In this paper, a formula, describing the threshold of regenerative multipass beam breakup (BBU) for a single dipole higher-order mode with arbitrary polarization in a two-pass accelerator with a ...general-form, 4×4 recirculation matrix, is derived. A new two-dimensional BBU code is also introduced. To illustrate specifics of the BBU in two dimensions, the formula is used to calculate the threshold in several cases including two-dimensional uncoupled optics, reflecting optics, and rotating optics. The analytical results are compared to results of simulations obtained with the new code. A mathematical relation between transfer matrices between cavities of the accelerating structure and recirculation matrices for each cavity, which must be satisfied in order to successfully suppress the BBU by reflection or rotation in several cavities, is presented.
Ion back bombardment is believed to be a main cause of degradation of quantum efficiency of photocathodes in fixed-voltage photoguns. Ions produced in collisions of the electron beam with residual ...gas in the cathode-anode gap are accelerated towards the cathode and bombard the cathode surface, reducing its quantum efficiency. In addition to ions produced in the accelerating gap, there is another source of ions that has been overlooked so far in existing models of ion bombardment: ions produced in a beam transport line beyond the anode and trapped in the electron beam. These ions can drift back to the cathode and increase the rate of ion bombardment. This article shows that the flux of trapped ions can significantly exceed the flux of ions produced directly in the accelerating cathode-anode gap. The paper also describes a simple and effective solution to the problem of trapped ions, a positive potential barrier.
Commissioning of the FRIB RFQ Ren, H.; Pozdeyev, E.; Morris, D. ...
Journal of physics. Conference series,
09/2018, Volume:
1067, Issue:
5
Journal Article
Peer reviewed
Open access
The radio-frequency quadrupole (RFQ) at the Facility for Rare Isotope Beams (FRIB) is a 4-vane type cavity designed to accelerate heavy ion beams with charge states Q/A between 1/7 and 1/3 from 12 ...keV/u to 0.5 MeV/u. The RFQ was assembled in the FRIB tunnel in November 2016. Bead-pull measurements and tuning were performed with low RF power. The RFQ has been conditioned to 59 kW in August 2017, which is sufficient to accelerate the Key Performance Parameter (KPP) beams, Argon and Krypton. The RFQ has been successfully commissioned with KPP beams in CW regime in October 2017. 40Ar9+ and 86Kr17+ beams were accelerated by the FRIB RFQ in the CW regime to the designed energy of 0.5 MeV/u. With the multi-harmonic buncher operational, the FRIB RFQ commissioning has been completed with bunched beam in February 2018. The beam transmission efficiency through the RFQ was in good agreement with PARMTEQ simulation results. The detailed results from the FRIB RFQ tuning, high power conditioning and beam commissioning will be presented in this paper.
The JLab high power ERL light source Neil, G.R.; Behre, C.; Benson, S.V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2006, Volume:
557, Issue:
1
Journal Article
Peer reviewed
Open access
A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources based on an Energy-Recovered, (superconducting) Linac (ERL). The machine has a 160
MeV electron beam ...and an average current of 10
mA in 75
MHz repetition rate hundred femtosecond bunches.
These electron bunches pass through a magnetic chicane and therefore emit synchrotron radiation. For wavelengths longer than the electron bunch the electrons radiate coherently a broadband THz ∼ half cycle pulse whose average brightness is >5 orders of magnitude higher than synchrotron IR sources. Previous measurements showed 20
W of average power extracted Carr, et al., Nature 420 (2002) 153. The new facility offers simultaneous synchrotron light from the visible through the FIR along with broadband THz production of 100
fs pulses with >200
W of average power.
The FELs also provide record-breaking laser power Neil, et al., Phys. Rev. Lett. 84 (2000) 662: up to 10
kW of average power in the IR from 1 to 14
μm in 400
fs pulses at up to 74.85
MHz repetition rates and soon will produce similar pulses of 300–1000
nm light at up to 3
kW of average power from the UV FEL. These ultrashort pulses are ideal for maximizing the interaction with material surfaces. The optical beams are Gaussian with nearly perfect beam quality. See
www.jlab.org/FEL for details of the operating characteristics; a wide variety of pulse train configurations are feasible from 10
ms long at high repetition rates to continuous operation.
The THz and IR system has been commissioned. The UV system is to follow in 2005. The light is transported to user laboratories for basic and applied research. Additional lasers synchronized to the FEL are also available. Past activities have included production of carbon nanotubes, studies of vibrational relaxation of interstitial hydrogen in silicon, pulsed laser deposition and ablation, nitriding of metals, and energy flow in proteins. This paper will present the status of the system and discuss some of the discoveries we have made concerning the physics performance, design optimization, and operational limitations of such a first generation high power ERL light source.
Studies of the longitudinal beam dynamics in the small isochronous ring (SIR) at Michigan State University revealed a fast, space-charge driven instability that did not fit the model of the negative ...mass instability. The observed beam behavior can be explained by the transverse horizontal component of the coherent space-charge force and its effect on the longitudinal motion. This force effectively modifies the slip factor, shifting the isochronous point and enhancing the negative mass instability. This paper presents results of numerical and experimental studies of the longitudinal beam dynamics in SIR and proposes a simple analytical model explaining these results.
Potential Uses of ERL-Based \gamma-Ray Sources Litvinenko, V.N.; Ben-Zvi, I.; Kayran, D. ...
IEEE transactions on plasma science,
08/2008, Volume:
36, Issue:
4
Journal Article, Conference Proceeding
Peer reviewed
We expand upon the idea of using gamma-rays for nuclear photoflssion of 238 U at the giant dipole resonance to generate rare neutron-reach nuclei. The SPIRAL II project proposes the employment of ...10-20-MeV Bremsstrahlung gamma-rays generated by a 45-MeV electron beam /http://ganinfo.in2p3.fr/research/ developments/ spiral2/ index.html/. In this paper, we explore the possibility of using a Compton gamma-ray source for such a process. The Collider Accelerator Department at Brookhaven National Laboratory is developing high-current (up to 1 A), high-brightness (down to 1-mm ldr mrad normalized emittance), and high-energy energy-recovery linacs (up to 20-GeV electron beam energy for eRHIC). These electron beams are perfectly suited for generating photon beams with tremendous average power, approaching the megawatt level. The range of photon's energy extends from subelectronvolts from free-electron lasers to 10 GeV from the Compton process. In this paper, we focus on a gamma-ray source for producing rare isotopes.
Cathode ion bombardment in rf photoguns Pozdeyev, E.; Kayran, D.; Litvinenko, V. N.
Physical review special topics. PRST-AB. Accelerators and beams,
04/2009, Volume:
12, Issue:
4
Journal Article
Peer reviewed
Open access
We use the ponderomotive potential of the rf field to accurately describe the motion of ions in an rf gun. We apply the method to the BNL 1/2-cell superconducting radio-frequency photogun and ...demonstrate that a significant portion of ions produced in the gun can reach the cathode if no special precautions are taken. Also, we propose simple mitigation techniques that can reduce the rate of ion bombardment.
Multipass beam breakup in energy recovery linacs Pozdeyev, E.; Tennant, C.; Bisognano, J.J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2006, Volume:
557, Issue:
1
Journal Article
Peer reviewed
Open access
This paper is a compilation of several presentations on multipass beam breakup (BBU) in energy recovery linacs (ERLs) given at the 32nd Advanced ICFA Beam Workshop on ERLs. The goal of this paper is ...to summarize the progress achieved in analytical, numerical, and experimental studies of the instability and outline available and proposed BBU mitigation techniques. In this paper, a simplified theory of multipass BBU in recirculating linacs is presented. Several BBU suppression techniques and their working principles are discussed. The paper presents an overview of available BBU codes. Results of experimental studies of multipass BBU at the Jefferson Laboratory (JLab) FEL Upgrade are described.
Ion back-bombardment is the dominant mechanism that limits the operating lifetime of DC high voltage GaAs photoelectron guns. In this work, an electrically isolated anode electrode was used to ...distinguish the QE damage contributions of ions produced within the cathode/anode gap and those produced downstream of the anode. This new anode design provides a means to suppress QE decay due to ionized gas in the beam line.
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