We report the results of experiments on a 'fast beam-ion instability' at the Advanced Light Source (ALS). This ion instability, which can arise even when the ions are not trapped over multiple beam passages, will likely be important for many future accelerators. In our experiments, we filled the ALS storage ring with helium gas, raising the pressure approximately two orders of magnitude above the nominal pressure. With gaps in the bunch train large enough to avoid conventional (multi-turn) ion trapping, we observed a factor of 2-3 increase in the vertical beam size along with coherent beam oscillations which increased along the bunch train. Ion trapping has long been recognized as a potential limitation in electron storage rings. The ions, generated by beam-gas collisions, become trapped in the negative potential of the beam and accumulate over multiple beam passages. The trapped ions are then observed to cause a number of deleterious effects such as an increasing beam phase space, a broadening and shifting of the beam transverse oscillation frequencies (tunes), collective beam instabilities, and beam lifetime reductions. All of these effects are of concern for the next generation of accelerators, such as the B-factories or damping rings for future linear colliders, which will store high beam currents with closely spaced bunches and ultra-low beam emittances. One of the standard solutions used to prevent ion trapping is to include a gap in the bunch train which is long compared to the bunch spacing. In this case, the ions are first strongly-focused by the passing electron bunches and then over-focused in the gap. With a sufficiently large gap, the ions can be driven to large amplitudes where they form a diffuse halo and do not affect the beam. In this paper, we describe experiments that study a new regime of transient ion instabilities predicted to arise in future electron storage rings, and linacs with bunch trains. These future rings and linacs, which will be operated with higher beam currents, small transverse beam emittances, and long bunch trains, will use ion clearing gaps to prevent conventional ion trapping. But, while the ion clearing gap may suppress the conventional ion instabilities, it will not suppress a transient beam-ion instability where ions generated and trapped during the passage of a single train lead to a fast instability. While both conventional and transient ion instabilities have the same origin, namely ions produced by the beam, they have different manifestations and, more importantly, the new transient instability can arise even after the conventional ion instability is cured. This new instability is called the 'Fast Beam-Ion Instability' (FBII). In many future rings, the FBII is predicted to have very fast growth rates, much faster than the damping rates of existing and proposed transverse feedback systems, and thus is a potential limitation. To study the FBII, we performed experiments at the ALS, a 1.5 GeV electron storage ring. At the nominal ALS pressure of about 0.24 nTorr, the FBII is not evident. To study the instability, we intentionally added helium gas to the storage-ring vacuum system until the residual gas pressure was increased about 80 nTorr. This brought the predicted growth rate of the instability at least an order of magnitude above the growth rate of conventional multibunch instabilities driven by the RF cavities and above the damping rate of the transverse feedback system (TFB) in the ALS and, thereby, established conditions very similar to those in a future storage ring. We then filled the ring with a relatively short train of bunches, suppressing conventional ion instabilities. In the following, we will first briefly describe This paper describes the experiment and results in more detail.
A nonlinear equation is derived that governs the evolution of the amplitude of unstable oscillations with account of quantum diffusion effects due to the synchrotron radiation. Numerical solutions to this equation predict a variety of possible scenarios of nonlinear evolution of the instability some of which are in good qualitative agreement with experimental observations.
A transverse geometrical wake generated by a beam passing through a smooth flat collimator with a gradually varying gap between the upper and lower walls is considered. Based on generalization of the approach recently developed for a smooth circular taper we reduce the electromagnetic problem of the impedance calculation to the solution of two much simpler static problems-a magnetostatic and an electrostatic ones. The solution shows that in the limit of not very large frequencies, the impedance increases with the ratio h/d where h is the width and d is the distance between the collimating jaws. Numerical results are presented for the NLC Post Linac collimator
Current communications between the SLAC Linear Collider control system central host and the SLCmicros is built upon the SLAC developed SLCNET communication hardware and protocols. We describe how the Internet Suite of protocols (TCP/IP) are used to replace the SLCNET protocol interface. The major communication pathways and their individual requirements are described. A proxy server is used to reduce the number of total system TCP/IP connections. The SLCmicros were upgraded to use Ethernet and TCP/IP as well as SLCNET. Design choices and implementation experiences are addressed.
The overmoded RF transmission and pulsed power compression system for SLAC's Next Linear Collider (NLC) program requires a high degree of transmission efficiency and mode purity to be economically feasible. To this end, a number of new, high power components and systems have been developed at X-band, which transmit RF power in the low loss, circular TE01 mode with negligible mode conversion. In addition, a highly efficient SLED-II pulse compressor has been developed and successfully tested at high power. The system produced a 200 MW, 250 ns wide pulse with a near-perfect flat-top. In this paper we describe the design and test results of the high power pulse compression system using SLED-II
The note describes results of studies of the single bunch stability in the low energy ring (LER) of the PEP-II B-factory. Simulations describe the potential well distortion (PWD) obtained by numerical solution of the Haiisinski equation and results on the beam stability obtained with the code TRISIM. Both longitudinal and transverse wakefields are taken into account
This paper describes the mechanical design of the primary mirror that images the visible portion of the synchrotron radiation (SR) extracted from the High Energy Ring (HER) of the PEP-II B-Factory. During off-axis operation, the water-cooled GlidCop mirror is subjected to a heat flux in excess of 2000 W/cm2. When on-axis imaging occurs, the heat flux due to scattered SR, resistive wall losses and Higher-Order-Mode (HOM) heating is estimated at 1 W/cm2. The imaging surface is plated with Electroless Nickel to improve its optical characteristics. The design requirements for the primary mirror are listed and discussed. Calculated mechanical distortions and stresses experienced by the mirror during on-axis and off-axis operation will be presented.
Insertion devices for Angstrom-wavelength free electron laser (FEL) amplifiers driven by multi-GeV electron beams generally require distributed focusing substantially stronger than their own natural focusing fields. Over the last several years a wide variety of focusing schemes and configurations have been proposed for undulators of this class, ranging from conventional current-driven quadrupoles external to the undulator magnets to permanent magnet (PM) lattices inserted into the insertion device gap. In this paper we present design studies of a flexible high-field hybrid/PM undulator with strong superimposed planar PM focusing proposed for a 1.5 Angstrom Linac Coherent Light Source (LCLS) driven by an electron beam with a 1 mm-mr normalized emittance. Attainable field parameters, tuning modes, and potential applications of the proposed structure are discussed
We describe the beam position monitor system built for PEP-II, the B-factory at SLAG. The system reports beam position for bunches of between 5 x 10(8) and 8 x 10(10) electron charges, either singly or as continuous streams of bunches every 4.2 ns. Resolution at full charge is to be better than 10 microns in a single turn. Higher resolution is available via on-board multi-turn averaging. The position signal is processed in a 20 MHz bandwidth around 952 MHz. This bandwidth, rather broader than that typical of RF position monitors, allows good resolution for low charge single bunches. Additional novel features include stringent control of return losses in order to minimize cross-talk between nearby bunches which may contain very different charges. The digitizing electronics is multiplexed between the two PER-Il storage rings. Design, construction, and installation experience, as well as first results with beam are presented.
The proposed MAX IV facility is meant as a successor to the existing MAX-lab. The accelerator part will consist of three storage rings, two new ones operated at 3 and 1.5 GeV respectively and the existing 700 MeV MAX III ring. The two new rings have identical lattices and are placed on top of each other. Both these rings have a very small emittance, 0.86 and 0.4 nm rad respectively, and offer synchrotron radiation of very high mean brilliance. As an injector, a 3 GeV linear accelerator is planned. The design philosophy and the special technical solutions called for are presented in this paper.
In the accelerator field, the instrumentation monitor system provides the machine online status to view, control and alert. A novel shared data engine developed by Labview provides the distributed PCs, PDAs, embedded devices, and local controllers to exchange data mutually via Ethernet or wireless Ethernet. The mechanism guarantees delivery with an additional function layer of the raw UDP protocol and use less network bandwidth than TCP/IP. The system's main function is to introduce a platform with reliable online information about the status of the instrumentation. The users can access data with graphic view, trend view etc. by some complementary software. Also, the users can easily take online data via binding monitor tags without programming. The mechanism benefits all system maintenance, operation, management and analysis.
The quadrupoles of the LNLS storage ring are divided into families with two or six units, each one being supplied by an only current source. Some experiments performed by the accelerator physics team require different currents for quadrupoles of a same family. Moreover, there is an interest in obtaining lower steps in the control of their currents. These were the main reasons that required the development of an active shunt.A prototype was built with range of -3A to +3A, what is approximately 3% of the maximum quadrupole current (200A). It was tested with a two-quadrupole family power supply.The full bridge topology was chosen, where the pulse width for the positive and negative output voltages are not the same, which gives an average output current different from zero.Some waveforms and results are shown, such as the long-term stability and output current ripple. Some measurements made in the storage ring electron beam using the active shunt are also described.
Photocathode RF guns depend on mode locked laser systems to produce an electron beam at a given phase of the RF. In general, the laser pulse is less than σ2=10° of the RF phase in length and the required stability is of the order of Δφ=1°. At 90 GHz (W-band), these requirements correspond to σz=333 fsec and Δφ=33 fsec. A laser system with pulse lengths in the fsec regime is commercially available, the timing stability is a major concern. We propose a multi-cell W-band photoinjector that does not require a mode locked laser system, thereby eliminating the stability requirements at W-band
A frequency-doubling magnicon amplifier at 11.4 GHz has been developed and built as the prototype of an alternative microwave source for the Next Linear Collider, and to test high power RF components and accelerating structures. The tube is designed to produce similar to60 MW, in similar to1.2 tsec pulses at 58% efficiency and 59 dB gain, using a 470 W, 220 A, 2 mm-diameter beam. Recent results of the tube performance are presented in this paper. Operation of this magnicon has established a research facility located at NRL as only the second laboratory in the USA, after SLAC, where high-power microwave development at the NLC X-band frequency can take place.
The passage of a multi-bunch beam through an X-band accelerator with cells and structures misaligned gives rise to wakefields which disrupt succeeding bunches. As a consequence, there is growth in the overall emittance of the final colliding bunches. Here we study this process in the context of a JLC-NLC which employs the recently developed RDDS (Rounded Damped Detuned Structures) accelerators with 120 s fill time and drives a 90 bunch, 250 ns bunch train. We investigate cumulative beam break-up (BBU) under various parameter regimes appropriate to the structure which is in the process of being fabricated by KEK and SLAC. We compute the resultant emittance growth by means of analytical expressions and find good agreement with the results we obtain from a particle tracking code. We set misalignment tolerances by specifying allowable emittance growth
Object oriented programming techniques make it possible for accelerator designers to independently develop C++ software components that can work together. As an example of this approach, we discuss some of the software components being developed at Tech-X Corporation, including: TxSTD, a library of standard utilities [1]; TxID, a library of data-holding and nonlinear dynamics classes [2]; TxAC, an accelerator modeling class library [3]; an X/Motif library used in the MAPA application [4] for interactive visualisation of dynamical systems such as particle accelerators; TxAN, a library of analysis and simulation classes relevant to dynamical systems; and the LION++ nonlinear optimization library [5].
The various orbit perturbations are enhanced after many insertion devices are installed in the storage ring of TLS. These sources will interfere to system performance. The local orbit feedback system is used to suppress miscellaneous local orbit perturbation. The feedback system consists of sensor and feedback control loop. The sensors are electron beam position monitor (BPM) and photon monitor of elliptical polarization undulator (EPU). The feedback control loop architecture share same hardware with global orbit feedback. The VME-based crates interconnected with high performance daisychained global reflective memory networks are used to share position data with DSP. The result is shown in this report.
Coherent betatron motion adiabatically excited by an RF dipole has been successfully employed to overcome strong intrinsic spin depolarization resonances in the AGS, while a solenoid partial snake has been used to correct imperfection spin resonances. The experimental results showed that a full spin flip was obtained in passing through an intrinsic spin resonance when all the beam particles were forced to oscillate coherently at a large amplitude without diluting the beam emittance. With this method, we have successfully accelerated polarized beam up to 23.5 GeV/c. A new type of second order spin resonances was also discovered. As a non-destructive manipulation, this method can also be used for nonlinear beam dynamics studies and beam diagnosis such as measuring phase advance and betatron amplitude function.
