Proton Linac Research Articles

Tuning of RF amplitude and phase for the separate-type drift tube linac in J-PARC

It is important to accurately adjust the amplitude and the phase of RF power sources for a high intensity proton linac. J-PARC (Japan proton accelerator research complex) linac is one of those high-intensity linacs. J-PARC linac has 30 SDTL (separate-type drift tube linac) tanks to accelerate the negative hydrogen ions from 50 to 181 MeV. Two neighboring SDTL tanks are driven by one klystron, where the phase and the amplitude of these two tanks are controlled in terms of the vector sum. The target-value of the vector sum control should be determined with a beam-based tuning for each klystron. During the beam commissioning, the RF tuning has been performed with a phase scan method introducing a concept of phase signature matching. In the tuning, the output beam energy from the SDTL module is monitored while scanning the RF phase. Comparing the obtained phase dependence of the output beam energy with those from a numerical model, the target-values for the low-level RF control system has been tuned within the required accuracy of 1° in phase and 1% in amplitude. The same tuning procedure has successfully been applied to the RF tuning of buncher and debuncher cavities.

Emittance dilution due to the betatron mismatch in high-intensity hadron accelerators

The importance of the betatron mismatch between two sections of an accelerator complex was recognized a long time ago. The mismatch together with the filamentation effect will result in a larger diluted beam emittance. However, the influence of the mismatch was underestimated largely in high-intensity hadron synchrotrons in the literature, as the rms emittance is used to represent the dilution. The dilution on the total emittance is significantly larger, which is of more importance in representing the beam loss in proton synchrotrons. This article points out the necessity of using the dilution factor of the total emittance together with the rms emittance in high-intensity hadron accelerators. A proof is given to show that the dilution factor of the rms emittance is the same for any initial beam distribution. The detailed beam distribution after the dilution is discussed for the initial uniform, Gaussian and parabolic distributions, and the numerical simulation results are presented. Examples and discussions about the betatron mismatch in the cases of injection, FODO channel transporting mixed H − and proton beams, fast-changing periodic focusing systems and proton linacs of a large tune depression are also presented.

Possibility of radionuclide production for PET diagnostics and brachyteraphy on the INR RAS linac

The technology of radionuclide production for positron-emission tomography on the proton linac of the Institute for Nuclear Research, Russian Academy of Sciences, is considered. A prototype of a combined target unit for production of positron-emitting radionuclides 11C, 13N, and 18F in the proton linac beam is presented. The production of medical isotopes 103Pd, 124, 125I, and 131Cs is briefly discussed.

PLANS for upgrading the CERN proton accelerator complex

With the construction of the Large Hadron Collider (LHC) in its final phase at CERN, it is now time to prepare for increasing its performance as much as possible and for preparing for the future needs of physics. A basic plan has been proposed by the working group on ‘Proton Accelerators of the Future’, using the input from an ad'hoc physics working group looking after ‘Physics Opportunities with Future Proton Accelerators’. Apart from upgrades in the LHC itself, mainly in the optics of the insertions, the proposal is to renew the injector complex and significantly improve its characteristics. In a first phase, a new 160 MeV H− linac (Linac4) will be built to replace the present 50 MeV proton linac (Linac2) and extensive consolidation will be made. In a second phase, the present 26 GeV PS and its set of injectors (Linac2 + PSB) are planned to be replaced with a ∽50 GeV synchrotron (PS2) with a ∽4 GeV superconducting proton linac (SPL) as injector. The SPS itself will be upgraded for injection at 50 GeV and for better performance with high brightness beams. These proposals will be described as well as their potential for other uses like a neutrino facility.

Beam Loading Effect and Its Compensation in the PEFP Proton Linac

Beam Loading Effect and Its Compensation in the PEFP Proton Linac

Development of an all-permanent-magnet microwave ion source equipped with multicusp magnetic fields for high current proton beam production

An all-permanent-magnet (APM) microwave hydrogen ion source was developed to reduce the size and to simplify structure of a conventional solenoid coil microwave ion source developed for reliability improvement of high current proton linac application systems. The difficulty in developing the APM source was sensitive dependence of the source performance on axial magnetic field in the microwave discharge chamber. It was difficult to produce high current proton beam stably without precise tuning of the magnetic field using solenoid coils. We lowered the sensitivity using multicusp magnetic fields for plasma confinement at the discharge chamber sidewall of the source. This enabled stable high current proton beam production with the APM microwave ion source with no tuning coil. The water cooling and the power supply for the coils are not necessary for the APM source, which leads to better reliability and system simplification. The outer diameter of the APM source was around 300 mm, which was 20% lower than the coil source. The APM source produced a maximum hydrogen ion beam current of 65 mA (high current density of 330 mA/cm(2), proton ratio of 87%, and beam energy of 30 keV) with a 5 mm diameter extraction aperture, pulse width of 400 micros, and 20 Hz repetition rate at 1.3 kW microwave power. This performance is almost the same as the best performances of the conventional coil sources. The extracted ion beams were focused with electrostatic five-grid lens to match beam to acceptance of radio-frequency quadrupole linacs. The maximum focused beam current through the orifice (5 mm radius) and the lens was 36 mA and the 90% focused beam half-width was 1-2 mm.

Test results of the proton injector of the Proton Engineering Frontier Project accelerator

One of the goals of the Proton Engineering Frontier Project (PEFP) is to develop a 100 MeV proton accelerator. As a low energy part, a 20 MeV proton linac has been developed and tested. The 20 MeV accelerator consists of a 50 keV proton injector, a 3 MeV radio frequency quadrupole, and a 20 MeV drift tube linac. The proton injector includes a duoplasmatron type ion source and a low energy beam transport. After a preliminary test with 1 mA peak current of the 20 MeV accelerator, the proton injector was modified with the goal of increasing the 20 MeV beam current up to 20 mA peak value. The modifications include the reduction of the proton injector length, installation of a beam current monitor, and electron trap and supplement of the solenoid and steering magnets. In this paper, the modifications of the PEFP proton injector are described and initial test results are presented.

Spatial and temporal beam profile monitor with nanosecond resolution for CERN's Linac4 and Superconducting Proton Linac

The Linac4, now being developed at CERN, will provide 160-MeV H - beams of high intensity N = 2 × 10 14 ions s - 1 . Before this beam can be injected into the CERN Proton Synchrotron Booster or future Superconducting Proton Linac for further acceleration, some sequences of 500-ps-long micro-bunches must be removed from it, using a beam chopper. These bunches, if left in the beam, would fall outside the longitudinal acceptance of the accelerators and make them radioactive. We developed a monitor to measure the time structure and spatial profile of this chopped beam, with respective resolutions Δ t ∼ 1 ns and Δ x ∼ 2 mm . Its large active area 40 mm × 40 mm and dynamic range also allows investigations of beam halos. The ion beam first struck a carbon foil, and secondary electrons emerging from the foil were accelerated by a series of parallel grid electrodes. These electrons struck a phosphor screen, and the resulting image of the scintillation light was guided to a thermoelectrically cooled, charge-coupled device camera. The time resolution was attained by applying high-voltage pulses of sub-nanosecond rise and fall times to the grids. The monitor has been tested with 700-ps-long UV laser pulses, and a 3-MeV proton beam. Its response over a wide range of beam intensities between N e ∼ 5 and 4 × 10 8 electrons emitted from the foil per pulse was studied. The monitor can also be used to measure the profiles of antiproton beams in the future facilities of Facility for Low-energy Antiproton Ion Research (FLAIR) or Extra Low Energy Antiproton Ring (ELENA).

RF reference distribution system for J-PARC linac

The linac used by the Japan Proton Accelerator Research Complex (J-PARC) is a high-intensity proton linac with a peak current of 50 mA. The error in the accelerating field needs to be maintained within ±1% in amplitude and ±1° in phase. Thus, high phase stability is required for the RF reference distribution system. Our objective is to maintain the phase stability of the reference to less than ±0.3°. The beam quality or intensity of a proton linac strongly depends on the stability of the accelerating fields of each cavity; therefore, the stability of the RF reference distribution system is essential for the performance of the J-PARC linac. A highly stable and unique RF reference distribution system was developed for the J-PARC linac. A 12-MHz RF reference signal is converted into an optical signal and amplified by an optical amplifier. Then it is distributed through optical fiber links to 60 low-level RF control systems comprising klystron and solid-state amplifier driving systems. Phase-stabilized optical fiber (PSOF) is employed in the optical transfer line. The thermal coefficient of the PSOF transmission time was measured: its value was 0.4 ppm/°C. This property is insufficient for the required stability; accordingly, the temperature change in the PSOF should be controlled to be within ±0.5 °C by means of a cooling water system. New stable and low-jitter optical-to-electric (O/E) and electric-to-optical (E/O) converters were developed for this linac. The O/E converter is so compact that is can be mounted on a compact PCI board: its temperature is maintained constant by a Peltie device. A pulse driver (limiting amplifier) is introduced in the E/O and O/E converters for signal modulation to reduce the detection jitters. It transforms the 12-MHz signal into a rectangular wave: its the rise time is shorter than 200 ps. Then, a low-transfer jitter of 0.8 ps (rms) was obtained in the optical link of the E/O and O/E converters. The installation of the RF reference distribution system was completed. The phase stability of the distributed signal was evaluated, and a phase stability of the ±0.2° was obtained for a frequency of 927 MHz; consequently, the required system stability was achieved. The beam acceleration to a design energy of 181 MeV for the first phase (Phase I) was successfully performed in February 2007 and the centroid momentum fluctuation of the beam pulse was within ±0.015%, while the required stability was within ±0.025%. Now the beam commissioning has been steadily continued.

A parallel 3D Poisson solver for space charge simulation in cylindrical coordinates

This paper presents the development of a parallel three-dimensional Poisson solver in cylindrical coordinate system for the electrostatic potential of a charged particle beam in a circular tube. The Poisson solver uses Fourier expansions in the longitudinal and azimuthal directions, and Spectral Element discretization in the radial direction. A Dirichlet boundary condition is used on the cylinder wall, a natural boundary condition is used on the cylinder axis and a Dirichlet or periodic boundary condition is used in the longitudinal direction. A parallel 2D domain decomposition was implemented in the ( r , θ ) plane. This solver was incorporated into the parallel code PTRACK for beam dynamics simulations. Detailed benchmark results for the parallel solver and a beam dynamics simulation in a high-intensity proton LINAC are presented. When the transverse beam size is small relative to the aperture of the accelerator line, using the Poisson solver in a Cartesian coordinate system and a Cylindrical coordinate system produced similar results. When the transverse beam size is large or beam center located off-axis, the result from Poisson solver in Cartesian coordinate system is not accurate because different boundary condition used. While using the new solver, we can apply circular boundary condition easily and accurately for beam dynamic simulations in accelerator devices.

Benchmarking of multiparticle phase scan and acceptance scan techniques for the Spallation Neutron Source linac

The importance of accurately setting the RF field amplitude and phase, called the RF set-point is well recognized for a high intensity proton linac such as the Spallation Neutron Source (SNS) linac. Techniques such as phase scan and acceptance scan have been used to determine RF set-points. However, benchmarking study of phase scan and acceptance scan techniques based on experiment was never undertaken before. The benchmarking study demonstrated that the multiparticle phase scan technique based on realistic tracking produces RF set-points consistent with those obtained from the acceptance scan technique. Previous work of phase scan type was based on single-particle tracking and the RF set-point from the single-particle phase scan sometimes did not agree well with either that from the multiparticle phase scan or that from the acceptance scan. The analysis based on multiparticle phase scan showed an accurate agreement between the measurement and simulation even when the beam bunch is rather long (the full-width at half-maximum (FWHM) beam bunch length entering the SNS Drift Tube linac tank 1 is about 27°).

CLUSTER: A high-frequency H-mode coupled cavity linac for low and medium energies

An innovative linear accelerating structure is proposed which is particularly suited for low-current hadrontherapy applications but can also conveniently substitute the conventional proton linacs at present considered for Accelerator Driven Systems and neutrino and muon factories. Its two main features are compactness and good power efficiency at low–medium beam velocities (0.05⩽ β⩽0.5). The first is achieved through a high working frequency and a consequent high accelerating gradient, the second is obtained by coupling several H-mode cavities together. The structure was dubbed CLUSTER for “ Coupled- cavity Linac USing Transverse Electric Radial field”. To compare the performance of this structure with other hadrontherapy linac designs involving high frequencies, a conceptual study has been performed for an operating frequency of 3 GHz. Moreover, a proof of principle has been obtained through RF measurements on a prototype operating at 1 GHz. An accelerator complex using a CLUSTER linac is also considered for protontherapy purposes. This total accelerator complex, called “cyclinac”, uses a commercial cyclotron as an injector to a high-frequency and high-gradient linac.

Characterization of plasma parameters, first beam results, and status of electron cyclotron resonance source

Electron cyclotron resonance (ECR) plasma source at 50 keV, 30 mA proton current has been designed, fabricated, and assembled. Its plasma study has been done. Plasma chamber was excited with 350 W of microwave power at 2450 MHz, along with nitrogen and hydrogen gases. Microwave power was fed to the plasma chamber through waveguide. Plasma density and electron temperature were studied under various operating conditions, such as magnetic field, gas pressure, and transversal distance. Langmuir probe was used for plasma characterization using current-voltage variation. The nitrogen plasma density calculated was approximately 4.5 x 10(11) cm(-3), and electron temperatures of 3-10 eV (cold) and 45-85 eV (hot) were obtained. The total ion beam current of 2.5 mA was extracted, with two-electrode extraction geometry, at 15 keV beam energy. The optimization of the source is under progress to extract 30 mA proton beam current at 50 keV beam energy, using three-electrode extraction geometry. This source will be used as an injector to continuous wave radio frequency quadrupole, a part of 100 MeV proton linac. The required root-mean-square normalized beam emittance is less than 0.2pi mm mrad. This article presents the study of plasma parameters, first beam results, and status of ECR proton source.

First operation of the rf-focused interdigital linac structure

The new rf-focused interdigital (RFI) linac structure came into operation at the Linac Systems laboratory in May of 2006, after a multi-year development program supported by the US Department of Energy. The RFI linac structure is basically an interdigital (or Wideröe) linac structure with rf quadrupole focusing incorporated into each drift tube. The RFI prototype operates at 200-MHz and consists of an ECR ion source, an Einzel lens LEBT, a radial-strut, four-bar RFQ linac section to 0.75MeV and an RFI linac section to a final energy of 2.5MeV. The total length of the prototype is 2.2m. The RFQ and RFI linac sections are resonantly coupled and require a total of 120kW of rf power for cavity excitation. The energy of the accelerated beam was confirmed by requiring it to pass through a 2.25-MeV energy-degrading foil. The specifications for the RFI linac prototype were chosen to address the demanding Boron Neutron Capture Therapy medical application. There are, however, many other potential applications for the structure as it has efficiency and size advantages for both protons and heavy ions at a variety of energies and currents. To date, we have achieved a beam current of approximately 1mA peak at a relatively low duty factor. We continue to improve the performance of the prototype structure on a daily basis as we better understand the optimal operational settings for the prototype system. Now that the first operational milestone for the RFI linac structure has been achieved, Linac Systems will vigorously pursue projects and partnerships for multiple applications such as compact and intense neutron sources, proton and carbon injector linacs for synchrotrons and PET isotope production.

Research of hybrid single cavity linac

We present a study of the compact proton linac for boron neutron capture therapy (BNCT) by using the nuclear reaction 10B(n,α)7Li. In order to downsize the linac system, we propose a hybrid type linac combined with radio frequency quadrupole (RFQ) electrodes and drift tube electrodes in a single cavity. We designed an interdigital-H (IH) mode linac with high power efficiency to accelerate proton beams from an injection energy of 40keV to an acceleration energy of 3MeV and an operation frequency of 80MHz. The resonance frequencies and electromagnetic fields were optimized by simulation. As a result, we were able to design cavity lengths of less than 2m in the simulation model. For this purpose, high frequency properties were carried out in the electromagnetic field simulation. The designed concept of the hybrid linac and the results of electromagnetic field simulation will be in this report.

Electro-nuclear neutron generator — XADS at ITEP

In this report, the purpose and status of the currently constructed ITEP experimental accelerator driven system (XADS) are discussed. This hybrid electro-nuclear facility of moderate power integrates the pulse proton linac (36 MeV, 0.5 mA) and heavy water sub-critical blanket assembly (heat power of 100 kW). Most parts of the equipment units are ordered for industrial manufacturing and some are under development. The facility is supposed to be used for investigations of a wide range of problems concerning both the target-blanket assembly and the accelerator-driver and at the same time explore the dynamical processes arising during their combined operation. Some other applications of the proton beam and neutron source are also discussed. It is possible in future to increase the current and energy of proton or heavy ion beam.

Muon Acceleration in a Superconducting Proton Linac

This note describes how a future Fermilab proton driver [1] based on TESLA superconducting linac modules can perform as both the source of protons to produce the muons and as the accelerator of the muons to be used for a neutrino factory or muon collider. Recent advances in muon cooling [2] have the promise of muon emittances that are compatible with the 1300 MHz accelerating structures that are the basis for the ILC design. In the design described here, H{sup -} ions are accelerated to 8 GeV in the superconducting Linac, then stripped, stored and bunched in a ring while the Linac cavities are rephased for muon acceleration. Then the protons are extracted from the ring to produce pions and muons which are cooled in a few hundred meters, accelerated to a few GeV and injected into the Linac at the {beta} = 1 point for acceleration to add 7 GeV. By recirculating the muons in the constant frequency section of such a proton driver Linac, even higher energies can be achieved quickly so that losses from muon decay are minimized. By adding additional refrigeration and RF power, the repetition rate of the Linac can be increased to make largemore » increases in the average flux of a neutrino factory and the average luminosity of a muon collider. driver linac to be able to accelerate muons, including the costs to produce and cool the muons, will be considerably less than the costs estimated in previous neutrino factory design studies. We also believe that such an approach can produce a much higher neutrino flux and, because of the necessity for effective muon cooling, also be on the path to an energy frontier muon collider.« less

Prompt radiation, shielding and induced radioactivity in a high-power 160 MeV proton linac

CERN is designing a 160 MeV proton linear accelerator, both for a future intensity upgrade of the LHC and as a possible first stage of a 2.2 GeV superconducting proton linac. A first estimate of the required shielding was obtained by means of a simple analytical model. The source terms and the attenuation lengths used in the present study were calculated with the Monte Carlo cascade code FLUKA. Detailed FLUKA simulations were performed to investigate the contribution of neutron skyshine and backscattering to the expected dose rate in the areas around the linac tunnel. An estimate of the induced radioactivity in the magnets, vacuum chamber, the cooling system and the concrete shield was performed. A preliminary thermal study of the beam dump is also discussed.

INR proton Linac operation and applications

The INR Proton Linear Accelerator is presently under operation for about 2400 h per year with energy about 250 MeV and average current up to 150 μA. The Linac applications are mainly as follows: neutron and condensed matter research at spallation neutron source and neutron spectrometers, isotope production for medicine and industry, beam therapy. The experimental area description and the Linac operational experience are given in the paper.

High Power Proton Accelerator Development at KAERI and its Vacuum System

The Proton Engineering Frontier Project (PEFP), approved and launched by the Korean government in July 2002, includes a 100 MeV proton linear accelerator (linac) development and programs for its utilization and application. The main goals in the first phase of the project, spanning from 2002 to 2005, were the design of a 100 MeV proton linac and the development of a 20 MeV linac consisting of a 50 keV proton injector, a 3 MeV radio frequency quadrupole (RFQ), and a 20 MeV drift tube linac (DTL). The 50 keV injector and 3 MeV RFQ have been installed and tested, and the 20 MeV DTL is being assembled, tuned and under a beam test. At the same time, the utilization programs using the proton beam have been planned, and some are now under way. The vacuum system of the 20 MeV proton linac and its related issues, especially in operation with a high duty, are discussed in detail.