed to accelerate ions. The issues in the laser ion accelerator include the energy efficiency from the laser to the ions, the ion beam collimation, the ion energy spectrum control, the ion beam bunching and the ion particle energy control. In the study particle computer simulations were performed to solve the issues, and each component was designed to control the ion beam quality. When an intense laser illuminates a target, electrons in the target are accelerated and leave from the target; temporarily a strong electric field is formed between the high-energy electrons and the target ions, and the target ions are accelerated. The energy efficiency from the laser to ions was improved by using a solid target with a fine sub-wavelength structure or by a near-critical density gas plasma. The ion beam collimation was realized by holes behind the solid target. The control of the ion energy spectrum and the ion particle energy, and the ion beam bunching were successfully realized by a multi-stage laser-target interaction. The present study proposed a novel concept for a future compact laser ion accelerator, based on each component study required to control the ion beam quality and parameters.

A nanoradian x-ray beam deviation-correction device for x-ray free electron laser oscillator

An energy-recovery linac (ERL)-based x-ray free electron laser (X-FEL) combined with a low-loss x-ray optical cavity can produce a high-intensity and fully coherent x-ray beam. The idea is to let the x-ray emission beam in the cavity become the seed beam of the FEL to realize x-ray stimulated emission conditions. Because the electron bunch size in the ERL is sub-micrometer and the x-ray cavity crystals are a few tens of meters away from the electron bunch, a deviation of a few nanoradians in the beam direction can cause the seed beam miss the electron bunches. Therefore, it is necessary to develop a high-precision beam-direction correction device that is independent of the x-ray cavity tuning to ensure collision of the narrow x-ray seed beam and electron bunches. To this end, we have assembled a pair of x-ray prisms on two rotary stages. We operated the device using 1.086 Å wavelength x-rays and demonstrate that the angular resolution can reach 1 nrad within a deviation range of ±3.1 mrad.

Neutrino speed: a report on the [formula omitted] speed measurements of the BOREXINO, ICARUS and LVD experiments with the CNGS beam

We report the measurement of the speed of muon neutrinos performed by the Borexino, ICARUS and LVD experiments, using narrow bunch CNGS neutrino beams with an average energy E = 17 GeV and a baseline of ∼ 730 km between Cern and Laboratori Nazionali del Gran Sasso (LNGS). The final result for the difference in time-of-flight between such muon neutrinos and a particle moving at the speed of light in vacuum is δt=0.8±0.7stat±2.9sys ns for Borexino, δt=−0.1±0.7stat±2.7sys ns for ICARUS and δt=−0.3±0.6stat±3.2−sys ns for LVD, well consistent with zero.

Analytical expressions of transfer functions for a hard edge dipole magnet using a basic geometrical approach

In charged particle accelerators, higher order optics studies become important from various points of view, such as dynamic aperture, emittance dilution, beam loss, etc. For some new applications, nonlinear study has become important in single pass optics also. For studying the higher order optics, each magnetic element is represented by a higher order transfer function (map, i.e., a function that relates output coordinates of a trajectory with initial coordinates and momentum deviation). Here in this paper we have provided an alternate method to obtain the analytical formulation of the transfer function for a dipole magnet. This formulation is obtained on the basis of basic geometrical analysis and is exact up to all orders under hard edge approximation. Being an analytical expression, the estimation of higher order effects of dipole magnet can be studied quickly. For checking the correctness of this formulation, we separated terms up to third order, which can be used to obtain the standard transfer matrices up to same order. An example of emittance growth and bunch length modification for a $C$-chicane-type electron beam bunch compressor is provided using the analytical expression.

The Automatic and Real Time Measurement of Tunnel Surrounding Rock Deformation

We designed a tunnel surrounding rock(TSR) deformation automatic and real time measurement system .The long distance laser datum line instrument (LDLI) is fixed in stable ceiling rock of the tunnel. The LDLI transmits a bunch of lateral linear benchmark beam with small facula, and projects to the linear array CCD which mounted on instable surrounding rock. The linear array CCD detected the facula centre position real time. The facula displacement within a period is equal to the displacement of instable rock. We used the wireless data transmission module and optical fiber transceiver to transfer the displacement data to the on duty room computer. We compiled the data processing software to display the measure result in graphical and give a judge for the instable surrounding rock. If it is in danger, the alarm module gives audible and visible alarm signal in site and send a message to the manager’s mobile phone. The measurement accuracy is less than 1mm. We used this system to measure the tunnel surrounding rock deformation automatically and real time to realize intelligent management in several tunnel