Intrinsic Energy Spread Research Articles

Experimental characterization of the optical klystron effect to measure the intrinsic energy spread of high-brightness electron beams

The intrinsic energy spread of electron beams needs to be measured to characterize and optimize high-brightness electron beam sources such as those driving x-ray free-electron lasers (FELs). We demonstrate the use of the optical klystron effect as a precise and high-resolution method to measure the electron beam energy spread. The optical klystron setup consists of undulator modules and magnetic chicanes placed between them. The energy spread is found by measuring the radiation power produced in the undulators as a function of the chicanes’ strengths. High resolution and simplicity are the advantages of this approach, in contrast to the standard method, which measures the longitudinal phase space of the electron beam with a transverse deflector. The demonstration was performed at Athos, the soft x-ray FEL beamline of SwissFEL, for which we measured energy spreads below 1 MeV at a central beam energy of 3.4 GeV. We have verified the consistency of the method for different parameters (radiation wavelengths, undulator polarization configurations, and electron bunch durations) and we have benchmarked it against the standard measurement approach using a transverse deflector. Our results confirm the optical klystron as a valid approach to measure the electron beam energy spread. The method can be especially useful to reconstruct low energy spread values, where the conventional approach may be resolution limited, such as in ultra high-brightness radiofrequency photoinjectors or plasma sources, or when transverse deflectors are not available. Published by the American Physical Society 2024

Semi-analytical analysis of high-brightness microbunched beam dynamics with collective and intrabeam scattering effects

The studies of incoherent single-particle and collective multi-particle effects are, in general, separated in accelerator beam dynamics in that the two dynamical phenomena involve quite different time scales. Recent experimental measurements indicate that in some parameter regime, the small-angle, multiple scattering effects within a high-brightness electron beam can have a strong influence on microbunched beam dynamics. In this paper, we apply our recently developed semi-analytical kinetic analysis to investigate the collective phase space microbunched dynamics in the presence of incoherent single-particle effects. Particular emphasis will be placed on evaluation of the intrinsic or slice energy spread. An example of two linear beam transport lines, followed by two identical, interleaving bunch compressor chicanes, is then presented. The semi-analytical calculations are consistent with particle tracking simulations. Moreover, the threshold condition is derived, indicating the relation among relevant physical quantities. At threshold, the incoherent effect can be beneficial for effective suppression of the collective microbunching instability. We expect that this work could shed light on high-brightness electron transport beamline design to improve short-wavelength free-electron laser performance.

Intrinsic energy spread and bunch length growth in plasma-based accelerators due to betatron motion

Plasma-based accelerators (PBAs), having demonstrated the production of GeV electron beams in only centimetre scales, offer a path towards a new generation of highly compact and cost-effective particle accelerators. However, achieving the required beam quality, particularly on the energy spread for applications such as free-electron lasers, remains a challenge. Here we investigate fundamental sources of energy spread and bunch length in PBAs which arise from the betatron motion of beam electrons. We present an analytical theory, validated against particle-in-cell simulations, which accurately describes these phenomena. Significant impact on the beam quality is predicted for certain configurations, explaining previously observed limitations on the achievable bunch length and energy spread. Guidelines for mitigating these contributions towards high-quality beams are deduced.

Using the optical-klystron effect to increase and measure the intrinsic beam energy spread in free-electron-laser facilities

We present a setup based on the optical klystron concept, consisting of two undulator modules separated by a magnetic chicane, that addresses two issues in free-electron-laser (FEL) facilities. On the one hand, it allows increasing the intrinsic energy spread of the beam at the source, which is useful to counteract the harmful microbunching instability. This represents an alternative method to the more conventional laser heater with the main advantage that no laser system is required. On the other hand, the setup can be used to reconstruct the initial beam energy spread, whose typical values in FEL injectors around 1 keV are very difficult to measure with standard procedures.

High-resolution measurements of the exited states (n,pn), (n,dn) C-12 cross sections

Measurements of C12 cross sections for the excited states (n,p 0 ) up to (n,p 4 ) and (n,d 0 ), (n,d 1 ) have been carried out. The Van de Graaff neutron generator of the EC-JRC-IRMM laboratory has been used for these measurements. A very thin tritiated target (263 μg/cm 2 ) was employed with deuteron beams energies impinging on the target in the range 2.5–4.0 MeV. Neutrons in the range 18.9–20.7 MeV were produced with an intrinsic energy spread of 0.2–0.25% FWHM. With such narrow neutron energy spread, using a high energy resolution device such as a single crystal diamond detector, several peaks from the outgoing charged particles produced by the (n,p n ), (n,d n ) and also (n,α 0 ) reactions appear in the pulse height spectrum. The peaks can be identified using the reaction Q-values. The diamond detector used for these measurements has shown an intrinsic energy resolution lower than 0.9% FWHM. The analysis of the peaks has permitted to derive the partial carbon reaction cross sections for several excited states. The results are presented in this paper with the associated uncertainties and they are compared with different versions of TENDL compilation when these data are available (e.g. versions 2009, 2010, 2011 and 2015) and also with experimental results available in the EXFOR database.

Effects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: II. Analysis of experimental data of the Neutralized Drift Compression eXperiment-I (NDCX-I)

Neutralized drift compression offers an effective means for particle beam focusing and current amplification with applications to heavy ion fusion. In the Neutralized Drift Compression eXperiment-I (NDCX-I), a non-relativistic ion beam pulse is passed through an inductive bunching module that produces a longitudinal velocity modulation. Due to the applied velocity tilt, the beam pulse compresses during neutralized drift. The ion beam pulse can be compressed by a factor of more than 100; however, errors in the velocity modulation affect the compression ratio in complex ways. We have performed a study of how the longitudinal compression of a typical NDCX-I ion beam pulse is affected by the initial errors in the acquired velocity modulation. Without any voltage errors, an ideal compression is limited only by the initial energy spread of the ion beam, ΔΕb. In the presence of large voltage errors, δU⪢ΔEb, the maximum compression ratio is found to be inversely proportional to the geometric mean of the relative error in velocity modulation and the relative intrinsic energy spread of the beam ions. Although small parts of a beam pulse can achieve high local values of compression ratio, the acquired velocity errors cause these parts to compress at different times, limiting the overall compression of the ion beam pulse.

Measurement of femtosecond electron bunches using a rf zero-phasing method

Bunch lengths as short as 84 fs (rms) have been measured at Jefferson Laboratory using a rf zero-phasing technique. To the best of our knowledge, this is the first accurate measurement of the longitudinal distribution function in this regime. In this paper, an analytical approach for computing the longitudinal distribution function and bunch length is described for arbitrary longitudinal and transverse distributions for the case where the intrinsic energy spread of the bunch is small compared to the correlated energy spread imparted by zero-phasing cavities. The measurement results are presented, which are in excellent agreement with numerical simulations.

Application of low temperature calorimeters for the detection of energetic heavy ions

The energy sensitive detection of energetic heavy ions with calorimetric low temperature detectors is investigated. The temperature readout was done with an aluminum transition edge thermometer operated at T ≈ 1.5 K. For 20 Ne-ions with an energy of E = 100 MeV/u from the SIS accelerator at GSI Darmstadt the best energy resolution obtained was ΔE E = 1.9 × 10 −3 . This value corresponds to the energy spread of the ion beam of the SIS. In a first application of such detectors the excitation of the giant resonance in lead nuclei via the reaction nat Pb( 20 Ne, 20 Ne′) nat Pb ∗ was investigated by separating inelastically from elastically scattered 20 Ne-ions in the energy spectrum. At a scattering angle Θ Lab = 3° the excitation energy and the strength of the giant resonance were found to be in good agreement with theoretical predictions. In a first test with an extracted cooled 238 U-beam with an energy of E = 360 MeV/u from the storage ring ESR with an intrinsic beam energy spread of ΔE E ≤ 2 × 10 −4 an energy resolution of ΔE = 97 MeV ( ΔE E = 1.1 × 10 −3 ) was measured. The baseline noise was ΔE = 17 MeV. Further improvement of the energy resolution seems possible.

The spectral dependence of electron central‐axis depth‐dose curves

Electron linac fields are usually characterized by the central-axis practical range in water, Rp, and the depth of half maximum dose, R50, for dosimetry, quality assurance, and treatment planning. The quantitative relations between the range parameters and the intrinsic linac beam's energy structure are critically reviewed. The spectral quantity <E0>* is introduced which is defined as the mean energy of the incident spectral peak, termed the "peak mean energy." An analytical model is constructed to demonstrate the predicted relation between polyenergetic spectral shapes and the resulting depth-dose curves. The model shows that, in the absence of electrons at the patient plane with energies outside about <E0>* +/- 0.1 <E0>*, Rp and R50 are both determined by <E0>*. This analytical approximation is confirmed by a Monte Carlo calculation comparing two different idealized incident spectra. The effect of contaminant lower energy or wide-angle scattered electrons is also discussed. The effect of the width of the intrinsic energy spread on the shape of the depth-dose curve is investigated using Monte Carlo depth-dose simulations based on measured linac energy spectra having energy spreads (full width at half maximum) as large as 20%. These simulations show that the energy spread has only a small effect on the shape of the central-axis depth-dose curve.

A low-energy and low-emittance ion beam source for use with the super-microbeam production system (abstract)

We are developing a new type of microbeam system, intentionally utilizing the process of acceleration, accompanied with the beam contraction effect (conservation of normalized emittance). This device will enable one to produce microbeams for any ion species, less than 0.1 μm in diameter. A tentative design of lens system (ion energy=100 kV), composed of an entrance aperture lens and an einzel lens, will be described, and it will be discussed why the spherical aberration can be depressed much lower than the usual nonaccelerating lenses. The chromatic aberration due to the fluctuation of the acceleration voltage can be avoided in principle. Hence the only source of this type of aberration is the energy spread of the ion beam from the ion source. The maximum performance of this microbeam system may be obtained when the energy increasing ratio is large enough so that the incident beam energy is kept as low as possible. For investigating these points a hydrogen ion source of special design has been tested. It was found that the intrinsic energy spread can be made considerably low (∼0.5 eV) and a narrow parallel ion beam of several tens eV, which is nearly perfectly neutralized in space charge, can be obtained.

Electron beam quality limitations and beam conditioning in free electron lasers

Free electron lasers (FELs) operate over a large portion of the electromagnetic spectrum, i.e. from the μ-wave to the UV. At the high frequency end of the spectrum, FEL operation is severely limited by a number of factors; prominent among them is the electron beam quality (electron axial velocity spread). The axial velocity spread is due to the electron beam's intrinsic energy spread and emittance. The general wavelength limitation in FELs due to electron beam quality is discussed. A method for reducing the axial velocity spread is proposed and analysed. This beam conditioning method redistributes the electrons' energy according to their betatron amplitude. This accomplished by interacting the beam with an axially symmetric, slow, TM waveguide mode.

Critical issues in the application of a gallium probe to high resolution secondary ion imaging

The use of liquid metal ion sources to form finely focused probes has enabled analytical imaging by secondary ion mass spectrometry to achieve, in favorable cases, spatial resolution approaching the theoretical localization limits of the method. As a drawback, however, the large intrinsic energy spread of such sources significantly constrains both the minimum size of the probe and the analytical sensitivity-analytical image resolution that are possible. In the context of these limitations, recent applications of a high resolution scanning ion microprobe to studies of Al-Li alloys, high T c superconductors and photoemulsion engineered microcrystals are discussed.

Emittance measurements of gallium liquid-metal ion sources

The emittances of momentum-analyzed 69Ga + ion beams extracted from a needle-type liquid-metal ion source (LMIS) are found to be approximately twice as large in the dispersive plane ( x-direction) as in the orthogonal, nondispersive plane ( y-direction). This effect is principally attributable to dispersion of the beam in the x-direction by the mass analyzing magnet used in the experiments. This dispersion results from space-charge effects and other sources of intrinsic energy spread within the ion beams. In addition, the growth of emittance with beam intensity is less dramatic in the y direction, also suggesting the effect of energy dispersion. It is argued that y-direction emittance values should be considered as representative of the gallium LMIS whenever energy dispersive devices are not incorporated in the beam transport system. Brief descriptions of the experimental hardware are given and x- and y-direction emittance data are presented in this report.

Velocities of Fragment Pairs fromU233,U235, andPu239Fission

Velocities of the fragment pairs from thermal-neutron-induced fission of ${\mathrm{U}}^{233}$, ${\mathrm{U}}^{235}$, and ${\mathrm{Pu}}^{239}$ have been measured by a time-of-flight method. The primary masses and energies of the fragments have been determined from the conservation of mass number and momentum. These results are compared with previous fission-fragment-mass and -energy measurements. A decrease of the total kinetic energy near the symmetric mode is observed, which is in agreement with previous double-ionization-chamber measurements. The intrinsic energy spread for mass-97 fragments was found to be 8.1\ifmmode\pm\else\textpm\fi{}1.6% with a 95% confidence interval.