SLAC, Menlo Park, California
LBNL, Berkeley, California
CERN, Geneva
CEA, Gif-sur-Yvette
Lancaster University, Lancaster
We present results from the measurement of the 3-D luminosity distribution with the ATLAS Inner Detector during early running. The spatial distribution of pp interactions is reconstructed by a dedicated algorithm in the High-Level Trigger that fits tracks and primary event vertices in real time, and by an offline algorithm that takes full advantage of the high tracking efficiency and resolution. The number of vertices provides online monitoring of the instantaneous luminosity, while luminous-centroid motion mirrors IP-orbit and RF-phase drifts. The x, y and z luminous widths reflect the evolution of the transverse and longitudinal emittances. The length scales of the IP orbit bumps, which directly impact the accuracy of the transverse convolved beam sizes measured during van der Meer scans, are calibrated offline against the measured displacement of the luminous centroid; this significantly improves the accuracy of the absolute luminosity calibration. The simultaneous determination, during such scans, of the transverse convolved beam sizes (from the luminosity variation) and of the corresponding luminous sizes can be used to disentangle the transverse IP sizes of the two beams.
Kyushu University, Center for Accelerator and Beam Applied Science, Fukuoka
Kyushu University, Department of Applied Quantum Physics and Nuclear Engineering, Fukuoka
Kyushu University, Fukuoka
KURRI, Osaka
KEK, Ibaraki
SAGA, Tosu
150 MeV FFAG accelerator is under construction at Center for Accelerator and Beam Applied Science on Ito Campus to promote activities in all related scientific, medical, engineering and educational field at Kyushu University. In this paper, status of the development of hardware and the results of the beam commissioning of the injector are described.
HIT, Heidelberg
While ramping the magnets in a synchrotron the magnetic fields deviate from their set values. Especially the field errors in dipole and quadrupole magnets result in different problems during operation. At the Heidelberg Ion Therapy Center HIT a measuring system with extremely high precision has been developed. It can measure in real time integral magnetic fields with a precision of better than 5*10-5 in a reproducible way. A feed-back control system for the magnetic fields is being installed and will be operational in May 2010. This control loop lets the magnets reach the nominal field much faster and thus shortens the dead time in a synchrotron cycle. The cycle can be reduced by 30% and more patients can be treated.
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.
U. Erlangen-Nurnberg LHFT, Erlangen
Siemens Med, Erlangen
The usability of conventional BPM topologies in compact linear accelerators used for medical and industrial applications is very limited due to tight space restrictions in such systems. To overcome these limitations, a different approach is introduced which is based on integrating the pickups into low-field regions of the accelerating structure and evaluating higher beam harmonics. Applications based on this approach will require RF frontends in frequency ranges beyond those covered by BPM dedicated hardware which is currently commercially available. Therefore, a demonstrator setup is presented which is capable of investigating suitable RF frontends for the proposed method. The demonstrator uses capacitive pickups of the button type for displacement sensing and allows for control of the beam position with the help of feedback steering coils which are typically used for compact linacs. Representative sensitivity measurement results based on the evaluation of the 2nd S-Band beam harmonic are also presented in this paper.
MPI-K, Heidelberg
Kyoto ICR, Uji, Kyoto
A cryogenic storage ring (CSR) is under construction at MPI für Kernphysik, which will be a unique facility for low velocity phase space cooled ion beams. Among other experiments the cooling and storage of molecular ions in there rotational ground state is planed. To meet this requirement the ring must provide a vacuum with a residual gas density below 10000 molecules/cm3, which will be achieved by cooling the vacuum chamber of the ion beam to 2-10 K. The projected stored beam current will be in the range of 1 nA - 1 μA. The resulting low signal strengths on the beam position pickups, current monitors and Schottky monitor put strong demands on these diagnostics tools. The very low residual gas density of the CSR does not allow using a conventional residual gas monitor to measure the profile of the stored ion beam. Other methods were investigated to measure the profile of a stored ion beam. In the paper an overview of the CSR diagnostics tool and diagnostics procedures will be given.
JASRI/SPring-8, Hyogo-ken
The signal processing electronics of the SPring-8 Storage Ring BPM were replaced during the summer shutdown of 2006, and put into operation. However, a large filling pattern dependence was observed. The cause was attributed to the nonlinear response of the diodes to large pulse signals. The diode were attached in front of the RF switches for protection from the electrostatic discharge damages on the switch IC. We took a countermeasure for the filling pattern dependence by reducing the pulse height with a band pass filter (BPF) in front of each channel. The BPF were attached and put into the operation from November 2008. The effect of the BPF was evaluated using the beam with changing the filling patterns and repeating the position measurements. The differences of the measured position data across the filling pattern change were found to be within 10μmeters, which was the same amount of the orbit drift during the filling pattern change.
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.
SSRF, Shanghai
Bunch charge uniformity control is very important for storage ring top-up operation. In order to monitor filling pattern and measure bunch charge precisely an PXI waveform digitizer based data acquisition system was developed to retrieve bunch charge information from BPM pickup signals. Effective sampling rate could be extended to 400GHz by waveform rebuilding technology, which folds multi turns data into single turn with real time sampling rate of 8GHz. Online evaluation shows charge resolution could be better than 0.5% for 1nC range.
IFIC, Valencia
A set of 16 Inductive Pick-Ups (IPU) for Beam Position Monitoring (BPM) with its associated electronics were designed, constructed and characterized at IFIC for the Test Beam Line (TBL) of the 3rd CLIC Test Facility (CTF3) at CERN. In October 2009 the full set of IPUs, (BPS) was successfully installed in the TBL line. In this paper, we describe the prototyping and series production phases of the BPSs development, focusing in the implementation and the results analysis derived from their characterization tests. Two special test benches were designed and built to perform the characterization tests at low and high frequencies. The low frequency set up based on a wire-method test bench for emulating the beam position variations helped us to determine the BPS performance parameters at beam pulse time scale from 100μs/10kHz to 10ns/100MHz. On the other hand, the high frequency test setup, based on an adapted coaxial transmission line, was dedicated to obtain the BPS longitudinal coupling impedance at the beam microbunches time scale (83ps/12GHz). Furthermore, we also present the first beam performance tests made in the TBL line.
CERN, Geneva
The beta function has a fundamental impact on the LHC performance and on the functioning of its machine protection and collimation systems. A new beta-beat diagnostic system, prototyped at the SPS, has been used to verify the time-dependent variations of the LHC lattice with unprecedented 1% beta-beta resolution and at a measurement bandwidth of about 1 Hz.
PSI, Villigen
For high intensity beam operation (3mA, 1.8MW) in the PSI cyclotron, a new current monitor for proton beams has been installed during the 2009 maintenance period. This current monitor is an actively cooled re-entrant cavity with its resonance tuned at the 2nd RF harmonic (101 MHz). Operating this system presents several challenges due to the heavy shower of energetic particles, the resonator being placed 8 m behind a graphite target. The resonator is actively cooled with water, its external surface was blackened to improve the radiation cooling and its mechanical structure was optimized for good heat conduction. The resonance characteristics are extremely sensitive to structural changes of the resonator. Because of non-uniform temperature distribution and dynamical changes the observed gain drift during operation is of the order of 10%. To correct these drifts 2 tests signals 50 kHz off the RF frequency are measured on-line during beam operation. They provide an innovative mean to estimate and to correct on-line the resonator gain. This paper will present the measurement method and the achieved performances.
PSI, Villigen
DESY, Hamburg
CEA, Gif-sur-Yvette
IPN, Orsay
The European XFEL is an X-ray free electron laser user facility that is currently being built in Hamburg by an international consortium. The electron BPM system of the XFEL is developed by a collaboration of PSI, DESY, and CEA/Saclay/Irfu. Cavity BPMs will be used in all parts of the E-XFEL where highest resolution and lowest drift is required, e.g. in the undulators and some locations in the beam transfer lines. In the cryostats of the superconducting 17.5GeV main linac, 2/3rds of the BPMs will be buttons, while 1/3rd will be re-entrant cavities that promise higher resolution than buttons at low bunch charges. The transfer lines will also be equipped with cost-efficient button BPMs. The BPM electronics is based on a modular system concept, with a common FPGA-based digital back-end design for all BPMs and pickup-specific analog RF front-ends. This paper introduces the design concepts and reports on the project status and measurement results of BPM pickup and electronics prototypes.
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
We present preliminary results of beam diagnostics for the world's first Non-Scaling FFAG Accelerator 'EMMA'. Amongst other means, a single-shot/turn-by-turn BPM system is used, that was first tested on the ALICE injector. The BPM system utilizes a front-end conversion of button pickup signals into flat-top-envelope 700 MHz bursts, time-domain multiplexing (in each plane, signals are made spaced by 13.8 ns), and the manufacture of both synchronous detector and ADC clocks directly from the beam signal. The system performance is discussed; results of beam-based resolution measurement are given. First turn beam trajectories furthest from the Septum and Kicker are presented.
JAI, Egham, Surrey
CERN, Geneva
Royal Holloway, University of London, Surrey
A setup for the investigation of Coherent Diffraction Radiation (CDR) from a conducting screen as a tool for non-invasive longitudinal electron beam profile diagnostics has been designed and installed in the Combiner Ring Measurement (CRM) line of the CLIC Test Facility (CTF3, CERN). In this report the status of the monitor development and results on the interferometric measurements of CDR spectra are presented. The CDR signal correlation with an RF pickup and a streak camera is reported. The future plans for the system improvements are also discussed.
ANL, Argonne
The Advanced Photon Source (APS) is a third-generation synchrotron light source in the United States. The BPM electronics plays an important part in the beam stability control. This paper presents comparative measurements of two BPM electronics: Libera Brilliance and APS FPGA-based BSP100. Some important parameters such as beam current dependence, electronics resolution and fill pattern dependence have been measured. These measurements were carried out in the lab and in the real system. The results will be useful for deciding which BPM electronics to deploy in the APS upgrade project.
INFN-Pisa, Pisa
University of Pisa and INFN, Pisa
Active devices based on piezoelectric actuators are widely used to dump unwanted vibrations in a variety of applications; for instance fast tuners for superconducting RF cavities. In another poster, we describe a low cost modular system of drivers for piezoelectric actuators developed at INFN-Pisa; we show here that the same system can easily be extended, with the inclusion of a simple plug-in board, to include sufficient I/O and computing capability to allow control of the device up to frequencies in the kHz range. This implementation is extremely cost effective and can be used in all situations where a high granularity distributed control system is desirable. We also show our first test results obtained using this system to control a warm single cell 1.3 GHz cavity. The cavity is perturbed using a piezoelectric actuator to generate random noise, while another piezo is used in the control loop to stabilize the resonance frequency. We use the phase of the RF pickup from the cavity as a measure of the deviation from the resonance caused by the perturbation. This simple setup allows to easily test various control algorithms without the need to work at large complex facilities.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
Danfysik A/S, Jyllinge
The pre-accelerator microtron supplies an electron beam at 105 MeV for the Metrology Light Source (MLS) of the Physikalisch-Technische Bundesanstalt (PTB) in Berlin. The beam is delivered via the transfer line to the injection septum and then into the storage ring. This septum magnet has its stainless steel vacuum beam pipe placed inside a laminated silicon iron magnet core. Hence, the pulsed magnetic field (half sine) used for the beam deflection must propagate through the thin metallic beam pipe. During the commissioning of the injection process, it became apparent that the calculated nominal pulse current for this energy and geometry had to be increased by 30 % to achieve proper beam transfer and accumulation. Two problems were apparent. Firstly, the injected beam trajectory had to be set at an angle away from the main beam axis. Secondly, the beam transfer from the septum entrance to exit was disturbed. As a first measure, the septum current pulse length was extended from 35 to 107 μs. Further on, the septum magnet was insulated from the transfer line beam pipe by a ceramic brake. This paper reports on measurements of pulsed magnetic fields inside the septum magnet.
* Commissioning and Operation of the Metrology Light Source, J. Feikes et al., BESSY, Berlin, Germany; R. Klein, G. Ulm, Physikalisch-Technische Bundesanstalt, Berlin, Germany; EPAC08, Genoa, Italy.
IMP, Lanzhou
Two electron cooling devices have been used at HIRFL-CSR in order to provide high quality heavy ion beams for nuclear and atomic research. The momentum spread is one of the most important characteristics of the beam quality. At HIRFL-CSR, the momentum spread is measured directly with the aid of longitudinal Schottky spectra system. In this paper, the measurements for various ion species are presented. At relatively high intensity, longitudinal Schottky spectra is double peak due to collective phenomena and the momentum spread can be obtained by fitting the spectra. The dependence of momentum spread on stored particle number is proportional to N**a. Moreover, the heating factor was investigated after switching off the electron cooling. The residual gas scattering, the intrabeam scattering and instabilities are studied according to the measured data.
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.
DESY, Hamburg
CLASSE, Ithaca, New York
Uni HH, Hamburg
At FLASH an optical synchronisation system with femtosecond stability is now being installed and commissioned. The system is based on pulses from a passively modelocked fibre laser which are distributed in length-stabilised fibres to various end-stations. Several modifications and improvements with respect to the original layout, especially concerning permanent operation and reliability, are already incorporated at this stage. The electron bunch arrival-time monitors (BAM), based on electro-optical modulation, are an integral part of the system. Built on the experiences with first prototypes, the most recent version of the BAM, installed prior to the first bunch compressor, includes essential changes affecting the optical layout, the mechanical and thermal stability as well as the electronics for read-out and controls. The revised BAM showed improved performance and will be complemented by a second congenerous BAM after the first bunch compressor during the present FLASH upgrade. The experiences with installation as well as the scope of improvements as to simplification and long-term stability will be presented.
JAEA/J-PARC, Tokai-mura
KEK, Ibaraki
MELCO SC, Tsukuba
J-PARC, KEK & JAEA, Ibaraki-ken
The Data Acquisition System of Beam Position Monitors(BPMs) in J-PARC Main Ring are consist of 186 Linux-based Data Processing Cirquits(BPMCs) and 12 EPICS IOCs. They are important tool to see the COD and turn-by-turn beam positions. This report describes the process of the data reconstruction which include how the various calibration constants are applied.
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.
EPFL, Lausanne
CERN, Geneva
A part of the beam losses at transition crossing of high intensity beams in the CERN PS have been attributed to an excursion of the closed orbit. The orbit jump occurs simultaneously with the jump of the transition energy triggered by pulsed quadrupoles. Investigations showed that the position of the pickups used for the radial loop system was not optimized with respect to the dispersion change caused by the fast change of the transition energy. Thanks to new electronics of the orbit measurement system, turn-by-turn orbit data could be recorded around transition crossing. Their analysis, together with calculations of the transverse optics, allowed determining a new choice of pickup positions for the radial loop. In comparison to the previous pickup configuration, the new configuration improves the mean radial position not only during transition crossing, but all along the acceleration cycle.
ANL, Argonne
A bunch-by-bunch feedback system was installed at the APS in 2008. Close-loop tests were conducted and improvements have been made to the system that include two 500-watt amplifiers, a new location for the horizontal drive stripline, a two-blade new horizontal stripline, and upgrade of front-end electronics. With these improvements we are able to stabilize beam with a reduced chromaticity of 0.45 in the horizontal plane and 2.5 in the vertical plane for the 24-singlet bunch pattern. Beam lifetime has increased from 8.5 hours to 15 hours. We did not observe any obvious increase in the effective beam emittance and rms beam motion. More studies will be performed to explore the potential of improving beam performance of the hybrids fill pattern, which has a 16-mA leading bunch. We report the system improvements and the results of our test results.
cyao@aps.anl.gov
ORNL RAD, Oak Ridge, Tennessee
ORNL, Oak Ridge, Tennessee
The prototype of an analog transverse (vertical and horizontal) feedback system to actively damp the electron-proton (e-p) instability has been developed and tested on the ORNL Spallation Neutron Source (SNS). We will describe the principle components, system configuration, and review several experimental studies geared towards understanding the current performance and limitations of the system.
BNL, Upton, Long Island, New York
CERN, Geneva
The SPS exponential coupler stripline are used to study single bunch instabilities. An accurate description of the response of the pickup is required to obtain high resolution measurements of the bunch vertical motion along the longitudinal axis. In this study we present the results of the comparison between dedicated beam experiments and electromagnetic simulations of a geometrical model of the stripline.
INFN/LNF, Frascati (Roma)
CNAO Foundation, Milan
CNAO, the Italian Centre of Oncological Hadrontherapy located in Pavia, is under commissioning and will be soon fully operational. It is based on a synchrotron that can accelerate carbon ions up to 400 MeV/u and protons up to 250 MeV for the treatment of patients. In this paper we present the subsystem, called B-Train, which has the purpose of measuring the magnetic field in a dedicated dipole connected in series with the sixteen dipoles of the synchrotron and to provide instantaneous values of the synchrotron field to the dipole power supply, to the RF, diagnostics and dump bumpers control systems, via optical lines, using a custom communication protocol. In order to measure the magnetic field with the specified precision (0.1G over 1.5T @ 3 T/s), a different approach has been taken with respect to previous versions of the system. The field is obtained by digitizing the voltage induced on a pick-up coil inserted in the gap of the dedicated dipole through a 18 bit, 1.25 Msamples/s ADC and integrating it by numerical methods. This paper describes the final design and features of the B-Train system, as well as the results obtained on the magnetic field readings precision.
KEK, Ibaraki
A superconducting cavity system has been developing for cERL injector Linac at KEK. Two prototype 2-cell niobium cavities and two prototype input couplers were fabricated. The vertical tests of the cavities at 2 K were carried out to qualify their performance. The rf conditioning of the input couplers were carried out at a high power test stand with a cw-300kW klystron. The results of the cavity performances at high gradients and the conditioning of the input couplers will be presented in this paper.
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.
KEK, Ibaraki
In our high gradient R&D of ICHIRO cavities at KEK, we have found some problems related to HOM coupler and high power RF input coupler port on beam tube: end group. One is the difficulties of rinsing in complex structures like HOM coupler. The other is Q-slope at high filed more than 40MV/m. The cavities without end group did not show such a high field Q-slope. At first step, we tested much stronger and aggressive rinsing method; wiping, brushing, and mega-sonic rinsing, against end group. The details and results of these rinsing effects will be reported.
Fermilab, Batavia
ANL, Argonne
Ionization cooling is a critical building block for the realization of a muon collider. To suppress breakdown in the presence of the external magnetic field, an idea of using an RF cavity filled with high pressure hydrogen gas is being considered for the cooling channel design. In the high pressure RF cavity, ionization energy loss and longitudinal momentum recovery can be achieved simultaneously. One possible problem expected in the high pressure RF cavity is, however, the dissipation of significant RF power through the electrons accumulated inside the cavity. The electrons are generated from the beam-induced ionization of the high pressure gas. To characterize this detrimental loading effect, we develop a simplified model that relates the electron density evolution and the observed pickup voltage signal in the cavity, with consideration of several key molecular processes such as the formation of the polyatomic molecules and ions, excitation, recombination and electron attachment. This model is expected to be compared with the actual beam test of the cavity in the MuCool Test Area (MTA) of Fermilab.
DAE/VECC, Calcutta
SAMEER, Mumbai
An isotope separator on-line Rare Isotope Beam (RIB) facility is presently under development at VECC, Kolkata around the existing K=130 room temp cyclotron. In first stage the low-energy (1.7 keV/u; q/A ≤ 1/14) RIB will be accelerated to about 470 keV/u in the Radio Frequency Quadrupole (RFQ) linac followed by three IH-LINAC. This consists of seven different rf systems for RFQ, three re-buncher and three IH-Linac cavities each operating in CW mode. The 3.4 meter rod type RFQ and the four gap λ/4 re-buncher is designed to operate at 37.8 MHz. The RFQ and re-buncher has been installed and successfully operated at CW rf power. The first beam testing for O5+ has been done with proper phase locking between rf transmitters. Two DTL accelerator systems consist of IH-mode tank operating at 37.8 MHz and other with 75.6 MHz. The first IH linac has been installed in beam line and tested with nominal RF power. The Second IH-linac cavity has been fabricated and is undergoing low power rf test. Two other buncher cavities are presently under development. The rf systems with low power as well as high power testing for above accelerator cavities will be described in this paper.
CERN, Geneva
PSI, Villigen
PSI-XFEL and Elettra-Fermi-require a X-band RF structure. As CLIC is pursuing a program for producing and testing x-band high-gradient RF structures, a collaboration between PSI, Elettra and CERN, has been established to build a multipurpose X-band accelerating structure. This paper focuses on its engineering design which is based on disk-shaped cells bonded together by different technologies (diffusion bonding, vacuum brazing and laser beam welding). The accelerating structure consists of 2 coupler subassemblies and 73 disks, and include wake field monitor waveguides. The engineering study also comprises the external cooling system, consisting of two parallel cooling circuits, and the tuning system, allowing for the fine-tuning by means of cell deformations. The engineering solution for installation and sealing of wake field monitor feed-through devices inside the accelerating structure RF-cavity is also proposed.
IIT, Chicago, Illinois
Fermilab, Batavia
ANL, Argonne
Muon cooling requires high-gradient normal conducting cavities operating in multi-Tesla magnetic fields for muon beam focusing in an ionization cooling channel. Recent experience with an 805-MHz pillbox cavity at the Fermilab MuCool Test Area has shown significant drop in accelerating field performance for the case of parallel electric and magnetic fields. It has been suggested that having the magnetic field perpendicular to the electric field should provide magnetic insulation and suppress breakdown. An 805-MHz Cu rectangular box cavity was built for testing with the fields perpendicular. It was mounted on an adjustable support to vary the angle between the rf electric and external magnetic field. We report on design and operation of the rectangular box cavity.
CERN, Geneva
At the start of the CERN Large Hadron Collider (LHC) 2008-2009 shutdown, all the LHC experimental vacuum chambers were vented to neon atmosphere. They were later pumped down shortly before beam circulation. In parallel, 2.3 km of vacuum beam pipes with NEG coatings were vented to air and re-activated to allow the installation or repair of several components such as roman pots, kickers, collimators, rupture disks and masks and re-activated thereafter. Beside these standard operations, "fast exchanges" of vacuum components and endoscopies inside cryogenic beam vacuum chambers were performed. This paper presents a summary of all the activities held during this period and the achieved vacuum performances.
PAL, Pohang, Kyungbuk
A superconducting RF cavity is used in the storage ring of the Pohang Light Source (PLS) upgrade project (PLS-II) at Pohang Accelerator Laboratory (PAL) for increasing the electron beam current and energy from 2.5GeV/200mA to 3.0GeV/400mA. In order to meet the requirement of lower beam emittance and higher photon energies, as well as more straight sections for insertion devices, the vacuum chambers in the storage ring need to be reconstructed. To control the spurious harmonic resonances' effect to beam position monitors (BPMs) in the PLS and PLS-II storage ring vacuum chamber, the TE mode distribution in vacuum chambers has been analyzed by both numerical simulation and experiment. Based on this analysis, the proper method to control the strength of TE mode at the position of BPMs is suggested.