Normalized Rms Emittance Research Articles

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.

Upgrade of the extraction system of permanent magnet electron cyclotron resonance ion source

A set of new ion extraction electrodes have been designed for the permanent magnetic electron cyclotron resonance ion source at Peking University to improve beam quality and transmission. PBGUNS has been used to optimize the extraction electrodes and simulate the beam behavior at the extraction region. The experiments showed that with the new system, the beam half divergence angle can be less than 40 mrad and the normalized rms emittance is about 0.13pi mm mrad when the extracted current is 100 mA at 50 keV in pulse mode. The voltage of the suppression electrode has great effect on beam divergence. The effect of the microwave power and gas flow is also studied.

Emittance Measurement of the Multicusp H- Ion Source by Using an Electrical Sweep Scanner

The lament multicusp H source on the ion source test stand was used to study the emittance of the H ion beam injected into the Tanderm accelerator. The emittance measurements in the H ion source are performed with an electrical sweep scanner. The emittance measuring instrument was constructed and optimized to improve the signal-to-noise ratio. To get an accurate emittance, we studied various noise-compensate tools by using a current ampli er with high performance. Background uctuations cause uctuations in the rms emittance estimate and these uctuations are an estimate of the uncertainty incurred through the analysis. Techniques to analyze the ellipse shapes and orientations were used to test the robustness of the results for the emittance and the acceptable emittance increased with the area of the ellipse. The normalized rms emittance of the ion source was measured to be less than 0.15 pi mm mrad.

Development of a pepper pot emittance probe and its application for ECR ion beam studies

A pepper pot–scintillator screen system has been developed and used to measure the emittance of DC ion beams extracted from a high-intensity permanent magnet ECR ion source. The system includes a fast beam shutter with a minimum dwell time of 18ms to reduce the degradation of the CsI(Tl) scintillator by DC ion beam irradiation and a CCD camera with a variable shutter speed in the range of 1μs–65s. On-line emittance measurements are performed by an application code developed on a LabVIEW platform. The sensitivity of the device is sufficient to measure the emittance of DC ion beams with current densities down to about 100nA/cm2. The emittance of all ion species extracted from the ECR ion source and post-accelerated to an energy of 75–90keV/charge have been measured downstream of the LEBT. As the mass-to-charge ratio of ion species increases, the normalized RMS emittances in both transverse phase planes decrease from 0.5–1.0πmmmrad for light ions to 0.05–0.09πmmmrad for highly charged 209Bi ions. The dependence of the emittance on ion's mass-to-charge ratio follows very well the dependence expected from beam rotation induced by decreasing ECR axial magnetic field. The measured emittance values cannot be explained by only ion beam rotation for all ion species and the contribution to emittance of ion temperature in plasma, non-linear electric fields and non-linear space charge is comparable or even higher than the contribution of ion beam rotation.

Thermal emittance and response time measurements of a GaN photocathode

We present the measurements of thermal emittance and response time for a GaN photocathode illuminated with 5 ps pulses at 260 nm wavelength. The thermal emittance was measured downstream of a 100 kV dc gun using a solenoid scan with a wire scanner and a beam viewscreen and was found to be 1.35±0.11 mm mrad normalized rms emittance per 1 mm rms of illuminated spot size. The response time of the photoemitted electrons was evaluated using a deflecting mode rf cavity synchronized to the laser pulses and was found to be prompt within the time resolution capability of our setup.

Emittance growth mechanisms for laser-accelerated proton beams

In recent experiments the transverse normalized rms emittance of laser-accelerated MeV ion beams was found to be < 0.002 mm mrad, which is at least 100 times smaller than the emittance of thermal ion sources used in accelerators [T. E. Cowan, Phys. Rev. Lett. 92, 204801 (2004)]. We investigate the origin for the low emittance of laser-accelerated proton beams by studying several candidates for emittance-growth mechanisms. As our main tools, we use analytical models and one- and two-dimensional particle-in-cell simulations that have been modified to include binary collisions between particles. We find that the dominant source of emittance is filamentation of the laser-generated hot electron jets that drive the ion acceleration. Cold electron-ion collisions that occur before ions are accelerated contribute less than ten percent of the final emittance. Our results are in qualitative agreement with the experiment, for which we present a refined analysis relating emittance to temperature, a better representative of the fundamental beam physics.

Measurements of the transverse emittance at the FLASH injector at DESY

The VUV and soft x-ray free electron laser FLASH (former VUV-FEL) is a user facility at DESY (Hamburg). In order to optimize the performance of the facility, an accurate characterization of the electron beam properties is essential. The transverse projected emittance, one of the important parameters characterizing the quality of an electron beam, is measured using a four monitor method with optical transition radiation monitors. A normalized rms emittance below 2 mm mrad for a 1 nC beam has been measured. In this paper we describe the experimental setup, data analysis methods, and present experimental results.

Development of an H−-ion source for the high-intensity proton accelerator (J-PARC)

A cesium-free tungsten-driven H−-ion source was fabricated and is under testing for the Japan Proton Accelerator Research Complex. Optimization of the filament shape and the positions of the plasma confinement and electron suppression magnets is being performed. An H−-ion beam of 28mA was obtained at an arc discharge power of 40kW. The emittance was measured for an H−-ion beam with 50keV energy and 20mA intensity. The measured values of the normalized rms emittance were 0.18 (horizontal plane) and 0.15 (vertical plane) πmmmrad.

Advances in the performance and understanding of the Spallation Neutron Source ion source

The ion source developed for the Spallation Neutron Source (SNS) is a radio-frequency, multicusp source designed to produce ∼40mA of H− with a normalized rms emittance of less than 0.2πmmmrad. To date, the source has been utilized in the commissioning of the SNS accelerator and has already demonstrated stable, satisfactory operation at beam currents of 10–40mA with duty factors of ∼0.1% for operational periods of several weeks. Ultimately the SNS facility will require beam duty factors of 6% (1ms pulse length, 60Hz repetition rate). To ascertain the capability of the source to deliver beams at this duty factor over sustained periods, ongoing experiments are being performed in which the ion source is continuously operated on a dedicated test stand. The results of these tests are reported as well as a theory of the Cs release and transport processes that was derived from these data. The theory was then employed to develop a more effective source-conditioning procedure and a direct-transfer Cs collar, which led to a considerable improvement in source performance.

Overview of the 100 mA average-current RF photoinjector

High-average-power FELs require high-current, low-emittance and low-energy-spread electron beams. These qualities have been achieved with RF photoinjectors operating at low-duty factors. To date, a high-average-current RF photoinjector operating continuously at 100% duty factor is yet to be demonstrated. The principal challenges of a high-duty-factor normal-conducting RF photoinjector are related to applying a high accelerating gradient continuously, thus generating large ohmic losses in the cavity walls, cooling the injector cavity walls and the high-power RF couplers, and finding a photocathode with reasonable Q.E. that can survive the poor vacuum of the RF photoinjector. We present the preliminary design of a normal-conducting 700 MHz photoinjector with solenoid magnetic fields for emittance compensation. The photoinjector is designed to produce 2.7 MeV electron beams at 3 nC bunch charge and 35 MHz repetition rate (100 mA average current). The photoinjector consists of a 2 1 2 -cell, π-mode, RF cavity with on-axis electric coupling, and a non-resonant vacuum plenum. Heat removal in the resonant cells is achieved via dense arrays of internal cooling passages capable of handling high-velocity water flows. Megawatt RF power is coupled into the injector through two tapered ridge-loaded waveguides. PARMELA simulations show that the 2 1 2 -cell injector can produce a 7 μm emittance directly. Transverse plasma oscillations necessitate additional acceleration and a second solenoid to realign the phase space envelopes of different axial slices at higher energy, resulting in a normalized rms emittance of 6.5 μm and 34 keV rms energy spread. We are developing a novel cesiated p-type GaN photocathode with 7% quantum efficiency at 350 nm and a cesium dispenser to replenish the cathode with cesium through a porous silicon carbide substrate. These performance parameters will be necessary for the design of the 100 kW FEL.

Recent results with Au ions from a multiampere electron beam ion source at Brookhaven National Laboratory (invited abstract)

An electron beam ion source (EBIS) that would satisfy Relativistic Heavy Ion Collider (at Brookhaven National Laboratory) (RHIC) requirements should be capable of producing intensities of, e.g., Au32+ ions of about 3×109 particles/pulse in 10–40 μs pulses. The total charge extracted (all charge states) would be 85 nC, assuming 20% in the peak charge state. To achieve this at Brookhaven National Laboratory, pulsed-electron beam currents up to 10 A, 100 ms are being used. A test EBIS has been constructed, designed for the full electron beam power and having close to half of the trap length of an EBIS for RHIC. As a result of successful experiments on the test EBIS, we are confident that an EBIS meeting RHIC requirements can be built. Initial electron beam tests have demonstrated a 100 ms, 8.6 A electron beam through the EBIS trap. The stable operation of 10 A, 50 ms electron beams through the EBIS trap has also been achieved. Gold spectra with a dominant charge state 34+ and total ion charge 55 nC measured on a current transformer have been obtained at the EBIS exit after a 30 ms confinement period. Recent studies with an in-line time-of-flight spectrometer with measurement of charge on a Faraday cup have shown 83% of the &amp;gt;28 nC extracted charge to be Au ions peaked at Au25+, for a 7 A electron beam and 10 ms confinement period. Typical normalized rms emittance values using a 6.8 A electron beam, 20–40 nC total ion charge, and 1–3 mA extracted ion current have been in the range of 0.08–0.1 π mm mrad. An energy analysis of the total extracted ion pulses &amp;gt;35 nC has indicated a longitudinal energy spread of &amp;lt;2 kV full width at half maximum after a 35 ms confinement period using a 7 A electron beam. Most design goals have been exceeded and much of the present work is geared toward improving reliability and providing larger safety margins. These include upgrading the electron gun, decoupling the electron beam launch energy from the electron collection energy, and tailoring the magnetic fields to reduce electron beam losses. Details of these measurements, tests in progress to improve performance, and plans for optimizing the design of the RHIC EBIS will be presented.

Micro-PHOENIX: Intense deuton beams production for SPIRAL II

The development of electron cyclotron resonance ion source (ECRIS) at LPSC Grenoble (previously ISN) covers a wide range of applications. Micro-PHOENIX is a compact source whose magnetic confinement is fully generated by permanent magnets. The extraction geometry has been specially designed to manage high currents with a double electrode extraction system to improve the beam characteristics at high voltage. The ECRIS can accept a microwave power frequency from 10 to 18 GHz. It has been installed as a universal injector on the new charge breeder test bench in order to perform the widest range of experiments including mono- or multicharged ion injections. To characterize the analyzed extracted beam, a new emittance meter based on electrostatic deflection plates has been set up and permits one to obtain online high resolution measurements. The first objective of the experiments was to fulfill the future SPIRAL II requirements. After a technical description of the Micro-PHOENIX ECRIS and its beam analysis system, the first experimental results obtained with a single puller electrode will be presented. Thus, a D+ intensity of 5 mA at 39 kV is easily delivered within a normalized rms emittance of 0.092 π mm mrad, which is well below the 0.2 π mm mrad limit assuring a 100% RFQ transport efficiency as computed for the LINAG project. A more extensive study of emittance versus plasma parameters is in progress.

Test EBIS operation and componentdevelopment for the RHIC EBIS*

Most design goals of the BNL Test EBIS Project have been exceeded and we areconfident that an EBIS meeting RHIC requirements can be built. Achieved parameters include10 A electron beam current, ion charge state above Au32+, and greater than 55 nC total extractedion charge. The Test EBIS utilizes the full electron beam power but has only half the trap lengthand operates at a reduced duty factor compared with an EBIS for RHIC, which would produce atleast 85 nC total ion charge in 10–40 microsecond pulses, containing ~3 × 109 particles/pulse ofAu32+ ions. Normalized rms emittance values for 1–3 mA extracted ion beams have been in therange of 0.08–0.1 pi mm mrad. Present development of the source is focused on establishingoperational reliability and facilitating future upgrades in ion intensity and species, since themajor emphasis is now on integrating the EBIS into a pre-injector facility, including an RFQ andlinac. Recent progress towards this goal includes the following: (1) An IrCe electron guncathode and modified anode have been installed in an electron gun chamber separable from thesource ionization region by a gate valve. A very low loss 10 A, electron beam has beenpropagated with the new configuration, with 100 kW peak power dissipation at the electroncollector. (2) A new electron collector power supply configuration has been tested which canlower the cost compared to our present setup, while improving the stability of the electron beamlaunch. This is an important first step towards placing the EBIS on a nominal 50 kV platform,necessary for efficient highly charged ion transport to the RFQ. (3) A hollow cathode ion sourceobtained from CEA Saclay, has been tested and is being installed. This will allow us toprovide a variety of ion species to the RHIC and NASA Space Radiation Laboratory facilities,and is valuable at the present project stage for beamline development and emittance studies ofheavy and light ion beams of highly charged ions from the EBIS. (4) An electron collector forRHIC has been designed which would allow operation exceeding 10 A electron beams at 100%duty factor. The RHIC collector design could allow upgrades to 300 kW electron beampower. (5) Controls for pulse to pulse switching and diagnostics for charge state and chargefraction verification have been developed.

Beam measurements on the H− source and low energy beam transport system for the Spallation Neutron Source (abstract)

The ion source and low energy beam transport section of the front-end systems presently being built by Lawrence Berkeley National Laboratory are required to provide 50 mA of H− beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance of less than 0.20 π-mm-mrad. Experimental results, including emittance, chopping, and steering measurements, on the performance of the ion source and LEBT system operated at the demanded beam parameters will be discussed.

A high intensity dc H− source for low energy injection

While a 20 mA dc H− source system at 25–30 keV beam energy has been developed at TRIUMF several years ago, another recent demand on the system is to provide a 4 to 5 mA H− at the 4–6 keV energy range. We found that at this low energy range, the existing source/extraction system can only give ∼1 mA with poor emittance due to strong space-charge effect. Fortunately, a very special source/extraction mechanism together with the use of neutralization was discovered and developed to overcome this difficulty. Up to 4 mA with a normalized rms emittance of 0.15 π mm mr has been achieved at 6 keV. This performance finds its usefulness for injection systems where lower beam energy and higher beam intensity are required. A copy of the TRIUMF system was constructed and successfully tested in the summer of 2000 for the “H− Acceleration Project” for the K130 cyclotron at Jyväskylä University, Finland.

Low emittance electron beam formation with a 17 GHz RF gun

We report on electron beam quality measurement results from the Massachusetts Institute of Technology 17 GHz RF gun experiment. The 1.5 cell RF gun uses a solenoid for emittance compensation. It has produced bunch charges up to 0.1 nC with beam energies up to 1 MeV. The normalized rms emittance of the beam after 35 cm of transport from the gun has been measured by a slit technique to be $3\ensuremath{\pi}\mathrm{mm}\mathrm{mrad}$ for a 50 pC bunch. This agrees well with PARMELA simulations at these beam energies. At the exit of the electron gun, we estimate the emittance to be about $1\ensuremath{\pi}\mathrm{mm}\mathrm{mrad}$, which corresponds to a beam brightness of about $80\mathrm{A}/(\ensuremath{\pi}\mathrm{mm}\mathrm{mrad}{)}^{2}$. Improved beam quality should be possible with a higher energy output electron beam from the gun.

Emittance Measurements for High Charge State Ion Beams Extracted from the AECR-U Ion Source

In order to investigate the ion-optical parameters of the AECR-U injection line into the 88-Inch Cyclotron, an electrostatic-deflection-type emittance scanner has been designed and constructed. It allows fast on-line measurements, while tuning the ion beam through the cyclotron. Emittance measurements have been performed for various high charge state ions. First results indicate a strong mass dependence of the normalized beam emittance. For example the normalized rms emittance for protons (0.24 π · mm · mrad) is four times higher than for O6+ (0.06 π · mm · mrad) and about 8 times higher than Kr19+ (0.03 π · mm · mrad). Furthermore it was found, that the emittance values are approximately independent of the current at the medium ion beam intensities. The predominant factor on the beam emittance is shown to be the plasma stability. The emittance measurements and the results are discussed in the paper.

High-current ion source development for the Korea Multipurpose Accelerator Complex

The Korea Multipurpose Accelerator Complex (KOMAC) project has been initiated to develop and build a high current proton/H− linear accelerator capable of delivering an 1 GeV cw proton beam with an intensity of 20 mA in the final stage. The major proton beam will be used for nuclear-waste transmutation, energy production, and nuclear physics experiments while utilizing the minor negative hydrogen beam for basic science research and medical therapy. A Duoplasmatron proton source for the KOMAC linear accelerator has been built at Korea Atomic Energy Research Institute. The hydrogen beam currents of up to 50 mA at the extraction voltage of 50 kV are routinely obtained. A low normalized rms emittance of 0.2 π mm mrad and a proton fraction of over 80% are obtained in this source. With the 100% duty factor of ion source operation, the arc filaments of the source have survived over 40 h. Except for the filament lifetime, the achieved parameters of the proton beam source are satisfying most requirements of the KOMAC ion source. The ion sources can extract the 10 mA nitrogen beam and 3 mA argon beam for the industrial surface modification processes.

Measurements on H− sources for spallation neutron source application

Lawrence Berkeley National Laboratory is engaged in the development of H− ion sources for the upgrade of the Los Alamos Neutron Science Center (LANSCE) facility and the spallation neutron source (SNS) to be built in the U.S. For the upgrade of the LANSCE facility, the H− ion generator has to deliver an output current of 40 mA. The repetition rate must be 120 Hz at a pulse length of 1 ms (12% duty factor). Furthermore, the normalized emittance must be less than 0.1π mm mrad. During the last years, the Ion Beam Technology Group of the LBNL improved the so-called surface conversion source for the generation of higher H− currents. In the first part of this article, we discuss the operation conditions of the source at the required 40 mA output current. The ion source for the 1 MW spallation neutron source is required to provide 35 mA of H− beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance of less than 0.2π mm mrad. The H− beam will be accelerated to 65 keV and matched into a 2.5 MeV RFQ. The ion source is expected to ultimately produce 70 mA of H− at 6% duty factor when the SNS is upgraded to 2 MW of power. For this application, a radio-frequency driven, magnetically filtered multicusp source is being developed at LBNL. Experimental results (including emittance measurements) on the performance of the prototype ion source operated at the demanded beam parameters will be presented in this article.

Transverse emittance measurements from a photocathode RF gun with variable laser pulse length

The gun test facility (GTF) at SSRL was started in 1996 to develop an appropriate injector for the proposed linac coherent light source (LCLS) at SLAC. The LCLS design requires the injector to produce a beam with at least 1 nC of charge in a 10 ps or shorter pulse with no greater than 1π mm mrad normalized rms emittance. The photoinjector at the GTF is 1.6 cell S-band symmetrized gun and emittance compensation solenoid. Emittance measurements, reported here, were made as function of laser pulse width using Gaussian longitudinal pulses. The lowest achieved emittance to date with 1 nC of charge is 5.6π mm mrad and was obtained with a pulse width of 5 ps (FWHM) and is in agreement with simulation. There are indications that the accelerator settings for these results may not have been optimal. Simulations also indicate that a normalized emittance meeting the LCLS requirement can be obtained using appropriately shaped transverse and temporal laser/electron beam pulses. Work has begun on producing temporal flat top laser pulses which combined with transverse clipping of the laser is expected to lower the emittance to approximately 1π mm mrad for 1 nC with optimal accelerator settings.