Proton Bunch Research Articles

Hundreds MeV monoenergetic proton bunch from interaction of 1020–21 W/cm2 circularly polarized laser pulse with tailored complex target

A complex target (CT) configuration tailored for generating high quality proton bunch by circularly polarized laser pulses at intensities of 1020-21 W/cm2 is proposed. Two-dimensional particle-in-cell simulations show that both the collimation and mono-energetic qualities of the accelerated proton bunch obtained using a front-shaped thin foil can be greatly enhanced by the backside inhomogeneous plasma layer. The main mechanisms for improving the accelerated protons are identified and discussed. These include stabilization of the photon cavity, providing hole-boring supplementary acceleration and suppressing the thermal-electron effects. A theory for tailoring the CT parameters is also presented.

Selection Tests of MnZn and NiZn Ferrites for Mu2e 300 kHz and 5.1 MHz AC Dipoles

Mu2e, a charged lepton flavor violation (CLFV) experiment is planned to start at Fermilab late in this decade. The proposed experiment will search for neutrinoless muon to electron conversions with unprecedented sensitivity, better than at 90% CL. To achieve this sensitivity the incoming proton beam must be highly suppressed during the window for detecting the muon decays. The current proposal for beam extinction is based on a collimator design with two dipoles running at 300 kHz and 5.1 MHz and synchronized to the proton bunch spacing. The appropriate choice of ferrite material for the magnet yoke is a critical step in the overall design of the dipoles and their reliable operation at such high frequencies over the life of the experiment. This choice, based on a series of the thermal and magnetic measurements of the ferrite samples, is discussed in the paper. Additionally, the first results from the testing at 300 kHz of a prototype AC dipole are presented.

Energy enhancement of quasi-monoenergetic proton bunches using a slice-cone target

A slice-cone target is proposed for the generation of quasi-monoenergetic proton bunches. In this new target structure, two symmetrical solid slices are adjoined obliquely to the tip of a hollow cone. Two-dimensional particle-in-cell simulations show that a large number of hot electrons are pulled out from the solid slices and accelerated forward by direct laser acceleration. Compared with the hollow cone target, a stronger electrostatic field at the rear surface of the slice-cone tip is set up by the hot electrons from the cone and the slices. As a result, the energy of the quasi-monoenergetic proton bunch produced through the target-normal sheath acceleration mechanism can be improved by 75%. It shows that the proton energy scales proportional to the square root of the laser intensity. For the incident laser with the focused intensity about 5 × 1020 W/cm2, one can obtain proton bunches with central energy 165 MeV and energy spread 13%.

A 6 kV arbitrary waveform generator for the Tevatron Electron Lens

This paper reports on a 6 kV modulator built and installed at Fermilab to drive the electron gun anode for the Tevatron Electron Lens (TEL). The TEL was built with the intention of shifting the individual (anti)proton bunch tunes to even out the tune spread among all 36 bunches with the desire of improving Tevatron integrated luminosity. This modulator is essentially a 6 kV arbitrary waveform generator that enables the TEL to define the electron beam intensity on a bunch-by-bunch basis. A voltage waveform is constructed having a 7 μs duration that corresponds to the tune shift requirements of a 12-bunch (anti)proton beam pulse train. This waveform is played out for any one or all three bunch trains in the Tevatron. The programmed waveform voltages transition to different levels at time intervals corresponding to the 395 ns bunch spacing. Thus, complex voltage waveforms can be played out at a sustained rate of 143 kHz over the full 6 kV output range. This paper describes the novel design of the inductive adder topology employing five transformers. It describes the design aspects that minimize switching losses for this multi-kilovolt, high repetition rate and high duty factor application.

Use of multiframe proton radiography to investigate fast hydrodynamic processes

This paper gives the results of investigation of fast hydrodynamic processes by flash proton radiography based on the U-70 proton synchrotron of the Institute of High Energy Physics (IHEP). The physical setup for proton radiography with a maximum energy of the proton bunch up to 70 GeV and intensity up to 1.5 · 1013 protons per cycle records up to 29 frames in one projection with the minimum interframe time interval of 165 nsec. At present, the recording area is ≈60 mm in diameter, with the prospect of increasing to 250 mm. The duration of the proton bunches equals 20–30 nsec and can be reduced to 10–15 nsec. Since 2004 and up to now, the Russian Federal Nuclear Center-Institute of Experimental Physics (RFNC-VNIIEF), together with IHEP, have performed static and dynamic experiments on this setup to study: the initiation and propagation of detonation in condensed explosives, shockwave propagation in inert materials; hydrodynamic instabilities in metals; dynamic deformation and fracture of liners and plates; spall fracture; the formation of shaped-charge jets and their interaction with obstacles; other applications of physics of the explosion. The proton radiography complex based on the U-70 accelerator and designed by researchers of RFNC-VNIIEF and IHEP is a unique tool for studying fast processes. The method of proton radiography opens up new opportunities for Russian researchers: multiframe recording, almost unlimited thickness of the objects studied, high spatial resolution, enormous dynamic recording range.

Plasma wakefield acceleration with a modulated proton bunch

The plasma wakefield amplitudes which could be achieved via the modulation of a long proton bunch are investigated. We find that in the limit of long bunches compared to the plasma wavelength, the strength of the accelerating fields is directly proportional to the number of particles in the drive bunch and inversely proportional to the square of the transverse bunch size. The scaling laws were tested and verified in detailed simulations using parameters of existing proton accelerators, and large electric fields were achieved, reaching 1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found in this case.

Measurement of DNA Double-Strand Break Yield in Human Cancer Cells by High-Current, Short-Duration Bunches of Laser-Accelerated Protons

To investigate the radiobiological effects of high dose rates that are attributed to high current, short bunch beam generation with laser-dreven ion acceleration, we have developed an experimental setup that uses laser-accelerated protons. In-vitro human lung cancer cells: A549 pulmonary adenocarcinoma are irradiated with a laser-accelerated proton bunches with a duration of 2×10-8 s and flux of ∼1015 cm-2 s-1, amounting to single bunch absorbed dose at the 1 Gy level. The double-strand break (DSB) yield in cell DNA is analyzed for the laser-accelerated proton beam at an average LET of 41 keV/µm.

Measurement of DNA Double-Strand Break Yield in Human Cancer Cells by High-Current, Short-Duration Bunches of Laser-Accelerated Protons

Measurement of DNA Double-Strand Break Yield in Human Cancer Cells by High-Current, Short-Duration Bunches of Laser-Accelerated Protons

High-quality proton bunch from laser interaction with a gas-filled cone target

Generation of high-energy proton bunch from interaction of an intense short circularly polarized (CP) laser pulse with a gas-filled cone target (GCT) is investigated using two-dimensional particle-in-cell simulation. The GCT target consists of a hollow cone filled with near-critical gas-plasma and a thin foil attached to the tip of the cone. It is observed that as the laser pulse propagates in the gas-plasma, the nonlinear focusing will result in an enhancement of the laser pulse intensity. It is shown that a large number of energetic electrons are generated from the gas-plasma and accelerated by the self-focused laser pulse. The energetic electrons then transports through the foil, forming a backside sheath field which is stronger than that produced by a simple planar target. A quasi-monoenergetic proton beam with maximum energy of 181 MeV is produced from this GCT target irradiated by a CP laser pulse at an intensity of 2.6 × 1020 W/cm2, which is nearly three times higher compared to simple planar target (67 MeV).

Wake waves generated by a proton bunch in an electron-positron-ion plasma

A nonlinear 1D model of longitudinal wake waves generated in a relativistic epi plasma by an ultrarelativistic modulated proton bunch is developed. The model is used for constructing the score of concentration profiles of the concentrations of the plasma component in the wake wave. It is shown that the wave period increases with the concentration of the ion component of the plasma and with the proton bunch density.

High-energy monoenergetic protons from multistaged acceleration of thin double-layer target by circularly polarized laser

Multistaged acceleration of solid-density thin foils by ultraintense circularly polarized laser pulse is investigated. A stable radiation pressure acceleration (RPA) stage is first established. Higher dimensional effects such as transverse instabilities and enhanced electron heating then gradually make the initially opaque foil transparent to the laser light. Accordingly, the dominant acceleration mechanism changes smoothly from RPA to target normal sheath acceleration (TNSA). The transition can therefore enhance the maximum energy of the accelerated ions but broaden their energy spectrum. For a double-layer target, however, the light ions (protons) in the backlayer can be efficiently accelerated in the RPA and TNSA regimes nearly monoenergetically. Two-dimensional particle-in-cell simulations show that with this scheme a circularly polarized laser pulse of peak intensity 3.9×1022 W/cm2 can produce a collimated proton bunch that persists for many Rayleigh lengths and its peak energy can reach 4.2 GeV with FWHM of 200 MeV.

An LHCb general-purpose acquisition board for beam and background monitoring at the LHC

In this paper we will present an LHCb custom-made acquisition board which was developed for a continuous beam and background monitoring during LHC operations at CERN. The paper describes both the conceptual design and its performance, and concludes with results from the first period of beam operations at the LHC.The main purpose of the acquisition board is to process signals from a pair of beam pickups to continuously monitor the intensity of each bunch, and to monitor the phase of the arrival time of each proton bunch with respect to the LHC bunch clock. The extreme versatility of the board also allowed the LHCb experiment to build a high-speed and high-sensitivity readout system for a fast background monitor based on a pair of plastic scintillators.The board has demonstrated very good performance and proved to be conceptually valid during the first months of operations at the LHC. Connected to the beam pickups, it provides the LHCb experiment with a real-time measurement of the total intensity of each beam and of the arrival time of each beam at the LHCb Interaction Point. It also monitors the LHC filling scheme and the beam current per bunch at a continuous rate of 40 MHz, and assures a proper global timing of LHCb. The continuous readout of the scintillators at bunch clock speed provides the LHCb experiment with high-resolution information about the beam halo and fast losses during both injection and circulating beam. It has also provided valuable information to the LHC during machine commissioning with beam. Recent results also shows that it could contribute as a luminosity monitor independent from the LHCb experiment readout system.Beam, background and luminosity measurements are continuously fed back to the LHC in the data exchange framework between the experiments and the LHC machine aimed at improving efficiently the experimental conditions real-time.

Development of laser-driven quasi-monoenergetic proton beam line for radiobiology

Abstract We report the development of a laser-driven quasi-monoenergetic proton beamline for the purpose of cell samples irradiation. Laser pulses are focused to an intensity of 5 × 10 19 W / cm 2 onto a polyimide foil target of 7.5 − μ m thickness. The emitted proton spectrum is continuous up to a maximum energy of 4 MeV. Energy selection for transport to cancer cells is determined by four pairs of dipole magnets, which consists of a pair of permanent magnets generating a central magnetic field of 0.78 T. Protons are steered by the first magnetic field, and again by the second one, such that transmitted proton trajectories in the middle of the four dipoles are shifted laterally from the target normal axis by an energy-dependent displacement. Proton energy is selected by a pinhole in this middle plane and subsequently steered downstream by the other two dipole magnets. We have obtained 2.25 MeV proton beams with an energy spread of 0.66 MeV (FWHM) and single bunch duration of 20 ns. The dose given in a single proton bunch was 0.2 Gy, hence, the single bunch dose rate is estimated to be 107 Gy/s. At the 1 Hz repetition-rate cell samples were irradiated with successive proton bunches with integrated dose levels up to 8 Gy.

Plasma wakefield excitation with a 24 GeV proton beam

Proton driven plasma wakefield acceleration has recently been proposed as a means of generating high energy electron beams. In this paper, different options for a demonstration experiment with the CERN PS beam are considered. We review a possible magnetic compression of the PS bunches and resulting electric fields in the plasma. Results are then presented for self-modulation of the proton bunch for different plasma densities and lengths. It is found that the latter option offers interesting possibilities for a first experiment.

Quasimonoenergetic Proton Bunch Generation by Dual-Peaked Electrostatic-Field Acceleration in Foils Irradiated by an Intense Linearly Polarized Laser

It is found that stable proton acceleration from a thin foil irradiated by a linearly polarized ultraintense laser can be realized for appropriate foil thickness and laser intensity. A dual-peaked electrostatic field, originating from the oscillating and nonoscillating components of the laser ponderomotive force, is formed around the foil surfaces. This field combines radiation-pressure acceleration and target normal sheath acceleration to produce a single quasimonoenergetic ion bunch. A criterion for this mechanism to be operative is obtained and verified by two-dimensional particle-in-cell simulation. At a laser intensity of ∼5.5×10(22) W/cm(2), quasimonoenergetic GeV proton bunches are obtained with ∼100 MeV energy spread, less than 4° spatial divergence, and ∼50% energy conversion efficiency from the laser.

Stable Laser-Driven Proton Beam Acceleration from a Two-Ion-Species Ultrathin Foil

By using multidimensional particle-in-cell simulations, we present a new regime of stable proton beam acceleration which takes place when a two-ion-species shaped foil is illuminated by a circularly polarized laser pulse. In the simulations, the lighter protons are nearly instantaneously separated from the heavier carbon ions due to the charge-to-mass ratio difference. The heavy ion layer expands in space and acts to buffer the proton layer from the Rayleigh-Taylor-like (RT) instability that would have otherwise degraded the proton beam acceleration. A simple three-interface model is formulated to explain qualitatively the stable acceleration of the light ions. In the absence of the RT instability, the high quality monoenergetic proton bunch persists even after the laser-foil interaction ends.

Ultraintense ion beams driven by a short-wavelength short-pulse laser

The results of particle-in-cell simulations are reported which demonstrate that a short-wavelength (λ≤0.5 μm) short-pulse laser driver can produce much more intense ion beams than the commonly used long-wavelength (λ∼1 μm) ones. In particular, such a driver allows for efficient generation of ultrashort (≤100 fs), multi-MeV proton bunches of extremely high intensities (>1021 W/cm2) and current densities (>1014 A/cm2) even at moderate values of dimensionless laser amplitude a0≤10.

Self-Modulation Instability of a Long Proton Bunch in Plasmas

An analytical model for the self-modulation instability of a long relativistic proton bunch propagating in uniform plasmas is developed. The self-modulated proton bunch resonantly excites a large amplitude plasma wave (wakefield), which can be used for acceleration of plasma electrons. Analytical expressions for the linear growth rates and the number of exponentiations are given. We use full three-dimensional particle-in-cell (PIC) simulations to study the beam self-modulation and transition to the nonlinear stage. It is shown that the self-modulation of the proton bunch competes with the hosing instability which tends to destroy the plasma wave. A method is proposed and studied through PIC simulations to circumvent this problem, which relies on the seeding of the self-modulation instability in the bunch.

Studies of back-streaming white neutrons at CSNS

Back-streaming neutrons through the incoming proton channel at the spallation target station of China Spallation Neutron Source (CSNS) are harmful to the proton beam line and should be dealt with carefully. On the other hand, those back-streaming neutrons may be useful for other applications. This paper presents preliminary studies on the characteristics of the neutrons, which have a very wide energy spectrum (white neutrons) and are very suitable for nuclear data measurements. The corresponding yields and time structures of the neutrons in the energy range of 1eV to 1MeV from a tungsten target for a proton beam of 1.6GeV in energy and 63μA in average current have been simulated. From the simulation results, one can obtain an uncollimated neutron flux of around 2.0×105n/cm2/pulse within the given energy range at 80m away from the target, which accounts for about 53% of the total neutrons. The time resolution of 0.3–0.9%, which is important for the time-of-flight method, is obtained for both the parasite operation mode with two proton bunches and the dedicated operation mode with a single proton bunch.

Simulation of Laser-Accelerated Proton Focusing and Diagnosis with a Permanent Magnet Quadrupole Triplet

(Received 10 January 2010 /Accepted 19 January 2010)The Monte Carlo Particle and Heavy Ion Transport code (PHITS) was used for diagnosing the focusingand defocusing action of a triplet of permanent magnet quadrupoles on laser-accelerated proton bunches of shortduration. ThecodepredictsreasonablywelltheobservedtransversebeamprofileasmeasuredwithaCR-39trackdetector demonstrating that PHITS can be used to simulate proton bunch transport by conventional ion optics inthe laser-driven case.