MIT/PSFC, Cambridge, Massachusetts, USA
We present the design of an overmoded photonic band gap (PBG) accelerator cavity, made from a 2D lattice of sapphire rods supported between copper plates, that operates in a TM02-like mode at 17 GHz. The cavity does not support the lower-frequency TM01-like mode. Higher-order modes are damped effectively by removing rods from the lattice so that only the operating mode is supported with a high quality factor. The TM02 cavity mitigates the high pulsed heating of the copper surface seen in some metal-rod TM01 PBG cavities, which may be an advantage for high-gradient operation. We discuss plans for testing a 17 GHz TM02 standing-wave cavity at gradients above 100 MV/m.
LANL, Los Alamos, New Mexico, USA
Niowave, Inc., Lansing, Michigan, USA
We present a design of a superconducting photonic band gap (PBG) accelerator cell operating at 700 MHz. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. Using PBG structures in superconducting particle accelerators will allow moving forward to significantly higher beam luminosities and lead towards a completely new generation of colliders for high energy physics. We designed the superconducting PBG cell which incorporates higher order mode (HOM) couplers to conduct the HOMs filtered by the PBG structure out of the cryostat. The accelerator characteristics of the cell were evaluated numerically. A scaled prototype cell was fabricated out of copper at the higher frequency of 2.8 GHz and cold-tested. The 700 MHz niobium cell will be fabricated at Niowave, Inc. and tested for high gradient at Los Alamos in the near future.
BNL, Upton, Long Island, New York, USA
In order to correct beam perturbations in RHIC around 10Hz, a new fast data distribution network was required to deliver BPM position data at rates several orders of magnitude above the capability of the existing system. The urgency of the project limited the amount of custom hardware that could be developed, which dictated the use of as much commercially available equipment as possible. The selected architecture uses a custom hardware interface to the existing RHIC BPM electronics together with commercially available Gigabit Ethernet switches to distribute position data to devices located around the collider ring. Using the minimum Ethernet packet size and a field programmable gate array (FPGA) based state machine logic instead of a software based driver, real-time and deterministic data delivery is possible using Ethernet. The method of adapting this protocol for low latency data delivery, bench testing of Ethernet hardware, and the logic to construct Ethernet packets using FPGA hardware will be discussed.
BNL, Upton, Long Island, New York, USA
ESS Bilbao, Bilbao, Spain
UPV-EHU, Leioa, Spain
Bilbao, Faculty of Science and Technology, Bilbao, Spain
University of the Basque Country, Faculty of Science and Technology, Bilbao, Spain
ESS-Bilbao, Zamudio, Spain
Elytt Energy, Madrid, Spain
BNL, Upton, Long Island, New York, USA
Among the accelerator projects under construction at the Relativistic Heavy Ion Collider (RHIC) is an R&D energy recovery LINAC (ERL) test facility. The ERL includes both a five-cell superconducting cavity as well as a superconducting, photoinjector electron gun. Because of the high-charge and high-current demands, effective higher-order mode (HOM) damping is essential, and several strategies are being pursued. Among these is the use of the fundamental power couplers as a means for damping some HOMs. Simulation studies have shown that the power couplers can play a substantial role in damping certain HOMs, and this presentation will discuss these studies along with measurements.
BNL, Upton, Long Island, New York, USA
Several future accelerator projects at the Relativistic Heavy Ion Collider are being developed using a super-conducting electron energy recovery LINAC along with a superconducting electron gun as the source. All of the projects involve high-current, high-charge operation and require effective higher-order mode (HOM) damping to achieve the performance objectives. Among the HOM designs being developed is a waveguide-type HOM load for the electron gun consisting of a ceramic break surrounded by ferrite tiles. This design is innovative in its approach and achieves a variety of ends including broadband HOM damping and protection of the superconducting cavity from potential damage to the ferrite tiles. Furthermore, the ceramic is an effective thermal transition. This design may be useful in various applications since it readily allows for replacement of the ferrite tiles with other materials and may also be useful for testing the absorbing properties of these materials. In this paper, the details of the design will be discussed along with current modelling and testing results as well as future plans.
BNL, Upton, Long Island, New York, USA
Niowave, Inc., Lansing, Michigan, USA
BNL, Upton, Long Island, New York, USA
Damping higher order modes (HOMs) significantly to avoid beam instability is a challenge for the high current Energy Recovery Linac-based eRHIC at BNL. To avoid the overheating effect and high tuning sensitivity, current, a new band-stop HOM coupler is being designed at BNL. The new HOM coupler has a bandwidth of tens of MHz to reject the fundamental mode, which will avoid overheating due to fundamental frequency shifting because of cooling down. In addition, the S21 parameter of the band-pass filter is nearly flat from first higher order mode to 5 times the fundamental frequency. The simulation results showed that the new couplers effectively damp HOMs for the eRHIC cavity with enlarged beam tube diameter and two 120° HOM couplers at each side of cavity. This paper presents the design of HOM coupler, HOM damping capacity for eRHIC cavity and prototype test results.
CLASSE, Ithaca, New York, USA
The Cornell ERL injector prototype is undergoing commissioning and testing for running unprecedented currents in an electron cw injector. This paper discusses preliminary measurements of HOMs in the injector prototype’s superconducting RF cryomodule. These include HOM spectra up to 30 GHz measured via small antennae located at the HOM beam line absorbers between the SRF cavities. The spectra are compared at different beam currents and repetition rates. The shape of the spectra are compared to ABCI simulations of the loss factor spectrum of the cryomodule beam line. The total HOM power dissipated in the HOM loads was also measured with beam on, which allowed for an estimate of the loss factor. This measurement was accomplished via temperature sensors on the loads, calibrated to input power by heaters on the loads.
CLASSE, Ithaca, New York, USA
Cornell is currently developing a high current Energy Recovery Linac. The baseline 7-cell cavity design for the main linac has already been completed, and prototyping has begun, as of Fall 2010. Previous work showed that increasing the relative cavity-to-cavity frequency spread increases the beam break-up current through the linac. Simulations show that expected machining variations will introduce a relative HOM frequency spread of 0.5·10-3, corresponding to 150 mA of threshold current. The key idea of this work is to increase the relative cavity-to-cavity frequency spread by designing several classes of 7-cell cavities obtained by making small changes to the baseline center cell shape. This allows a threshold current in excess of 450 mA, which is well above the 100 mA goal for the Cornell Energy Recovery Linac.
Fermilab, Batavia, USA
Fermilab, Batavia, USA
Fermilab, Batavia, USA
University of Delhi, Delhi, India
Fermilab, Batavia, USA
University of Delhi, Delhi, India
Muons, Inc, Batavia, USA
CLASSE, Ithaca, New York, USA
SLAC, Menlo Park, California, USA
Superconducting RF (SRF) systems typically contain resonances at unwanted frequencies, or higher order modes (HOM). For storage ring and linac applications, these higher modes must be damped by absorbing them in ferrite and other lossy ceramic materials. Typically, these absorbers are brazed to substrates that are often located in the drift tubes adjacent to the SRF cavity. These HOM absorbers must have broadband microwave loss characteristics and must be thermally and mechanically robust, but the ferrites and their attachments are weak under tensile and thermal stresses and tend to crack. Based on prior work on HOM loads for high current storage rings and for an ERL injector cryomodule, a HOM absorber with improved materials and design is being developed for high-gradient SRF systems. This work will use novel construction techniques (without brazing) to maintain the ferrite in mechanical compression. Attachment techniques to the metal substrates will include process techniques for fully-compressed ferrite rings. Prototype structures will be fabricated and tested for mechanical strength under thermal cycling conditions.
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
ODU, Norfolk, Virginia, USA
JLAB, Newport News, Virginia, USA
Texas A&M University, College Station, Texas, USA
The polyhedral cavity is a superconducting cavity structure in which a multi-cell cavity is built from a Roman-arch assembly of arc segments. Each segment has a Tesla-like r-z profile, and is fabricated either by bonding a Nb foil to a Cu substrate wedge or by depositing a Nb surface on the Cu substrate. The segments are assembled with an arrangement of locking rings and alignment pins, with a controlled narrow gap between segments over much of the arc-span of adjoining segments. A tubular channel is machined in the mating surfaces of the Cu wedges. Dipole modes are suppressed by locating along each channel a tube coated with rf-terminating ferrite. A first model of the cavity is being built to investigate mode structure, evaluate alternatives for the Nb surface fabrication, and develop assembly procedures.
JLAB, Newport News, Virginia, USA
Tech-X, Boulder, Colorado, USA
To benchmark a multi-physics code VORPAL developed by Tech-X, the High Order Mode (HOM) coaxial coupler design implemented in Jefferson Lab’s 12GeV upgrade cryomodules is analyzed by use of commercial codes, such as ANSYS, HFSS and Microwave Studio. Testing data from a Horizontal Test Bed (HTB) experiment on a dual-cavity prototype are also utilized in the verification of simulation results. The work includes two stages: first, the HOM feedthrough that has a high RRR niobium probe and sapphire insulator is analyzed for the RF-thermal response when there is traveling wave passing through; second, the HTB testing condition is simulated and results from simulation are compared to thermal measurements from HTB tests. The analyses are of coupled-field nature and involve highly nonlinear temperature dependent thermal conductivities and electric resistivities for the eight types of materials used in the design. Accuracy and efficiency are the main factors in evaluation of the performance of the codes.
Advanced Design Consulting, Inc, Lansing, New York, USA
ANL, Argonne, USA
The Advanced Photon Source requires damping of higher-order modes in the storage ring rf cavities in order to prevent beam instability at beam currents in excess of 100 mA proposed for the APS Upgrade. Due to constraints imposed by available space and by existing 35-mm pick-up ports on the cavity, a compact design has been analyzed with a quarter-wave rejection filter of the fundamental mode. Separate broadband, low-frequency and high-frequency dampers are utilized to span the frequency range from 500 MHz to 1500 MHz. The dampers have been designed to reject the fundamental cavity mode, couple strongly to HOM’s, utilize an external rf load, minimize the overall size, and incorporate rf diagnostics. In addition, the mechanical design has been optimized to simplify construction, improve mechanical stability, and reduce thermally induced stresses.
Tech-X, Boulder, Colorado, USA
JLAB, Newport News, Virginia, USA
Nuclear physics accelerators are powered by microwaves which must travel in waveguides between room-temperature sources and the cryogenic accelerator structures. The ohmic heat load from the microwaves is affected by the temperature-dependent surface resistance and in turn affects the cryogenic thermal conduction problem. Integrated EM & thermal analysis of this difficult non-linear problem is now possible with the VORPAL finite-difference time-domain simulation tool. We highlight thermal benchmarking work with a complex HOM feed-through geometry, done in collaboration with researchers at the Thomas Jefferson National Accelerator Laboratory, and discuss upcoming design studies with this emerging tool. This work is part of an effort to generalize the VORPAL framework to include generalized PDE capabilities, for wider multi-physics capabilities in the accelerator, vacuum electronics, plasma processing and fusion R&D fields, and we will also discuss user interface and algorithmic upgrades which facilitate this emerging multiphysics capability.
JLAB, Newport News, Virginia, USA
ANL, Argonne, USA
Two single-cell, superconducting, squashed elliptical crab cavities with waveguides to damp Higher Order Modes (HOM) and Lower Order Mode (LOM) have been designed and prototyped for the Short Pulse X-ray (SPX) project at the Advanced Photon Source (APS). The Baseline cavity with LOM damper on the beam pipe has been vertically tested and exceeded its performance specification with over 0.5MV deflecting voltage. The Alternate cavity design which uses an “on-cell” waveguide damper is preferred due to its larger LOM impedance safety margin. Its prototype cavity has been fabricated by a Computer Numerical Controlled (CNC) machine and is subject to further testing. The conceptual design, layout and analysis for various cryomodule components are presented.
ANL, Argonne, USA
A method that tracks particles directly through a general magnetic field described in a 3D field table was added to the code elegant recently. It was realized by converting an arbitrary particle's motion to a combination of free-drift motion and centripetal motion through the coordinate system rotation and using a general linear interpolation tool developed at the Advanced Photon Source (APS). This method has been tested by tracking particles through conventional magnetic elements (dipole, sextupole, etc.) to verify reference coordinate system conversions, tracking accuracy, and long-term tracking stability. Results show a very good agreement between this new method and the traditional method. This method is not designed to replace mature traditional methods that have been used in most tracking codes. Rather, it is useful for magnets with complicated field profiles or for studying edge effects.
JLAB, Newport News, Virginia, USA
University of Connecticut, Storrs, Connecticut, USA
BNL, Upton, Long Island, New York, USA
SLAC, Menlo Park, California, USA
The vacuum chamber of the ILC Interaction Region (IR) is optimized for best detector performance. It has special shaping to minimize additional backgrounds due to the metal part of the chamber. Also, for the same reason this thin vacuum chamber does not have water cooling. Therefore, small amounts of power, which may be deposited in the chamber, can be enough to raise the chamber to a high temperature. One of the sources of “heating” power is the electromagnetic field of the beam. This field diffracts by non-regularities of the beam pipe and excites free-propagating fields, which are then absorbed by the pipe wall. In addition we have a heating power of the image currents due to finite conductivity of the metallic wall. We will discuss these effects as updating the previous results.
SLAC, Menlo Park, California, USA
Fermilab, Batavia, USA
SLAC, Menlo Park, California, USA
A compact 400-MHz half-wave spoke resonator (HWSR) superconducting crab cavity is being developed for the LHC upgrade. The cavity shape and the LOM/HOM couplers for such a design have been optimized to meet the space and beam dynamics requirements, and satisfactory RF parameters have been obtained. As it is known that multipacting is an issue of concern in a superconducting cavity which may limit the achievable gradient. Thus it is important in the cavity RF design to eliminate the potential MP conditions to save time and cost of cavity development. In this paper, we present the multipacting analysis for the HWSR crab cavity using the Track3P code developed at SLAC, and to discuss means to mitigate potential multipacting barriers.
UMAN, Manchester, United Kingdom
CERN, Geneva, Switzerland
We report on the suppression of long-range wakefields in the main linacs of the CLIC collider. This structure operates with a 120 degree phase advance per cell. The wakefield is damped using a combination of detuning the frequencies of beam-excited higher order modes and by light damping, through slot-coupled manifolds. This serves as an alternative to the present baseline CLIC design which relies on heavy damping. Detailed simulations of both the optimised surface fields resulting from the monopole mode, and from wakefield damping of the dipole modes, are discussed. We report on fabrication details of a structure consisting of 24 cells, diffusion bonded together. This design, known as CLICDDSA, takes into practical mechanical engineering issues and is the result of several optimisations since the earlier CLICDDS designs. This structure is due to be tested for its capacity to sustain high gradients at CERN.
ANL, Argonne, USA
The Advanced Photon Source is a 7-GeV hard x-ray synchrotron light source. Operation for users is delivered at a nominal current of 100 mA in one of three bunch patterns. The APS Upgrade calls for a minimum planned operating current of 150 mA, with an option to deliver beam up to 200 mA. The high-current threshold in the storage ring has been explored, and storage ring components have been identified that either drive collective instabilities or are subjected to excessive beam-drive higher-order-mode (HOM) heating. In this paper, we describe machine studies at 150 mA in a special lattice that simulates the upgraded APS. We also describe the accelerator upgrades that are required to accommodate 200-mA operation, as well as the ongoing machine studies plan.
ANL, Argonne, USA
JLAB, Newport News, Virginia, USA
Superconducting cavities have been analyzed for the short-pulse x-ray (SPX) project at the Advanced Photon Source (APS). Due to the strong damping requirements in the APS storage ring, single-cell superconducting cavities have been designed. The geometry has been optimized for lower-order and higher-order mode damping, reduced peak surface magnetic fields, and compact size. The integration of the cavity assembly, with dampers and waveguide input coupler, into a cryomodule will be discussed.
CLASSE, Ithaca, New York, USA
BNL, Upton, Long Island, New York, USA
In order to meet the requirements of high average current accelerators, such as the Superconducting Proton Linac (SPL) at CERN and the electron–ion collider (eRHIC) at BNL, a high current 5-cell SRF cavity, called BNL3 cavity, was designed. The optimization process aimed at maximizing the R/Q of the fundamental mode and the geometry factor G under an acceptable RF field level of Bpeak/Eacc or Epeak/Eacc. In addition, a pivotal consideration for the high current accelerators is efficient damping of dangerous higher-order modes (HOM) to avoid inducing emittance degradation, cryogenic loading or beam-breakup (BBU). To transport the HOMs out of the cavity, the BNL3 cavity employs a larger beam pipe, allowing the propagation of HOMs but not the fundamental mode. Moreover, concerning the BBU effect, the BNL3 cavity is aimed at low (R/Q)Qext for dangerous modes, including dipole modes and quadrupole modes. This paper presents the design of the BNL3 cavity, including the optimization for the fundamental mode, and the BBU limitation for dipole and quadrupole modes. The BBU simulation results show that the designed cavity is qualified for high-current, multi-pass machines such as eRHIC.