| 1. |
- Bettoni, S., et al.
(författare)
-
Impact of laser stacking and photocathode materials on microbunching stability in photoinjectors
- 2020
-
Ingår i: Physical Review Accelerators and Beams. - : AMER PHYSICAL SOC. - 2469-9888. ; 23:2
-
Tidskriftsartikel (refereegranskat)abstract
- Microbunching instability is a well-known phenomenon that may deteriorate the performance of accelerators. The instability may be triggered by a shot-noise mechanism or by some initial intensity modulations at the generation of the electron bunch (or both) and can be amplified all along the machine. At SwissFEL, the free-electron laser (FEL) facility operating at the Paul Scherrer Institute (PSI), the initial design stipulated a shaping of the photocathode laser output to obtain a flat-top longitudinal profile. This scheme is attractive in terms of the uniformity of the beam properties along the bunch. The drawback of this approach is that some unavoidable modulations are generated along the laser pulse. We investigate, both experimentally and by numerical simulations, the longitudinal dynamics of a beam obtained illuminating a copper cathode with a laser profile shaped by the stacking technique. We repeat the analysis for several compression factors and initial laser profile modulations. We find that the microbunching instability gain renders the use of the stacking technique not efficient to run a free-electron laser facility using as photocathode a material with a short response time. We experimentally demonstrate that the use of a material with a longer response time efficiently damps the structures originating from the laser profile obtained with stacking, and helps to improve the performance of the facility. In general, this is an approach to minimize the microbunching instability at any FEL (also not using stacking) or at least reduce the use of other countermeasures, which, such as the laser heater, may degrade the final FEL performance.
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| 2. |
- Bhattacharyya, Anirban, et al.
(författare)
-
ESS RF Source and Spoke Cavity Test Plan
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report describes the test plan for the first high power RF source, ESS prototype double spoke cavity and ESS prototype cryomodule at the FREIA Laboratory.
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| 3. |
- Bhattacharyya, Anirban
(författare)
-
From Macroscopic to Microscopic Dynamics of Superconducting Cavities
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Superconducting (SC) radio frequency (RF) cavities are at the heart of many large-scale particle accelerators such as the European Spallation Source (ESS), the X-ray Free Electron Laser (XFEL), the Linac Coherent Light Source (LCLS)-II and the proposed International Linear Collider (ILC). The SC cavities are essentially resonant structures with very high intrinsic quality factors (Q0) of the order of 1010. The high Q0 of the cavities leads to increased reflection during charging of the cavities to nominal voltage because the bandwidth of the signal exceeding that of the cavity. This results in high energy losses in case of pulsed machines. In this thesis I explore and present a novel technique to optimally charge the superconducting cavities with the particular example of the spoke cavities to be used for the ESS project in Lund, Sweden. The analysis reveals that slow charging with hyperbolic sine cavity voltage profile matches the signal bandwidth to that of the cavity which leads to energy efficient filling.However, a filling rate lower than some particular value is counter-productive. The energy expended in cryogenic cooling to evacuate the heat due to ohmic losses in the cavity starts to dominate the lost energy. Such cryogenic losses are dependent on cavity Q0 through the residual resistance. The residual resistance changes with the applied electromagnetic field due to the pair-breaking mechanism of Cooper-pairs. Hence, methods for accurate measurement of the cavity Q0 are essential for accurate characterization and operation of the superconducting cavities. In this thesis I propose a novel method to accurately measure Q0 as a function of the applied electromagnetic field and present experimental results from the prototype spoke cavity in the Facility for Research Instrumentation and Accelerator Development (FREIA), at Uppsala University.The cavity quality factor (Q0) is also dependent on the material’s purity and the trapped magnetic flux in the superconducting material. Recent studies have revealed that the rate of cooling of materials through the critical temperature has an effect on the residual flux trapped in the material. In this thesis I use the time-dependent Ginzburg-Landau equations to model the process of state transition from a normal to a superconducting state. This theoretical study may allow an explanation of the experimentally observed results from the basic principles of the general theory of state transitions as proposed by Ginzburg and Landau.
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| 4. |
- Bhattacharyya, Anirban Krishna, et al.
(författare)
-
Minimization of power consumption during charging of superconducting accelerating cavities
- 2015
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 801, s. 78-85
-
Tidskriftsartikel (refereegranskat)abstract
- The radio frequency cavities, used to accelerate charged particle beams, need to be charged to their nominal voltage after which the beam can be injected into them. The standard procedure for such cavity filling is to use a step charging profile. However, during initial stages of such a filling process a substantial amount of the total energy is wasted in reflection for superconducting cavities because of their extremely narrow bandwidth. The paper presents a novel strategy to charge cavities, which reduces total energy reflection. We use variational calculus to obtain analytical expression for the optimal charging profile. Enemies, reflected and required, and generator peak power are also compared between the charging schemes and practical aspects (saturation, efficiency and gain characteristics) of power sources (tetrodes, IOTs and solid state power amplifiers) are also considered and analysed. The paper presents a methodology to successfully identify the optimal charging scheme for different power sources to minimize total energy requirement.
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| 5. |
- Bhattacharyya, Anirban, et al.
(författare)
-
Precise measurements of hot S-parameters of superconducting cavities : Experimental setup and error analysis
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Superconducting accelerating cavities used in modern particle accelerators change their intrinsic properties when excited to very high field levels close to the critical field where the superconductivity is affected. In this report we describe a test-bench and data analysis procedure to determine the so-called hot S-parameters from strongly driven cavities and use them to quantify the properties of the cavity at varying field levels. The method is based on analysing reflection coefficient for a large number of configurations in a self-excited loop setup and determining the cavity coupling coefficient $\kappa=Q_0/Q_{ext}$ as a function of cavity voltage to high accuracy. Since $Q_{ext}$ is determined independently and is a constant, from the information of $\kappa$ the Q-slope can be determined.
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| 6. |
- Chulkov, Ruslan, 1972-, et al.
(författare)
-
Effects of emittance and energy spread in an electron bunch on THz radiation generated by a super-radiant source : report III of the series of reports by the Swedish FEL Center and FREIA Group
- 2014
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this report we summarize our results on simulation of a super-radiant sourceoperating at the THz spectral range. We consider an open-type undulator com-prising plane magnets but without any guiding structure for generated THz eld.The undulator is assumed to be driven by electron bunches of femtosecond durationwhich are produced by an rf Linac. Using a numerical model developed, we analyzeeects of the bunch parameters on output performance of the super-radiant sourceand reveal some surprising results. Specically, we show that degradation in bunchspatial quality (increase in the bunch emittance) should lead to decrease in angulardivergence and spectral narrowing of the THz radiation. We also demonstrate thatelectron energy spread which commonly leads to bunch broadening and radiativeenergy drop can be eventually suppressed under appropriate conditions.
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| 7. |
- Chulkov, Ruslan, et al.
(författare)
-
Multimode dynamics in a short-pulse THz free electron laser
- 2014
-
Ingår i: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of waveguide modes and consequences on laser operation are studied numerically in a THz free electron laser (FEL) driven by short electron bunches. The considered FEL cavity configuration is represented by a parallel-plate waveguide extending over the complete distance between cylindrical cavity mirrors with energy out-coupling through a rectangular slit in one of the mirrors. We describe the multimode FEL cavity desynchronization dynamics and predict strong enhancement in FEL power at special cavity configurations, when modes are degenerate. Furthermore, we predict that simultaneous excitation of several waveguide modes can occur but do not negatively influence the lasing process
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| 8. |
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| 9. |
- Di Mitri, Simone, et al.
(författare)
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Scaling of Beam Collective Effects with Bunch Charge in the CompactLight Free-Electron Laser
- 2020
-
Ingår i: Photonics. - : MDPI. - 2304-6732. ; 7:4
-
Tidskriftsartikel (refereegranskat)abstract
- The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges in the range 75-300 pC. Space-charge forces in the injector, linac transverse wakefield, and coherent synchrotron radiation in bunch compressors are all taken into account. The study confirms efficient lasing in the soft X-rays regime with pulse energies up to hundreds of microjoules at repetition rates as high as 1 kHz.
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| 10. |
- Domina, Kateryna L., et al.
(författare)
-
Bonding and Antibonding Modes in Metal–Dielectric–Metal Plasmonic Antennas for Dual‐Band Applications
- 2020
-
Ingår i: Advanced Optical Materials. - : Wiley. - 2162-7568 .- 2195-1071. ; 8:5
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant optical antennas supporting plasmon polaritons (SPPs) – collective excitations of electrons coupled to electromagnetic fields in a medium – are relevant to sensing, photovoltaics and light emitting devices, among others. Due to the SPP dispersion, a conventional antenna of fixed geometry, exhibiting a narrow SPP resonance, cannot simultaneously operate in two different spectral bands. In contrast, this study demonstrates that in metallic disks, separated by a nanometric spacer, the hybridized anti-bonding SPP mode stays in the visible range, while the bonding one can be pushed down to the mid-infrared range. Such an SPP dimer can sense two materials of nanoscale volumes, whose fingerprint central frequencies differ by a factor of 5. Additionally, the mid-infrared SPP resonance can be tuned by employing a phase-change material (VO2) as a spacer. The dielectric constant of the phase-change material is controlled by heating the material at the frequency of the anti-bonding optical mode. Our findings open the door to a new class of optoelectronic devices able to operate in significantly different frequency ranges in the linear regime, and with the same polarization of the illuminating wave.
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| 11. |
- Goryashko, Vitaliy, 1982-, et al.
(författare)
-
12-Way 100 kW Reentrant Cavity-Based Power Combiner With Doorknob Couplers
- 2018
-
Ingår i: IEEE Microwave and Wireless Components Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1531-1309 .- 1558-1764. ; 28:2, s. 111-113
-
Tidskriftsartikel (refereegranskat)abstract
- We present radio frequency (RF) and thermal characterization of a compact 12-way power combiner designed for operation at 352 MHz at a power level of 100 kW with 5% duty factor. The combiner is based on a reentrant cavity with 12 input doorknob couplers and one output coupler that is integrated with the post of the cavity and forms doorknob type geometry. We introduce convenient design formulas that allow easy identification of a suitable parameter space, which is then refined with numerical simulations. Low-power RF measurements of a prototype show 0.2% insertion loss and a relative rms amplitude imbalance between the ports of 0.1% and phase imbalance of 0.036 degrees rms. The matching is better than -25 dB over a 3-dB bandwidth around the design frequency. We also tested the combiner up to 200 kW and found the RF loss to be comparable to that of the low-power measurement. In a long test run at 100 kW with 5% duty factor, the combiner temperature stabilized at 10 degrees above ambient.
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| 12. |
- Goryashko, Vitaliy A., et al.
(författare)
-
A megawatt class compact power combiner for solid-state amplifiers
- 2014
-
Ingår i: Journal Electromagnetic Waves and Applications. - : Informa UK Limited. - 0920-5071 .- 1569-3937. ; 28:18, s. 2243-2255
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a compact multiport two-stage combiner capable of handling peak power up to 10MW at the UHF band and suitable for particle accelerator applications. The detailed electromagnetic and thermal simulations of the combiner operating at the ESS specifications of 400kW at 352MHz are presented. At the first stage, the power is combined to a 100kW level by means of a non-resonant 12-way radial combiner, which is assumed to be fed by 8kW solid-state amplifiers. At the second stage, a waveguide combiner with T-shape couplers separated by a half-wavelength of the fundamental waveguide mode is used in order to bring the combined power to the required level. The combiner is broadband and has a relative power non-uniformity less than 5% over a 10MHz frequency band around the central frequency. The size of the proposed combiner is several times smaller than the existing ones. We also present low-power measurement results of a prototype of the radial combiner.
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| 13. |
- Goryashko, Vitaliy A., et al.
(författare)
-
A Method for High-Precision Characterization of the Q-Slope of Superconducting RF Cavities
- 2016
-
Ingår i: IEEE transactions on microwave theory and techniques. - 0018-9480 .- 1557-9670. ; 64:11, s. 3764-3771
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a novel method for high-precision determination of a quality factor Q(0) of a superconducting radio-frequency cavity as a function of the strength of the field excited in the cavity, the so-called Q-slope. Usually, the cavity parameters are measured only at resonance for different cavity field strengths, but such a single data point measurement for a given field strength results in a 10%-15% uncertainty in Q(0). In contrast, we propose a method that improves the accuracy of Q(0) determination by an order of magnitude. We vary the phase of an excited stabilized field in the cavity and measure the reflection coefficient of the cavity as a function of the phase. The procedure is repeated for different strengths of the excited field. Given the fact that the complex reflection coefficient of a cavity describes a perfect circle in polar coordinates as a function of the field phase for a constant field strength, we find the coupling coefficient much more accurately by fitting the overdetermined set of measured data to the circle for each value of the cavity field. From the time-decay measurement, which allows least-squares minimization, we accurately find the total (loaded) quality factor and deduce Q(0) with an uncertainty of around 1%.
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| 14. |
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| 15. |
- Goryashko, Vitaliy A., 1982-
(författare)
-
Quasi-half-cycle pulses of light from a tapered undulator
- 2017
-
Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 20:8
-
Tidskriftsartikel (refereegranskat)abstract
- Strong-field few-cycle terahertz (THz) pulses are an invaluable tool for engineering highly non-equilibrium states of matter. A scheme is proposed to generate quasi-half-cycle GV/m-scale THz pulses with a multikilohertz repetition rate. It makes use of coherent spontaneous emission from a prebunched electron beam traversing an optimally tapered undulator. The scheme is the further development of the slippage control in free-electron lasers [T. Tanaka, Phys. Rev. Lett. 114, 044801 (2015)]. An explicit condition for the spectral amplitude of undulator radiation and a phase condition for the electron density distribution, required for the generation of desired pulses, are presented. The amplitude condition is met by proper undulator tapering, and a generic optimal undulator profile is found analytically. In order to meet the phase condition, the distance between the adjacent bunches is varied according to the instantaneous resonant undulator wavelength. A 3D analytical theory is complemented by a detailed numerical study based on a direct solution to the 3D wave equation.
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| 16. |
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| 17. |
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| 18. |
- Goryashko, Vitaliy, 1982-
(författare)
-
Giant single-cycle THz pulsesfor pump-probe experiments
- 2016
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Strong-field single-cycle THz pulses are an invaluable tool forprobing and controlling low-energy excitations in matter such asmagnons, plasmons, phonons and Josephson waves. A novel scheme isproposed to generate quasi-half-cycle GV/m THz pulses with a mutlikilohertzrepetition rate. It makes use of coherent spontaneous emissionfrom a pre-bunched electron beam traversing an optimally taperedundulator. The scheme is the further development of the novel conceptof the slippage control in free-electron lasers [T. Tanaka, PRL 114 (2015)044801]. The pump-probe THz/X-ray/optical configuration is discussed.
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| 19. |
- Goryashko, Vitaliy, et al.
(författare)
-
HIGH-PRECISION MEASUREMENTS OF THE QUALITY FACTOR OFSUPER CONDUCTING CAVITIES AT THE FREIA LABORATORY
- 2015
-
Konferensbidrag (refereegranskat)abstract
- The dependence of cavity quality factor Q0 on accelerating gradient gives insight into the intrinsic limit of RFsurface impedance that determines the cavity performance. In this paper we propose a high-precision method of measuringQ0 of SRF cavities. A common way to study the performance of an SRF cavity is to build an oscillator around it that is referred to as a self-excited loop. In the standard approach, by tuning the loop phase for a maximum field level in thecavity and measuring forward and reflected waves, one finds the cavity coupling. Then, performing a time-decay measurement and finding the total quality factor, one gets Q0. However, this approach suffers from a deficiency originating from a single data-point measurement of the reflection coefficient. In our method by varying the loop phase shift, one obtains amplitudes of the reflection coefficient of the cavity as a function of its phases. The complex reflection coefficient describes a perfect circle in polar coordinates. Fitting the overdetermined set of data to that circle allows more accurate calculation of Q0 via the least-squares procedure. The method has been tested at the FREIA Laboratory on two cavities from IPN Orsay: a single spoke and a prototype ESS double spoke.
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| 20. |
- Goryashko, Vitaliy O., et al.
(författare)
-
The sharpness-induced mode stopping and spectrum rarefication in waveguides with periodically corrugated walls
- 2013
-
Ingår i: Waves in Random and Complex Media. - : Informa UK Limited. - 1745-5030 .- 1745-5049. ; 23:2, s. 89-113
-
Tidskriftsartikel (refereegranskat)abstract
- Starting from the rigorous excitation equation, the propagation of waves through a 2D waveguide with the periodically corrugated finite-length insert is examined in detail. The corrugation profile is chosen to obey the property that its amplitude is small as compared to the waveguide width, whereas the sharpness of the asperities is arbitrarily large. With the aid of the method of mode separation, which was developed earlier for inhomogeneous-in-bulk waveguide systems [Waves Random Media 2000; 10: 395], the corrugated segment of the waveguide is shown to serve as the effective scattering barrier whose width is coincident with the length of the insert and the average height is controlled by the sharpness of boundary asperities. Due to this barrier, the mode spectrum of the waveguide can be substantially rarefied and adjusted so as to reduce the number of extended modes to the value arbitrarily less than that in the absence of corrugation (up to zero), without changing considerably the waveguide average width.
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| 21. |
- Goryashko, Vitaliy, 1982-, et al.
(författare)
-
Proposal for Design and Test of a 352 MHz Spoke RF Source
- 2012
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- More than a dozen of spoke resonators prototypes (SSR, DSR, TSR) have been constructed and tested worldwide. None have accelerated beam until now and the ESS LINAC will be the first accelerator to operate with spoke cavities. Experience with other types of superconducting cavities indicates that high-power test is vital for reliable operation of the cavity in an accelerator. Although characteristics of a bare cavity can be obtained in a low-power test some important features of a `dressed' cavity like the electroacoustic stability and tuning system can be studied only in a high-power test stand. The ESS LINAC is a pulsed machine and the Lorentz detuning originating from the electromagnetic pressure on the cavity walls is expected to be strong. The Lorentz force along with the cavity sensitivity to mechanical excitations at some resonant frequencies may lead to self-sustained mechanical vibrations which make cavity operation dicult. Practical experience shows that increasing the boundary stiness will decrease the static Lorentz force detuning but not necessarily the dynamic one. Therefore, the FREIA group at Uppsala University is building a high-power test stand able to study performance of the ESS spoke cavity at high power. The RF test stand will be able to drive the cavity not only in the self-excitation mode but also with closed RF loop and fixed frequency. The later technique will be used to reproduce the shape of the cavity voltage pulse as it is expected to be in the cavity operating in the ESS LINAC such that the cavity tuning compensation system will be tested under realistic conditions.
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| 22. |
- Goryashko, Vitaliy, 1982-, et al.
(författare)
-
RF Power Consumption in the ESS Spoke LINAC : ESS TDR Contribution
- 2013
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In the ESS LINAC the transition energy between the DTL and the spoke LINAC was changed by adding the fourth DTL tank in order to match the spoke LINAC in terms of the velocity acceptance. We present calculation of the RF power required to be fed to each spoke cavity to achieve the nominal acceleration gradient. The RF power overhead needed to compensate the beam loading and the Lorentz detuning is calculated and the peak and average values of the total RF power are presented. Overhead in terms of the power averaged over the pulse is only a few percents whereas the peak power overhead can reach 20\% and lasts for around 200 microseconds. It turns out that the power overhead is mainly determined by the strong beam loading because of a high beam current whereas the Lorentz detuning is weak due to high stiffness of the spoke cavity and almost does not require extra power to the cavity. In our simulations the cavity voltage and phase are stabilized within nominal tolerances by feedback and feed-forward.A slow feed-forward is used to cure the Lorentzdetuning whereas a fast feedback through a signal oscillator is applied to compensate the beam loading effect.
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| 23. |
- Goryashko, Vitaliy, et al.
(författare)
-
Self-amplified coherent spontaneous emission in a free electron laser with "quiet" bunches
- 2013
-
Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 16:3, s. 030702-
-
Tidskriftsartikel (refereegranskat)abstract
- For a planar free electron laser (FEL) configuration we study self-amplified coherent spontaneous emission driven by a gradient of the bunch current in the presence of different levels of noise in bunches. The longitudinal granularity of the electron bunch density originating from shot noise is maintained throughout the analysis. For the FEL model with the SwissFEL injector bunch parameters, we calculate the probability density distribution of the maximum power of the radiation pulses for different levels of shot noise. It turns out that the temporal coherence quickly increases as the noise level reduces. We also show that the FEL based on coherent spontaneous emission produces almost Fourier transform limited pulses. The analysis indicates that the time-bandwidth product is mainly determined by the bunch length and the interaction distance in an undulator. Calculations of the FEL characteristics for different rise times of the front of the current pulse are performed, and it is found that a reduced level of the power fluctuations is preserved for the bunch current pulse with a front duration up to several FEL wavelengths. We also propose a novel scheme that permits the formation of electron bunches with a reduced level of noise and a high gradient of the current at the bunch tail to enhance coherent spontaneous emission. The presented scheme uses effects of noise reduction and controlled microbunching instability and consists of a laser heater, a bunch compressor, and a shot noise suppression section. We show that shot noise reduction by 2 orders of magnitude in electron bunches produced by the SwissFEL injector can be achieved in a compact noise suppression section. The noise factor and microbunching gain of the overall proposed scheme with and without laser heater are estimated.
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| 24. |
- Han, Li, et al.
(författare)
-
Calibration procedure for RF test
- 2016
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Precision measurements of quality factors of superconducting resonators are desired in the determination of ESS superconducting cavities. Components of the measurement setup, such as interconnecting cables and adapters, introduce variations in magnitude and phase that can mask the actual response of the device under test. In order to have an accurate measurement, calibration becomes the first and most important step. FREIA has developed a test stand based on a self-exited loop for demonstrating the performance of superconducting cavities at low power level. So far, a single spoke cavity Hélène and a double spoke cavity Germaine from IPNO have undergone a cold test with FREIA SEL. Several calibration procedures are studied in these tests. Similar test results as IPNO's previous test were obtained with the FREIA system, which means the accuracy control fulfills the requirements.This report presents the calibration procedure of the FREIA SEL test.
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| 25. |
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| 26. |
- Hoang Duc, Long, et al.
(författare)
-
Time Domain Characterization of High Power Solid State Amplifiers for the Next Generation Linear Accelerators
- 2018
-
Ingår i: Microwave and optical technology letters (Print). - : Wiley. - 0895-2477 .- 1098-2760. ; 60:1, s. 163-171
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the time domain characterization of high power pulsed solid state amplifiers to be used forlinear accelerator applications. The study comprises nonlinear circuit envelope simulations and time domainenvelope measurements. Measurements and simulations are performed under the pulsed conditions (3.5 mspulse width, 5% duty cycle) specific to the European Spallation Source (ESS) high intensity proton accelerator.We measure the characteristics of pulsed LDMOS based power amplifiers such as: pulse droop along the pulse,efficiency, average envelope pulse amplitude and phase, pulse drain current waveform, pulse drain voltagewaveform, etc. A comparison between the measured results and the simulated results is also presented. Inaddition to the pulse profile characterization, the pulse to pulse (P2P) stability of the presented solid state poweramplifier (SSPA) is investigated as variations of amplitude and phase. The P2P stability simulations areintroduced as a combination of the Monte-Carlo simulations and the nonlinear circuit envelope simulations. Thesimulated results are used for fitting the P2P measurements to give an early insight of causes of instabilities ofthe nonlinear LDMOS models.
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| 27. |
- Li, Han, et al.
(författare)
-
Characterization of a beta=0.5 double spoke cavity with a fixed power coupler
- 2019
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 927, s. 63-69
-
Tidskriftsartikel (refereegranskat)abstract
- ESS, the European Spallation Source, will adopt a single family of double spoke cavities for accelerating the beam from the normal conducting section to the first family of the elliptical superconducting cavities. It will be the first double spoke cavities in the world to be commissioned for a high power proton accelerator. The first double spoke cavity for the ESS project was tested with high power in the HNOSS cryostat at Uppsala University. A pulse-mode test stand based on a self-excited loop was used in this test. The qualification of the cavity package involves a double-spoke superconducting cavity, a fixed fundamental power coupler, tuner, a low-level radiofrequency (LLRF) system and a high-power radiofrequency (RF) station. The test represents an important verification milestone before the module assembly. This cavity had unfortunately a high dynamic loss of 12W @ 9 MV/m, where potential causes for such a high value have been studied and corresponding suggestions are listed. This paper presents the test configuration, RF conditioning history, first high power performance and experience of this cavity package.
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| 28. |
- Li, Han, et al.
(författare)
-
First High Power Test of the ESS Double Spoke Cavity
- 2017
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The first double spoke cavity for ESS project was tested with high power in the HNOSS cryostat at FREIA Laboratory. This cavity is designed for 325.21MHz, a pulse mode with 14 Hz repetition rate, up to peak power of 360 kW. The qualification of the cavity package in a high power test, involved a spoke superconducting cavity, a fundamental power coupler, LLRF system and a RF station, represented an important verification before the module assembly. This report presents the test configuration, RF conditioning history and first high power performance of this cavity package.
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| 29. |
- Li, Han, et al.
(författare)
-
RF test of ESS superconducting spoke cavities at Uppsala University
- 2016
-
Ingår i: Proceedings of IPAC2016. - 9783954501472 ; , s. 791-794
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The European Spallation Source (ESS) is an accelerator-driven neutron spallation source built in Sweden. It will deliver the first protons to a rotating tungsten target by 2019 and will reach the full 5 MW average beam power in the following years. The superconducting Spoke cavities are considered compact structures at low frequencies and having an excellent RF performance in both low and medium velocity regimes, therefore ESS will include a total of 26 double-spoke cavities. The testing of the double-spoke prototype cavity at high power has been conceded to Uppsala University, Sweden, where the Facility for Research Instrumentation and Accelerator development (FREIA) has been equipped with superconducting cavity test facility. A bare spoke cavity has been tested at the FREIA Laboratory with a self-exited loop at low power level to confirm its vertical test performance at IPNO. Similar test results as IPNO's previous test were obtained with FREIA system. In this paper we present the methods and preliminary study results of the cavity performance.
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| 30. |
- Li, Han, et al.
(författare)
-
RF Test of the ESS Double Spoke Cavity
- 2016
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A bare spoke cavity has been tested at FREIA Laboratory with a Self-exited loop at low power level to confirm its vertical test performance at IPNO. Similar test results as IPNO's previous test were obtained with FREIA system. This report presents the details of each measurement.
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| 31. |
- Li, Han, 1985-, et al.
(författare)
-
RF Test of the Hélène Single Spoke Cavity
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- FREIA has developed a test stand based on a self-exited loop for demonstrating the performance of superconducting cavities at low power level. Before the arrival ESS double spoke cavities, a single spoke cavity Hélène from IPNO has undergone a cold test with FREIA SEL to check our test method, hardware set-up and cryo-system, etc. Similar test results as IPNO's previous test were obtained with the FREIA system. This report presents the details of the FREIA SEL setup and each measurement.
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| 32. |
- Li, Han, et al.
(författare)
-
Test Characterization Of Superconducting Spoke Cavities At Uppsala University
- 2015
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Konferensbidrag (refereegranskat)abstract
- As part of the development of the ESS spoke linac, the FREIA Laboratory at Uppsala University, Sweden, hasbeen equipped with a superconducting cavity test facility. The cryogenic tests of a single and double spoke cavitydeveloped by IPN Orsay have been performed in the new HNOSS horizontal cryostat system. The cavities areequipped with a low power input antenna and a pick-up antenna. Different measurement methods wereinvestigated to measure the RF signal coupling from thecavity. Results from the tests confirm the possibility to transport the cavities from France to Sweden without consequences. We present the methods and preliminary study results of the cavity performance.
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| 33. |
- Mak, Alan, et al.
(författare)
-
Attosecond single-cycle undulator light : a review
- 2019
-
Ingår i: Reports on progress in physics (Print). - : IOP Publishing. - 0034-4885 .- 1361-6633. ; 82:2
-
Forskningsöversikt (refereegranskat)abstract
- Research at modern light sources continues to improve our knowledge of the natural world, from the subtle workings of life to matter under extreme conditions. Free-electron lasers, for instance, have enabled the characterization of biomolecular structures with sub-angstrom spatial resolution, and paved the way to controlling the molecular functions. On the other hand, attosecond temporal resolution is necessary to broaden our scope of the ultrafast world. Here we discuss attosecond pulse generation beyond present capabilities. Furthermore, we review three recently proposed methods of generating attosecond x-ray pulses. These novel methods exploit the coherent radiation of microbunched electrons in undulators and the tailoring of the emitted wavefronts. The computed pulse energy outperforms pre-existing technologies by three orders of magnitude. Specifically, our simulations of the proposed Soft X-ray Laser at MAX IV (Lund, Sweden) show that a pulse duration of 50-100 as and a pulse energy up to 5 mu J is feasible with the novel methods. In addition, the methods feature pulse shape control, enable the incorporation of orbital angular momentum, and can be used in combination with modern compact free-electron laser setups.
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| 34. |
- Mak, Alan, et al.
(författare)
-
Compact undulator line for a high-brilliance soft-X-ray free-electron laser at MAX IV
- 2019
-
Ingår i: Journal of Synchrotron Radiation. - : INT UNION CRYSTALLOGRAPHY. - 0909-0495 .- 1600-5775. ; 26, s. 891-898
-
Tidskriftsartikel (refereegranskat)abstract
- The optimal parameter space for an X-ray free-electron laser (FEL) in the self-amplified spontaneous emission (SASE) operation mode is examined. This study focuses on FEL operation with a shorter undulator period and higher undulator strength made available through recent developments in in-vacuum, cryogenic and superconducting undulators. Progress on short-period undulator technologies is surveyed and FEL output characteristics versus undulator parameters are computed. The study is performed on a case of the planned soft-X-ray FEL at the MAX IV Laboratory in Sweden. An extension of the SASE mode into the harmonic lasing self-seeded mode is also analysed.
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| 35. |
- Mak, Alan, et al.
(författare)
-
Overview of Undulator Concepts for Attosecond Single-Cycle Light
- 2018
-
Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1067
-
Tidskriftsartikel (refereegranskat)abstract
- The production of intense attosecond light pulses is an active area in accelerator research, motivated by the stringent demands of attosecond science: (i) short pulse duration for resolving the fast dynamics of electrons in atoms and molecules; (ii) high photon flux for probing and controlling such dynamics with high precision. While the free-electron laser (FEL) can deliver the highest brilliance amongst laboratory x-ray sources today, the pulse duration is typically 10-100 femtoseconds. A major obstacle to attaining attosecond duration is that the number of optical cycles increases with every undulator period. Hence, an FEL pulse typically contains tens or hundreds of cycles. In recent years, several novel concepts have been proposed to shift this paradigm, providing the basis for single-cycle pulses and paving the way towards high-brilliance attosecond light sources. This article gives an overview of these concepts.
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| 36. |
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| 37. |
- Mak, Alan, et al.
(författare)
-
Undulator Considerations in the Baseline Design of the MAX IV Soft X-Ray Laser
- 2018
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We examine the optimal parameter space for an x-ray free-electron laser (FEL) in the operation mode of self-amplified spontaneous emission (SASE). The study focuses on FEL operation with a shorter undulator period and higher undulator strength made available through recent developments in in-vacuum, cryogenic and superconducting undulators. We survey the progress on short-period undulator technologies and compute the FEL output characteristics versus the undulator parameters. We perform the study on a case of the planned soft-x-ray FEL at the MAX IV Laboratory in Sweden. An extension of the SASE mode into the harmonic lasing self-seeded mode is also analysed.
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| 38. |
- Nguyen, F., et al.
(författare)
-
Undulators and Light Production with the XLS-CompactLight Design Study
- 2022
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Ingår i: MOSCOW UNIVERSITY PHYSICS BULLETIN. - : Allerton Press. - 0027-1349 .- 1934-8460. ; 77:2, s. 241-244
-
Tidskriftsartikel (refereegranskat)abstract
- Free electron laser (FEL) facilities provide broadly tunable and highly coherent photon beams. These machines still have an unexplored potential and development. The XLS-CompactLight design aims at a flexible hard plus soft X-ray FEL facility exploiting the latest concepts in terms of short period magnetic undulators, paving the road towards more compact photon sources.
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| 39. |
- Olvegård, Maja, et al.
(författare)
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PROGRESS AT THE FREIA LABORATORY
- 2015
-
Ingår i: Proceedings of IPAC'15. - JACoW : The Joint Accelerator Conferences Website.
-
Konferensbidrag (refereegranskat)abstract
- The FREIA Facility for Research Instrumentation and Accelerator Development at Uppsala University, Sweden, has reached the stage where the testing of superconducting cavities for the European Spallation Source (ESS) is starting. The new helium liquefaction plant has been commissioned and now supplies a custom-made, versatile horizontal cryostat, HNOSS, with liquid helium at up to 140 l/h. The cryostat has been designed and built to house up to two accelerating cavities, or, later on, other superconducting equipment such as magnets or crab cavities. A prototype cavity for the spoke section of the ESS linac will arrive mid 2015 for high-power testing in the horizontal cryostat. Two tetrode-based commercial RF power stations will deliver 400 kW peak power each, at 352 MHz, to the cavity through an RF distribution line developed at FREIA. In addition, significant progress has been made with in-house development of solid state amplifier modules and powercombiners for future use in particle accelerators. We report here on these and other ongoing activities at the FREIA laboratory.
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| 40. |
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| 41. |
- Opanasenko, A., et al.
(författare)
-
Design study of a low-emittance high-repetition rate thermionic rf gun
- 2017
-
Ingår i: Physical Review Accelerators and Beams. - 2469-9888. ; 20:5
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a novel gridless continuous-wave radiofrequency (rf) thermionic gun capable of generating nC ns electron bunches with a rms normalized slice emittance close to the thermal level of 0.3 mm mrad. In order to gate the electron emission, an externally heated thermionic cathode is installed into a stripline-loop conductor. Two high-voltage pulses propagating towards each other in the stripline-loop overlap in the cathode region and create a quasielectrostatic field gating the electron emission. The repetition rate of pulses is variable and can reach up to one MHz with modern solid-state pulsers. The stripline attached to a rf gun cavity wall has with the wall a common aperture that allows the electrons to be injected into the rf cavity for further acceleration. Thanks to this innovative gridless design, simulations suggest that the bunch emittance is approximately at the thermal level after the bunch injection into the cavity provided that the geometry of the cathode and aperture are properly designed. Specifically, a concave cathode is adopted to imprint an.-shaped distribution onto the beam transverse phase-space to compensate for an S-shaped beam distribution created by the spherical aberration of the aperture-cavity region. In order to compensate for the energy spread caused by rf fields of the rf gun cavity, a 3rd harmonic cavity is used. A detailed study of the electrodynamics of the stripline and rf gun cavity as well as the beam optics and bunch dynamics are presented.
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| 42. |
- Opanasenko, Anatoliy, et al.
(författare)
-
Half-wavelength velocity bunching : non-adiabatic temporal focusing of charged particle beams
- 2023
-
Ingår i: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 25:12
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers (XFELs) and megaelectronvolt ultrafast electron diffractometers (MeV UEDs) are revolutionary scientific instruments that allow visualizing the dynamics of elementary excitations in a wide range of systems from atoms and molecules to phonons, magnons and plasmons. Femtosecond (fs) electron beams are at the heart of XFELs and MeV UEDs, and the formation of fs electron beams with ultrahigh brightness is the subject of active research. We report an interesting regime of non-adiabatic temporal compression of electron beams by two orders of magnitude. Via analytical calculations and numerical simulations, we show that few MeV electron bunches can be trapped and compressed by a strong electromagnetic field within a half of the field wavelength. Furthermore, in a multi-cell accelerating cavity, the bunch is first compressed and then accelerated, thus allowing one to preserve very short bunch duration. For example, a 3 ps 16 pC 1 MeV electron bunch is compressed to 21 fs rms and accelerated to 12 MeV in a TESLA superconducting cavity. Another example is the production of 1.2 fs 16 fC 3.3 MeV bunches with a coherence length of 20 nm and and an energy spread less than 3 keV. The discovered mechanism of compression, which is another mode of velocity bunching, opens the door for obtaining very high electron brightness.
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| 43. |
- Opanasenko, A. M., et al.
(författare)
-
Multislice Model Of Electron Bunch For Study Of Ballistic Bunching Of Low Emittance Beams
- 2018
-
Ingår i: Problems Of Atomic Science And Technology. - 1562-6016. ; :3, s. 73-80
-
Tidskriftsartikel (refereegranskat)abstract
- At ballistic bunching of an electron beam the transverse distribution of space-charge field varies along a bunch greatly. It can lead to emittance growth unless to provide its compensation. To study this problem, a multislice model of a bunch of relativistic charged particles that needs no smallness of energy spread between slices are developed. This removes the limit on the value of the RF field that modulates the slices by velocity before their injection into a drift space. The longitudinal dynamics of each slice is determined by its interaction with the field of the entire bunch averaged over the slice. Transverse beam characteristics are found from a differential equation for root-mean-square envelope of a beam.
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| 44. |
- Opanasenko, Anatoliy, 1961-, et al.
(författare)
-
Towards a combined THz/X-ray source : report IV of the series of reports by the Swedish FEL Center and the FREIA Group
- 2014
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In the framework of development of a Free Electron Laser (FEL) by the Swedish FEL Center and theFREIA laboratory, we discuss the design of a versatile combined THz/X-ray source driven by high-brightness electron bunches produced by a superconducting linear accelerator. The ultimate goal isto build a versatile photon source for multidisciplinary research at the FREIA laboratory of UppsalaUniversity. A signicant part of equipment is potentially available via the FREIA project at UppsalaUniversity after 2018 such as the cryogenic system, the system of power generation and transportation,control and data acquisition systems. For pump-probe experiments, we discus a possibility to combinethe THz source with an X-ray source based on the inverse Compton scattering of quantum laser pulsesfrom electron bunches. The X-ray source will operate in the \water window" with an output intensitycomparable to a second generation synchrotron. The envisioned THz/X-ray source is compact andcomparable in budget to the cost of one beamline at MAX IV. The source can also be used to trainstudents in accelerator physics and applications of THz and synchrotron radiation.
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| 45. |
- Qin, Weilun, et al.
(författare)
-
The FEL in the SXL project at MAX IV
- 2021
-
Ingår i: Journal of Synchrotron Radiation. - : International Union Of Crystallography. - 1600-5775 .- 0909-0495. ; 28, s. 707-717
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper the design of the free-electron laser (FEL) in the SXL (Soft X-ray Laser) project at the MAX IV Laboratory is presented. The target performance parameters originate in a science case put forward by Swedish users and the SXL FEL is foreseen to be driven by the existing MAX IV 3 GeV linac. The SXL project is planned to be realized in different stages and in this paper the focus is on Phase 1, where the basic operation mode for the FEL will be SASE (self-amplified spontaneous emission), with an emphasis on short pulses. Simulation results for two linac bunches (high and low charge) with different pulse duration are illustrated, as well as the performance for two-color/two-pulses mode and power enhancement through tapering. Besides standard SASE and optical klystron configurations, the FEL setup is also tailored to allow for advanced seeding schemes operations. Finally possible upgrades that will be implemented in a second phase of the project are discussed.
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| 46. |
- Ruber, Roger, et al.
(författare)
-
Accelerator development at the FREIA Laboratory
- 2021
-
Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 16:7
-
Tidskriftsartikel (refereegranskat)abstract
- The FREIA Laboratory at Uppsala University focuses on superconducting technology and accelerator development. It actively supports the development of the European Spallation Source, CERN, and MAX IV, among others. FREIA has developed test facilities for superconducting accelerator technology such as a double-cavity horizontal test cryostat, a vertical cryostat with a novel magnetic field compensation scheme, and a test stand for short cryomodules. Accelerating cavities have been tested in the horizontal cryostat, crab-cavities cavities in the vertical cryostat, and cryomodules for ESS on the cryomodule test stand. High power radio-frequency amplifier prototypes based on vacuum tube technology were developed for driving spoke cavities. Solid-state amplifiers and power combiners are under development for future projects. We present the status of the FREIA Laboratory complemented with results of recent projects and future prospects.
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| 47. |
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| 48. |
- Salén, Peter, et al.
(författare)
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Matter manipulation with extreme terahertz light: Progress in the enabling THz technology
- 2019
-
Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 836-837, s. 1-74
-
Tidskriftsartikel (refereegranskat)abstract
- Terahertz (THz) light has proven to be a fine tool to probe and control quasi-particles and collective excitations in solids, to drive phase transitions and associated changes in material properties, and to study rotations and vibrations in molecular systems. In contrast to visible light, which usually carries excessive photon energy for collective excitations in condensed matter systems, THz light allows for direct coupling to low-energy (meV scale) excitations of interest. The development of light sources of strong-field few-cycle THz pulses in the 2000s opened the door to controlled manipulation of reactions and processes. Such THz pulses can drive new dynamic states of matter, in which materials exhibit properties entirely different from that of the equilibrium. In this review, we first systematically analyze known studies on matter manipulation with strong-field few-cycle THz light and outline some anticipated new results. We focus on how properties of materials can be manipulated by driving the dynamics of different excitations and how molecules and particles can be controlled in useful ways by extreme THz light. Around 200 studies are examined, most of which were done during the last five years. Secondly, we discuss available and proposed sources of strong-field few-cycle THz pulses and their state-of-the-art operation parameters. Finally, we review current approaches to guiding, focusing, reshaping and diagnostics of THz pulses.
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| 49. |
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| 50. |
- Shamuilov, Georgii, et al.
(författare)
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Analytical model of waveform-controlled single-cycle light pulses from an undulator
- 2018
-
Ingår i: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 43:4, s. 819-822
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter builds upon a recent concept [Phys. Rev. Lett. 113, 104801 (2014)] for producing ultrashort optical pulses through the coherent radiation of electrons in an undulator. Each pulse contains only a single oscillation cycle, and has a controlled waveform (and hence a stable carrier-envelope phase). While the concept had been demonstrated numerically, this Letter provides an analytical model for the radiation mechanism, thereby revealing three key observations: (i) the correlation between the waveforms of the optical and undulator fields; (ii) the free-space dispersion of transversely confined light; and (iii) the dependence of the optical pulse shape on the undulator field strength.
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