Future Light Sources Research Articles

SATELLITE-MOUNTED LIGHT SOURCES AS PHOTOMETRIC CALIBRATION STANDARDS FOR GROUND-BASED TELESCOPES

A significant and growing portion of systematic error on a number of fundamental parameters in astrophysics and cosmology is due to uncertainties from absolute photometric and flux standards. A path toward achieving major reduction in such uncertainties may be provided by satellite-mounted light sources, resulting in improvement in the ability to precisely characterize atmospheric extinction, and thus helping to usher in the coming generation of precision results in astronomy. Using a campaign of observations of the 532 nm pulsed laser aboard the CALIPSO satellite, collected using a portable network of cameras and photodiodes, we obtain initial measurements of atmospheric extinction, which can apparently be greatly improved by further data of this type. For a future satellite-mounted precision light source, a high-altitude balloon platform under development (together with colleagues) can provide testing as well as observational data for calibration of atmospheric uncertainties.

Generation of attosecond coherent X-ray radiation through modulation compression

In this paper, we propose a scheme to generate tunable attosecond coherent X-ray radiation for future light source applications. This scheme uses a short-pulse seeding laser, two bunch compressors, and a laser chirper to generate a prebunched, kilo-Ampere current electron beam from an initial 10-Ampere low-current electron beam. Such an electron beam sent into a short undulator generates attosecond coherent soft X-ray radiation. The final X-ray radiation wavelength can be tuned by adjusting the compression factor. It also allows one to control the final radiation pulse length by controlling the seeding laser pulse length or the compression factor. As an illustration, we present an example to generate 1 GW, 200 attosecond, 1 nm coherent X-ray radiation from a 28 A current, 200 nm laser modulated beam.

Generation of multi-color attosecond x-ray radiation through modulation compression

In this paper, we propose a scheme to generate tunable multi-color attosecond coherent X-ray radiation for future light source applications. This scheme uses an energy chirped electron beam, a laser modulators, a laser chirper and two bunch compressors to generate a multi-spike prebunched kilo-Ampere current electron beam from a few tens Ampere electron beam out of a linac. Such an electron beam transports through a series of undulator radiators and bunch compressors to generate multi-color coherent X-ray radiation. As an illustration, we present an example to generate two attosecond pulses with $2.2$ nm and $3$ nm coherent X-ray radiation wavelength and more than $200$ MW peak power using a $30$ Ampere $200$ nm laser seeded electron beam.

Suppression of beam-ion instability in electron rings with multibunch train beam fillings

The ion-caused beam instability in the future light sources and electron damping rings can be serious due to the high beam current and ultrasmall emittance of picometer level. One simple and effective mitigation of the instability is a multibunch train beam filling pattern which can significantly reduce the ion density near the beam, and therefore reduce the instability growth rate up to 2 orders of magnitude. The suppression is more effective for high intensity beams with low emittance. The distribution and the electric field of trapped ions are benchmarked to validate the model used in the paper. The wakefield of ion cloud and the beam-ion instability is investigated both analytically and numerically. We derived a simple formula for the buildup of ion cloud and instability growth rate with the multibunch train filling pattern. The simulation in NSLSII, PEPX, SuperKEKB, and the observation in SPEAR3 are used to compare with our analyses. The analyses agree well with simulations and observations.

A low emittance and high efficiency visible light photocathode for high brightness accelerator-based X-ray light sources

Free-electron lasers and energy recovery linacs represent a new generation of ultra-high brightness electron accelerator based x-ray sources. Photocathodes are a critical performance-limiting component of these systems. Here, we describe the development of photocathodes based on potassium-cesium-antimonide that satisfy many of the key requirements of future light sources, such as robustness, high quantum efficiency when excited with visible light, and low transverse emittance.

Conceptual design of a novel insertion device using bulk superconducting magnet

An undulator or a wiggler with a strong magnetic field will play an important role in future synchrotron light sources, free electron lasers, and linear colliders. We proposed the bulk high critical temperature superconductor staggered array undulator (Bulk HTSC SAU) in order to generate a strong periodic field. The Bulk HTSC SAU consists of stacked bulk high-Tc superconductors (HTSs) and a solenoid magnet which is used to magnetize the bulk HTSs. A periodic magnetic field was produced and controlled using a prototype of the Bulk HTSC SAU using 11 pairs of REBaCuO bulk HTSs at 77K. The expected performance at low temperatures around 20K is calculated using a loop current model.

Mercury-free high pressure discharge lamps dominated by molecular radiation

High intensity discharge (HID) lamps dominated by molecular radiation offer a very promising alternative for use in future light sources. They are able to deliver competitive efficacies of about 110 lm W−1 and higher, excellent colour rendering index above 90 and a correlated colour temperature in the 3000–4000 K region at the operating point near the Planckian locus. Moreover, these lamps are opening up the possibility of dimming. Due to the fact that they are able to omit mercury they are environmentally friendly.The emission spectra generated by these HID lamps differ significantly from those of conventional lamps. The reason for this is the dominance of molecular radiation processes. In comparison with conventional HID lamps atomic contributions are usually rather small. In the present case they amount to less than about 10% of the total intensity in the visible range.

Development trends for insertion devices of future synchrotron light sources

The in-vacuum undulator with a permanent magnet at room temperature is a mature technology and is widely used; with a short period length in a medium-energy facility, it can enhance photon brilliance in the hard x-ray region. A cryogenic permanent magnet has been investigated as an in-vacuum undulator; this undulator will become the best prospective device to satisfy the requirements of a photon source with great brilliance in the hard x-ray region. For the further hard x-ray region, a superconducting wiggler can provide great flux with a continuous spectrum, whereas a superconducting undulator will provide great brilliance with a discrete spectrum. High-temperature superconducting wires are highly promising for use in the development of superconducting undulators; unique algorithms for their development with an extremely short period in a small-magnet gap have been devised. Some out-of-vacuum planar undulators with special functions must also be fabricated to enable diverse applications in various light-source facilities. This article describes current and future developments for insertion devices in storage-ring and free-electron-laser facilities and discusses their feasibility for use therein.

Generation of coherent X-ray radiation through modulation compression

In this paper, we propose a scheme to generate tunable coherent X-ray radiation for future light source applications. This scheme uses an energy chirped electron beam, a laser modulator, a laser chirper and two bunch compressors to generate a prebunched kilo-Ampere current electron beam from a few tens Ampere electron beam out of a linac. The initial modulation energy wavelength can be compressed by a factor of 1 + h b R 56 a in phase space, where h b is the energy bunch length chirp introduced by the laser chirper, R 56 a is the momentum compaction factor of the first bunch compressor. As an illustration, we present an example to generate more than 400 MW, 170 attoseconds pulse, 1 nm coherent X-ray radiation using a 60 A electron beam out of the linac and 200 nm laser seed. Both the final wavelength and the radiation pulse length in the proposed scheme are tunable by adjusting the compression factor and the laser parameters.

Perspectives for future light source lattices incorporating yet uncommon magnets

Although octupoles, decapoles, and longitudinal gradient bending magnets (LGB) have been studied for many years, they are not usually included in light source lattices. They can, however, be beneficial in order to realize ultralow emittance and attain sufficient dynamic aperture. We present methods for achieving ultralow emittance and discuss optimization of the nonlinear dynamics with multipoles. We demonstrate how control of amplitude-dependent tune shift makes octupoles a powerful tool for dynamic aperture optimization. Control of higher-order chromaticity by octupoles and decapoles is straightforward; however, since this turns out to be not quite as efficient in high-brightness lattices with low arc dispersion, we apply it to a conventional lattice to demonstrate the potential. This paper also illustrates how high-field LGBs can be used to build a compact, bright hard x-ray source. Finally, we demonstrate in detail the application of octupoles as integral components of the MAX IV 3 GeV storage ring lattice.

Measurement of self-shaped ellipsoidal bunches from a photoinjector with postacceleration

Recent work has shown the possibility of generating self-shaped ellipsoidal beams with properties commensurate with the requirements of future light sources such as free-electron lasers and inverse Compton sources. In this so-termed ``blowout'' regime, short laser bunches are transformed via photoemission into short electron bunches which then self-consistently evolve into nearly uniform-density ellipsoids under space-charge forces. We report here on the first blowout studies conducted in collaboration between the UCLA Particle Beam Physics Lab and the Photo Injector Test Facility, Zeuthen (PITZ). The measurements conducted at the PITZ photoinjector facility examine the evolution of 750 pC, 2.7 ps FWHM electron bunches born in an L-band photoinjector and subsequently accelerated through a nine-cell L-band booster for a resulting energy of 12 MeV. These measurements represent the first observations of self-shaped ellipsoid evolution under postinjector acceleration, a key step in demonstrating the utility of such self-shaped beams at higher energy, where the advantages in both transverse and longitudinal and transverse phase space may be exploited in creating very high brightness beams.

Single-particle dynamics in electron storage rings with extremely low emittance

Electron storage rings are widely used for high luminosity colliders, damping rings in high-energy linear colliders, and synchrotron light sources. They have become essential facilities to study high-energy physics and material and medical sciences. To further increase the luminosity of colliders or the brightness of synchrotron light sources, the beam emittance is being continually pushed downward, recently to the nanometer region. In the next decade, another order of reduction is expected. This requirement of ultra-low emittance presents many design challenges in beam dynamics, including better analysis of maps and improvement of dynamic apertures. To meet these challenges, we have refined transfer maps of common elements in storage rings and developed a new method to compute the resonance driving terms as they are built up along a beamline. The method is successfully applied to a design of PEP-X as a future light source with 100-pm emittance. As a result, we discovered many unexpected cancelations of the fourth-order resonance terms driven by sextupoles within an achromat.

PEP-X: Concepts for a Future Light Source for SSRL

In a world where new storage ring light sources are pushing electron beam emittances to the nanometer-radian scale and below, producing photon beam brightness exceeding 1021 (ph/s/mm2/mrad2/0.1% BW) for multi-keV photons, the long-term future of the Stanford Synchrotron Radiation Lightsource (SSRL) may depend on a much higher performing light source than that provided by the 3-GeV SPEAR3 storage ring. SPEAR3, having an emittance of 10 nm-rad and commissioned in 2003, produces an order of magnitude lower brightness than these new sources, although with 500-mA stored beam current it is a prodigious source for flux-limited applications such as many spectroscopy applications. Incremental improvements to the machine over the next few years, which include reducing the emittance by another factor of two, will enhance science capabilities even further. Nevertheless, the lab is looking forward to a future source that far exceeds the performance of SPEAR3, enabling advanced capabilities in imaging and other areas made possible with very high coherence and brightness, and that could establish a new state of the art for performance from a ring-based light source.

X-ray sources by energy recovered linacs and their needed R&D

In this paper we review the current state of research on energy recovered linacs as drivers for future X-ray sources. For many types of user experiments, such sources may have substantial advantages compared to the workhorse sources of the present: high energy storage rings. Energy recovered linacs need to be improved beyond present experience in both energy and average current to support this application. To build an energy recovered linac based X-ray user facility presents many interesting challenges. We present summaries on the Research and Development (R&D) topics needed for full development of such a source, including the discussion at the Future Light Sources Workshop held in Gaithersburg, Maryland on September 15–17, 2009. A first iteration of an R&D plan is presented that is founded on the notion of building a set of succeedingly larger test accelerators exploring cathode physics, high average current injector physics, and beam recirculation and beam energy recovery at high average current. Our basic conclusion is that a reviewable design of such a source can be developed after an R&D period of five to ten years.

Particle-field decomposition and domain decomposition in parallel particle-in-cell beam dynamics simulation

Particle-in-cell (PIC) simulation is widely used in many branches of physics and engineering. In this paper, we give an analysis of the particle-field decomposition method and the domain decomposition method in parallel particle-in-cell beam dynamics simulation. The parallel performance of the two decomposition methods was studied on the Cray XT4 and the IBM Blue Gene/P Computers. The domain decomposition method shows better scalability but is slower than the particle-field decomposition in most cases (up to a few thousand processors) for macroparticle dominant applications. The particle-field decomposition method also shows less memory usage than the domain decomposition method due to its use of perfect static load balance. For applications with a smaller ratio of macroparticles to grid points, the domain decomposition method exhibits better scalability and faster speed. Application of the particle-field decomposition scheme to high-resolution macroparticle-dominant parallel beam dynamics simulation for a future light source linear accelerator is presented as an example.

Reduction of Multipole Fields in Photocathode RF Gun

Photocathode rf gun, the high-brightness electron source with extremely low emittance is highly required for future light sources such as X-ray free electron lasers (XFEL). The coupling hole between the waveguide and the cavity of a photocathode rf gun causes asymmetries in the rf fields at the coupler cell. The dipole and quadruple fields are the dominant sources of the transverse rf emittance growth. In the BNL Gun-III, the dipole field is reduced by adding a symmetric pumping hole at the opposite side of the waveguide coupling hole. The dipole field can be reduced further by adjusting the size of the pumping hole. However, the quadruple field cannot be suppressed by the single pumping hole. We have designed new rf cavity in which the quadruple field as well as the dipole one are suppressed. In this design, two additional pumping ports are placed at the 90° positions with respect to the coupling hole and the pumping holes. Beam dynamics simulation for newly designed rf gun shows that the vertical transverse emittance is reduced by about 60% compared to the old one.

Adapting TESLA technology for future cw light sources using HoBiCaT

The HoBiCaT facility has been set up and operated at the Helmholtz-Zentrum-Berlin and BESSY since 2005. Its purpose is testing superconducting cavities in cw mode of operation and it was successfully demonstrated that TESLA pulsed technology can be used for cw mode of operation with only minor changes. Issues that were addressed comprise of elevated dynamic thermal losses in the cavity walls, necessary modifications in the cryogenics and the cavity processing, the optimum choice of operational parameters such as cavity temperature or bandwidth, the characterization of higher order modes in the cavity, and the usability of existing tuners and couplers for cw.

New source technologies and their impact on future light sources

Emerging technologies are critically evaluated for their feasibility in future light sources. We consider both new technologies for electron beam generation and acceleration suitable for X-ray free-electron lasers (FELs), as well as alternative photon generation technologies including the relatively mature inverse Compton scattering and laser high-harmonic generation. Laser-driven plasma wakefield acceleration is the most advanced of the novel acceleration technologies, and may be suitable to generate electron beams for X-ray FELs in a decade. We provide research recommendations to achieve the needed parameters for driving future light sources, including necessary advances in laser technology.

Cathode R&D for future light sources

This paper reviews the requirements and current status of cathodes for accelerator applications, and proposes a research and development plan for advancing cathode technology. Accelerator cathodes need to have long operational lifetimes and produce electron beams with a very low emittance. The two principal emission processes to be considered are thermionic and photoemission with the photocathodes being further subdivided into metal and semi-conductors. Field emission cathodes are not included in this analysis. The thermal emittance is derived and the formulas used to compare the various cathode materials. To date, there is no cathode which provides all the requirements needed for the proposed future light sources. Therefore a three part research plan is described to develop cathodes for these future light source applications.

High-voltage testing of a 500-kV dc photocathode electron gun

A high-voltage dc photocathode electron gun was successfully conditioned up to a voltage of 550 kV and a long-time holding test for 8 h was demonstrated at an acceleration voltage of 500 kV. The dc photocathode electron gun is designed for future light sources based on energy-recovery linac and consists of a Cockcroft-Walton generator, a segmented cylindrical ceramic insulator, guard-ring electrodes, a support-rod electrode, a vacuum chamber, and a pressurized insulating gas tank. The segmented cylindrical ceramic insulator and the guard-ring electrodes were utilized to prevent any damage to the insulator from electrons emitted by the support-rod electrode.