Prebunching via echo-enabled harmonic generation (EEHG) is an efficient way to reduce the radiator length and improve the longitudinal coherence as well as output stability in storage-ring-based ...free-electron lasers. We propose a conceptual design, which uses two straight sections to seed coherent extreme-ultraviolet (EUV) and soft X-ray emission with nearly MHz repetition rate. To take the large energy spread (10
) of a storage ring into account and utilize the existing bending magnets between the two straight sections as the first chicane, we implement a special modeling tool, named EEHG optimizer. This tool has been successfully applied to maximize the prebunching with a reasonably low energy modulation, thereby generating intense coherent X-ray pulses within a short undulator length (a few meters) limited by the available space of a storage ring. Numerical simulations confirm that the optimized EEHG parameters can be directly applied to generate a 10 MW scale peak power with fully coherent ultrafast EUV to soft X-ray pulses based on the NSLS-II parameters. This method can be easily extended to other types of diffraction-limited storage rings.
Free-electron-laser-based beamlines utilize fully coherent laser pulses with extremely narrow bandwidth allowing direct use of X-rays without monochromators. This could be very beneficial for all ...users of current and future fourth-generation diffraction-limited synchrotron light sources (DL-SLSs) who need narrowband full-coherence high-brightness X-ray pulses. Based on our previous finding,
i.e.
that separating the two stages of echo-enabled harmonic generation (EEHG) with a few extra bending-magnet sections provides an effective way to increase the momentum compaction of chicane 1, one can simultaneously achieve adequate prebunching at extremely high harmonics as well as keep the energy modulation to the ideal minimum. This could open the door for cascaded EEHG, toward fully coherent tender and hard X-ray wavelengths. Built on our compact design of a twin-pulse seeding electron beam with an adjustable delay and timing jitter at the level of a few femtoseconds, a cascaded EEHG can be implemented, which includes two EEHG beamlines, where the radiation pulse generated by the first beamline with harmonic
h
1
could be used as the input seed laser pulse to the second beamline with harmonic
h
2
. Hence, the second radiator could potentially reach very high harmonics
h
=
h
1
(20)
h
2
(25–100) from 500 to 2000, corresponding to tender and hard X-ray wavelengths. It is demonstrated that the cascaded EEHG scheme is compatible with almost any current or planned fourth-generation DL-SLS, with significant benefits for space-limited storage rings in particular. The main advantage is that this scheme requires almost no change of the storage-ring lattice and is fully compatible with other beamlines. Current proposals for rings with much longer straight sections would add self-amplified spontaneous emission as another viable option for storage-ring-based free-electron lasers.
Having previously reported that separating the two stages of echo-enabled harmonic generation (EEHG) with one or more bending magnet (BM) sections allows the BMs to serve as the desired source of ...momentum compaction, here we demonstrate that this arrangement can greatly reduce the total energy modulation required by any 4th generation synchrotron light source, leading to higher repetition rates as well as stronger coherent radiation output power, with significant benefits. Since the EEHG beamline performance is mainly determined by the momentum compaction, beam emittances and beta functions of a storage ring lattice, allowing for different separations between the two stages is a straightforward way to increase the momentum compaction of chicane 1. This also enables pump-probe capabilities in a novel context, where twin-pulse seeding on the same electron bunch would allow two distinct radiation pulses with an adjustable delay in the range of 0.1 to 10 ps. In the twin-pulse seeding scheme, the same electron bunch could undergo modulation from two distinct laser pulses. Later stages would produce independent harmonics in subsequent straight sections. There are two variations of this twin-pulse seeding scheme, supporting different scientific applications. With a common modulation in stage 1, the first option allows simultaneously two independent radiation sources, with a full coverage of the EUV (2.5 to 50 nm) to soft X-ray (1.25 to 2.5 nm) spectrum; for the second option, the same stage 2 undulator could generate two coherent pulses both fitting within the FEL bandwidth, or at distinct harmonics. We present particle tracking simulation studies based on the APS-U lattice, including quantum excitation and radiation damping. These simulations indicate that there is no degradation of the modulated longitudinal phase space even when the two stages are separated by as many as 10 BM sections.
NSLS-II longitudinal impedance budget Blednykh, A.; Bassi, G.; Hetzel, C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2021, Volume:
1005
Journal Article
Peer reviewed
Open access
From the beginning of the NSLS-II project, the vacuum chamber of the NSLS-II storage ring has been optimized to reduce its impedance. The optimization, performed in close collaboration with the ...Diagnostic, Vacuum, RF, and Mechanical Engineering groups, has been achieved via calculating the impedance of the vacuum chamber components with the use of both analytical and numerical tools, with the numerical computations carried out with the GdfidL code. For reliable NSLS-II operation with the total beam current of 500 mA, each component of the vacuum chamber has been individually optimized to minimize the beam-induced heating and to prevent single-bunch and coupled-bunch instabilities. In this article, the impedance calculation and optimization know-how are summarized for all the chamber components, and the total longitudinal impedance budget is analyzed. As a result of this extensive research and engineering effort, the design beam current of 500 mA has been recently accumulated in NSLS-II without any major problem caused by the collective effects.
Abstract
Alignment and mechanical-stability specifications are essential to the performance of low-emittance storage rings. Beam dynamics simulations are usually performed to establish these ...specifications. However, the simulation procedures and the input parameters related to magnet positions are not well established which leads to differences in the final specifications. In this paper we discuss important parameters of the mechanical/structural systems of the storage ring that impact on the alignment and stability specification. We reviewed the alignment and stability specifications used at modern light sources across the world that will help to propose an efficient model for a low-emittance upgrade of NSLS-II.
Impedance modeling for accelerator applications has improved over the years, largely as a result of advances in simulation capabilities. While this modeling has been successful in reproducing certain ...measurements, it is still a significant challenge to predict collective effects in real machines. In this paper, we review our approach to impedance modeling and the subsequent simulations of collective effects. We discuss the choice of the electrodynamics codes and the required computer power resources, modeling of the geometric, and resistive wall impedances, their comparison with analytical approaches, and their application for simulating of the collective effects with tracking and beam-induced heating.
Beam impedance and heating analysis of the diagnostic stripline Blednykh, A.; Bacha, B.; Bassi, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2020, Volume:
963, Issue:
C
Journal Article
Peer reviewed
Open access
The heat transfer analysis has been performed for the stripline kicker, design of which is used at many accelerator facilities as a part of the transverse bunch-by-bunch feed-back system, including ...NSLS-II. The experimental data of the electrode temperature have been collected from a special diagnostic stripline designed with six infrared view ports. The temperature analysis is based on the power loss calculations and the loss factor computed by the 3-D electromagnetic simulation code GdfidL. To estimate the power loss, we analyze the real part of the longitudinal impedance and the loss factor for two different regimes. We use the ANSYS finite element code to correlate the temperature with the power loss. Lambertson and Shafer formalisms of the longitudinal and transverse beam impedances are discussed for the simplified stripline geometries. The required characteristic impedances and the geometric factors are determined analytically for the simplified geometries and compared with the results for the designed stripline geometry using the 2-D POISSON code by solving the Laplace’s equation in two dimensions. Lambertson’s equations are compared with numerical results. We introduce the frequency range, within which we can apply the analytical approach.
A superconducting wiggler (SCW) with a peak field of 4.3 T has recently been installed at NSLS-II. The wiggler generates a high-flux X-ray beam with a photon energy range from 20 keV to 200 keV for ...the High Energy Engineering X-ray Scattering beamline. This device induces significant distortions in the electron beam orbit and optics. We have corrected these adverse effects using feed-forward tables. The effects of the SCW on the electron beam emittance, energy spread, and bunch length were calculated and measured. The beam-induced heating of the cryogenic vacuum chamber was also studied. Finally, the superconducting wiggler has been commissioned for user operations.
Measurement of Γee(J/ψ) with KEDR detector Anashin, V. V; Aulchenko, V. M; Baldin, E. M ...
The journal of high energy physics,
05/2018, Volume:
2018, Issue:
5
Journal Article
Peer reviewed
Open access
A
bstract
The product of the electronic width of the
J/ψ
meson and the branching fractions of its decay to hadrons and electrons has been measured using the KEDR detector at the VEPP-4M
e
+
e
−
...collider. The obtained values are
Γ
e
e
J
/
ψ
=
5.550
±
0.056
±
0.089
keV
,
Γ
e
e
J
/
ψ
·
ℬ
hadrons
J
/
ψ
=
4.884
±
0.048
±
0.078
keV
,
Γ
e
e
J
/
ψ
·
ℬ
e
e
J
/
ψ
=
0.3331
±
0.0066
±
0.0040
keV
.
The uncertainties shown are statistical and systematic, respectively. Using the result presented and the world-average value of the electronic branching fraction, one obtains the total width of the
J/ψ
meson:
Γ
=
92.94
±
1.83
keV
.
These results are consistent with the previous experiments.
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