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David Douglas

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Papers by David Douglas

High Power Operation of the JLab IR FEL Driver Accelerator

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Aug 1, 2007

Operation of the JLab IR Upgrade FEL at CW powers in excess of 10 kW requires sustained productio... more Operation of the JLab IR Upgrade FEL at CW powers in excess of 10 kW requires sustained production of high electron beam powers by the driver ERL. This in turn demands attention to numerous issues and effects, including: cathode lifetime; control of beamline and RF system vacuum during high current operation; longitudinal space charge; longitudinal and transverse matching of irregular/large volume phase space distributions; halo management; management of remnant dispersive effects; resistive wall, wake-field, and RF heating of beam vacuum chambers; the beam break up instability; the impact of coherent synchrotron radiation (both on beam quality and the performance of laser optics); magnetic component stability and reproducibility; and RF stability and reproducibility. We discuss our experience with these issues and describe the modus vivendi that has evolved during prolonged high current, high power beam and laser operation.

Multistage CSR microbunching gain development in transport or recirculation arcs

arXiv (Cornell University), Aug 19, 2015

Coherent synchrotron radiation (CSR) induced microbunching instability has been one of the most c... more Coherent synchrotron radiation (CSR) induced microbunching instability has been one of the most challenging issues in the design of modern accelerators. A linear Vlasov solver has been developed [1] and applied to investigate the physical processes of microbunching gain amplification for several example lattices [2]. In this paper, by further extending the concept of stage gain as proposed by Huang and Kim [3], we develop a method to characterize the microbunching development in terms of stage orders that allow the quantitative comparison of optics impacts on microbunching gain for different lattices. We find that the microbunching instability in our demonstrated arcs has a distinguishing feature of multistage amplification (e.g, up to 6th stage amplification for our example transport arcs, in contrast to two-stage amplification for a typical 4-dipole bunch compressor chicane). We also try to connect lattice optics pattern with the obtained stage gain functions by a physical interpretation. This Vlasov analysis is validated by ELEGANT [4] tracking results with excellent agreement.

Linear Vlasov solver for microbunching gain estimation with inclusion of CSR, LSC and linac geometric impedances

arXiv (Cornell University), Aug 19, 2015

As is known, microbunching instability (MBI) has been one of the most challenging issues in desig... more As is known, microbunching instability (MBI) has been one of the most challenging issues in designs of magnetic chicanes for short-wavelength free-electron lasers or linear colliders, as well as those of transport lines for recirculating or energy recovery linac machines. To more accurately quantify MBI in a single-pass system and for more complete analyses, we further extend and continue to increase the capabilities of our previously developed linear Vlasov solver [1] to incorporate more relevant impedance models into the code, including transient and steady-state free-space and/or shielding coherent synchrotron radiation (CSR) impedances, the longitudinal space charge (LSC) impedances, and the linac geometric impedances with extension of the existing formulation to include beam acceleration [2]. Then, we directly solve the linearized Vlasov equation numerically for microbunching gain amplification factor. In this study we apply this code to a beamline lattice of transport arc [3] following an upstream linac section. The resultant gain functions and spectra are presented here, and some results are compared with particle tracking simulation by ELEGANT [4]. We also discuss some underlying physics with inclusion of these collective effects and the limitation of the existing formulation. It is anticipated that this more thorough analysis can further improve the understanding of MBI mechanisms and shed light on how to suppress or compensate MBI effects in lattice designs.

Driver Accelerator Design for the 10 kW Upgrade of the Jefferson Lab IR FEL

arXiv (Cornell University), Aug 10, 2000

An upgrade of the Jefferson Lab IR FEL [1] is now under construction. It will provide 10 kW outpu... more An upgrade of the Jefferson Lab IR FEL [1] is now under construction. It will provide 10 kW output light power in a wavelength range of 2-10 µm. The FEL will be driven by a modest sized 80-210 MeV, 10 mA energy-recovering CW superconducting RF (SRF) linac. Stringent phase space requirements at the wiggler, low beam energy, and high beam current subject the design to numerous constraints. These are imposed by the need for both transverse and longitudinal phase space management, the potential impact of collective phenomena (space charge, wakefields, beam break-up (BBU), and coherent synchrotron radiation (CSR)), and interactions between the FEL and the accelerator RF system. This report addresses these issues and presents an accelerator design solution meeting the requirements imposed by physical phenomena and operational necessities.

High-Current Energy-Recovering Electron Linacs

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Dec 1, 2003

The use of energy recovery provides a potentially powerful new paradigm for generation of the cha... more The use of energy recovery provides a potentially powerful new paradigm for generation of the charged particle beams used in synchrotron radiation sources, high-energy electron cooling devices, electron-ion colliders, and other applications in photon science and nuclear and high-energy physics. Energy-recovering electron linear accelerators (called energy-recovering linacs, or ERLs) share many characteristics with ordinary linacs, as their six-dimensional beam phase space is largely determined by electron source properties. However, in common with classic storage rings, ERLs possess a high average-current-carrying capability enabled by the energy recovery process, and thus promise similar efficiencies. We discuss the concept of energy recovery and its technical challenges and describe the Jefferson Lab (JLab) Infrared Demonstration Free-Electron Laser (IR Demo FEL), originally driven by a 35-48-MeV, 5-mA superconducting radiofrequency (srf) ERL, which provided the most substantial demonstration of energy recovery to date: a beam of 250 kW average power. We present an overview of envisioned ERL applications and a development path to achieving the required performance. We use experimental data obtained at the JLab IR Demo FEL and recent experimental results from CEBAF-ERa GeV-scale, comparatively low-current energy-recovery demonstration at JLab-to evaluate the feasibility of the new applications of high-current ERLs, as well as ERLs' limitations and ultimate performance.

CSR induced microbunching gain estimation including transient effects in transport and recirculation arcs

6th Int. Particle Accelerator Conf. (IPAC'15), Richmond, VA, USA, May 3-8, 2015, Sep 1, 2015

The coherent synchrotron radiation (CSR) of a high brightness electron beam traversing a series o... more The coherent synchrotron radiation (CSR) of a high brightness electron beam traversing a series of dipoles, such as transport or recirculation arcs, may result in the microbunching instability (μBI). To accurately quantify the direct consequence of this effect, we further extend our previously developed semi-analytical Vlasov solver [1] to include more relevant coherent radiation models than the steady-state free-space CSR impedance, such as the entrance and exit transient effects derived from upstream beam entering to and exiting from individual dipoles. The resultant microbunching gain functions and spectra for our example lattices are presented and compared with particle tracking simulation. Some underlying physics with inclusion of these effects are also discussed.

Architectural Considerations for Recirculated and Energy-Recovered Hard XFEL Drivers

A confluence of events motivates discussion of design options for hard x-ray free electron laser ... more A confluence of events motivates discussion of design options for hard x-ray free electron laser (XFEL) driver accelerators. Firstly, multiple superconducting radio-frequency (SRF) driven systems are coming online (European XFEL), in construction (LCLS-II, SCLF), or in design (MARIE); these provide increasing evidence of the transformational potential they offer for fundamental science with its concomitant benefits. Secondly, successful operation of 12 GeV CEBAF [1] validates use of recirculation in the design of high energy SRF linacs. Thirdly, advances in the analysis and control of various effects – including coherent synchrotron radiation (CSR) and the microbunching instability (BI) – have been recently achieved. Taken collectively, these developments offer opportunities to extend facility science reach, reduce cost, provide multiplicity (i.e., support numerous FELs operating over a range of wavelengths), and enhance scalability and upgradability (to higher powers and energies)...

CBETA: The Cornell/BNL 4-Turn ERL with FFAG Return Arcs for eRHIC Prototyping

Cornell University has prototyped technology essential for any high brightness electron ERL. This... more Cornell University has prototyped technology essential for any high brightness electron ERL. This includes a DC gun and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current CW cryomodule, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams, e.g. slid measurements for 6-D phase-space densities, a fast wire scanner for beam profiles, and beam loos diagnostics. All these are now available to equip a one-cryomodule ERL, and laboratory space has been cleared out and is radiation shielded to install this ERL at Cornell. BNL has designed a multi-turn ERL for eRHIC, where beam is transported more than 20 times around the RHIC tunnel. The number of transport lines is minimized by using two non-scaling (NS) FFAG arcs. A collaboration between BNL and Cornell has been formed to investigate the new NS-FFAG optics and the multi-turn eRHIC ERL design by building a 4-turn, one-cryomodule ERL at Cornel...

A Novel Use oF FFAGs in ERLs - in Colliders: eRHIC, LHeC and a Prototype at Cornell University

The future Electron Ion Collider (EIC) LHeC will be able to collide electrons with protons/ions, ... more The future Electron Ion Collider (EIC) LHeC will be able to collide electrons with protons/ions, while the eRHIC will have additional ability to collide polarized electron with polarized proton/He3+to study origin of the proton spin. Electron acceleration is based on a concept of Energy Recovery Linacs (ERL) with maximum energies of 60 GeV for LHeC and 20 GeV for eRHIC. It will almost completely recover electron energy during deceleration to the initial energy. We present: LHeC, eRHIC, an ERL at Cornell University the eRHIC prototype. An example of the LHeC with almost doubling a reduction in size of the linac, from 2 x 10 GeV to 2 x 5.345 GeV from the present LHeC solution, using two NS-FFAG’s beam lines. This would reduce the three beam lines to two, and raise the luminosity for 34% as the electron current of 6.6 mA  8.9 mA, due to the synchrotron radiation limit of 15 MW. For the LHeC FFAG solution with 2x5.345 GeV linacs the total synchrotron radiation loss for 25 mA is 36.4 MW...

ER@CEBAF, a 7 GeV, 5-Pass, Energy Recovery Experiment

A multiple-pass, high-energy ERL experiment at the JLab CEBAF will be instrumental in providing n... more A multiple-pass, high-energy ERL experiment at the JLab CEBAF will be instrumental in providing necessary information and technology testing for a number of possible future applications and facilities such as Linac-Ring based colliders, which have been designed at BNL (eRHIC) and CERN (LHeC), and also drivers for high-energy FELs and 4th GLS. ER@CEBAF is aimed at investigating 6D optics and beam dynamics issues in ERLs, such as synchrotron radiation effects, emittance preservation, stability, beam losses, multiple-pass orbit control/correction, multiple-pass beam dynamics in the presence of cavity HOMs, BBU and other halo studies, handling of large (SR induced) momentum spread bunches, and development of multiple-beam diagnostics instrumentation. Figure 1: 12 GeV CEBAF recirculating linac. Location of chicane and dump line for ER@CEBAF. Since it was launched 2+ years ago, the project has progressed in defining the necessary modifications to CEBAF (Fig. 1, Tab. 1, 2), including a 4-d...

ER@CEBAF - A High Energy, Multi-pass Energy Recovery Experiment at CEBAF

PERLE - Lattice Design and Beam Dynamics Studies

PERLE (Powerful ERL for Experiments) is a novel ERL test facility, initially proposed to validate... more PERLE (Powerful ERL for Experiments) is a novel ERL test facility, initially proposed to validate choices for a 60 GeV ERL foreseen in the design of the LHeC and the FCC-eh. Its main thrust is to probe high current, CW, multi-pass operation with superconducting cavities at 802 MHz (and perhaps testing other frequencies of interest). With very high virtual beam power (~ 10 MW), PERLE offers an opportunity for controllable study of every beam dynamic effect of interest in the next generation of ERL design; becoming a ‘stepping stone' between present state-of-art 1 MW ERLs and future 100 MW scale applications. PERLE design features Flexible Momentum Compaction lattice architecture for six vertically stacked return arcs and a high-current, 6 MeV, photo-injector. With only one pair of 4 cavity cryomodules, 400 MeV beam energy can be reached in 3 re-circulation passes, with beam currents in excess of 15 mA. The beam is decelerated in 3 consecutive passes back to the injection energy, ...

Applications of Caustic Methods to Longitudinal Phase Space Manipulation

Longitudinal phase space management is a key feature of recirculating machines. Careful considera... more Longitudinal phase space management is a key feature of recirculating machines. Careful consideration of the longitudinal matching is required not only in order to ensure a high peak current, low energy spread bunch is delivered to the FEL but also to support the deceleration and energy recovery of the spent beam. In a similar manner, longitudinal phase space manipulation can be utilised for pulse shaping in bunch compression, to minimise the influence of CSR-induced emittance growth. In this paper, we present a method for longitudinal phase space matching based upon the avoidance of electron trajectory caustics. Through considering the conditions under which caustics will form, we generate exclusion plots identifying the viable parameter space at numerous positions through beam acceleration and energy recovery. The result is a method for selecting the linear momentum compaction and the higher-order momentum compaction to satisfy the non-caustic condition whilst achieving the bunch ...

Suppression of Multipass, Multibunch Beam Breakup in Two Pass Recirculating Accelerators

Proc. of …, 2004

Beam Breakup (BBU) occurs in all accelerators at sufficiently high currents. In recirculating acc... more

CBETA - Cornell University Brookhaven National Laboratory Electron Energy Recovery Test Accelerator

Cornell's Lab of Accelerator-based Sciences and Education (CLASSE) and the Collider Accelerat... more Cornell's Lab of Accelerator-based Sciences and Education (CLASSE) and the Collider Accelerator Department (BNL-CAD) are developing the first SRF multi-turn energy recovery linac with Non-Scaling Fixed Field Alternating Gradient (NS-FFAG) racetrack. The existing injector and superconducting linac at Cornell University are installed together with a single NS-FFAG arcs and straight section at the opposite side of the the linac to form an Electron Energy Recovery (ERL) system. Electron beam from the 6 MeV injector is injected into the 36 MeV superconducting linac, and accelerated by four successive passes: from 42 MeV up to 150 MeV using the same NS-FFAG structure made of permanent magnets. After the maximum energy of 150 MeV is reached, the electron beam is brought back to the linac with opposite Radio Frequency (RF) phase. Energy is recovered and reduced to the initial value of 6 MeV with 4 additional passes. There are many novelties: a single NS-FFAG structure, made of permanent...

CBETA, the 4-Turn ERL with SRF and Single Return Loop

A collaboration between Cornell University and Brookhaven National Laboratory has designed and is... more A collaboration between Cornell University and Brookhaven National Laboratory has designed and is constructing CBETA, the Cornell-BNL ERL Test Accelerator on the Cornell campus. The ERL technology that has been prototyped at Cornell for many years is being used for this new accelerator, including a DC electron source and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current linac cryomodule optimized for ERLs, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams. BNL has designed multi-turn ERLs for several purpose, dominantly for the electron beam of eRHIC, its Electron Ion Collider (EIC) project and for the associated fast electron cooling system. Also in JLEIC, the EIC designed at JLAB, an ERL is envisioned to be used for electron cooling. The number of transport lines in an ERL is minimized by using return arcs that are comprised of a Fixed Field Alternating-gradient (FFA) design. Th...

Operational Aspects of High Power Energy Recovery Linacs

We have been operating a high-power energy-recovery linac (ERL) at Jefferson Lab for several year... more We have been operating a high-power energy-recovery linac (ERL) at Jefferson Lab for several years. In the process we have learned quite a bit about both technical and physics limitations in high power ERLs. Several groups are now considering new ERLs that greatly increase either the energy, the current or both. We will present some of our findings on what to consider when designing, building, and operating a high power ERL. Our remarks for this paper are limited to lattice design and setup, magnets, vacuum chamber design, diagnostics, and beam stability.

Longitudinal Space Charge Effects in the JLAB IR FEL SRF Linac ��

The injector consists of a high-voltage-DC GaAs photocathode gun driven by a frequency-doubled Nd... more The injector consists of a high-voltage-DC GaAs photocathode gun driven by a frequency-doubled Nd:YLF laser, a 10 MeV quarter cryo-unit with two 5-cell CEBAF cavities, a transverse match section and a bunch compressor [3]. The photocathode gun delivers 135 pC, 23 ps rms-long electron bunches operating at 350 kV in pulse (demonstrated up to 8 mA) and CW (demonstrated up to 9.1 mA) modes [4]. The photocathode gun performance has been studied earlier [5]. After initial acceleration at 10 MeV, the electron beam is transversely matched to the linac by means of a quadrupole telescope, longitudinal match is provided by an achromatic compressor chicane [6]. Observations of energy spread asymmetry when operating the Linac on either side of crest and longitudinal emittance growth have been confirmed by extending PARMELA simulations from the injector to the end of the first SRF Linac module. The asymmetry can be explained by the interaction of the accelerating electric field with that from longitudinal space charge effects within the electron bunch. This can be a major limitation to performance in FEL accelerators.

Design Considerations for Recirculating and Energy Recovering Linacs

Introduction Success of the energy-recovering SRF driver accelerator for the JLab IR Demo FEL has... more

Vlasov analysis of microbunching instability for magnetized beams

Physical Review Accelerators and Beams, 2017

For a high-brightness electron beam with high bunch charge traversing a recirculation beam line, ... more For a high-brightness electron beam with high bunch charge traversing a recirculation beam line, coherent synchrotron radiation and space charge effects may result in microbunching instability (MBI). Both tracking simulation and Vlasov analysis for an early design of a circulator cooler ring (CCR) for the Jefferson Lab Electron Ion Collider (JLEIC) reveal significant MBI [Ya. Derbenev and Y. Zhang,

High Power Operation of the JLab IR FEL Driver Accelerator

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Aug 1, 2007

Operation of the JLab IR Upgrade FEL at CW powers in excess of 10 kW requires sustained productio... more Operation of the JLab IR Upgrade FEL at CW powers in excess of 10 kW requires sustained production of high electron beam powers by the driver ERL. This in turn demands attention to numerous issues and effects, including: cathode lifetime; control of beamline and RF system vacuum during high current operation; longitudinal space charge; longitudinal and transverse matching of irregular/large volume phase space distributions; halo management; management of remnant dispersive effects; resistive wall, wake-field, and RF heating of beam vacuum chambers; the beam break up instability; the impact of coherent synchrotron radiation (both on beam quality and the performance of laser optics); magnetic component stability and reproducibility; and RF stability and reproducibility. We discuss our experience with these issues and describe the modus vivendi that has evolved during prolonged high current, high power beam and laser operation.

Multistage CSR microbunching gain development in transport or recirculation arcs

arXiv (Cornell University), Aug 19, 2015

Coherent synchrotron radiation (CSR) induced microbunching instability has been one of the most c... more Coherent synchrotron radiation (CSR) induced microbunching instability has been one of the most challenging issues in the design of modern accelerators. A linear Vlasov solver has been developed [1] and applied to investigate the physical processes of microbunching gain amplification for several example lattices [2]. In this paper, by further extending the concept of stage gain as proposed by Huang and Kim [3], we develop a method to characterize the microbunching development in terms of stage orders that allow the quantitative comparison of optics impacts on microbunching gain for different lattices. We find that the microbunching instability in our demonstrated arcs has a distinguishing feature of multistage amplification (e.g, up to 6th stage amplification for our example transport arcs, in contrast to two-stage amplification for a typical 4-dipole bunch compressor chicane). We also try to connect lattice optics pattern with the obtained stage gain functions by a physical interpretation. This Vlasov analysis is validated by ELEGANT [4] tracking results with excellent agreement.

Linear Vlasov solver for microbunching gain estimation with inclusion of CSR, LSC and linac geometric impedances

arXiv (Cornell University), Aug 19, 2015

As is known, microbunching instability (MBI) has been one of the most challenging issues in desig... more As is known, microbunching instability (MBI) has been one of the most challenging issues in designs of magnetic chicanes for short-wavelength free-electron lasers or linear colliders, as well as those of transport lines for recirculating or energy recovery linac machines. To more accurately quantify MBI in a single-pass system and for more complete analyses, we further extend and continue to increase the capabilities of our previously developed linear Vlasov solver [1] to incorporate more relevant impedance models into the code, including transient and steady-state free-space and/or shielding coherent synchrotron radiation (CSR) impedances, the longitudinal space charge (LSC) impedances, and the linac geometric impedances with extension of the existing formulation to include beam acceleration [2]. Then, we directly solve the linearized Vlasov equation numerically for microbunching gain amplification factor. In this study we apply this code to a beamline lattice of transport arc [3] following an upstream linac section. The resultant gain functions and spectra are presented here, and some results are compared with particle tracking simulation by ELEGANT [4]. We also discuss some underlying physics with inclusion of these collective effects and the limitation of the existing formulation. It is anticipated that this more thorough analysis can further improve the understanding of MBI mechanisms and shed light on how to suppress or compensate MBI effects in lattice designs.

Driver Accelerator Design for the 10 kW Upgrade of the Jefferson Lab IR FEL

arXiv (Cornell University), Aug 10, 2000

An upgrade of the Jefferson Lab IR FEL [1] is now under construction. It will provide 10 kW outpu... more An upgrade of the Jefferson Lab IR FEL [1] is now under construction. It will provide 10 kW output light power in a wavelength range of 2-10 µm. The FEL will be driven by a modest sized 80-210 MeV, 10 mA energy-recovering CW superconducting RF (SRF) linac. Stringent phase space requirements at the wiggler, low beam energy, and high beam current subject the design to numerous constraints. These are imposed by the need for both transverse and longitudinal phase space management, the potential impact of collective phenomena (space charge, wakefields, beam break-up (BBU), and coherent synchrotron radiation (CSR)), and interactions between the FEL and the accelerator RF system. This report addresses these issues and presents an accelerator design solution meeting the requirements imposed by physical phenomena and operational necessities.

High-Current Energy-Recovering Electron Linacs

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Dec 1, 2003

The use of energy recovery provides a potentially powerful new paradigm for generation of the cha... more The use of energy recovery provides a potentially powerful new paradigm for generation of the charged particle beams used in synchrotron radiation sources, high-energy electron cooling devices, electron-ion colliders, and other applications in photon science and nuclear and high-energy physics. Energy-recovering electron linear accelerators (called energy-recovering linacs, or ERLs) share many characteristics with ordinary linacs, as their six-dimensional beam phase space is largely determined by electron source properties. However, in common with classic storage rings, ERLs possess a high average-current-carrying capability enabled by the energy recovery process, and thus promise similar efficiencies. We discuss the concept of energy recovery and its technical challenges and describe the Jefferson Lab (JLab) Infrared Demonstration Free-Electron Laser (IR Demo FEL), originally driven by a 35-48-MeV, 5-mA superconducting radiofrequency (srf) ERL, which provided the most substantial demonstration of energy recovery to date: a beam of 250 kW average power. We present an overview of envisioned ERL applications and a development path to achieving the required performance. We use experimental data obtained at the JLab IR Demo FEL and recent experimental results from CEBAF-ERa GeV-scale, comparatively low-current energy-recovery demonstration at JLab-to evaluate the feasibility of the new applications of high-current ERLs, as well as ERLs' limitations and ultimate performance.

CSR induced microbunching gain estimation including transient effects in transport and recirculation arcs

6th Int. Particle Accelerator Conf. (IPAC'15), Richmond, VA, USA, May 3-8, 2015, Sep 1, 2015

The coherent synchrotron radiation (CSR) of a high brightness electron beam traversing a series o... more The coherent synchrotron radiation (CSR) of a high brightness electron beam traversing a series of dipoles, such as transport or recirculation arcs, may result in the microbunching instability (μBI). To accurately quantify the direct consequence of this effect, we further extend our previously developed semi-analytical Vlasov solver [1] to include more relevant coherent radiation models than the steady-state free-space CSR impedance, such as the entrance and exit transient effects derived from upstream beam entering to and exiting from individual dipoles. The resultant microbunching gain functions and spectra for our example lattices are presented and compared with particle tracking simulation. Some underlying physics with inclusion of these effects are also discussed.

Architectural Considerations for Recirculated and Energy-Recovered Hard XFEL Drivers

A confluence of events motivates discussion of design options for hard x-ray free electron laser ... more A confluence of events motivates discussion of design options for hard x-ray free electron laser (XFEL) driver accelerators. Firstly, multiple superconducting radio-frequency (SRF) driven systems are coming online (European XFEL), in construction (LCLS-II, SCLF), or in design (MARIE); these provide increasing evidence of the transformational potential they offer for fundamental science with its concomitant benefits. Secondly, successful operation of 12 GeV CEBAF [1] validates use of recirculation in the design of high energy SRF linacs. Thirdly, advances in the analysis and control of various effects – including coherent synchrotron radiation (CSR) and the microbunching instability (BI) – have been recently achieved. Taken collectively, these developments offer opportunities to extend facility science reach, reduce cost, provide multiplicity (i.e., support numerous FELs operating over a range of wavelengths), and enhance scalability and upgradability (to higher powers and energies)...

CBETA: The Cornell/BNL 4-Turn ERL with FFAG Return Arcs for eRHIC Prototyping

Cornell University has prototyped technology essential for any high brightness electron ERL. This... more Cornell University has prototyped technology essential for any high brightness electron ERL. This includes a DC gun and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current CW cryomodule, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams, e.g. slid measurements for 6-D phase-space densities, a fast wire scanner for beam profiles, and beam loos diagnostics. All these are now available to equip a one-cryomodule ERL, and laboratory space has been cleared out and is radiation shielded to install this ERL at Cornell. BNL has designed a multi-turn ERL for eRHIC, where beam is transported more than 20 times around the RHIC tunnel. The number of transport lines is minimized by using two non-scaling (NS) FFAG arcs. A collaboration between BNL and Cornell has been formed to investigate the new NS-FFAG optics and the multi-turn eRHIC ERL design by building a 4-turn, one-cryomodule ERL at Cornel...

A Novel Use oF FFAGs in ERLs - in Colliders: eRHIC, LHeC and a Prototype at Cornell University

The future Electron Ion Collider (EIC) LHeC will be able to collide electrons with protons/ions, ... more The future Electron Ion Collider (EIC) LHeC will be able to collide electrons with protons/ions, while the eRHIC will have additional ability to collide polarized electron with polarized proton/He3+to study origin of the proton spin. Electron acceleration is based on a concept of Energy Recovery Linacs (ERL) with maximum energies of 60 GeV for LHeC and 20 GeV for eRHIC. It will almost completely recover electron energy during deceleration to the initial energy. We present: LHeC, eRHIC, an ERL at Cornell University the eRHIC prototype. An example of the LHeC with almost doubling a reduction in size of the linac, from 2 x 10 GeV to 2 x 5.345 GeV from the present LHeC solution, using two NS-FFAG’s beam lines. This would reduce the three beam lines to two, and raise the luminosity for 34% as the electron current of 6.6 mA  8.9 mA, due to the synchrotron radiation limit of 15 MW. For the LHeC FFAG solution with 2x5.345 GeV linacs the total synchrotron radiation loss for 25 mA is 36.4 MW...

ER@CEBAF, a 7 GeV, 5-Pass, Energy Recovery Experiment

A multiple-pass, high-energy ERL experiment at the JLab CEBAF will be instrumental in providing n... more A multiple-pass, high-energy ERL experiment at the JLab CEBAF will be instrumental in providing necessary information and technology testing for a number of possible future applications and facilities such as Linac-Ring based colliders, which have been designed at BNL (eRHIC) and CERN (LHeC), and also drivers for high-energy FELs and 4th GLS. ER@CEBAF is aimed at investigating 6D optics and beam dynamics issues in ERLs, such as synchrotron radiation effects, emittance preservation, stability, beam losses, multiple-pass orbit control/correction, multiple-pass beam dynamics in the presence of cavity HOMs, BBU and other halo studies, handling of large (SR induced) momentum spread bunches, and development of multiple-beam diagnostics instrumentation. Figure 1: 12 GeV CEBAF recirculating linac. Location of chicane and dump line for ER@CEBAF. Since it was launched 2+ years ago, the project has progressed in defining the necessary modifications to CEBAF (Fig. 1, Tab. 1, 2), including a 4-d...

ER@CEBAF - A High Energy, Multi-pass Energy Recovery Experiment at CEBAF

PERLE - Lattice Design and Beam Dynamics Studies

PERLE (Powerful ERL for Experiments) is a novel ERL test facility, initially proposed to validate... more PERLE (Powerful ERL for Experiments) is a novel ERL test facility, initially proposed to validate choices for a 60 GeV ERL foreseen in the design of the LHeC and the FCC-eh. Its main thrust is to probe high current, CW, multi-pass operation with superconducting cavities at 802 MHz (and perhaps testing other frequencies of interest). With very high virtual beam power (~ 10 MW), PERLE offers an opportunity for controllable study of every beam dynamic effect of interest in the next generation of ERL design; becoming a ‘stepping stone' between present state-of-art 1 MW ERLs and future 100 MW scale applications. PERLE design features Flexible Momentum Compaction lattice architecture for six vertically stacked return arcs and a high-current, 6 MeV, photo-injector. With only one pair of 4 cavity cryomodules, 400 MeV beam energy can be reached in 3 re-circulation passes, with beam currents in excess of 15 mA. The beam is decelerated in 3 consecutive passes back to the injection energy, ...

Applications of Caustic Methods to Longitudinal Phase Space Manipulation

Longitudinal phase space management is a key feature of recirculating machines. Careful considera... more Longitudinal phase space management is a key feature of recirculating machines. Careful consideration of the longitudinal matching is required not only in order to ensure a high peak current, low energy spread bunch is delivered to the FEL but also to support the deceleration and energy recovery of the spent beam. In a similar manner, longitudinal phase space manipulation can be utilised for pulse shaping in bunch compression, to minimise the influence of CSR-induced emittance growth. In this paper, we present a method for longitudinal phase space matching based upon the avoidance of electron trajectory caustics. Through considering the conditions under which caustics will form, we generate exclusion plots identifying the viable parameter space at numerous positions through beam acceleration and energy recovery. The result is a method for selecting the linear momentum compaction and the higher-order momentum compaction to satisfy the non-caustic condition whilst achieving the bunch ...

Suppression of Multipass, Multibunch Beam Breakup in Two Pass Recirculating Accelerators

Proc. of …, 2004

Beam Breakup (BBU) occurs in all accelerators at sufficiently high currents. In recirculating acc... more

CBETA - Cornell University Brookhaven National Laboratory Electron Energy Recovery Test Accelerator

Cornell's Lab of Accelerator-based Sciences and Education (CLASSE) and the Collider Accelerat... more Cornell's Lab of Accelerator-based Sciences and Education (CLASSE) and the Collider Accelerator Department (BNL-CAD) are developing the first SRF multi-turn energy recovery linac with Non-Scaling Fixed Field Alternating Gradient (NS-FFAG) racetrack. The existing injector and superconducting linac at Cornell University are installed together with a single NS-FFAG arcs and straight section at the opposite side of the the linac to form an Electron Energy Recovery (ERL) system. Electron beam from the 6 MeV injector is injected into the 36 MeV superconducting linac, and accelerated by four successive passes: from 42 MeV up to 150 MeV using the same NS-FFAG structure made of permanent magnets. After the maximum energy of 150 MeV is reached, the electron beam is brought back to the linac with opposite Radio Frequency (RF) phase. Energy is recovered and reduced to the initial value of 6 MeV with 4 additional passes. There are many novelties: a single NS-FFAG structure, made of permanent...

CBETA, the 4-Turn ERL with SRF and Single Return Loop

A collaboration between Cornell University and Brookhaven National Laboratory has designed and is... more A collaboration between Cornell University and Brookhaven National Laboratory has designed and is constructing CBETA, the Cornell-BNL ERL Test Accelerator on the Cornell campus. The ERL technology that has been prototyped at Cornell for many years is being used for this new accelerator, including a DC electron source and an SRF injector Linac with world-record current and normalized brightness in a bunch train, a high-current linac cryomodule optimized for ERLs, a high-power beam stop, and several diagnostics tools for high-current and high-brightness beams. BNL has designed multi-turn ERLs for several purpose, dominantly for the electron beam of eRHIC, its Electron Ion Collider (EIC) project and for the associated fast electron cooling system. Also in JLEIC, the EIC designed at JLAB, an ERL is envisioned to be used for electron cooling. The number of transport lines in an ERL is minimized by using return arcs that are comprised of a Fixed Field Alternating-gradient (FFA) design. Th...

Operational Aspects of High Power Energy Recovery Linacs

We have been operating a high-power energy-recovery linac (ERL) at Jefferson Lab for several year... more We have been operating a high-power energy-recovery linac (ERL) at Jefferson Lab for several years. In the process we have learned quite a bit about both technical and physics limitations in high power ERLs. Several groups are now considering new ERLs that greatly increase either the energy, the current or both. We will present some of our findings on what to consider when designing, building, and operating a high power ERL. Our remarks for this paper are limited to lattice design and setup, magnets, vacuum chamber design, diagnostics, and beam stability.

Longitudinal Space Charge Effects in the JLAB IR FEL SRF Linac ��

The injector consists of a high-voltage-DC GaAs photocathode gun driven by a frequency-doubled Nd... more The injector consists of a high-voltage-DC GaAs photocathode gun driven by a frequency-doubled Nd:YLF laser, a 10 MeV quarter cryo-unit with two 5-cell CEBAF cavities, a transverse match section and a bunch compressor [3]. The photocathode gun delivers 135 pC, 23 ps rms-long electron bunches operating at 350 kV in pulse (demonstrated up to 8 mA) and CW (demonstrated up to 9.1 mA) modes [4]. The photocathode gun performance has been studied earlier [5]. After initial acceleration at 10 MeV, the electron beam is transversely matched to the linac by means of a quadrupole telescope, longitudinal match is provided by an achromatic compressor chicane [6]. Observations of energy spread asymmetry when operating the Linac on either side of crest and longitudinal emittance growth have been confirmed by extending PARMELA simulations from the injector to the end of the first SRF Linac module. The asymmetry can be explained by the interaction of the accelerating electric field with that from longitudinal space charge effects within the electron bunch. This can be a major limitation to performance in FEL accelerators.

Design Considerations for Recirculating and Energy Recovering Linacs

Introduction Success of the energy-recovering SRF driver accelerator for the JLab IR Demo FEL has... more

Vlasov analysis of microbunching instability for magnetized beams

Physical Review Accelerators and Beams, 2017

For a high-brightness electron beam with high bunch charge traversing a recirculation beam line, ... more For a high-brightness electron beam with high bunch charge traversing a recirculation beam line, coherent synchrotron radiation and space charge effects may result in microbunching instability (MBI). Both tracking simulation and Vlasov analysis for an early design of a circulator cooler ring (CCR) for the Jefferson Lab Electron Ion Collider (JLEIC) reveal significant MBI [Ya. Derbenev and Y. Zhang,