TUB, Beijing
In this paper, the design of a C-band SW accelerating tube is presented and its high power test set is shown. The tube can accelerate electrons to 9 MeV or 6 MeV. Its length is about 620mm, and a Pierce electron gun is used. A 2.5MW pulsed magnetron at 5712 MHz is served as the tube's RF power source. Two energy modes are performed by changing the input RF power and the injecting voltage of electron gun.
SAMEER, Mumbai
Sokendai, Ibaraki
A successful development of a 6 MeV electron radiotherapy machine at SAMEER, India was reported earlier*. Now a 15 MeV electron linac prototype is designed, developed and tested at our site. We have measured a beam current of 80 mA at the X-ray target attached to the linac. Energy gained by electrons in a cavity chain of about 1.2 m length is measured to be more than 15 MeV using a 6 MW klystron power source. An RF window capable of handling 12kW average power is attached to the linac tube and it is cooled by water. The final linac parameters measured were at par with the designed values. A high voltage modulator and control console for the linac are designed and developed in house. This paper will describe key aspects of the design and development process of the complete system. Also future applications are planned like-dual energy dual mode linac for radiotherapy, cargo scanning system and compact compton X-ray source using this technology is briefed in this paper.
* R.Krishnan et. al. "S band linac tube developmental work in SAMEER", FR5REP083, PAC09, Vancouver, Canada.
KEK, Ibaraki
MELCO SC, Tsukuba
J-PARC, KEK & JAEA, Ibaraki-ken
Efforts have been made to reduce the magnetic field ripple of the bending, quadrupole and sextupole magnets of the J-PARC main ring using the trim coils of the magnets. The quadrupole magnet has 24 turn main coil and 11 turn trim coil per pole those can be considered as a primary winding and a secondary winding of a transformer. When the trim coil is shorted, the induced trim coil current cancels the field ripple. The field ripple of the quadrupole magnet was reduced by a factor of 6 by shorting trim coil. The trim coil current, however, deforms the acceleration field pattern if the coil is shorted all the time of the current pattern of flat bottom, acceleration, flat top and recovery. The MOSFET relay was used to short the coil and to reduce the field ripple during the flat bottom and flat top. The circuits were built for the quadrupole and sextupole magnets. The plan has been made to wind optimized trim coils for the bending magnets.
SLAC, Menlo Park, California
Crab cavities are proposed for the LHC upgrade to improve the luminosity. There are two possible crab cavity installations for the LHC upgrade: the global scheme at Interaction Region (IR) 4 where the beam-beam separation is about 420-mm, and the local scheme at the IR5 where the beam-beam separation is only 194-mm. One of the design requirements as the result of a recent LHC-Crab cavity workshop is to develop a 400-MHz cavity design that can be utilized for either the global or local schemes at IR4 or IR5. Such a design would offer more flexibility for the final upgrade installation, as the final crabbing scheme is yet to be determined, and save R&D cost. The cavity size of such a design, however, is limited by the beam-beam separation at IR5 which can only accommodate a cavity with a horizontal size of about 145-mm, which is a design challenge for a 400-MHz cavity. To meet the new design requirements, we have developed a compact 400-MHz half-wave spoke resonator (HWSR) crab cavity that can fit into the tight spaces available at either IR4 or IR5. In this paper, we present the optimization of the HWSR cavity shape and the design of HOM, LOM, and SOM couplers for wakefield damping.
KEK, Ibaraki
STFC/RAL/ISIS, Chilton, Didcot, Oxon
ANL, Argonne
Tsukuba University, Ibaraki
A low-output-impedance RF system for the second harmonic cavity in the ISIS synchrotron has been developed by collaboration between Argonne National Laboratory (US), KEK (Japan) and Rutherford Appleton Laboratory (UK). The system has less than 30 Ω of output impedance over wide frequency range of 2.7-6.2 MHz. However, distortions of voltage waveform in the driver stage have been a long-standing issue. It was found such distortions were generated depending upon the higher-order-modes of the anode-choke impedance. In this report, method to realize the smooth sinusoidal waveform in the wideband system is presented.
KEK/JAEA, Ibaraki-Ken
KEK, Ibaraki
JAEA/J-PARC, Tokai-mura
The Japan Proton Accelerator Complex includes the 3GeV rapid cycling synchrotron (RCS) and the 50GeV main ring synchrotron (MR). Both synchrotrons use the high field gradient magnetic alloy (MA) loaded cavities. In RCS, 11 RF systems have been fully operational since December 2008. The RCS RF systems are operated with dual-harmonic acceleration voltages. Beam acceleration and bunch shape manipulation are efficiently taking place. 120kW of the neutron user operation was started at the Material and Life science facilities in November 2009. In MR synchrotron, the 5th RF system were installed in August 2009, and therefore 5 RF systems are now in operation. Beam commissioning for delivering protons to the hadron facility and neutrino beam experimental facility are under way. The neutrino user experiment is intended to start January 2010. Proton beam operation with more than 100kW is required. The approaches to realizing high intensity operation and the MR upgrade plan will be presented.
SLAC, Menlo Park, California
CERN, Geneva
In order for the LHC to reach an ultimate luminosity goal of 1035, CERN is considering upgrade options for the LHC injector chain, including a new 50 GeV synchrotron of about 1.3 km length for protons and heavy ions, to be called the PS2. In this ring the proton energy is ramped from 4 GeV in 1.2 s, and the design (proton) current is 2.7 A. The present baseline of the vacuum system considers elliptical stainless steel chambers bakeable up to 300°C, various coatings to mitigate electron cloud are under study. For a bare stainless steel or Inconel chamber, the resistive wall wake alone will lead to multi-bunch instability, whereas for transverse mode coupling (TMCI), the threshold is above the design beam current, though this instability may become an issue once other impedance contributions are taken into account. A copper layer of varying thickness is shown to raise the TMCI threshold but to have relatively little effect on the multi-bunch resistive-wall growth rate unless the coating is very thick. We are also studying the effect of the copper coating on the penetration of the guide field during the energy ramp, which sets an upper limit on the allowable thickness.
Siemens AG, Healthcare Technology and Concepts, Erlangen
Air insulated Cockcroft-Walton (Grienacher) cascades have been historically used to generate high voltages for accelerating particles. This paper explores how this technology can be utilised through a system level approach to develop more compact accelerator configurations with much higher voltages and gradients. One such concept is presented that realises a 20MeV, 1mA tandem accelerator that has a footprint ~2m^2
IAP, Frankfurt am Main
Kress GmbH, Biebergemuend
NSCL, East Lansing, Michigan
A new reaccelerator facility ReA3 is currently under construction for National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). As part of that project a new 3.5 m long 4-rod Radio Frequency Quadrupole (RFQ) has been build. This RFQ accelerates ions with a Q/A ratio of 0.2 up to 0.5 from an input energy of 12 keV/u to the final energy of 600 keV/u. We have designed the 80.5 MHz-RFQ with a square cavity cross section. It was build and tuned in Frankfurt and has been delivered to MSU. The design and the tuning process of the ReA3-RFQ will be discribed in this paper.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
KEK, Ibaraki
A new RFQ for the J-PARC linac is under construction for more stable operation. The requirement of this RFQ is almost same as the now-operating one; the resonant frequency is 324MHz, the injection energy is 50 keV, the extraction energy is 3 MeV, peak beam current is 30 mA, and RF duty is 1.5%. The resonant frequency tuning during operation will be done by adjusting the temperatures of the cooling waters. In this paper, thermal characteristics of this RFQ and control system of the cooling water temperature is described.
RIKEN Nishina Center, Wako
Kyoto ICR, Uji, Kyoto
A new additional injector (RILAC2) is constructed at RIKEN Nishina Center in order to enable the independent operation of the RIBF experiments and super-heavy element synthesis. The RILAC2 consists of a 28 GHz superconducting ECR ion source, a low-energy beam transport with a pre-buncher, a four-rod RFQ linac, a rebuncher, three DTL tanks, and strong Q-magnets between the rf resonators for the transverse focusing. Very heavy ions with m/q of 7 such as 136Xe20+ and 238U35+ will be accelerated up to the energy of 680 keV/u in the cw mode and be injected to the RIKEN Ring Cyclotron without charge stripping. The RFQ linac, the last tank of the DTL, and the bunchers have been converted from old ones in order to save the cost. Construction of the RILAC2 started at the end of the fiscal 2008. The RFQ and DTLs will be installed in the AVF cyclotron vault and be tested in March 2010. The ECR ion source and low-energy beam transport will be set on the RILAC2 in 2010 summer, and the first beam will be accelerated in 2010 autumn. We will present the details of the linac part of RILAC2 as well as the progress of construction which includes the result of high power test of resonators.
USTC/NSRL, Hefei, Anhui
The energy spread measurement by use the energy spectrum analysis system at HLS LINAC now is an intercepting measurement which can't measure the real injection beam. To achieve the non-intercepting measurement, a new Beam position monitor (BPM) with eight stripline electrodes in four-axis symmetry is designed, which can measure the energy spread at HLS LINAC in real time. This paper has introduced the physical structure of this new BPM which include eight 20 degree opening angle, 1/4 wavelength (26.2mm) length Stripline electrodes in detail, analyzed and calculated the electrode response and picking up the quadrupole component, and got the theoretical sensitivities of different methods. The BPM is simulated and calculated by CST Microwave Studio Program. The results shows the parameters such as characteristic impedance, electrode coupling degree, time-domain response and frequency-domain response etc are all meet the requirement of HLS LINAC and transfer line.
BNL, Upton, Long Island, New York
CERN, Geneva
The 3rd LHC Crab Cavity workshop (LHC-CC09) took place at CERN in October 2009. It reviewed the current status and identified a clear strategy towards a future crab-cavity implementation. Following the success of crab cavities in KEK-B and the strong potential for luminosity gain and leveling, CERN will pursue crab crossing for the LHC upgrade. We present the summaries of the various workshop sessions which have led to the LHC crab-cavity strategy, covering topics like layout, cryomodule design, construction, integration, validation, and planning.
NSC/KIPT, Kharkov
Acceleration of intensive electron beams in transient mode with energy spread less than 1% is the actual problem for rf linacs. The transient beam loading phenomenon, consisting in coherent radiation of sequence of charged bunches, results in time dependence of electron energy loss within a beam pulse. In this work a method of delay of a beam relatively rf pulse for energy compensation at accelerating intense short-pulsed electron beams is discussed. An efficiency of the given method in depending on dispersion of group speed, phase advance per cell of an rf structure, an envelope profile of pulses both current and input rf field is studied. Contribution of non-resonant counter waves in the beam energy spread is estimated.
SLAC, Menlo Park, California
CERN, Geneva
The LHC Low Level RF system (LLRF) is a complex multi-loop system used to regulate the superconductive cavity gap voltage as well as to reduce the impedance presented by RF stations to the beam. The RF system can have a profound impact on the stability of the beam; a mis-configured RF system has the potential of causing longitudinal instabilities, beam diffusion and beam loss. To configure the RF station for operation, a set of parameters in the LLRF multi-loop system have to be defined. Initial system commissioning as well as ongoing operation requires a consistent method of computer based remote measurement and model-based design of each RF station feedback system. This paper describes the suite of Matlab tools used for configuring the LHC RF system during the start up in Nov2009-Feb2010. We present a brief overview of the tool, examples of commissioning results, and basics of the model-based design algorithms. This work complements our previous presentation [1], where the algorithms and methodology followed in the tools were described.
[1] D. Van Winkle et. al. 'Feedback Configuration Tools for LHC Low Level RF System,' PAC'09, Vancouver, Canada, May 2009, THZCH03, p. 249 (2009); http://www. JACoW.org.
INFN/LNF, Frascati (Roma)
Metallic clearing electrodes have been designed to absorb the photo-electrons in the DAΦNE positron ring. They have been inserted in the wigglers and dipoles vacuum chambers and have been connected to external high voltage generators. In the paper we present the design of the devices and the results of the electromagnetic simulations related to both the transfer and longitudinal beam coupling impedances. We also present the results of the RF measurements and the first results with the DAΦNE circulating positron beam.
KEK, Ibaraki
SLAC, Menlo Park, California
Coherent synchrotron radiation (CSR) is generated when a bunched beam traverses a dipole magnet or a wiggler/undulator. It can degrade the beam quality in both storage rings and linacs through enhancing the beam energy spread and lengthening the bunch length, even cause single-bunch microwave instabilities. Using several methods, CSR impedances in the positron damping ring (DR) of the SuperKEKB which is under design were calculated. From the impedances due to CSR, resistive wall and various vacuum components, quasi-Green function wake potentials were constructed and used in simulations of Particle-In-Cell (PIC) tracking. We present the CSR related results in this paper.
SLAC, Menlo Park, California
The Phase II upgrade to the LHC collimation system calls for complementing the 30 high robust Phase I graphite secondary collimators with 30 high Z Phase II collimators. The Phase II collimators must be robust in various operating conditions and accident scenarios. This paper reports on the final construction and testing of the prototype collimator to be installed in the SPS (Super Proton Synchrotron) at CERN. Bench-top measurements have demonstrated the device is fully operational and has the mechanical and vacuum characteristics acceptable for installation in the SPS.
SLAC, Menlo Park, California
The Phase II upgrade to the LHC collimation system calls for complementing the 30 high robust Phase I graphite secondary collimators with 30 high Z Phase II collimators. This paper reports on BPM and impedance considerations and measurements of the integrated BPMs in the prototype rotatable collimator to be installed in the Super Proton Synchrotron (SPS) at CERN. The BPMs are necessary to align the jaws with the beam. Without careful design the beam impedance can result in unacceptable heating of the chamber wall or beam instabilities. The impedance measurements involve utilizing both a single displaced wire and two wires excited in opposite phase to disentangle the driving and detuning transverse impedances. Trapped mode resonances and longitudinal impedance are to also be measured and compared with simulations. These measurements, when completed, will demonstrate the device is fully operational and has the impedance characteristics and BPM performance acceptable for installation in the SPS.
Rome University La Sapienza, Roma
INFN/LNF, Frascati (Roma)
ENEA C.R. Frascati, Frascati (Roma)
LBNL, Berkeley, California
Velocity bunching (or RF compression) represents a promising technique complementary to magnetic compression to achieve the high peak current required in the linac drivers for FELs. Here we report on recent progress aimed at characterizing the RF compression from the point of view of the microbunching instability. We emphasize the development of a linear theory for the gain function of the instability and its validation against macroparticle simulations that represents a useful tool in the evaluation of the compression schemes for FEL sources.
TEMF, TU Darmstadt, Darmstadt
GSI, Darmstadt
Beam coupling impedances have been identified as an appropriate quantity to describe collective instabilities caused through beam-induced fields in heavy ion synchrotron accelerators such as the SIS-18 and the SIS-100 at the GSI facility. The impedance contributions caused by the multiple types of beamline components need to be determined to serve as input condition for later stability studies. This paper will discuss different approaches to calculate the Coupling Impedance contribution of ferrite devices, exploiting the abilities of both commercial codes such as CST STUDIO SUITE® and specific extensions of this code to address kicker related problems in particular. Before addressing actual beamline devices, benchmark problems with cylindrical and rectangular geometry will be simulated and the results will be compared with the corresponding analytical formulations.
SLAC, Menlo Park, California
A new method, using the parabolic equation (PE), for the calculation of both high-frequency and small-angle taper (or collimator) impedances is developed in [1]. One of the most important advantages of the PE approach is that it eliminates the spatial scale of the small wavelength from the problem. As a result, the numerical solution of the PE requires coarser spatial meshes. We developed a new code based on Finite Element Method (FEM) which can handle arbitrary profile of a transition. As a first step, we completed and benchmarked a two-dimensional code. One of the important advantages of the code is its fast execution time.
SLAC, Menlo Park, California
SLAC is proposing a rotatable collimator design for the LHC phase II collimation upgrade. This design has 20 facet faces on each cylindrical jaw surface and the two jaws, which will move in and out during operation, are rotatable in order to introduce a clean surface in case of a beam hitting a jaw in operation. When the beam crosses the collimator, it will excite broadband and narrowband modes that can contribute to the beam energy loss and power dissipation on the vacuum chamber wall and jaw surface. In this paper, the parallel eigensolver code Omega3P is used to search for all the trapped modes in the SLAC collimator design. The power dissipation generated by the beam in different vacuum chamber designs with different jaw end geometries is simulated. It is found that the longitudinal trapped modes in the circular vacuum chamber design with larger separation of the two jaws may cause excessive heating. Adding ferrite tiles on the vacuum chamber wall can strongly damp these trapped modes. The short-range wakefields will also be calculated to determine the broadband beam heating and transverse kick on the beam. We will present and discuss the simulation results.
KIT, Karlsruhe
FZK, Karlsruhe
The ANKA light source is regularly operated with a low momentum compaction factor lattice where short bunches are created for the generation of coherent synchrotron radiation (CSR). Short bunches with high electron density can generate strong self fields which act back on the bunch. This can lead to bunch shape deformation and a microbunching instability which were studied theoretically for the ANKA low alpha parameters (Klein et al. PAC 09). We extended these studies to a comparison of calculated electron distributions and bunch profiles measured with a streak camera. The Haissinski equation was solved for the CSR impedance to obtain a prediction for the distortion of the bunches for different bunch lengths and bunch currents. The comparison shows that the theory predicts a much stronger deformation caused by CSR than the streak camera observes. However, high frequency components of measured FTIR spectra show a clear indication for strong deformation or small
KEK, Ibaraki
KEKB, an asymmetric electron/positron double-ring collider, utilizes the crab cavity to perform the head-on collision at the interaction point. We observed peculiar phenomena at the transition from the collision to non-collision, where the bunch length slightly changed, even though the beam current and the RF related parameters were almost constant. We also observed that the transverse beam size of both beams changed at the transition. An experimental study was carried out to investigate whether the bunch length would change or not, when the vertical beam size was intentionally changed. The bunch length was measured using a monitor based on the beam spectrum with a resolution of 0.01 mm. We found that the bunch length slightly changed together with the vertical beam size under non-colliding condition. We expect that the change in the bunch length is not caused by the colliding effects, but is related to the longitudinal space charge transformed from the transverse plane. Since the longitudinal space charge effect is negligible for the relativistic beams, some tilting effect of a bunch is suspected.
KEK, Ibaraki
Electron cloud instabilities are a great concern for the KEKB, an electron/positron collider. In order to study wakefield effects of electron cloud, a test bunch was injected behind a bunch train with the solenoid fields off, where cloud density rapidly decayed. A current-dependent tune shift and the tune spread of a test bunch were measured as a function of the bunch current while varying the bucket position of a test bunch. The vertical tune shift indicated a strong defocusing force together with widened tune spread in a region of relatively low cloud density and low bunch current. However, the vertical tune shift changed to a focusing force at high cloud density and high bunch current. On the other hand, the horizontal and vertical tune spreads tended to approach a constant value as increasing the bunch current. The turning current is approximately equal to the threshold current of the vertical size blow-up.
ASCo, Clayton, Victoria
Melbourne
The Australian Synchrotron storage ring must maintain a stable electron beam for user operations. The impedance characteristics of the storage ring can give rise to instabilities that adversely affect the beam quality and need to be well understood. Collective effects driven by the resistive wall impedance are particularly relevant at the Australian synchrotron and their strengths are enhanced by small gap insertion devices, such as IVUs. This study will explore the impedance issues identified in the Australian Synchrotron storage ring and current mitigation techniques.
Karlsruhe Institute of Technology (KIT), Karlsruhe
KIT, Karlsruhe
FZK, Karlsruhe
LNLS, Campinas
We present results of a series of measurements aimed at characterizing the beam coupling impedances in the ANKA electron storage ring. The measurements include transverse coherent tune shifts, bunch lengthening and synchronous phase shift as a function of single bunch current. These were performed under a variety of conditions in the ANKA ring, including injection energy (500 MeV), nominal operating energy (2.5 GeV) as well as at 1.3 GeV and in the low alpha mode and are part of a longer term effort to understand the ANKA impedance over a wide frequency range.
GSI, Darmstadt
ITEP, Moscow
Octupole magnets can be used as a passive cure against transverse collective instabilities. The octupole field creates a betatron frequency spread due to amplitude-dependent tune shift and thus enhances Landau damping. The drawback is the reduction of the dynamic aperture (DA). Ultimately, a balance between collective damping and DA must be found. Here we analyse the transverse coherent instability thresholds in SIS100 with octupoles and nonlinear space-charge taken into account. As the major impedance sources at low frequencies, the resistive wall and the kickers are considered. A coasting beam is assumed, which results in a conservative stability estimation. On the other hand, we simulate the DA of the SIS100 lattice using the MADX code, with systematic multipole errors, random multipole errors, and closed-orbit errors taken into account.
ELETTRA, Basovizza
FERMI@ELETTRA is a single pass FEL Facility in construction at the ELETTRA Laboratory in Trieste. To linearize the beam longitudinal phase space, it is planned to use a short X-band accelerating structure installed before the first bunch compressor. Since both the end tubes of the structure have a reduced radius of 5.0 mm, much smaller than the 13.5 mm radius of the beam pipes before and after the structure, a transition, either stepped or tapered, will be necessary between the two components. Using the ABCI code, we have investigated the short range wake fields at the step-out and taper-out transitions and we have compared them with some conventional analytical models. We have developed specific ABCI-based analytical models that simulate accurately the short range wake field for a wide range of rms bunch lengths (σ: 100 - 1000μm).
ELETTRA, Basovizza
Step-out transition is one of the most frequent component, commonly used on the new generation light source facilities where very short and dense electron bunches are considered. The numerical calculation of the short-range wake at this type of transition requires a spatial mesh size equal to a fraction of bunch length. This calculation becomes for a very short bunch, e.g. σ = 25μm, very time consuming due to the large number of mesh points required. On the other hand, the available analytical models that calculate the transverse wake field are applicable only on a narrow range of bunch lengths. We developed an ABCI-based analytical model that can calculate accurately the kick factor. The advantage of this model is quick, accurate and covers wide range of rms bunch lengths (up to σ = 1000μm). The model also covers a wide range of beam pipe ratio b/a.
KEK, Ibaraki
As part of the design works of the interaction region (IR) of SuperKEKB (the upgrade of KEKB B-factory (KEKB)), the loss factor and impedance of beam ducts for the interaction point (IP duct) were calculated by GdfiedL. The IP duct is round and connected to beam ducts for electron and positron beams with a diameter of 20 mm via Y-shaped crotch ducts at both ends. The lengths of the straight section and crotch section are about 200 mm, respectively. The beam crossing angle is 83 mrad. Calculations for two types of IP duct were performed. Both ducts are almost same in design except for the diameter of the straight section (20 mm and 30 mm). The loss factors were about 0.001 V/pC in both cases when the bunch length was 6 mm. The longitudinal impedances showed that there were no modes trapped longitudinally in IP duct. However, from the results of the transverse impedance and eigenmode calculation, it was found that many TE modes can be trapped at the crotch section if the beam is off-center of the beam duct. For comparison, the loss factor and impedance of the IR beam duct of KEKB are also being calculated now. Full details of the calculation results will be provided in this report.
KEK, Ibaraki
SLAC, Menlo Park, California
Grooved surfaces are effective to suppress the secondary electron emission, and can be a possible technique to mitigate the electron cloud instability (ECI) in positron/proton storage rings. Various types of triangular grooved surfaces have been studied in a laboratory, and also using an intense positron beam of the KEKB B-factory. The grooves have vertex angles of 20 ~ 30 degrees, and depths of 2.5 mm. In the laboratory, the secondary electron yield (SEY) of sample pieces were measured using an electron beam in a magnetic-free condition. The maximum SEY well below 1.0 was obtained after some extent of electron bombardment for most of grooved surfaces. To test he groove efficacy in magnetic field regions of particle accelerators, insertions with several types of grooved surfaces were installed into a test chamber in a wiggler magnet of KEKB positron ring. In a dipole-like chamber wit magnetic field (0.78 T), the reduction in the electron density around the beam was observed for a grooved section when compared to the case of a flat surface with TiN coating. An R&D effort is underway to optimize and manufacture the grooved surface in accelerator beam pipes for practical use.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
J-PARC, KEK & JAEA, Ibaraki-ken
There is the famous formula of the horizontal impedance for the matched-traveling wave kicker. However, the real and the imaginary parts of the impedance do not satisfy the Hilbert transformations. On the other hand, the impedance measured by a loop method does not directly give the beam impedance. In this paper we theoretically derive the beam impedance and reproduce the impedance by using the estimated inductances of the kicker by the loop measurement.
CERN, Geneva
Since many years the Proton Synchrotron Booster (PSB) high intensity beams have shown head-tail instabilities in all of the four rings at around 100 ms after the injection. In this paper we present the latest observations together with the evaluation of the instability rise time and its dependence on the bunch intensity. The acquired head-tail modes and the growth rates are compared with HEADTAIL numerical simulations, which together with the Sacherer theory points at the resistive wall impedance as a possible source of the instability.
EPFL, Lausanne
CERN, Geneva
Transition crossing in the CERN PS is critical for the stability of high intensity beams, even with the use of a second order gamma jump scheme. The intense single bunch beam used for the neutron Time-of-Flight facility (n-ToF) needs a controlled longitudinal emittance blowup at flat bottom to prevent a fast single-bunch vertical instability from developing near transition. This instability is believed to be of Transverse Mode Coupling (TMCI) type. A series of measurements taken throughout 2008 and 2009 aim at using this TMCI observed on the ToF beam at transition, as a tool for estimating the transverse global impedance of the PS. For this purpose, we compare the measurement results with the predictions of the HEADTAIL code and find the matching parameters. This procedure also allows a better understanding of the different mechanisms involved and can suggest how to improve the gamma jump scheme for a possible intensity upgrade of the n-ToF beam.
EPFL, Lausanne
CERN, Geneva
Using B. Zotter's formalism, we present here a novel, efficient and exact matrix method for the field matching determination of the electromagnetic field components created by an offset point charge travelling at any speed in an infinitely long circular multilayer beam pipe. This method improves by a factor of more than one hundred the computational time with three layers and allows the computation for more layers than three. We also generalize our analysis to any azimuthal mode and finally perform the summation on all such modes in the impedance formulae. In particular the exact multimode direct space-charge impedances (both longitudinal and transverse) are given, as well as the wall impedances to any order of precision.
EPFL, Lausanne
CERN, Geneva
The exact formalism from B. Zotter to compute beam coupling impedances has been fully developed only in the case of an infinitely long circular beam pipe. For other two dimensional geometries, some form factors are known only in the ultrarelativistic case and under certain assumptions of conductivity and frequency of the pipe material. We present here a new and exact formalism to compute the beam coupling impedances in the case of a collimator-like geometry where the jaws are made of two infinite plates of any linear material. It is shown that the impedances can be computed theoretically without any assumptions on the beam speed, material conductivity or frequency range. The final formula involves coefficients in the form of integrals that can be calculated numerically. This way we obtain new generalized form factors between the circular and the flat chamber cases, which eventually reduce to the so-called Yokoya factors under certain conditions.
CERN, Geneva
EPFL, Lausanne
The kickers are major contributors to the CERN SPS beam coupling impedance. As such, they may represent a limitation to increasing the SPS bunch current in the frame of an intensity upgrade of the LHC. In this paper, CST Particle Studio time domain electromagnetic simulations are performed to obtain the longitudinal and transverse impedances/wake potentials of simplified models of ferrite loaded kickers. The simulation results have been successfully compared with some existing analytical expressions. In the transverse plane, the dipolar and quadrupolar contributions to the wake potentials have been estimated from the results of these simulations. For some cases, simulations have also been benchmarked against measurements on PS kickers. It turns out that the large simulated quadrupolar contributions of these kickers could explain both the negative total (dipolar+quadrupolar) horizontal impedance observed in bench measurements and the positive horizontal tune shift measured with the SPS beam.
EPFL, Lausanne
CERN, Geneva
In this study B. Zotter's formalism is applied to a circular infinitely long beam pipe made of a conductor of infinite thickness where an offset point-charge travels at any given speed. Simple formulae are found for the impedances and electromagnetic fields both at intermediate frequencies (recovering Chao's results) and in the low frequency regime where the usual classic thick wall impedance formula does not apply anymore due to the large skin depth compared to the pipe radius.
EPFL, Lausanne
PSI, Villigen
CERN, Geneva
Wake fields in the CLIC Beam Delivery System (BDS) can cause severe single or multi-bunch effects leading to luminosity loss. The main contributors in the BDS are geometric and resistive wall wake fields of the collimators and resistive wall wakes of the beam pipe. The present work focuses only on the multi-bunch effects from resistive wall. Using particle tracking with wake fields through the BDS, we have established the aperture radius, above which the effect of the wake fields becomes negligible. Our simulations were later extended to include a realistic aperture model along the BDS as well as the collimators. The two cases of 3TeV and 500GeV have been examined in this paper.
EPFL, Lausanne
CERN, Geneva
The SPS kickers are major contributors to the SPS transverse beam coupling impedance. The current "flat chamber" impedance model for a kicker is obtained by applying form factors to the theoretical impedance of an axisymmetric ferrite beam pipe. This model was believed to be acceptable for the vertical dipolar impedance, as two-wire measurements on SPS kickers revealed a satisfactory agreement. However, one-wire measurements on PS kickers suggested that this model underestimates the kickers' transverse quadrupolar (detuning) impedance. The longitudinal and transverse dipolar impedances of another kicker model that accounts for the metallic plates on each side of the ferrite were derived in the past by H. Tsutsui. The same formalism is used in this paper to derive the quadrupolar impedance. These formulae were then successfully benchmarked to electromagnetic simulations. Finally, simulating the interaction of an SPS bunch with the improved kickers' model results in a positive horizontal tune shift, which is very close to the tune shift measured with the SPS beam.
EPFL, Lausanne
CERN, Geneva
INFN/LNF, Frascati (Roma)
Honorary CERN Staff Member, Grand-Saconnex
The beam coupling impedance of the CERN SPS is expected to be one of the limitations to an intensity upgrade of the LHC complex. In order to be able to reduce the SPS impedance, its main contributors need to be identified. An impedance model for the SPS has been gathered from theoretical calculations, electromagnetic simulations and bench measurements of single SPS elements. The current model accounts for the longitudinal and transverse impedance of the kickers, the horizontal and vertical electrostatic beam position monitors, the RF cavities and the 6.7 km beam pipe. In order to assess the validity of this model, macroparticle simulations of a bunch interacting with this updated SPS impedance model are compared to measurements performed with the SPS beam.
NSRRC, Hsinchu
Taiwan Photon Source (TPS) is a new third generation synchrotron storage ring which will be built at the present site of the NSRRC. The paper summarizes results of the impedance studies of the storage ring vacuum components for the TPS project. The main goal of this work was to support the design of the vacuum chamber and, at the same time, to get a detailed model of the machine impedance, which can be used later for detail studies of collective effects. Wake potentials and impedances for each component of the storage ring have been simulated with a 3D electromagnetic code GdfidL. Numerically obtained data have been compared to analytical results for simplified geometries of the vacuum chamber components.
SLAC, Menlo Park, California
In accelerator design, there is often a need to evaluate the threshold to the (longitudinal) microwave instability for a bunched beam in a storage ring. Several computational tools are available that allow us, once given a wakefield, to numerically find the threshold current and to simulate the development of the instability. In this work, we present the results of computer simulations with codes recently developed at the SLAC National Accelerator Laboratory. Our simulations include the cases of the resonator broadband impedance, the resistive wall impedance and the coherent synchrotron radiation impedance. We compare the accuracy of the threshold prediction and discuss the capabilities and limitations of the codes.
SLAC, Menlo Park, California
PEP-X, a next generation, ring-based light source is designed to run with beams of high current and low emittance. Important parameters are: energy 4.5 GeV, circumference 2.2 km, beam current 1.5 A, and horizontal and vertical emittances, 150 pm by 8 pm. In such a machine it is important that impedance driven instabilities not degrade the beam quality. In this report we study the strength of the impedance and its effects in PEP-X. For the present, lacking a detailed knowledge of the vacuum chamber shape, we create a straw man design comprising important vacuum chamber objects to be found in the ring, for which we then compute the wake functions. From the wake functions we generate an impedance budget and a pseudo-Green function wake representing the entire ring, which we, in turn, use for performing instability calculations. In this report we consider in PEP-X the microwave, transverse mode-coupling, multi-bunch transverse, and beam-ion instabilities.
SLAC, Menlo Park, California
BNL, Upton, Long Island, New York
Collimators and other similar accelerator structures usually include small-angle tapering to lower the wakefields generated by the beam. While the low-frequency impedance is well described by Yokoya's formula (for axisymmetric geometry), much less is known about the behavior of the impedance in the high frequency limit. In this paper we develop an analytical approach to the high-frequency regime for round collimators and tapers. Our analytical results are compared with computer simulations using the code ECHO.
SLAC, Menlo Park, California
The geometry of storage ring collider interaction regions present an impedance to beam fields resulting in the generation of additional electromagnetic fields (higher order modes or wake fields) which affect the beam energy and trajectory. These affects are computed for the Super B interaction region by evaluating longitudinal loss factors and averaged transverse kicks for short range wake fields. Results indicate at least a factor of 2 lower wake field power generation in comparison with the interaction region geometry of the PEP-II B-factory collider. Wake field reduction is a consideration in the Super B design. Transverse kicks are consistent with an attractive potential from the crotch nearest the beam trajectory. The longitudinal loss factor scales as the -2.5 power of the bunch length. A factor of 60 loss factor reduction is possible with crotch geometry based on an intersecting tubes model.
BNL, Upton, Long Island, New York
In this paper, we present an overview of the impact of collective effects upon the performance of the NSLS-II booster.
KEK, Ibaraki
SLAC, Menlo Park, California
In order to mitigate the electron cloud instability (ECI) in a positron ring, an electron clearing electrode with a very thin structure has been developed. The electrode has been tested with an intense positron beam of the KEKB B-factory using a test chamber. A drastic reduction in the electron density around the beam was demonstrated in a dipole magnetic field (0.78 T). The clearing electrode was then applied to the actual copper beam pipe (94 mm in diameter) with antechambers for wiggler magnets of KEKB. The feed-through was revised to improve reliability, and the length was modified to fit a real magnet. The input power into the electrode was estimated to be approximately 80 W/m. The clear reduction in the electron density was also observed by applying a voltage of +500 V to the electrode. The design of clearing electrodes has now reached a high reliability and it is suitable for accelerator applications.
DESY, Hamburg
At DESY the PETRA ring has been converted into a synchrotron radiation facility, called PETRA III. The commissioning with beam started in April 2009. The betatron tune versus beam intensity was measured for different configurations of the wiggler magnets which are installed in PETRA III to achieve the small emittance of 1 nm. These measurements are compared with predictions from the impedance model. The measured tune shift is well within the impedance budget and the design single bunch intensities of up-to 2.5 mA can be stored in PETRA III. The predicted vertical tune shift is about 30 % smaller than the measured one.
KIT, Karlsruhe
A dedicated optics with a low momentum compaction factor is used at the ANKA storage ring to reduce the bunch length to generate coherent synchrotron radiation (CSR). A double sweep streak camera is employed to determine the bunch length and shape for different optics and as a function of the beam current. Measurements of the longitudinal bunch profile have been performed for many different momentum compaction factors and various bunch currents. This paper describes the set up of the streak camera experiments and compares the measured bunch lengths to theoretical expectations.
SSRF, Shanghai
SINAP, Shanghai
To investigate the higher order mode(HOM) damping in the higher harmonic cavity for Shanghai Synchrotron Radiation Facility(SSRF) when using HOM absorbers,simulations have been done for changing the position and the length as well as the thickness of ferrite of HOM damper. The best values under which the Q value of HOMs can be greatly lowered and the impedance of harmonic cavity will be trapped in the impedance threshold have been found.
BNL, Upton, Long Island, New York
The booster synchrotron for NSLS-II accepts beam with 200 MeV from a linac and raises its energy up to 3 GeV. In order to raise beam energy up to 3 GeV, a 7-cell PETRA cavity is installed. Beam instabilities related with the cavity are discussed. In particular, in order to avoid coupled-bunch instability, we consider that cooling water temperature for the cavity should be changed to shift frequencies of higher order modes (HOM) to avoid beam revolution lines. To obtain the relation between the temperature dependence of amount of frequency shift in each HOM and cavity body temperature, we carried out the measurement by changing cavity body temperature. From the measurement data, we calculate the required temperature variation. We summarize the results and describe the system design.
SOLEIL, Gif-sur-Yvette
JASRI/SPring-8, Hyogo-ken
In this paper we introduce and discuss the recent developments made in our digital transverse bunch by bunch feedback system at SOLEIL, which is routinely in service since the first user operation in both the high average current and high bunch current modes. The above includes installation of a third chain with a dedicated 4-electrode stripline intended to operate in the horizontal plane, an attempt to sample the BPM signal directly at the RF frequency without down-converting to the baseband following the success at SPring-8, a refined tuning procedure by measuring the feedback damping times as a function of the band frequency, as well as exploration of different digital filters ensuring a larger working range in terms of betatron tunes or a faster response against single bunch instabilities. The achieved performance and results are described. The observed evolution of the machine impedance and instabilities shall also be presented.
INFN/LNF, Frascati (Roma)
CERN, Geneva
In the two beam acceleration scheme the Main Beam must be precisely synchronized with respect to the RF power produced by the Drive Beam. Timing errors would have an impact on the collider performances. The Drive Beam phase errors should be controlled, by means of a feed forward system, within 0.1° (23fs @ 12GHz) to avoid a luminosity reduction larger than 2%. A beam phase arrival monitor is an essential component of the system. Its design has been based on the following main requirements: resolution of the order of 20fs, very low coupling impedance due to the very high beam current and integrated filtering elements to reject RF noise and weak fields in the beam pipe that could otherwise affect the measurements.
University of Delhi, Delhi
Fermilab, Batavia
Eleven cell elliptical cavity is designed for acceleration of particles traveling at 81 % of the speed of light. It will operate at 1.3 GHz and will be used to accelerate the particles from 0.4 GeV to 1.2 GeV. The cavity is studied for higher order mode (HOM) and trapped modes. The shapes of end cells of cavity is optimized to increase the field amplitude in end cells so that coupling of trapped modes may increase with HOM coupler and they can be extracted easily but keeping the field flatness & operating frequency undisturbed.
BARC, Mumbai
BARC-EBC, Mumbai
The performance of superconducting cavity, couplers and ceramic windows is greatly affected due to multipacting. The present paper describes the multipacting simulations carried out on the co-axial coupler. The equation of motion of electron in RF field is calculated numerically. The enhanced counter function (ECF) is calculated to find out whether a particular electron will give rise to the multipacting. The simulation was carried out for a co-axial coupler having the inner conductor diameter of 34.78 mm and outer conductor diameter of 80 mm at a RF frequency of 350MHz, 700MHz and 1050MHz.
PAL, Pohang, Kyungbuk
In the PLS-II storage ring, the available length of a long straight section for RF system is 6.28 m, which is from quadrupole magnet to quadrupole magnet beam-pipe valves with an elliptical transverse cross section. In this room, two beam-pipe transitions from elliptical to circle cross section, two commercial cryomodules with a circle transverse cross section, three bellows for adjusting cryomodule length and four vacuum valves could need to be installed. Two commercial cryomodules are too long to be installed into this section. In order to install two cryomodules into this section, we need to modify the tapers for reducing the total length of these parts. In this paper, the HOM damping effects for different taper shapes has been studied. The beam loss factor influence and broad-band impedance change due to taper shape changes have been estimated.
Muons, Inc, Batavia
JLAB, Newport News, Virginia
The design and construction of electron-ion colliders will be facilitated by the development of an SRF "crab crossing" cavity with 0.5 to 1.5 GHz frequency and 20 to 50 MV integrated voltage. These RF cavities provide a transverse kick to the particle beam. Current state of the art crab cavities provide 2-5 MV of integrated voltage, and most of the existing designs require complex schemes to damp unwanted RF modes. We propose a novel system for implementing TEM-like two-bar structures. Two phase-locked sources 180° out of phase each drive a half-wavelength coax antenna inside of a cavity designed for the fewest possible unwanted modes. The cavity design will required a high-Q system composed of coax windows designed for maximizing the shunt impedance of the structure. A series of cavities could be installed in a beam line, and individual phase adjustment for each module will accommodate their longitudinal spacing and will provide the required integrated voltage.
Private Address, Freeville
CLASSE, Ithaca, New York
Ferrites and lossy ceramics used in HOM (higher order mode) load for superconducting accelerators, have shortcomings such as poor batch-to-batch reproducibility of electromagnetic properties, extremely low electric conductivity at cryogenic temperatures leading to accumulation of charge on the material surface, brittleness, which may cause contamination of the nearby SRF cavities by lossy dust, etc. A proposal to use a resistive material free of these shortcomings is presented.
JLAB, Newport News, Virginia
The College of William and Mary, Williamsburg
ODU, Norfolk, Virginia
NSU, Newport News
In the past years, energetic vacuum deposition methods have been developed in different laboratories to improve Nb/Cu technology for superconducting cavities. Jefferson Lab and collaborators are pursuing energetic condensation deposition via Electron Cyclotron Resonance. As part of this study, the influence of the deposition energy, the coating temperature and the substrate's nature on the material and RF properties of the Nb thin film is investigated. The film surface and structure analyzes are conducted with various techniques like X-ray diffraction, Transmission Electron Microscopy, Auger Electron Spectroscopy and RHEED. The microwave properties of the films are characterized on 50 mm disk samples with a 7.5 GHz surface impedance characterization system. This paper presents surface impedance measurements in correlation with surface and material characterization for Nb films produced on various substrates with different bias voltages. Emerging opportunities for developing multi-layer superconducting rf films are also highlighted with the commissioning results of a new deposition system.
ODU, Norfolk, Virginia
JLAB, Newport News, Virginia
The superconducting parallel-bar cavity* has properties that makes it attractive as a deflecting or crabbing rf structure. For example it is under consideration as an rf separator for the Jefferson Lab 12 GeV upgrade and as a crabbing structure for a possible LHC luminosity upgrade. Initial cavity shape optimization has been performed to obtain a high transverse deflecting voltage with low surface fields. We present here a study of the Higher Order Mode (HOM) properties of this structure. Frequencies, R/Q and field profiles of HOMs have been evaluated and are reported.
* J.R. Delayen and H. Wang, Phys. Rev. ST Accel. Beams 12, 062002 (2009).
KEK, Ibaraki
J-PARC, KEK & JAEA, Ibaraki-ken
The power supply current ripple of the quadrupole magnets of the J-PARC main ring has been measured to be the order of 10-4. The magnetic field of the quadrupole magnets has been measured and the ripple frequency distribution of each magnet was observed to be depending on where the magnet is in the magnet chain. A transmission line model for the cable and magnets was able to explain the distribution. The field ripple made by the common mode current ripple was reduced by changing the magnet cabling to be symmetrical with respect to the N and S poles of the quadrupole magnets. The common mode ripple was drastically reduced. The normal mode ripple of 600, 1200 and 1800 Hz however remained. The field ripple was further reduced using resistors those are connected in parallel to the magnet coils and bypass the current ripple. It was effective to the higher frequency ripple of 1200 and 1800 Hz and the effect was in a good agreement with an electric circuit simulation program LTspice.
RCNP, Osaka
The ordinary electric circuits produce and receive electromagnetic noise. The noise is a problem for stable operation of synchrotron accelerators. We do not know the origin of the noise generation due to the lack of electric circuit theory, which takes into account the noise sources. The proper treatment of electric circuit together with noise requires a proper knowledge of multiconductor transmission-line theory. We have developed a new multiconductor transmission-line theory in which we are able to describe the performance of multiconductor transmission-line system*. In this theory, it is essential to use the coefficients of potential instead of capacities and the introduction of the normal and common modes. After understanding the multiconductor transmission-line theory, we propose the introduction of the middle line (three lines) and symmetric arrangements of electric loads**. The use of this concept made the J-PARC MR successful in operation.
* H. Toki and K. Sato, J. Phys. Soc. Jpn 78 (2009) 094201.
** K. Sato and H. Toki, Nucl. Inst. Methods A565 (2006) 351.
NSRRC, Hsinchu
The purpose of this paper is to estimate the conductive Electromagnetic Interference (EMI) from magnet power supply in NSRRC. A LISN system was conducted to measure the EMI spectrum of power supply. The different frequency range of conductive EMI was measured. For the future TPS(Taiwan Photon Source) power supply design, the EMI signals must be lower than TLS kicker. Therefore reducing and eliminating the interference of electromagnetic waves will be a very important issue. A filter and shielding method were used to test the effects of reducing EMI. The EMI prevention scheme will be used in the future.
NSRRC, Hsinchu
We design and implement a power convert to supply dc power bus for the MCOR30 correction supply. The dc power supply's characteristics were variable frequency at heavy and medium/light load. These characteristics matched with the correction supply working requirement. The dc power bus has a relaxation oscillator generating a symmetrical triangular waveform, which MOSFET's switching is locked to. The frequency of this waveform is related to a current that will be modulated by feedback circuitry. As a result, the tank circuit driven by half-bridge will be stimulated at a frequency dictated by the feedback loop to keep the output voltage regulated, thus exploiting its frequency-dependent transfer characteristics. The high performance characteristics of the resonant dc power bus are illustrated in this paper.
CIEMAT, Madrid
CERN, Geneva
The goal of the present CLIC Test Facility (CTF3) is to demonstrate the technical feasibility of specific key issues of the CLIC scheme. The extracted drive beam from the combiner ring (CR), a pulse of 35 A magnitude and 140 ns duration, is sent to the new CLic EXperimental area (CLEX). A Tail Clipper (TC) kicker is required, in the CR to CLEX transfer line, to allow the duration of the beam pulse to be adjusted: the unwanted bunches are kicked into a collimator. The TC must have a fast field rise-time, of not more than 5 ns, in order to minimize uncontrolled beam loss. Striplines are used for the TC: to establish the required fields, the applied pulse wave front must fully propagate along the striplines. To reduce the wave front propagation time, the overall length of the stripline assembly is sub-divided into 4 sections. The TC has been designed with the aid of detailed numerical modelling: the stripline cross-section and coaxial-to-stripline transitions were carefully optimized using a 3D code. The results of simulations and the measured behaviour of the striplines are presented; in addition measured current pulses are shown.
CERN, Geneva
The Compact Linear Collider (CLIC) study is exploring the scheme for an electron-positron collider with high luminosity (1034 - 1035 cm2/s) and a nominal centre-of-mass energy of 3 TeV: CLIC would complement LHC physics in the multi-TeV range. The CLIC design relies on the presence of Pre-Damping Rings (PDR) and Damping Rings (DR) to achieve the very low emittance, through synchrotron radiation, needed for the luminosity requirements of CLIC. In order to limit the beam emittance blow-up due to oscillations the combined flat-top ripple and droop of the field pulse, for the DR extraction kickers, must be less than 0.015%. In addition, the allowed beam coupling impedance for the kicker systems is also very low: a few Ohms longitudinally and a few MΩ/m transversally. This paper discusses initial ideas for achieving the extremely demanding requirements for the PDR and DR kickers.
CERN, Geneva
A five-turn continuous extraction is currently used to transfer the proton beam from the CERN PS to the SPS. This extraction uses an electrostatic septum to cut the filament beam into five slices, causing losses of about 15 %. These losses would be an even greater drawback when the beam intensity is further increased for the CERN Neutrinos to Gran Sasso facility. To overcome this, a Multi-Turn Extraction (MTE) has been implemented, in which the beam is separated, prior to extraction, into a central beam core and four islands. Each beamlet is extracted using a set of kickers and a magnetic septum. For the kickers two new pulse generators have been built, each containing a lumped element Pulse Forming Network (PFN) of 12.5 Ohms, 80 kV and 10.5 μs. For cost reasons existing 15 Ω transmission line kicker magnets are reused. The PFN characteristic impedance deliberately mismatches that of the magnets to allow a higher maximum kick. The PFN design has been optimised such that undesirable side-effects of the impedance mismatch on kick rise-time and flat-top remain within acceptable limits. The kicker systems put in place for the current first phase of MTE are presented.
CERN, Geneva
The vertical beam dump system of the CERN Super Proton Synchrotron (SPS) uses two matched magnets with an impedance of 2 Ω and combined kick strength of 1.152 Tm at 60 kV supply voltage. For historical reasons the two magnets are powered from three 3 Ω pulse forming networks (PFN) through three thyratron-ignitron switches. Recently flashovers were observed at the entry of one of the magnets, which lead, because of the electrical coupling between the kickers, to a simultaneous breakdown of the pulse in both magnets. To improve the reliability an upgrade of the system was started. In a first step the radii of surfaces at the entry of the weak magnet were increased, and the PFN voltage was reduced by 4 %; the kick strength could be preserved by reducing the magnet termination resistance by 10 %. The PFNs were protected against negative voltage reflections and their last cells were optimised. In a second step the two magnets will be electrically separated and powered individually by new 2 Ω PFNs with semiconductor switches.
LBNL, Berkeley, California
The Next Generation Light Source (NGLS) at Lawrence Berkeley Laboratory is a 2.4 GeV linear accelerator with up to ten FELs. Each of the FELs require a fast kicker, with the exception of the final one which can use a normal bend magnet. The requirements for the kickers are to deflect the linac beam by an angle of 3 mrad with a magnetic length of 2 m, and an aperture size of 17 by 17 mm. A strip line magnet with an impedance of 50 Ohms being feed from the opposite direction as the beam has been selected for prototyping. The modulator requirements to drive such a magnet are ±15 kV and ±300 A, with rise and fall times of 5 ns and a flat top of 10 ns. The pulse to pulse stability must be better than 0.01% of the peak value. The design of the modulator is an inductive adder with 20 cells, each driven by 12 power MOSFETs. This paper describes details of the design as well as present preliminary test data.
KEK, Ibaraki
Dr. Matsumoto in KEK and his colleague have developed the MO flange for vacuum sealing of normal conducting high peak power RF wave-guide. This is impedance free sealing. We have applied this sealing to SRF cavity technology instead of indium sealing. We used pure aluminum gasket for the sealing material. We had a difficulty on the titanium flange but succeeded to establish leak tightness in super-fluid Helium by stainless flange. In this paper, we will report the R&D results.
KEK, Ibaraki
A damping ring of positron beams is under consideration for the upgrade of KEKB (SuperKEKB) because low emittance of beams injected to the main rings is required by the SuperKEKB optics in the nano-beam scheme. We present the design of the RF accelerating structure, especially on the higher-order-mode (HOM) damped structure. This structure is based on the normal-conducting accelerating cavity system ARES, which has successful records of the long-term stable operations so far with low trip rates at KEKB. All the HOM absorbers are made of silicon carbide, bullet-shaped, and to be directly water cooled, so that the structure presented in this paper can be also a prototype for accelerating beams of the order of 10A in the SuperKEKB main ring in the high-current scheme.
Euclid TechLabs, LLC, Solon, Ohio
LETI, Saint-Petersburg
CERN, Geneva
In this presentation, dielectric collimator concepts for the linear collider will be described. Cylindrical and planar dielectric collimator designs for CLIC and ILC parameters will be presented, and results of simulations to minimize the beam impedance will be discussed. The prototype collimator system is planned to be fabricated and experimentally tested at Facilities for Accelerator Science and Experimental Test Beams (FACET) at SLAC.
KEK, Ibaraki
KEK/JAEA, Ibaraki-Ken
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
Magnetic alloy cavities are successfully used for J-PARC synchrotrons. These cavities generate much higher RF voltage than ordinary ferrite cavities. For future upgrades of J-PARC facilities, a higher field gradient is necessary. It was found that the characteristics of magnetic alloy is improved by a new annealing scheme under magnetic field. A large production system using an old cyclotron magnet is under construction for the J-PARC upgrade. The status of core development will be reported.
KEK, Ibaraki
BNL, Upton, Long Island, New York
An RF system using Magnetic Alloy is considered as an option to study the beam dynamics of a linear non-scaling FFAG. Such an FFAG may have many resonances, which affect the beam more when the beam crosses them slowly. The RF system aims at ordinary RF bucket acceleration with an RF frequency sweep of 3 % in 100 turns. The cavity has only 10 cm length to fit in a short straight section. The required RF voltage is 100 kV per turn and each of the three cavities is designed to generate 50 kV.
JAEA/J-PARC, Tokai-mura
KEK/JAEA, Ibaraki-Ken
KEK, Ibaraki
We have been operating the RF cavities loaded with MA cores with a high field gradient of more than 20 kV/m since October 2007. We have been measuring the RF cavity impedance at the shutdown periods, and we detected the impedance reductions of RCS RF cavities on January and June 2009. Taking out the RF cavities from the beam line and opening them, we found that many of cores showed a buckling at the inner radius. Also detachment of the epoxy coating intended to prevent rusting was observed. We report the detail of condition of MA cores and the relation between the impedance reduction and core condition.
RIKEN Nishina Center, Wako
A new injector RILAC2 for RIKEN RI-Beam Factory is under construction. The three Drift Tube Linac (DTL) cavities, located downstream of an RFQ linac, are designed to operate at a fixed RF frequency of 36.5 MHz, and to accelerate very heavy ions such as 136Xe20+ and 238U35+ from 100 keV/u to 680 keV/u for the injection to the RIKEN Ring Cyclotron. The first two cavities (DTL1 and 2) are newly constructed, and an existing cavity is modified for the last one (DTL3). The structure is based on the quarter-wavelength resonator. The inner diameter ranges from 0.8 to 1.3 m. In order to save the construction cost and space for the equipments, direct coupling scheme has been adopted for the RF amplifier. A capacitive coupler was designed to match the input impedance to 700, which corresponds to the optimum output impedance of a tetrode. Design of the cavities and couplers will be described in detail.
MEPhI, Moscow
Nowadays the DC potential using was proposed for ion beam focusing in linear accelerators. It was proposed to use the DC potential for combined beam focusing (electrostatic focusing and focusing by using of higher RF field spatial harmonics) in bunching section of linac *. These accelerators use an IH-type resonator. So-called linear undulator accelerator (UNDULAC) was proposed for ribbon ion beam bunching and acceleration **. One of possible scheme of UNDULAC can be realized using an electrostatic undulator in E-type resonator. In this report the different types of the electrostatic potential inputting into resonator will discussed.
* P.А. Demchenko at al., Problems of Atomic Science and Technology, 2008, 5 (50), pp. 28-32.
** E.S. Masunov at al., Radiation Physics and Chemistry, 2001, v. 61, рр. 491-493.
IUCF, Bloomington, Indiana
In this report, we present our design of a fast extraction kicker for ALPHA. Due to the fast rise time and high voltage requirement, we choose the traveling wave kicker. Both 2D Posisson and 3D Microwave Studio simulation are carried out. Uniformity of electric field, energy transmission through the stripline structure and time response of the kicker are studied carefully. A prototype kicker will be built and tested soon.
SLAC, Menlo Park, California
KEK, Ibaraki
INFN/LNF, Frascati (Roma)
We report results of ongoing high power tests of single cell standing wave structures. These tests are part of an experimental and theoretical study of rf breakdown in normal conducting structures at 11.4 GHz. The goal of this study is to determine the accelerating gradient capability of normal-conducting rf powered particle accelerators. The test setup consists of reusable mode-launchers and short test structures powered by SLAC's XL-4 klystron. We have tested structures of different geometries, cell joining techniques, and materials, including hard copper alloys and molybdenum. We found that the behavior of the breakdown rate is reproducible for different structures of the same geometry and material. The breakdown rate dependence on peak magnetic fields is stronger than on peak surface electric fields for structures of different geometries.
KEK, Ibaraki
OHTSUKA, Tsukuba-shi
The MO (Matsumoto-Ohtsuka) -type flange is suitable for connection flanges of beam pipes for accelerators. The flange uses a metal gasket that exactly fits the aperture of the beam pipe, and has a small beam impedance. The flange can be applied to a complicated aperture. We developed a stainless-steel MO-type flange for a copper beam pipe with antechambers. Several beam pipes were installed in the KEKB B-factory positron ring and were tested using beams. No serious problem was observed up to a beam current of 1600 mA (~10 nC/bunch and ~6 ns bunch spacing). Based on experiences in the stain-less steel case, a possibility of employing copper-alloy and aluminum-alloy MO-type flange has been experimentally studied. They can mitigate the heating problems found in the case of stainless-steel flanges, and simplify the manufacturing procedure of beam pipes made of copper or aluminum alloy. Copper-alloy (CrZrCu) flanges show a comparable vacuum sealing property to the stainless-steel one, and several beam pipes with this flange has been successfully installed in the KEKB. The R&D on aluminum-alloy (A2219 and A2024) flanges has recently started, and a promising result was obtained.
NSRRC, Hsinchu
The RF power source using solid-state amplifier for accelerator application has become popular in recent years. The amplifiers array using power divider and power combiner could obtain equivalent power level as those using klystron or IOT. Such solid-state RF power source also has the advantage of easy maintenance, low cost, low DC power voltage and high flexibility. The development of solid-state power amplifier module at 499.65 MHz using the latest RF power chip has been built to have the power level of 900 Watts with above 60% efficiency of single power module. The more power that one module can provide, the less number of modules would be required under the same total output power of amplifiers array. Thus, the construction of a transmitter by solid-state technique for RF system would be less complex for easy maintenance.
NSRRC, Hsinchu
The electric power system of Taiwan Photon Source (TPS) will be installed during the construction of TPS. Many power electronic devices which produce large nonlinear loads will be used in the new power system and the accelerator facility. The capacitor banks will also be used for the power factor correction. Thus, the excessive harmonic waveform distortion level on the normal waveform will be presented continuously. These excessive harmonic current flows will result in transformer and cable over-heating and many types of circuit faults, and also wasting energy. A project is initiated to study these harmonic effects which will appear in the electric power system of TPS. A computer simulation approach is used to study the harmonic waveform distortion phenomena, and also to investigate an effective approach to reduce it. The harmonic effects of selected section of TLS (Taiwan Light Source) electric power system, and those appear at the mock segment of 1/24 accelerator of TPS system are measured and compared with the simulated results.
CERN, Geneva
INFN-Roma, Roma
The UA9 experiment was performed in 6 MDs from May to November 2009 with the goal of studying the collimation properties of a crystal in the framework of a future exploitation in the LHC collimation system. An important parameter evaluated for the characterization of the crystal collimation is the efficiency of halo extraction when the crystal is in channeling mode. In this paper it is explained how this efficiency can be measured using a pixel detector, the Medipix, installed in the Roman Pot of UA9. The number of extracted particles counted by the Medipix is compared with the total number of circulating particles measured by the Beam Current Transformers (BCTs): from this comparison the efficiency of the system composed by the crystal, used in channeling mode, and a tungsten absorber is proved to be greater than 85%.
CAEP/IFP, Mainyang, Sichuan
Linear Induction Accelerator (LIA) is a unique type of accelerator, which is capable to accelerate kilo-Ampere beam current to tens of MeV. The LIA acceleration modules, filled with ferrite or ferromagnetic toroid cores, can be conveniently stacked to obtain high energy. During the evolution of LIA, several models for the LIA acceleration module and the function of the cores have been proposed. Authors of this paper surveyed these models and tried to bridged them to form a consistent understanding of the LIA acceleration module. The unified understanding should be helpful in the further development and design of the LIA acceleration module.