Author: Peter Richard MengePublisher:
ISBN:
Category :
Languages : en
Pages : 276
Book Description
Experimental Excitation and Reduction of the Beam Breakup Instability in Long-pulse Electron Beam Transport
Author: Peter Richard MengeAdvanced Transport Systems for Electron Beams in High-Brightness Accelerators and FELs
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 48
Book Description
Research has concentrated on the excitation and stabilization of the beam-breakup (BBU) instability in high current, long-pulse electron beam transport through microwave cavity systems. Electron beams are generated by the Michigan Electron Long Beam Accelerator (MELBA) at parameters: 0.7 to 0.8 MV, I injected =40-400 A, and pulselength - 0.5 microsecs. Major accomplishments include: (1) Successful excitation of the beam-breakup (BBU) instability by microwave priming of the first cavity of a ten-RF cavity system, (2) Measurements of BBU growth as a function of priming frequency, confirming that the TM110 BBU mode was responsible for the growth, (3) Characterization of the BBU growth rate as a function of magnetic field and e-beam current, (4) The first experiments demonstrating that external-coupled-cavities reduce the growth rate for the BBU instability, and (5) Development of a theory for the beam breakup instability in quadrupole and solenoidal electron beam transport systems.
Scientific and Technical Aerospace Reports
Author: Experimental Investigation of Certain Beam Transport Issues in a Pulsed Transmission Line Linear Accelerator
Author: M. G. MazarakisPublisher:
ISBN:
Category :
Languages : en
Pages : 35
Book Description
The successful development of a new generation of high current, high voltage, linear induction accelerators relies on the solution of a number of beam transport problems, including radial oscillations, diocotron instabilities, transverse beam break-up (BBU), etc. Most of the instabilities appear to onset either at the injector region or at the accelerating gaps. Radial oscillations were first observed in RADLAC I, while transverse beam break-up was first observed on the SLAC accelerator, and more recently on the ETA accelerator. A low emittance, high current, high voltage injector precisely aligned with the guiding magnetic field axis and beam vacuum pipe axis is of prime importance for successful beam acceleration and transport. Similarly, an accelerating gap design which maintains radial force balance and an accelerating cavity with low Q and very small transverse shunt impedance Z perpendicular should eliminate the most dangerous radial oscillations and beam break-up instabilities. The design and experimental studies of a new 4 MeV, 40 kA electron beam injector and accelerating gap will be presented. Test bench measurements of Z perpendicular and Q on a typical radial transmission line accelerating cavity prove that BBU is not of concern unless the number of accelerating gaps become excessively large. (Author).
Calculating Beam Breakup in Superconducting Linear Accelerators
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
As the intensity of a particle beam passing through a linear accelerator is raised, interactions between particles play an increasingly prominent role in determining the overall dynamics of the beam. These many body effects, known collectively as beam breakup, tend to degrade the quality of the transported beam, and hence they must be calculated to accurately predict the evolution of the beam as it traverses the accelerator. Several codes which compute various collective effects have been developed and used to simulate the dynamics of beams passing through superconducting accelerator structures. All the codes use the same basic algorithm: the beam is tracked through elements giving the focusing forces on the particles, and at the appropriate locations in the linac, localized forces are impressed on the particles which model the electromagnetic interactions. Here, a difficulty is that the usual ''Coulomb'' interaction between particles is changed by the electromagnetic environment of the accelerator. By such calculations it has been shown that recirculating linear accelerators such as the one being built at the Continuous Electron Beam Accelerator Facility (CEBAF) should remain stable against multipass beam breakup instability as long as the average current does not exceed about 20 mA, that the beam quality at CEBAF will be degraded when the single bunch charge approaches 109 electrons, and that the beam quality of superconducting linacs that are optimized for high current transport begins to decrease at around 101° electrons per bunch. The latter result is of interest to individuals who would use superconducting linacs as beam sources for free electron lasers or for superconducting colliders for high energy physics research.
Energy Research Abstracts
Author: Beam Breakup Instabilities in High Current Electron Beam Racetrack Induction Accelerators
Author: Brendan B. GodfreyPublisher:
ISBN:
Category :
Languages : en
Pages : 33
Book Description
Beam breakup and negative mass instability growth rates for a 1 kA, 40 MeV electron beam racetrack induction accelerator are computed. The device is taken to have four accleration gaps, each with 0.2 MeV applied voltage and 15 ohm transverse impedence; the guide field is 2 kg. We find that the total amplification of the beam breakup mode is limited to five e-findings provided that the cavity mode quality factor Q is 6. Thus, the negative mass instability, which grows several times faster, is the dominant consideration. However, we also find that they energy range over which the negative mass instability occurs can be narrowed substantially by reducing the guide field strength after the beam has been accelerated to about 12 MeV. This approach, coupled with beam thermal effects, not considerated here, probably is sufficient to limit negative mass growth to acceptable levels in tge racetrack accelerator. (Author).
Beam Breakup (BBU) Instability Experiments on the Experimental Test Accelerator (ETA) and Predictions for the Advanced Test Accelerator (ATA).
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
In linear accelerators the maximum achievable beam current is often limited by the Beam Breakup (BBU) instability. This instability arises from the interaction of a transversely displaced beam with the dipole modes of the acceleration cavities. The modes of interest have non-zero transverse magnetic fields at the center of the cavity. This oscillating field imparts a time varying transverse impulse to the beam as it passes through the accelerating gap. Of the various modes possible only the TM130 mode has been observed on the Experimental Test Accelerator (ETA) and it is expected to surface on the Advanced Test Accelerator (ATA). The amplitude of the instability depends sensitively on two cavity parameters; Q and Z/sub perpendicular//Q. Q is the well-known qualtiy factor which characterizes the damping rate of an oscillator. Z/sub perpendicular//Q is a measure of how well the beam couples to the cavity fields of the mode and in turn, how the fields act back on the beam. Lowering the values of both these parameters reduces BBU growth.
Effects of Tapering on High Current, Long Pulse Gyrotron Backward Wave Oscillator Experiments
Author: Mark Thomas WalterMicrowave Emission of Large and Small Orbit Rectangular Gyrotron Devices
Author: Jonathan Mark HochmanPublisher:
ISBN:
Category :
Languages : en
Pages : 454
Book Description