• Y. Shoji
  LASTI, Hyogo

　Sub-THz coherent synchrotron radiation (CSR) from the SPing-8 linac beam was observed after the injection into the NewSUBARU storage ring. The beam from the linac has much sorter bunch length than the stationary stored bunch in the ring. It had been reported that the injected linac beam emits CSR at just after the injection until it diluted to a longer bunch by its energy spread. However we observed CSR at after more revolutions. At some tens of microseconds after the injection we observed CSR produced by a fine time structure in a bunch. At after more revolutions, a half of the synchrotron oscillation period (0.1 ms), CSR was back because the bunch length became shorter again. At this timing we also expect CSR emitted from a structure produced by longitudinal and transverse coupling, which should depend on the chromaticity. We report results of CSR observation through these periods.

• S. Okuda, T. Kojima, R. Taniguchi
  Osaka Prefecture University, Sakai

Transient phenomena induced by pulsed electron beams have been investigated with a pulse-radiolysis system with a 18 MeV S-band electron linac at Osaka Prefecture University (OPU). In our recent work the coherent transition radiation from the electron bunches of linac beams, which is highly intense pulsed light in a submillimeter to millimeter wavelength range, has been applied to absorption spectroscopy with an L-band electron linac in the Research Reactor Institute, Kyoto University. In these experiments the effect of intensity of the radiation has been observed for several kinds of matters. In this work a new pump-probe system has been developed to investigate the transient phenomena induced by the pulsed coherent radiation by improving the OPU pulse-radiolysis system. The transition radiation is emitted from an Al foil. A part of the coherent radiation is also used as probe light. The pulse lengths of the radiation are from 5 ns to 4 μs. The characteristics of the system have been measured and the system has been optimized. The coherent synchrotron radiation source is under preparation in order to obtain half-cycle light.

• S. Fukuda
  KEK, Ibaraki

Distributed RF Scheme (DRFS) was proposed for International Linear Collider (ILC) as a new HLRF scheme. After the ITRP recommendation, ILC technology was chosen to be superconducting technology and basic design was discussed and reported in the RDR on 2007. Aiming for the cost reduction, there have been proposed many ideas and summarized as SB2009 proposal. DRFS is the one of these proposals, and it is linked to the single tunnel plan. DRFS employs many small klystrons (750kW output power) which feed power to two superconducting cavities. 13 modulating anode klystrons are operated by a DC power supply and a modulating anode pulser. All required components are installed in a tunnel and therefore this scheme is a complete single tunnel layout. DRFS was proposed in 2008 and thereafter it has been discussed in web-ex meeting and GDE workshop. In this conference, concept and detailed design of DRFS are presented including the availability and operability. In order to show the feasibility of DRFS, KEK has a plan of demonstration employing the DRFS with two klystrons in the S1 global in the end of 2010. Presenter also discussed pros and cons comparing with the competing proposed scheme.

• R. Taniguchi, N. Ito, T. Kojima, S. Okuda
  Osaka Prefecture University, Sakai

A pulsed electron radiography system has been developed, which consisted of an electron linear accelerator, a scintillation screen and a high sensitivity image sensor. The system was capable for high speed strobo-imaging by the use of the pulse feature of the electron beam with the pulse width about a few micro-second. On the other hand, the characteristics of electron images were different from X-ray images and neutron images. Absorption behavior of energetic electrons in materials is Bragg-like rather than exponential. Therefore, a high contrast transparent image was obtained by modulating of energy of the electron beam. By the use of this system and utilizing these features, we observed successfully an ozone explosion phenomenon of liquid nitrogen induced by electron irradiation, which has been considered to be a serious problem in material irradiation experiments.

• O. A. Konstantinova
  Tomsk State University, Tomsk

In this paper the new phenomenon of nature, called electromagnetic torque radiation from the relativistic charged particles is discussed. To begin it is shown that two well ' known alternative definitions of density of angular momentum of electromagnetic field by Ivanenko-Sokolov* and by Teitelboim and Villarroel** give the identical integral characteristics with application of the relativistic radiation theory. And both of it yield the same results for the total power of the angular momentum, which is characterized the torque of the radiation. Then we have found that the angular distribution of torque from the Linac has the azimuthal symmetry with respect to the direction of the velocity of the particle. It is also oppositely directed to the acceleration of the particle. On the condition of the high speed the angular distribution has an expressive relativistic effect of the sharp directed radiation. With the construction of a good detectors of the torque it is possible to measure such effect.

* D. Ivanenko, A. Sokolov, Classical Field Theory, GITTL, 1949.
** C. Teitelboim, D. Villarroel, Rivista Nuovo Cim. 3, 1, 1980.

• M. Yoshioka
  KEK, Ibaraki

It was proposed to change from a 2-tunnel scheme in the ILC Reference Design Report to a single tunnel plan by the GDE, Global Design Effort in order to reduce the construction cost. Two proposals of RF source have been presented to realize this scheme. One is 'Klystron Cluster System', which moves every RF source related components from the underground tunnel to the above ground buildings. This would require that the surface topology be rather flat. Another one is the 'Distributed RF System', which does not greatly increase the above ground facilities, and instead every accelerator components are put into a single main tunnel. Instead of powering with large-scale klystrons, downsized modules are distributed throughout. We propose to make a single accelerator tunnel for active accelerator components based on the latter RF system and a sub-tunnel, in which cooling water piping is installed. The sub-tunnel can also be used for the emergency escape, underground water drainage, maintenance work and etc. This scheme fits to the Japanese mountainous site.

• F. Naito, K. Nanmo, H. Tanaka
  KEK, Ibaraki
• H. Asano, T. Ito
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken

X-ray radiation from the SDTL of J-PARC linac has been observed with the beam loss monitor by the cavity. The results show that the X-ray intensity depends not only on the RF power level of the tank but also on the RF structure of the tank. In the paper we will show the results of the investigation for the origin of the X-ray radiation from the tank.

• A. Miura, M. Ikegami
  JAEA/J-PARC, Tokai-mura
• H. Sako
  JAEA, Ibaraki-ken
• G.H. Wei
  KEK/JAEA, Ibaraki-Ken

Residual gas in beam transport line essentially affects the beam loss and residual radiation on the accelerator. J-PARC linac is usually operated under 1.0 ·10^-6 to 1.0 ·10^-5 Pa in SDTL and A0BT sections. In this situation, no serious beam loss was observed during the beam operation. In future development of J-PARC linac, because the peak beam energy and output will be increased, it is getting more serious problem. Before the development, it is important to understand a cause of beam loss and relation between beam loss and residual gas pressure. We measured beam loss at the normal and worse vacuum condition in both SDTL and A0BT sections. The result indicates that the beam loss depends on the residual gas pressure and position where the beam loss occurs is about 20 to 30 meter downstream. This suggests the optimum position for installation of vacuum system to minimize the beam loss. In this paper, we describe the experimental result and its discussions. In addition, the cause of the beam loss is considered to be a stripping from negative hydrogen ions to neutral hydrogen atoms. This mechanism is also discussed in this paper.

• K. Lekomtsev, G.A. Blair, G.E. Boorman, V. Karataev, M. Micheler
  JAI, Egham, Surrey
• R. Corsini, T. Lefèvre
  CERN, Geneva

Compact Linear Collider (CLIC) is a multi-TeV electron-positron collider for particle physics based on an innovative two-beam acceleration scheme. The CLIC Test Facility 3 (CTF3, CERN) aims to demonstrate feasibility of this concept. The monitoring of a longitudinal profile will be very important for the CLIC. The optimization of the longitudinal charge distribution in a bunch is crucial for the maximisation of the luminosity and also for an optimal performance of a CLIC drive beam. A setup for the investigation of Coherent Diffraction Radiation (CDR) from targets with various configurations as a tool for non-invasive longitudinal electron beam profile diagnostics has been designed and installed in the CRM line of the CTF3 [1, 2]. In this report we present the status of the experiment and results on interferometric measurements of CDR from a single target configuration. Studies on downstream background contribution in the CRM line have been performed. Recently we have upgraded the system by installing a second target. In this report we shall also demonstrate the results on simulations of CDR spatial distribution from the two target configuration.

[1] M. Micheler et al., Longitudinal Beam Profile Measurements at CTF3 using CDR, PAC'09, "**".
[2] M. Micheler et al., Longitudinal beam profile monitor at CTF3 based on CDR, RREPS-09, "**".

• R. Ischebeck, B. Beutner, G.L. Orlandi, M. Pedrozzi, T. Schietinger, V. Schlott, V.G. Thominet
  PSI, Villigen

The SwissFEL Injector Test Facility consists of an RF gun, an accelerating section for a final energy of 250 MeV, and two diagnostics sections. Transverse profiles of the electron beam can be recorded at 27 locations by imaging fluorescent crystals that can be inserted into the beam. At 21 of these, the fluorescent screens are complemented by optical transition radiation monitors and wire scanners. Here, we will evaluate the performance of transverse profile monitors experimentally and numerically and compare the measured profiles with a numerical model of the accelerator. Profile monitors are used in conjunction with a slit and a pepper pot to determine the transverse phase space distribution of the bunches. Experimental measurements at the SwissFEL Injector Test Facility will be presented.

• Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, M. Satoh, T. Shishido, K. Umemori, K. Watanabe
  KEK, Ibaraki

MHI#10 and #11 cavities are measured in KEK-STF as the s0 plan for ILC. After these vertical tests, they will be sent to J-Lab and tested at least once there. Moreover, two new cavities without HOM coupler are fabricated and measured in STF, which are made by two new vendors (HITACHI and TOSHIBA). As the international collaboration, one cavity from IHEP in Beijing will be sent to KEK, optical inspected, high pressure rinsed and vertical tested. Although MHI#8 cavity for S1-Global reached 38MV/m, it could not achieve ILC specification (35MV/m, 0.8x10⁹) due to the heavy field emission. To overcome this problem, the various tests were done in the stage of the surface treatment. For example, the EP parameters and the rinsing procedure were changed. In this report, the recent results of the vertical tests including the surface treatment in KEK-STF will be presented in detail.

• V.A. Lebedev, J.-F. Ostiguy, N. Solyak
  Fermilab, Batavia
• A.V. Aleksandrov, A.P. Shishlo
  ORNL, Oak Ridge, Tennessee

A beam loss in the superconducting part of the SNS linac has been observed during its commissioning and operation. Although this loss does not prevent the SNS high power operation it results in an almost uniform irradiation of linac components and increased radiation levels in the tunnel. A multi-particle tracking could not explain the beam loss and its dependence on the machine parameters. It was recently found that the loss is related to the intrabeam particle collisions resulting in a stripping of one of two H^- ions. The paper describes experimental observations and corresponding calculations of the intrabeam stripping.

• N. Nishimori
  JAEA, Ibaraki-ken
• R. Hajima, R. Nagai
  JAEA/ERL, Ibaraki
• Y. Honda, T. Miyajima, M. Yamamoto
  KEK, Ibaraki
• H. Iijima, M. Kuriki
  HU/AdSM, Higashi-Hiroshima
• M. Kuwahara, T. Nakanishi, S. Okumi
  Nagoya University, Nagoya
• T. Muto
  Tohoku University, School of Scinece, Sendai

An electron gun capable of delivering high current and high brightness electron beam is indispensable for next generation energy recovery linac light sources. A high voltage photocathode DC gun is a promising gun for such new light sources. It is however difficult to apply DC high voltage on a ceramic insulator with a rod supporting cathode electrode because of field emission from the rod. In order to mitigate the problem, we have employed a segmented insulator with rings which guard the ceramics from the field emission and recently succeeded in applying 500-kV on the ceramics for eight hours without any discharge. This high voltage testing was performed with a simple configuration without NEG pumps and electrodes. The next step is to repeat the same high voltage testing with a full configuration necessary for beam generation. We have designed electrodes for the maximum surface electric field not to exceed 11 MV/m at 500 kV while keeping the distance between the electrodes 100 mm. NEG pumps with a pumping speed of 7200 L/s have been installed in the gun chamber. A photocathode preparation system was connected to the gun chamber and beam generation is planned this summer.