EVALUATION OF THE BACK-BOMBARDMENT EFFECT IN THE ITC-RF GUN FOR T-ACTS PROJECT AT TOHOKU UNIVERSITY

Abstract An ITC (independently tunable cells) RF gun is currently used to produce sub-picosecond electron pulses as part of the injector for coherent terahertz radiation at Tohoku University. Experiments and simulations of particle tracing by GPT show that the back-bombardment effect on the LaB6 cathode's surface is serious and should be controlled carefully. To evaluate the temperature increase due to backbombardment a 2D model is created for heat transfer inside the cathode. In the 2D model, the back-streaming electrons are treated as external heat source as well as the cathode heater that heats the cathode from its side along with thermal radiation from its surface. The energy deposit of backbombardment inside the cathode is calculated by EGS5 or Geant4 by use of the information of back-streaming electrons derived from GPT simulation. In addition, we will also compare the simulating results with experimental data on the increase of emission current density of cathode due to back-bombardment

First simultaneous detection of electron and positron bunches at the positron capture section of the SuperKEKB factory

Abstract The direct simultaneous detection of electron and positron bunch signals was successfully performed for the first time with wideband pickups and a detection system at the positron capture section of the SuperKEKB factory. The time interval between the electron and positron bunches, their bunch lengths, and bunch intensities depending on the phase of accelerating structures were measured to investigate their capture process and to maximally optimize the positron intensity. The results show that the time intervals were measured in the range of 135–265 ps, and the line-order switch of the electron and positron bunches in the axial direction was clearly observed as a function of the phase. The positron (electron) intensity was maximized at the optimal phase (180 $$^{\circ }$$ ∘ shifted from the optimum). These series of measurements have never been experimentally conducted so far. It is demonstrated that the positron intensity can be systematically optimized with this system as functions of beam parameters in multidimensional spaces for any positron capture section

DEVELOPMENT OF FPGA-BASED TDC WITH WIDE DYNAMIC RANGE FOR MONITORING THE TRIGGER TIMING DISTRIBUTION SYSTEM AT THE KEKB INJECTOR LINAC

Abstract A new field-programmable gate array (FPGA)-based time-to-digital converter (TDC) with a wide dynamic range greater than 20 ms has been developed to monitor the timing of various pulsed devices in the trigger timing distribution system of the KEKB injector linac. The pulsed devices are driven by feeding regular as well as any irregular (or event-based) timing pulses. For monitoring the timing as precisely as possible, a 16-ch FPGA-based TDC has been developed on a Xilinx Spartan-6 FPGA equipped on VME board with a time resolution of 1 ns. The resolution was achieved by applying a multisampling technique, and the accuracies were 2.6 ns (rms) and less than 1 ns (rms) within the dynamic ranges of 20 ms and 7.5 ms, respectively. The various nonlinear effects were improved by implementing a high-precision external clock with a built-in temperaturecompensated crystal oscillator

Benchmarking the FCC-ee positron source simulation tools using the SuperKEKB results

International audienceFor the Future Circular Collider (FCC-ee), particular attention is drowned to the crucial role of the positron source. Two positron production schemes are considered for the FCC-ee: conventional and crystal-based (hybrid), implying the use of channeling radiation in the oriented crystals. To design and optimize the positron production and capture by considering the positron injector parameters, including the electron drive beam and the final system acceptance, a start-to-end simulation toolkit should be developed. This paper will present the first results of benchmarking the FCC-ee positron source simulation tools using the SuperKEKB positron source currently in operation. The model starts with the production of positrons and target studies in Geant4. Then, a new tracking code RF-Track is used for capturing and tracking the generated positrons through the capture section composed of the matching device and several accelerating structures embedded in the solenoid field to accelerate the positrons until ~120 MeV. Afterward, the positrons are further accelerated to the energy of the Damping Ring (1.1 GeV)

Towards a Preliminary FCC-ee Injector Design

The Future Circular Collider-ee aims to get high luminosity which mainly relies upon high charge and low geometric emittance in the collider. The FCC-ee is a future project of CERN to operate as Z, W, H and tt factories with varying energies between 45.6 to 175 GeV. Among those, the total charge requirement is peaked for Z-operation (i.e. 91500 bunches of electron and positron with 3.3·10¹⁰ particles per bunch) meanwhile this mode targets the smallest geometric emittance in the Collider. To reach the goal, the normal conducting S-band Linac has been designed to accelerate 4·10¹⁰ particles in a bunch to 6 GeV and send two bunches per RF pulse within a repetition of 100 Hz. The FCC-ee positrons will also be created inside the linac at 4.46 GeV and accelerated to 1.54 GeV. These positrons are damped at the designed Damping Ring at that energy, and then transferred back to the Linac to meet the same characteristics of electrons. Therefore, in this paper, we'd like to discuss the transmission and robustness of the Linac and the dynamic aperture of the Damping Ring which has to be large enough to accept the incoming beam and cover the probable shrink due to the misalignments

Experimental Activities on High Intensity Positron Sources Using Channeling

International audienceThe positron source under investigation is using channeling radiation of multi-GeV electrons in a tungsten crystal. The radiated photons are impinging on the amorphous targets creating e⁺e⁻ pairs. A dipole magnet between the crystal-radiator and the amorphous-converter allows the charged particles to be swept off and only emitted photons to generate e⁺e⁻ pairs in the converter. Granular targets of different thicknesses, made of small tungsten spheres, have been recently investigated as a target-converter. This paper is describing the experimental studies conducted at the KEKB linac with such device. After the description of the experimental set-up and beam parameters, the measurement methods and preliminary results are presented

STUDY ON THE BACK-BOMBARDMENT EFFECT IN THE ITC-RF GUN FOR t-ACTS PROJECT AT TOHOKU UNIVERSITY

Abstract An ITC (independently tunable cells) RF gun is currently used to produce sub-picosecond electron pulses as part of the injector for coherent terahertz radiation at Tohoku University. Both experiments and simulations of particle tracing by GPT have shown that the back-bombardment(B.B.) effect on the LaB6 cathode's surface is serious and should be controlled carefully. To evaluate the temperature increase due to B.B. a 2D model is created for heat transfer inside the cathode. In the 2D model, the back-streaming electrons are treated as external heat source as well as the cathode heater that heats the cathode from its side along with thermal radiation from its surface. The energy deposit of B.B. inside the cathode is calculated by EGS5 or Geant4 by use of the information of back-streaming electrons derived from GPT simulation. The results of simulation on time dependent evolutions of temperature and emission current density of the cathode caused by B.B. were compared with experimental data

Installation of a Dipole Electromagnet RTAGX(I. Nuclear Physics)

A dipole electromagnet RTAGX has been installed in the GeV-γ experimental hall. It sweeps out charged particles contaminated in the incident γ beam for meson photo-production experiments. It also supplies momentum-analyzed electrons or positrons in a newly constructed test beamline