Computer Technologies Laboratory

We have studied a multi-mode Delay Line Distribution System (DLDS) [2] as the RF power distribution system from klystrons to RF structures for linear colliders. In particular, a 2×2 DLDS has been proposed and studied at KEK for Japan Linear Collider(JLC). It has been proved that the 2×2 DLDS is simple, bus has good transmission efficiency. We have designed RF components of a basic unit of a DLDS using the High Frequency Structure Simulator (HFSS) code . They include the TE 01 extractor, the TE 11 to TE 01 converter, and the TE 11 to TE 12 converter for TE 12 mode. HFSS calculation of the system, which consists of TE 01 extractor and TE 11 to TE 01 converter, shows that the transmission efficiency of each mode is better than 95%. The components, as well as the system are being studied experimentally. A low power test model for the mode stability experiment in 55m long wave guide in DLDS is also being developed..

We have studied a multi-mode Delay Line Distribution System (DLDS) [2] as the RF power distribution system from klystrons to RF structures for linear colliders. In particular, a 2×2 DLDS has been proposed and studied at KEK for Japan Linear Collider(JLC). It has been proved that the 2×2 DLDS is simple, bus has good transmission efficiency. We have designed RF components of a basic unit of a DLDS using the High Frequency Structure Simulator (HFSS) code . They include the TE 01 extractor, the TE 11 to TE 01 converter, and the TE 11 to TE 12 converter for TE 12 mode. HFSS calculation of the system, which consists of TE 01 extractor and TE 11 to TE 01 converter, shows that the transmission efficiency of each mode is better than 95%. A low power test model for the mode stability experiment in 55m long wave guide in DLDS is also being developed. Further study is underway.

The main X-band linac consists of klystrons, modulators, DLDS pulse compression/delivery systems, and RF accelerating structures. The periodic permanent magnet (PPM) klystrons are under development in the two-year/two-stage project with Toshiba. The goal is to produce 50MW output power at 1.5 µs pulse length at the first klystron and then to advance to 75MW at the second one. The first PPM klystron has been tested, and it achieved 56MW power with 50% efficiency at 1.5 µs pulse length. The second PPM klystron is currently under testing. Up to date (June 6,2001), the klystron already produced 73.2MW at 500 kV at the 1.4 µs pulse length. The maximum efficiency reached 56% at the specified cathode voltage. As for the modulator, KEK is now developing a new IGBT (Insulated Gate Bipolar Transistor) modulator as a two-year project. Two prototypes, with three and ten stages of modules for 6kV and for 20kV output pulse each, were built and tested successfully. KEK is developing the multi-mode 2x2 DLDS (Delay Line Distribution System) power distribution system. For the study the stability of propagation modes on a delay line and for the measurement of their transmission losses, joint experiments with SLAC and BINP were performed at KEK on a 55 m long waveguide assembled in the ATF linac. The experiments showed the best combination of two modes to be TE 01 and TE 02 modes. The design of all RF components for the TE 01 /TE 02 2x2 DLDS was completed and their cold models will be tested soon. Details of these developments and measurement results are presented.

Our searches for new oxide chalcogenides of rare earths and Fe, Co, Ni, and Zn resulted in preparation of two new compounds Ce 2 Fe 2 O 3 S 2 and Pr 2 Fe 2 O 3 S 2 which are isostructural to La 2 Fe 2 O 3 Se 2 and Sm 2 Ti 2 O 3 Sb 2 . Crystal structures of the new compounds Ce 2 Fe 2 O 3 S 2 and Pr 2 Fe 2 O 3 S 2 were determined from powder X-ray diffraction data. Magnetic measurements were performed for Ce 2 Fe 2 O 3 S 2 and revealed behavior very similar to that of isostructural oxide chalcogenides of iron and pnictides of titanium. In particular, no superconductivity was observed down to 4 K. Crystal chemical factors determining the stability of the La 2 Fe 2 O 3 Se 2 structure type are discussed.

Simultaneous substitution of W VI by U VI and Bi 3+ by La 3+ in the structure of ferroelectric Bi 2 WO 6 results in stabilization of the archetypic tetragonal I4/mmm structure which is observed for the first time among [Bi 2 O 2 ][BO 4 ] Aurivillius-type oxides. Studies at the largest U content revealed a new Aurivillius-like compound Bi 1.5 La 0.5 UO 6 which exhibits a novel distorted orthorhombic version of the archetypic structure.

Femtosecond pump probe experiments are reported on quasiparticle relaxation and recombination in YBa 2 Cu 4 O 8 as a function of temperature and polarization. We compare our results with the data obtained on YBa 2 Cu 3 O 7−δ and show that similar two-component relaxation is present in both cases. A strong polarization anisotropy of the picosecond response is observed below T c and interpreted with the aid of a simple model which considers the anisotropy of the probe transition matrix elements.

In this paper, we summarize our activities on X-band klystron development for the Japan Linear Collider (JLC) project. Our goal is to produce a 120-MW class klystron at 11.424 GHz with a pulse length of 1.5 µs and with an efficiency better than 47%. For this end, we have advanced three programs simultaneously. First, we adopted the particle-in-cell (PIC) code, MAGIC, for a realistic simulation of klystron and for a better design of Traveling-Wave (TW) output cavity. Simulation results for the XB72K No. 8 and No. 9 klystrons and the SLAC XL-4 klystron show excellent agreements with measurements. A new solenoid-focused klystron, XB72K No.10, is the first klystron designed by using the MAGIC code. Its predicted performance is 126 MW output power (efficiency 48.5%) with peak surface field of about 77 MV/m, low enough to sustain a 1.5 µs long pulse. It is now in manufacturing and the high power testing is scheduled to start from November 1998. Second, new RF windows with 100-MW power-handling capability have been designed and the cold model test is about to start. They utilize TW mixed modes (TE11 plus TE12 modes, or TE11 plus TM11 modes) to reduce the surface field at the brazing edge of the ceramic, instead of a single TW TE01 mode window that needs expensive mode converters. Third, the Blumlein modulator is upgraded to produce a pulse with 2 µs flat top and 200 ns rise time at 550 kV output voltage. Details of the klystron development are presented.

The magnetic penetration depth λ(0) in polycrystalline MgB2 for different boron isotopes ( 10 B/ 11 B) was investigated by transverse field muon spin rotation. No boron isotope effect on the penetration depth λ(0) was found within experimental error: ∆λ(0)/λ(0) = −0.8(8)%, suggesting that MgB2 is an adiabatic superconductor. This is in contrast to the substantial oxygen isotope effect on λ(0) observed in cuprate high-temperature superconductors.

In this paper, we summarize the status of X-band PPM klystron development for the Japan Linear Collider (JLC) project. The periodic permanent magnet (PPM) klystrons are under development in the two-stage/two-year project with Toshiba. The goal is to produce 50 MW output power with efficiency >50% at 1.5 μs pulse length at the first klystron and then to advance to 75 MW with efficiency =55% at the second one. The first PPM klystron has been tested, and it achieved 56 MW power with 50% efficiency at the standard 1.5 μs pulse length. Neither oscillation of the parasitic mode nor gun oscillations were observed. The particle transmission was found to be 100% when no RF signal is applied. The second PPM klystron is currently under high-power testing. It has improved water cooling system of a PPM circuit and the output cavity for 150 Hz operation. The RF system was also revised for a higher efficiency. To date (June 6, 2001), the PPM-2 klystron produced 73.2 MW at 1.4 μs pulse length an...

Polythermic studies of Bi 2 WO 6 eBi 2 UO 6 system revealed existence of a broad Bi 2 W 1Àx U x O 6 solid solution with the Aurivillius-type structure. Below 750 C, the homogeneity area is narrow (x 0.12) but extends significantly at higher temperatures (up to ca. 75% Bi 2 UO 6 at 1025 C). The solid solution retains orthorhombic symmetry over the entire compositional range, but substitution of U for W results in significant lowering of second harmonic intensity and Curie point suggesting, at high substitution degrees, a very close approach to the archetypic body-centered tetragonal centrosymmetric structure. The known Bi 2 WO 6 -based solid solutions are discussed in terms of thermal stability, and a general geometrical explanation is suggested. Incorporation of large cations into the B perovskitic positions of [Bi 2 O 2 ][A nÀ1 B n O 3nþ1 ] Aurivillius structures seems yet to be restricted by the n ¼ 1 case.

We report the observation of superconducting vortices in pure and lightly Al doped MgB2 single crystals. Low field experiments allow for the estimation of the London penetration depth, lambda 1900Å for T∼6 K. Experiments in higher fields (e.g. 200 Oe) clearly show a triangular vortex lattice in both real space (13 µm by 13 µm Bitter decoration image of over 1000 vortices) and reciprocal space.

It has been reported at EPAC-96 Conference on successful experimental results on achievement of 100 MW output rf power in a wide aperture, 15 mm, high gain, 80 dB, 14 GHz VLEPP klystron with distributed suppression of parasitic oscillations [1]. This report presents design of an electrodynamic structure of the X-band klystron for linear collider with a higher efficiency up to 54 % to be achieved at the same parameters of the electron beam (U = 1 MeV, I = 250 A, emittance 0.05π cm·rad). Design rf output power of the klystron is equal to 135 MW.

Results of experimental study of a wide-aperture relativistic klystron for VLEPP are presented. Investigations have been performed using the driving beam of the JINR LIA-3000 induction accelerator. To suppress self-excitation parasitic modes we have used technique of RF absorbing drift tubes. We have obtained 75 MW of output power in a long pulse (250 ns) and 100 MWin a short pulse (50 ns).

This paper is devoted to a problem of the optimal design of the electrodynamic structure of the X-band klystron for a linear collider. It is shown that the optimal design should provide a large aperture and a high power gain, about 80 dB. The most severe problem arising here is that of parasitic self-excitation of the klystron, which becomes more complicated at increasing aperture and power gain. Our investigations have shown that traditional methods for suppressing the selfexcitation become ineffective at the desired technical parameters of the klystron. In this paper we present a novel concept of a wide aperture klystron with distributed suppression of parasitic oscillations. Results of an experimental study of the wide-aperture relativistic klystron for VLEPP are presented. Investigations have been performed using the driving beam of the JINR LIA-3000 induction accelerator (E = 1 MeV, I = 250 A, r = 250 ns). To suppress self-excitation parasitic modes we have used the technique of RF absorbing drift tubes. As a result, we have obtained design output parameters of the klystron and achieved a level of 100 MW output power.

In this paper, we describe a genetic algorithm for induction of finite automata with continuous and discrete output actions. Input data for the algorithm is a set of tests. Each test consists of two sequences: input events and output actions. In previous works output actions were discrete, i.e. selected from the finite set, in this work output actions can also be continuous, i.e. represented by real numbers. Only the structure of automaton transitions graph is evolved by the genetic algorithm. Values of output actions are found using transition labeling algorithm, which aim is to maximize the value of fitness function. New transition labeling algorithm is proposed. It also works with continuous output actions and is based on equations system solving. In case of proper selection of fitness function, equations in this system are linear and it can be solved by the Gaussian elimination method. The unmanned airplane performing the loop is considered as an example of the controlled object.

In this paper we present the results of experimental study of a wide aperture (15 mm), high gain (80 dB) VLEPP klystron upgraded with RF absorbing insertions. Investi- gations have been performed using the driving beam of the JINR LIA-3000 induction accelerator ( MeV, A, ns). The proposed technique for suppress- ing parasitic self-excitation proved to be extremely fruitful: we