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| MOP009 | Dragon-I Linear Induction Accelerator | induction, emittance, electron, linac | 49 | ||
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The best quality induction linac in the world, named Dragon-I, has been built at Institute of Fluid Physics, China Academy of Engineering Physics. It can produce 2.5~3kA high current electron beam with energy of 20MeV and pulse width of 70ns. The spot size of about 1mm diameter has been achieved with beam current greater than 2.5kA. The design of Dragon-I facility is introduced briefly. The commissioning and results of Dragon-I are presented in the paper including the most recent time resolved measurements of beam parameters.
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| MOP013 | Low-Intensity, Pulsed-Beam Generation System Using the OPU Linac | electron, gun, radiation, linac | 58 | ||
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An ultra low intensity pulsed electron beam generation system has been developed, which consists of an electron linear accelerator (linac), highly sensitive beam current monitors and beam profile monitors. The beam current has been attenuated to be about ten orders of magnitude weaker than the ordinary beam current by using several methods, e.g. the reduction of the cathode emission in an injector and the use of a narrow slit. The minimum beam charge so far obtained has been estimated to be about several attocoulomb in one beam macropulse. The beam from a linac is controllable, collimated and synchronized with the trigger signal of the linac. The features are much advantageous compared with those of β-rays from radioisotopes which have been used in low intensity beam irradiation experiments. The final goal of this work is to generate a single electron beam.
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| MOP020 | Status of the PITZ Facility Upgrade | gun, emittance, diagnostics, booster | 76 | ||
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The upgrade of the Photo Injector Test Facility at DESY in Zeuthen towards the PITZ2 stage is continuously ongoing. In Spring 2006, an intermediate stage was taken into operation (PITZ1.6), including a new gun cavity that has been tuned and conditioned. Currently, three new emittance measurement systems are being installed along the beamline. After their commissioning, studies of the emittance conservation principle will be possible when using the available booster cavity. In the paper, the results of the RF commissioning of the new gun and the first beam measurements using recently installed diagnostics devices will be presented. The ongoing developments of further new diagnostics components will be discussed as well.
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| MOP024 | Electromagnetic Green's-Function-Based Simulations of Photocathode Sources | simulation, space-charge, electromagnetic-fields, gun | 88 | ||
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We show the results of beam simulations for photocathode sources using a newly developed Green's function based code called IRPSS (Indiana Rf Photocathode Source Simulator). In general, a fully electromagnetic treatment of space-charge fields within simulations of photocathode sources is typically difficult since the beam is most often tightly bunched. The problem is further complicated by the inclusion of nearby conducting structures, i.e. cathode and cavity walls, from which the fields are reflected. The entire problem can be solved self-consistently using an electromagnetic Green's function method. Since Green's functions are generated by a Delta function source while simultaneously satisfying the boundary conditions of the system, they are an effective tool when solving for fields within photocathode source simulations. Using IRPSS we show the results of multiparticle simulations for a variety of photocathode source experiments.
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| TU1003 | Modern Electron Induction Linacs | electron, target, induction, linac | 208 | ||
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Several high power induction linacs are in existence and a couple are being built around the world. Typically, they are capable of delivering about 100 micro-coulombs of e-beam to the target in a single burst and are built for radiographic application. DARHT 2nd Axis induction linac under construction at Los Alamos National Laboratory is the first of its kind, designed to deliver multiple e-beam pulses to the target. This incorporates the latest advances in the induction linac technology. An overview of the existing as well as the DARHT induction linac will be presented in this paper.
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| TUP008 | The Low Emittance Photoinjector in Tsinghua University | emittance, gun, laser, electron | 259 | ||
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A photocathode rf gun system is under developing in Tsinghua University for Thomson scattering. The microwave properties and the high power processing of this rf gun were finished. The UV laser system can provide a 266nm laser pulse with 1~10ps and 200μJ photo energy per pulse. The beam experiments are under way. This paper gives a general description of this photocathode rf gun and its preparation.
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| TUP038 | Status of the Sparc Photoinjector | laser, emittance, gun, electron | 333 | ||
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The SPARC Project is starting the commissioning of its photo-injector. RF gun, RF sources, RF network and control, power supplies, emittance meter, beam diagnostics and control to measure the RF gun beam have been installed. The photocathode drive laser has been characterized in terms of pulse shape and quality. We will report also about first tests made on RF gun and on the emittance meter device. Additional R&D on X-band and S-band structures for velocity bunching are in progress, as well as studies on new photocathode materials . We will also discuss studies on solenoid field defects, beam based alignments and exotic electron bunch production via blow-out of short laser pulses.
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| TUP040 | Progress on a Cryogenically Cooled RF Gun Polarized Electron Source | gun, vacuum, electron, ion | 339 | ||
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RF guns have proven useful in multiple accelerator applications. An RF gun capable of producing polarized electrons is an attractive electron source for the ILC or an electron-ion collider. Producing such a gun has proven elusive. The NEA GaAs photocathode needed for polarized electron production is damaged by the vacuum environment in an RF gun. Electron and ion backbombardment can also damage the cathode. These problems must be mitigated before producing an RF gun polarized electron source. In this paper we report continuing efforts to improve the vacuum environment in a normal conducting RF gun by cooling it with liquid Nitrogen after a high temperature vacuum bakeout. We also report on a design of a cathode preparation chamber to produce bulk GaAs photocathodes for testing in such a gun. Future directions are also discussed.
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| TUP044 | Shunt Impedance Measurement of the APS BBC Gun | impedance, gun, electron, photon | 346 | ||
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The Advanced Photon Source (APS) ballistic bunch compression (BBC) injector is presently in use as a beam source for a number of experiments, including THz generation, beam position monitor testing for the Linac Coherent Light Source (LCLS), novel cathode testing, and radiation therapy source development. The APS BBC gun uses three independently powered and phased rf cavities, one cathode cell and two full cells, to provide beam energies from 2 – 10 MeV with variable energy spread, energy chirp, and, to an extent, bunch duration. The shunt impedance of an rf accelerator determines how effectively the accelerator can convert supplied rf power to accelerating gradient. The calculation of the shunt impedance can be complicated if the beam energy changes substantially during its transit through a cavity, such as in a cathode cell. We present the results of direct measurements of the shunt impedance of the APS BBC gun on an individual cavity basis, including the cathode cell, as well as report on achieved gradients. We also present a comparison of the measured shunt impedance with theoretical values calculated from the rf models of the cavities.
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| TUP045 | Photothermal Cathode Measurements at the Advanced Photon Source | laser, gun, klystron, electron | 349 | ||
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The Advanced Photon Source (APS) ballistic bunch compression (BBC) injector presently uses an M-type thermionic dispenser cathode as a photocathode. This “photothermal” cathode offers substantial advantages over conventional metal photocathodes, including easy replacement and easy cleaning via the cathode’s built-in heater. We present the results of quantum efficiency measurements as a function of cathode heater power, laser pulse energy, and applied rf field strength.
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| TUP049 | Metal-Based Photocathodes For High-Brightness RF Photoinjectors | laser, gun, vacuum, target | 358 | ||
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Advanced high brightness RF gun injectors require photocathodes with fast response, high quantum efficiency and good surface uniformity. Metal films deposited by various techniques on the gun back wall could satisfy these requirements. Two new deposition techniques have been recently proposed, i.e. pulsed laser ablation and vacuum arc. Several samples of various materials have been deposited by the two techniques: The emission performance and morphological changes induced on the cathode surface by laser beam are compared and discussed.
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| TUP057 | A Compact, Normal-conducting, Polarized Electron, L-band PWT Photoinjector for the ILC | emittance, electron, vacuum, gun | 376 | ||
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The International Linear Collider (ILC) needs a polarized electron beam with a low transverse emittance. High spin-polarization (>85%) is attainable with a GaAs photocathode illuminated by a circularly polarized laser. Low emittance is achievable with an rf photoinjector. DULY Research has been developing an rf photoinjector called the Plane Wave Transformer (PWT) which may be suitable as a polarized electron source for the ILC. A 1+2(1/2) cell, L-band PWT photoinjector with a coaxial rf coupler is proposed for testing the survivability of GaAs cathode. It is planned to produce a high-aspect-ratio beam using a round-to-flat-beam transformation. In addition to its large vacuum conductance, the modified PWT has a perforated stainless steel sieve as a cavity wall, making it easy to pump the structure to better than 10-11 Torr at the photocathode. An L-band PWT gun can achieve a low emittance (0.45 mm-mrad for a 0.8nC round beam) with a low operating peak field (<25MV/m). A low peak field is beneficial for the survivability of the GaAs photocathode because electron backstreaming is greatly mitigated.
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| TUP058 | The RF Design of a HOM Polarized RF Gun for the ILC | gun, emittance, electron, vacuum | 379 | ||
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The ILC requires a polarized electron beam. While a highly polarized beam can be produced by a GaAs-type cathode in a DC gun of the type currently in use at SLAC, JLAB and elsewhere, the ILC injector system can be simplified and made more efficient if a GaAs-type cathode can be combined with a low emittance RF gun. Since this type of cathode is known to be extremely sensitive to contamination including back bombardment by ions, any successful polarized RF gun must have a significantly improved operating vacuum compared to existing RF guns. We present a new RF design for an L-Band NC RF gun for the ILC polarized electron source. This design incorporates a higher order mode (HOM) structure, whose chief virtue in this application is an improved conductance for vacuum pumping on the cathode. Both 2-D and 3-D models have been used to optimize the RF parameters with two principal goals: first to minimize the required RF power; second to reduce the peak surface field relative to the field at the cathode in order to suppress field emitted electron bombardment. The beam properties have been simulated initially using PARMELA. Vacuum and cooling considerations for this design are discussed.
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| TUP063 | Commissioning of a New S-Band RF Gun for the Mark III FEL Facility at Duke University | gun, linac, electron, emittance | 394 | ||
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At the Free Electron Laser (FEL) Laboratory of Duke University, there is an S-band linac based Mark III FEL facility which can supply coherent FEL photon in the infrared wavelength range. To supply high quality electron beams and to have excellent pulse structure, we installed one S-band RF gun with the LaB6 cathode for the Mark III FEL facility in 2005. Its longest macropulse length is about 6 us, and maximum repetition rates of macropulse and micropulse are 15 Hz and 2856 MHz, respectively. Therefore our new RF GUN can generate maximum 17142 bunches within a bunch train and maximum 257130 bunches within one second. In this paper, we describe recent commissioning experiences of our newly installed S-band RF GUN for the Mark III FEL facility.
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| TH3001 | Photoinjectors R&D for Future Light Sources and Linear Colliders | gun, electron, emittance, laser | 549 | ||
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Linac-driven light sources and linear proposed colliders require high brightness electron beams. In addition to the small emittances and high peak currents, linear colliders also require spin-polarization and possibly the generation of asymmetric beam in the two transverse degree-of-freedom. Other applications (e.g. high power free-electron lasers) call for high duty cycle and/or angular-momentum-dominated electron beams (electron cooling). We review on-going R&D programs aiming at the production of electron beams satisfying these various requirements. We especially discuss R&D on photoemission electron sources (especially based on radio-frequency gun) along with the possible use of emittance manipulation techniques.
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| THP021 | Study of Vacuum Insulator Flashover for Pulse Lengths of Multi-Microseconds | plasma, vacuum, electron, diagnostics | 610 | ||
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We have studied the flashover of vacuum insulators for applications where high voltage conditioning of the insulator and electrodes is not practical and for pulse lengths on the order of several microseconds. The study was centered about experiments performed with a 100-kV, 10-μs pulsed power system and supported by a combination of theoretical and computational modeling. The base line geometry for the experiments was a cylindrically symmetric, +45° insulator between flat electrodes. In the experiments, flashovers or breakdowns were localized by operating at field stresses slightly below the level needed for explosive emissions with the base line geometry. The electrodes and/or insulator were then seeded with an emission source, e.g. a tuff of velvet, or a known mechanical defect. Our study differs from most vacuum insulator studies in that our emphasis was on flashovers originating at the anode triple junction as well as bulk breakdowns within the insulator. Various standard techniques were employed to suppress cathode-originating flashovers/breakdowns. We present the results of our experiments and discuss the capabilities of modeling insulator flashover.
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| THP025 | R&D of the Long-Life Thyratron Tube | collider, controls, feedback, pick-up | 622 | ||
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Long lifetime over 50k hours for the thyratron is essential to provide the reasonable availability of the accelerator such as X-FEL and future e+e- linear collider. The lifetime and reliability of a solid-state device are not well confirmed yet. There are some examples that show long life of a thyratron. Many thyratrons were dead due to several common causes related to circuits and operation environment rather than intrinsic problems of a device itself. Several valuable feedback systems are easily adopted to enhance the lifetime. There are still unidentified questions to be verified in the thyratron. Close collaboration between laboratories and companies is strongly requested in order to improve the lifetime and performance of a thyratron.
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| THP027 | Study of PPM-Focused X-band Pulse Klystron | klystron, linear-collider, simulation, collider | 628 | ||
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The R&D of PPM (Periodic Permanent Magnet)-focused X-band pulse klystrons has been conducted since 1999, originally for Global Linear Collider (GLC) project. So far six prototype tubes have been tested. Some of them successfully produce the power required in GLC (75MW, 1.6μsec pulse width). However their performance was not perfect as a GLC tube. The problems are the stability of RF output and the gun performance. Since GLC programs were terminated in 2004, some limited work on the improvement of the PPM tubes continues at X-Band Test Facility (XTF) in KEK. The work includes the test to evaluate the performance of revised (rebuilt) tubes as well as disassembling these tubes after the test for further inspection. Recent results are reported.
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| THP033 | Pulsed RF Heating Particularities in Normal-Conducting L-band Cavities | gun, booster, linac, positron | 646 | ||
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For present projects, such as X-FEL and ILC, the SC technology is chosen for the main linacs. However, in some special parts, NC cavities are applied, operating with high electric and magnetic fields. RF gun cavities with an electric field up to 60 MV/m at the photo cathode are now under development. Capture cavities in the ILC positron source should operate with an accelerating gradient of up to 15 MV/m, practically the same value (14 MV/m), as for the CDS booster cavity in the Photo Injector Test Facility at DESY in Zeuthen (PITZ). High field strength leads to high specific RF heat loading. In combination with long RF pulses (~ 1ms) it results in substantial surface temperature rise, small cavity shape deformations and measurable frequency shifts. In this report we discuss both particularities and some general regularities related to long pulse operation of L-band cavities. Results of 3D numerical simulations for cavity surface temperature, displacements distributions and corresponding frequency shifts for different cavities are presented and compared with existing experimental data. The presented results will give the input for cavities optimization and sub-systems improvements.
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| THP097 | FPGA BASED DIGITAL RF CONTROL FOR FLASH | controls, klystron, feedback, gun | 809 | ||
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Most parts of the LLRF control system used in FLASH are based on the DSP processors. Actual computation power of the system is close to the limit, the algorithm is performed in a time longer than 1μs. The only way to extend the system with new features was to add more DSP processors. This solution requires integration of new DSP board into existing system. It may cause some additional problems and delays in the machine operations. During past years very fast progress on the FPGA market was observed. Nowadays FPGA chips have reached the computation power that can be compared with DSP processors. These chips offer variety of the embedded solutions such as PowerPC, Microblaze, Nios which can be easily used in addition to fast, parallel signal processing. Moreover large number of user pins makes it possible to integrate all the elements necessary for the control into one PCB board. Therefore, for the evaluation purposes, some parts of the system were replaced by FPGA based boards. This article summarizes the FPGA boards that are currently in use and describes algorithms executed by these boards.
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| FR1002 | SPring-8 Compact SASE Source | emittance, electron, undulator, radiation | 813 | ||
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The 8-GeV Japanese XFEL Project has been funded in 2006. Construction is scheduled 2006-2010, first beam in 2010. In order to develop technology required to XFEL, we have been carrying out R&D program at RIKEN since 2002, where thelow emittance thirmionic-gun and various key technologies were developed. To verify technologies, SCSS Prototype Accelerator has been constructed. The first lasing was obserbed in the prototype accelerator at June 20 at 60 nm.
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SCSS-Web Site: www-xfel.spring8.or.jp. |
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| FR1004 | Recent Developments in SRF Cavity Science and Performance | superconductivity, linear-collider, collider, controls | 818 | ||
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The performances of SRF cavities made of high purity bulk niobium have been improving in the last few years and surface magnetic fields (Bp) close to the thermodynamic critical field of niobium have been achieved in a few cases. The recommendation made in 2004 in favor of SRF as the technology of choice for the International Linear Collider (ILC), requires to improve the reliability of multi-cell cavities operating at accelerating gradients (Eacc) of the order of 35 MV/m . Additionally, a better understanding of the present limitations to cavity performance, such as the high-field Q-drop is needed. This contribution presents some recent developments in SRF cavity science and performance. Among the most significant advances of the last few years, new cavity shapes with lower ratio Bp/Eacc were designed and tested. Cavities made of large-grain niobium became available, promising lower cost at comparable performance to standard fine-grain ones and several tests on single-cell cavities were done to gain a better understanding of high-field losses. In addition, studies to improve the reliability of electropolishing are being carried out by several research groups.
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