| Paper | Title | Other Keywords | Page | ||
|---|---|---|---|---|---|
| TUAX01 | Accumulation of High Intensity Beam and First Observations of Instabilities in the SNS Accumulator Ring* | kicker, extraction, lattice, electron | 59 | ||
|
The Spallation Neutron Source accumulator ring, designed to accumulate up to 1.5·1014 protons per pulse, was commissioned in January of 2006. During the run, over 1.·1014 protons were accumulated in the ring in the natural chromaticity state without any sign of instabilities. The first beam instabilities were observed for a high intensity coasting beam with zero chromaticity. Preliminary analysis of data indicates instabilities related to extraction kicker impedances, and electron-proton instability. Here we review the background theory and design philosophy of the ring, as it relates to instabilities, and compare the pre-commissioning predictions with the experimental measurements.
|
|
|
||
| TUAX02 | Coherent Instabilities at the Fermilab Booster | vacuum, dipole, booster, injection | 69 | ||
|
Fermilab booster is a fast cycling synchrotron operating on 15 Hz. To exclude problem of eddy currents excited in the vacuum chamber by fast changing magnetic field Booster does not have a conventional vacuum chamber. Instead, the vacuum chamber is formed by poles of the laminated combined function magnets. The exposed magnet laminations result in large transverse and longitudinal impedances affecting both the transverse and longitudinal stability of the beam. Presently, the transverse instability is suppressed by large chromaticity negatively affecting the dynamic aperture and the beam lifetime. Earlier attempts to stabilize the instability by transverse feedback system were unsuccessful. Recently we performed experimental studies to find out the reason. We observed that at reduced chromaticity at injection the most unstable mode is the multibunch high order head-tail mode with growth time of about 12 turns. It develops at synchro-betatron tune with very small fractional part where the transverse impedance is at a maximum. Analytical calculations and numerical simulations verify the observations and allowed us to compute the value of transverse impedance. Another persistent probl
|
Work supported by the Universities Research Assos., Inc., under contract DE-AC02-76CH03000 with the U. S. Dept. of Energy. |
|
||
| TUAX04 | Test of a prototype active damping system for the e-p instability at the LANL PSR | feedback, damping, kicker, electron | 94 | ||
|
Our collaboration from LANL, SNS, LBNL and SLAC has developed and successfully tested a prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold (as measured by the RF buncher voltage) by ~30%. Beam leakage into the gap at lower RF buncher voltage and resulting higher growth rates from more trapped electrons is the likely cause of this limitation. We will describe the system configuration and results of several experimental tests of system performance. We will also discuss our studies and analysis of the factors limiting system performance.
|
|
|
||
| TUBX01 | Impedance and radiation generated by a ceramic chamber with RF shields and TiN coating | space-charge, electromagnetic-fields, synchrotron, extraction | 125 | ||
|
In the RCS (Rapid Cycle Synchrotron) ring of J-PARC, we use ceramic chambers with the interior TiN coating and exterior Cu RF shields in the magnet sections. A new theory has been developed for calculation of impedance in this unusual configuration. When it was applied to a prototype RCS ceramic chamber, the calculation results got good agreement with the measurement results. We also considered the dipole radiation from gaps between Cu shields of the ceramic chamber in the bending magnets. The effects turn out to be rather small thanks to the special configuration of the ceramic chambers. We measured the radiation from a ceramic break with and without RF shields and capacitors in the KEK, PS and found that the RF shields with capacitors considerably suppress the radiation from the ceramic break. We summarize all these studies in this paper.
|
|
|
||
| TUBX02 | Collective Transverse Instabilities in the GSI Synchrotrons | damping, simulation, space-charge, octupole | 131 | ||
|
One of the primary challenges for the design of the FAIR synchrotrons at GSI Darmstadt is the high current operation close to the stability limits, with small tolerable beam losses. Collective instabilities are a potential limiting factor for the performance of the rings. We discuss results of experimental and numerical investigations of transverse collective beam behavior in the SIS 18 synchrotron. Also damping mechanisms in the presence of space charge, including the linear Landau damping and decoherence due to nonlinearities are discussed. These are the essential factors to define impedances budgets for the GSI synchrotrons. As a computational tool accounting the beam nonlinear dynamics with impedances and self-consistent space charge, the particle tracking code PATRIC is used.
|
|
|
||
| TUBX03 | Coupling impedance of the J-PARC kicker magnets | kicker, extraction, coupling, synchrotron | 140 | ||
|
The single- and twin-wire measurements both for the longitudinal ( ZL ) and transverse impedances ( ZT ) will be discussed for the J-PARC kicker magnets: a lumped circuit kicker and several types of traveling wave kickers. The question if a position shifted single-wire can measure ZT is discussed. The measurement results are compared with the equivalent circuit analysis. The relation between the imaginary part of the impedance and causality will also be discussed.
|
|
|
||
| TUBX06 | Betatron Tune Shift due to Nonlinear Resistive-Wall Wake Field | emittance, damping, betatron, dipole | 159 | ||
|
I present formulae for the coherent and incoherent tune shifts of a single bunch traveling between two parallel resistive plates. It is shown that for the parameters of an LHC prototype collimator in the SPS, both the nonlinear wake-field components, calculated by Piwinski, and the correct time dependence, e.g., as derived by Burov and Lebedev, must be taken into account.
|
|
|
||
| WEBZ01 | Correction of unevenness in Recycler beam profile | feedback, beam-loading, synchrotron, proton | 244 | ||
|
When a beam is confined between two rf barriers in the Fermilab Recycler Ring, it is observed that the longitudinal beam profile between the barriers is in general very uneven (typically about 20% for a beam of intensity 5E11). This leads to the consequence that the momentum-mined antiproton bunches may have an intolerable variation in bunch intensity. It is shown that the observed unevenness in beam profile is the result of a tiny amount (around 2%) of rf potential imperfection and a tiny amount (around 0.5%) of rf beam loading. The beam profile can be made even by feeding back the unevenness of the effective rf potential to the low-level rf.
|
|
|
||
| THAW07 | Transverse electron-antiproton instability in the Recycler Ring | coupling, electron, ion, resonance | 334 | ||
|
Lifetime degradation of electron-cooled ions was observed at several electron coolers. In the Recycler, both the lifetime drop and emittance growth of the e-cooled pbars are seen. A possible reason for that can be a coherent interaction between the electron and antiproton beams. A theoretical model of this instability is presented, and a practical recommendation for its suppression is explained and discussed.
|
|
|
||
| FRAP01 | SUMMARY OF WORKING GROUP A AND A+B+D JOINT SESSION | electron, simulation, emittance, feedback | 358 | ||
|
We summarize the presentations and discussions of the HB2006 Working Group A, devoted to beam instabilities, and of the joint session of Working Groups A, B (on space charge), and D (beam cooling and experiments). First we review the progress on conventional instabilities and impedances, and then the advances on electron cloud.
|
|
|