EPAC08 - Classification:03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques/A08 Linear Accelerators

03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques

A08 Linear Accelerators

Paper	Title	Page
MOZCM01	Commissioning and Operation of the 1.5 GeV Harmonic Double Sided Microtron at Mainz University	51
	A. Jankowiak, K. Aulenbacher, D. Bender, O. Chubarov, M. Dehn, H. Euteneuer, F. Fichtner, B. Gutheil, F. Hagenbuck, R. H. Herr, P. Jennewein, K.-H. Kaiser, W. Klag, H. J. Kreidel, U. Ludwig-Mertin, A. Nuck, J. R. Röthgen, B. Seckler, G. S. Stephan, V. Tioukine, G. Woell, Th. Zschocke IKP, Mainz
	In December 2006 the 4th stage of the Mainz Microtron MAMI has been succesfully set into operation expanding the 855MeV output energy of the existing three racetrack microtron cascade (MAMI B) to 1508MeV. This new recirculating cw electron accelerator is realised as a worldwide unique Harmonic Double Sided Microtron (HDSM, []). Since February 2006, after only 14 day of commissioning, the HDSM serves as part of the MAMI C accelerator cascade in routine 24h a day operation for nuclear physics experiments. We will give a brief overview of the design and construction of the HDSM and describe in detail the experiences gained during commissioning and the first year of operation. [] A. Jankowiak et al., "Status Report on the Harmonic Double Sided Microtron of MAMI C", Proceedings EPAC2006, Edinburgh, p. 834**
	Slides
WEPC015	Baseline Design of HLS Linac Upgrade	2019
	G. Feng, W. Li, L. Shang, L. Wang, C.-F. Wu, H. Xu, S. C. Zhang USTC/NSRL, Hefei, Anhui
	The existing 200MeV linac of Hefei Light Source (HLS) mainly consists of electron gun, prebuncher, buncher, one 3m S-band linac section, and four 6m S-band linac sections. Energy gain of electron beam at the end of the linac is 200MeV and energy spread is ±0.8%. In order to improve the electron beam quality, An upgrade project is required. Four 80MW klystrons will be used to instead the old ones, which can improve the beam energy stability. This upgrade can also make it possible to increase the linac energy from 200 MeV to 400 MeV without changing the accelerating structure. In the meantime, New operation modes of HLS linac has been found by extensive computer modelling and optimization. Electron beam dynamics simulation from electron gun to the end of linac has been given, which considering space charge effects and wakefields.
WEPP075	Effects of the Cryogenic Operational Conditions on the Mechanical Stability of the FLASH Linear Accelerator Modules	2692
	R. Amirikas, A. Bertolini, J. Eschke, M. Lomperski DESY, Hamburg
	The Free electron LASer in Hamburg (FLASH) accelerating modules have been instrumented with vertical geophones on their corresponding quadrupoles and their vacuum vessels. The signals from these geophones are constantly monitored and the data are integrated into the control system of the accelerator. Therefore, vibration stability studies of a string of superconducting accelerating modules, in various cryogenic conditions, are now possible for the first time. The results of this experiment will be an important reference for both the European X-ray Free Electron Laser (XFEL) and the International Linear Collider (ILC) linear accelerators which are expected to take advantage from the separation between the feed lines of the 4.5 K shield and of the quadrupole, which will operate in a 2 K Helium-II bath.
WEPP077	The XFEL Laser Heater	2695
	V. G. Ziemann, G. Angelova UU/ISV, Uppsala M. Dohlus, Y. A. Kot DESY, Hamburg
	The high-brilliance photo-cathode gun foreseen for the X-FEL will provide beams with extremely small momentum spread that will make the beam susceptible to micro-bunching instabilities which will spoil SASE operation. It is therefore desirable to increase the momentum spread to a level that prevents these instabilties but still is compatible with SASE operation. The laser heater will achive this by superimposing a transversely polarized laser and the electron beam in a properly tuned undulator, thereby producing a momentum modulation that is smeared out in a dogleg chicane to obtain the desired momentum spread increase. We present the initial design and layout of the laser heater system for the X-FEL in Hamburg.
WEPP078	PHIL: a Test Beam line at LAL	2698
	R. Roux, M. Bernard, G. Bienvenu, S. Cavalier, M. Jore, B. Leblond, B. M. Mercier, B. Mouton, C. P. Prevost, V. Variola LAL, Orsay
	For 2004, in the framework of a European contract, LAL is in charge of the construction of one photo-injector for the drive beam linac of the CLIC Test Facility 3 at CERN. This contract together with national funds allowed LAL to build a test accelerator with the same photo-injector as for CTF3. The goal is to undergo experiments on advanced RF guns but a part of the beam time will be also shared with users of the electron beam. So far, the construction of this accelerator at LAL was very much delayed because of the legal obligation to upgrade the radiation shielding in agreement with the actual radiation safety thresholds. The required civil engineering is now finished and the installation of the components is under way. We will first present a design of the accelerator and few dynamic simulation results. Finally we will give a status of the accelerator construction up to date.
WEPP079	Beam Dynamics Layout and Loss Studies for the FAIR P-Injector	2701
	G. Clemente, L. Groening GSI, Darmstadt S. Minaev ITEP, Moscow U. Ratzinger, R. Tiede IAP, Frankfurt am Main
	The development of coupled CH-DTL cavities represents a major achievement in the development of the 325 MHz, 70 MeV FAIR P-Injector. This coupled-cavity solution has important consequencies on the beam dynamics design which has to be adapted to this new kind of resonator. In combination with the KONUS beam dynamics, this solution allows to achieve all the requirements of the FAIR project in terms of beam intensity and quality reducing at the same time the number of focusing elements along the machine. A layout based on 6 CH coupled modules is presented and compared with a solution composed of three coupled modules up to 35 MeV followed by three long single resonators up to the energy of 70 MeV. A redesigned 35 MeV intertank section became necessary to avoid beam losses and emittance growth. Finally, the effect of random mistakes such as quadrupole misalignments and phase as well as voltage setting errors have been investigated to determine the tolerances of mechanical construction and rf controls during operation.
WEPP080	Baseline Design of the ESS Bilbao Linac	2704
	R. Enparantza, L. Uriarte Fundación TEKNIKER, Eibar (Gipuzkoa) F. J. Bermejo Bilbao, Faculty of Science and Technology, Bilbao J. Lucas Elytt Energy, Madrid
	The baseline design for the ESS-B accelerator adheres to suggestions made by ESS-I, and seeks to enter a design phase for a machine based upon a 150 mA +H proton beam. Such intensity was to be delivered, as stated in the 2003 Technical Report by a tandem of two proton ion sources of some 85 mA each funnelled after the two beams are accelerated up to about 20 MeV. Current activities developed during the last few years within the CARE and EUROTRANS efforts have resulted in significant advances in both ion source and low-energy acceleration technologies which will surely have a relevant impact on the proposed accelerator design. More into specifics, our current activities are being directed towards the exploration of: The use of a single proton source capable to deliver proton currents of 150 mA or above. Proton sources such as SILHI at CEA have already produced currents of 130 mA at low duty factors. The use of superconducting cavities (spokes, quarter-wave etc.) for medium energy (40 - 100 MeV) acceleration (IFMIF and SPIRAL2). The behaviour of beams extracted from present day proton ECR sources at medium and high energies.
WEPP081	Wake-fields and Beam Dynamics Simulations for ILC ACD Accelerating Cavities	2707
	C. J. Glasman, R. M. Jones UMAN, Manchester
	The ILC aims at colliding bunches of electrons and positrons at a centre of mass energy of 0.5 TeV and in a proposed upgrade to 1 TeV. These bunches of charged particle are accelerated in superconducting linacs. The baseline design for the ILC relies on the relatively mature TESLA-style cavities, with a proposed gradient of more than 30 MV/m and is known as the baseline configuration document (BCD). However, here we investigate electromagnetic fields in superconducting cavities, with the potential to reach accelerating gradients in excess of 50 MV/m, and these are the subject of the alternative configuration document (ACD). We analyse the band structure and necessary damping requirement of the wake-fields in two design configurations: Cornell's re-entrant cavity and KEK's Ichiro cavity. The emittance dilution arising from beams subjected to injection offsets and from cavity misalignments are studied in beam dynamics simulations.
WEPP082	Recirculator SALO Project in NSC KIPT	2710
	I. S. Guk, A. N. Dovbnya, S. G. Kononenko, F. A. Peev, A. S. Tarasenko NSC/KIPT, Kharkov J. I.M. Botman TUE, Eindhoven
	In NSC KIPT the electron recirculator project on energy up to 730 MeV is developing. The accelerator is designed first of all as a facility for basic research in the field of a nuclear physics. Superconducting accelerating structure TESLA on frequency of 1.3 GHz, developed in DESY, is used for a speed-up of electrons. Isochronous and achromatic system of injection and magneto-optical system recirculator arcs allow to gain good beam parameters on an exit of the accelerator. Channels of an extraction of particles on experimental stations are presented. Opportunities for use of recirculator beams for applied research are considered.
WEPP083	Development of an X-band Hybrid Dielectric-iris-loaded Accelerator	2713
	X. D. He, S. Dong, G. Feng, Y. J. Pei, C.-F. Wu USTC/NSRL, Hefei, Anhui
	A compact x-band hybrid dielectric-iris-loaded travelling-wave linac with constant impendence structure has been designed. By adjusting the values of and the numbers of cells, the beam energy of 29 MeV, the capture efficiency about 50% and the energy spread about with the beam current being 70 mA and the electric gun voltage being 50KeV are obtained through longitudinal dynamics calculation. The length of accelerator tube is 1.12m . The maximum accelerating gradient is less than 45MV/m. By using electromagnetic code such as MAFIA, the attenuation per unit length of structure , the shunt impedance , the quality factor Q, the group velocity and the phase velocity are got by optimizing the dimensions of the cavities.
WEPP084	Fabrication of a Quadrant-type Accelerator Structure for CLIC	2716
	T. Higo, Y. Higashi, H. Kawamata, T. T. Takatomi, K. Ueno, Y. Watanabe, K. Yokoyama KEK, Ibaraki A. Grudiev, G. Riddone, M. Taborelli, W. Wuensch, R. Zennaro CERN, Geneva
	In order to heavily damp the higher order modes of an accelerator structure for CLIC, two kind of damping mechanisms are implemented in one of the designs. Here each cell is equipped with electrically coupled damping channels in addition to the magnetically coupled waveguides. This design requires an assembly of longitudinally cut four quadrants to form a structure and the parts are necessarily made with milling. Since KEK has developed a high-precision machining of X-band accelerator cells with milling and turning at the same time, the experience was extended to the milling of this quadrant. Firstly, the fabrication test of a short quadrant was performed with multiple vendors to taste the present-day engineering level of milling. Following this, a full-size quadrant is also made. In this course, some of the key features are addressed, such as flatness of the reference mating surfaces, alignment grooves, 3D profile shape of the cells, surface roughness and edge treatment. In this paper, these issues are discussed from both fabrication and evaluation point of views.
WEPP085	RF Coupler Kicks and Wake-fields in SC Accelerating Cavities	2719
	N. Juntong, R. M. Jones, I. R.R. Shinton UMAN, Manchester C. D. Beard STFC/DL/ASTeC, Daresbury, Warrington, Cheshire G. Burt Cockcroft Institute, Warrington, Cheshire
	The main accelerating cavities of the ILC provide acceleration of both positron and electron beams to 250 GeV per beam and 500 GeV per beam in a proposed upgrade. The wake-field excited by each ultra-relativistic beam in the accelerating cavities can seriously dilute the emittance of the particles within the beams. Each cavity is supplied with both fundamental and higher order mode couplers. The geometrical configuration of these RF couplers results in an asymmetrical field and this gives rise to both an RF kick being applied to the beam and transverse wake-field. Detailed e.m. fields are simulated in the vicinity of the couplers in order to assess the impact on the beam dynamics. We investigate modified geometries with a view to alleviating the emittance dilution resulting from the e.m. field associated with the RF couplers.
WEPP087	Observation and Mitigation of Multipass BBU in CEBAF	2722
	R. Kazimi, A. Freyberger, C. Hovater, G. A. Krafft, F. Marhauser, T. E. Plawski, C. E. Reece, J. S. Sekutowicz, C. Tennant, M. G. Tiefenback, H. Wang Jefferson Lab, Newport News, Virginia
	The CEBAF recirculating accelerator at Jefferson Lab consists of two linacs carrying beam for up to five passes of acceleration. The Beam Break-Up (BBU) phenomenon was anticipated during design of the accelerator. The threshold beam current to induce BBU was calculated to be approximately 20 milliamperes, far above operational current. No sign of BBU was ever seen in more than a decade of operation. A specially designed acceleration cavity in a recently installed cryomodule was found to cause a BBU instability under special conditions with as low as 40 uA of injected beam current. This presented an opportunity to study BBU in a five-pass accelerator. In this paper we will discuss multipass BBU, show observational data, and discuss the ways we have developed to maintain the instability threshold current to values above those required for operation.
WEPP089	Wake-field Suppression in the CLIC Main Linac	2725
	V. F. Khan, R. M. Jones UMAN, Manchester
	The CLIC linear collider aims at accelerating multiple bunches of electrons and positrons and colliding at a centre of mass energy of 3 TeV. These bunches are accelerated through X-band linacs operating at an accelerating frequency of 12 GHz. Each beam readily excites wake-fields in the accelerating cavities of each linac. The transverse components of the wake-fields, if left unchecked, can dilute the beam emittance. The present CLIC design relies on heavy damping of these wake-fields in order to ameliorate the effects of the wake-field on the beam emittance. Here we present initial results on a modified design which combines both damping and detuning of the cell frequencies of each cavity structure in order to enhance the overall decay of the wake-field. Interleaving of cell frequencies is explored as a means to improve the damping.
WEPP090	Accelerator Design for a 1/2 MW Electron Linac for Rare Isotope Beam Production	2728
	S. R. Koscielniak, F. Ames, I. V. Bylinskii, R. E. Laxdal, M. Marchetto, A. K. Mitra, I. Sekachev, V. A. Verzilov TRIUMF, Vancouver
	TRIUMF, in collaboration with university partners, proposes to construct a megawatt-class electron linear accelerator (linac) as a photo-fission driver for radioactive ion beam production (RIB) for nuclear astrophysics studies and materials science. The design strategy, including upgrade path, for this cost-effective facility is elaborated. The 50 MeV, 10 mA, c.w. linac is based on TESLA/ILC super-conducting radio-frequency (SRF) technology at 1.3 GHz and 2K; and consists of an electron gun, buncher and capture sections, followed by 10 MeV and 40 MeV cryomodules containing one and four 9-cell cavities, respectively. Preliminary results from PARMELA beam dynamics simulations are presented. C. W. operation leads to challenges of large cryogenic heat load, input coupler power handling and beam loss mitigation similar to those encountered in ERL-based light sources. Unlike those sources there is no need for high beam brilliance, and a triode thermionic gun modulated at 1.3 GHz is employed; nor are short bunches required, and so the HOM excitation is modest. Many of the major sub-system components have been identified and where possible existing designs will be adopted.
WEPP091	Injector Upgrade for the S-DALINAC	2731
	T. Kuerzeder, A. Araz, M. Brunken, J. Conrad, R. Eichhorn, H.-D. Gräf, M. Hertling, F. Hug, M. Konrad, M. Platz, A. Richter, S. Sievers, T. Weilbach TU Darmstadt, Darmstadt W. Ackermann, W. F.O. Müller, B. Steiner, T. Weiland TEMF, Darmstadt J. D. Fuerst ANL, Argonne, Illinois
	Since 1991 the superconducting Darmstadt linear accelerator S-DALINAC provides an electron beam of up to 130 MeV for nuclear and astrophysical experiments. Currently its injector delivers beams of up to 10 MeV with a current of up to 60 μA. The upgrade aims to increase both parameters to 14 MeV and 150 μA in order to allow more demanding astrophysical experiments. Therefore, a modified cryostat module equipped with two new cavities is required. Due to an increase in RF power to 2 kW the old coaxial RF input couplers, being designed for a maximum power of 500 W, have to be replaced by new waveguide couplers. We review the design principles and report on the fabrication of the coupler and the whole module.
WEPP092	Tuning of Waveguide to Cavity Coupling Coefficient Beta for a PWT Linac and a Photocathode Gun	2734
	S. Krishnagopal BARC, Mumbai U. Kale, S. Lal, K. K. Pant RRCAT, Indore (M. P.)
	The waveguide to cavity coupling coefficient beta for two types of accelerating structures: a Plane Wave Transformer (PWT) linac and a 1.6 cell photocathode gun has been tuned to obtain critical coupling in both. Analytical calculation of the dimensions of slot required for critical coupling have been done using Gao’s formulation based on Bethe’s theory for hole coupling. While the PWT linac structure, with high inter-cell coupling, shows good agreement between measured and predicted slot dimensions for different values of beta, the agreement is not so good in the photocathode gun on account of poor inter-cell coupling. This paper discusses details of the analytical calculation of slot dimensions for the two structures, their comparison with experimentally measured results, and the procedure adopted for tuning the two structures to critical coupling.
WEPP093	Prototype of Parallel Coupled Accelerating Structure	2737
	A. E. Levichev, V. M. Pavlov BINP SB RAS, Novosibirsk Y. D. Chernousov ICKC, Novosibirsk V. Ivannikov, I. V. Shebolaev ICKC SB RAS, Novosibirsk
	The prototype of parallel coupled accelerating structure is developed. It consists of five accelerating cavities, common excitation cavity and RF power waveguide feeder. The excitation cavity is a segment of rectangular waveguide loaded by cupper pins. The excitation cavity operate mode is TE₁₀₅. Connection between excitation cavity and accelerating cavities is performed by magnetic field. The expressions for coupled factor excitation cavity to accelerating cavities and coefficient of efficiency for RF power transmission from generator to accelerating cavities are obtained using coupled cavities theory. The parallel coupled accelerating structure electrodynamic characteristics are measured.
WEPP096	Nextef: The 100MW X-band Test Facility in KEK	2740
	S. Matsumoto, M. Akemoto, S. Fukuda, T. Higo, N. Kudoh, H. Matsushita, H. Nakajima, T. Shidara, K. Yokoyama, M. Yoshida KEK, Ibaraki
	Nextef is a new X-band test facility in KEK. By combining the power from two klystrons, 100MW-class X-band RF power will be available. The facility is for researches on future high gradient linear accelerators. The commissioning operation of the whole facility was started in November 2007. It is planed to conduct high power testing of X-band accelerator structures as well as the fundamental researches such as the RF breakdown experiment with specially designed waveguides.
WEPP097	Simulation of Wakefield Effect in ILC IR Chamber	2743
	S. Pei, T. O. Raubenheimer, A. Seryi, J. C. Smith SLAC, Menlo Park, California
	To achieve super high luminosity, high current beams with very short bunch length are needed, which carry high intensity EM fields. For ILC, two bunch trains with bunch length of 300μm and bunch charge of 3.2nC are needed to collide at the IR to achieve the ILC luminosity goals. When the 300μm bunches pass through the IR chamber, wakefields will be excited, which will cause HOM power flowing through the IR chamber beam pipe to the final doublets due to the high frequency characteristic of the induced wakefields. Since superconducting technology is adopted for the final doublets of ILC BDS, whose operation stability might be affected by the HOM power produced at the IR chamber, quench might happen. In this paper, we did some analytical estimation and numerical simulation on the wakefield effects in ILC IR chamber.
WEPP098	Efficient Traveling-wave Accelerating Structure for Linear Accelerators	2746
	V. M. Pirozhenko MRTI RAS, Moscow
	The shaped traveling-wave (STW) structure contains periodic structure of cavities with optimal shape and magnetic coupling operating in the forward traveling-wave mode. The structure combines the advantages of conventional standing-wave (SW) and traveling-wave (TW) structures. It ensures high efficiency of the use of radio-frequency (RF) power for the particle acceleration inherent in the SW structures. Also it gives a possibility to vary output energy of the particles by changing the beam loading and provides for good matching with RF generator without application of special matching devices that is inherent in the TW structures. The STW structure is well suited for compact variable-energy electron linear accelerators used for radiation technologies.
WEPP099	Results from Atomic Layer Deposition and Tunneling Spectroscopy for Superconducting RF Cavities	2749
	J. Norem, J. W. Elam, M. J. Pellin ANL, Argonne, Illinois C. Z. Antoine CEA, Gif-sur-Yvette L. Cooley Fermilab, Batavia, Illinois J. F. Moore MassThink LLC, Naperville, IL Th. Proslier, J. Zasadzinski IIT, Chicago, Illinois
	Atomic Layer Deposition is a process that synthesizes materials in successive monolayers, at rates on the order of 1 micron/hour. We have been using this technique at Argonne as a possible way to improve both superconducting rf (SCRF) and normal rf structure performance. Initial experiments have led to a new model of high field Q-slope and new ways of controlling SCRF surfaces, as well as suggesting ways to significantly improve the operating gradients of both superconducting and normal structures. We have also been testing this technique in superconducting structures. Initial measurements show significant improvement over “cavity-grade” Nb samples.
WEPP102	Design of the ILC RTML Extraction Lines	2752
	S. Seletskiy, P. Tenenbaum, D. R. Walz SLAC, Menlo Park, California N. Solyak Fermilab, Batavia, Illinois
	The Damping Ring to the Main Linac beamline (RTML) is equipped with three extraction lines (EL). Each EL can be used both for an emergency abort dumping of the beam and the tune-up continual train-by-train extraction. Two of the extraction lines are located downstream of the first and second stages of the RTML bunch compressor, and must accept both compressed and uncompressed beam with energy spread of 2.5 % and 0.15 % respectively. In this paper we report optical design that allowed us to minimize the length of the extraction lines while offsetting the beam dumps from the main line by the distance required for acceptable radiation level in the service tunnel. Proposed extraction lines can accommodate beams with different energy spreads at the same time providing the beam size suitable for the aluminum dump window.
WEPP105	First Operation Results of the Superconducting Photoinjector at ELBE	2755
	J. Teichert, A. Arnold, A. Buechner, H. Buettig, D. Janssen, M. Justus, U. Lehnert, P. Michel, P. Murcek, R. Schurig, G. Staats, F. Staufenbiel, R. Xiang FZD, Dresden T. Kamps BESSY GmbH, Berlin G. Klemz, I. Will MBI, Berlin A. Matheisen DESY, Hamburg
	In November 2007 the first electron beam was generated from the superconducting RF photo electron gun installed at the ELBE linear accelerator facility. The injector together with a sophisticated laser system and a diagnostic beam line were developed and constructed within a collaboration of BESSY, DESY, MBI and FZD. Delivering a CW beam with up to 1 mA average current, a significant improvement of the beam quality like an increase of the bunch charge up to 1 nC and a reduced transverse emittance will be obtained. After the cool-down of the cryostat the RF properties of the 3½-cell niobium cavity like pass band mode frequencies, unloaded quality factor versus accelerating gradient, Lorentz force detuning, and He pressure influence were measured. The first beam was extracted of a Cu photo cathode using a 262 nm UV laser system with a repetition rate of 100 kHz and about 0.4 W laser power. Later, caesium telluride photo cathodes will be applied. The installed diagnostics allow beam current, energy, energy spread, transverse emittance and bunch length measurements of the beam. The results of these measurements and the operational experiences with the gun will be presented.
WEPP106	High-gradient Experiments with Narrow Waveguides	2758
	K. Yokoyama, S. Fukuda, Y. Higashi, T. Higo, N. K. Kudo, S. Matsumoto KEK, Ibaraki
	High-gradient RF breakdown studies are presently being conducted at Nextef. To study the characteristics of different materials on high-field RF breakdown, we have performed experiments by using a reduced cross-sectional waveguide that has a field of approximately 200MV/m at an RF power of 100MW. A description of the high-gradient testing of copper and stainless-steel waveguides is reported.