Hideki Hamagaki

Fine-pitch and thick-foil gas electron multipliers for cosmic x-ray polarimeters

We have produced various gas electron multiplier foils (GEMs) by using laser etching technique for cosmic X-ray polarimeters. The finest structure GEM we have fabricated has 30 μm-diameter holes on a 50 μm-pitch. The effective gain of the GEM reaches around 5000 at the voltage of 570 V between electrodes. The gain is slightly higher than that of the CERN standard GEM with 70 μm-diameter holes on a 140 μm-pitch. We have fabricated GEMs with thickness of 100 μm which has two times thicker than the standard GEM. The effective gain of the thick-foil GEM is 104 at the applied voltage of 350 V per 50 μm of thickness. The gain is about two orders higher than that of the standard GEM. The remarkable characteristic of the thick-foil GEM is that the effective gain at the beginning of micro-discharge is quite improved. For fabricating the thick-foil GEMs, we have employed new material, liquid crystal polymer (LCP) which has little moisture absorption rate, as an insulator layer instead of polyimide. One of the thick-foil GEM we have fabricated has 8 μm copper layer in the middle of the 100 μm-thick insulator layer. The metal layer in the middle of the foil works as a field-shaper in the multiplication channels, though it slightly decreases the effective gain.

Development of cosmic x-ray polarimeter

We present a performance study of a cosmic X-ray polarimeter which is based on the photoelectric effect in gas, and sensitive to a few to 30 keV range. In our polarimeter, the key device would be the 50 μm pitch Gas Electron Multiplier (GEM). We have evaluated the modulation factor using highly polarized X-ray, provided by a synchrotron accelerator. In the analysis, we selected events by the eccentricity of the charge cloud of the photoelectron track. As a result, we obtained the relationship between the selection criteria for the eccentricity and the modulation factors; for example, when we selected the events which have their eccentricity of > 0.95, the polarimeter exhibited with the modulation factor of 0.32. In addition, we estimated the Minimum Detectable Polarization degree (MDP) of Crab Nebula with our polarimeter and found 10 ksec observation is enough to detect the polarization, if we adopt suitable X-ray mirrors.

Observation of ring-imaging Cherenkov photons with an image intensifier

Abstract We have constructed a prototype of a ring-imaging Cherenkov detector based on the idea that single photons can be directly detected with an image intensifier coupled with a CCD camera. A test using high-energy electron beams was performed with a 2 m long gas radiator at 1 atm. We could successfully see clear Cherenkov rings composed of 21 photons on the average per single event with a Freon-12 gas radiator, and of 12 photons with a nitrogen radiator.

Gain properties of gas electron multipliers (GEMs) for space applications

Fine-pitch and thick-foil GEMs have been produced using a laser etching technique for photoelectric X-ray polarimeters onboard future missions. The finest hole pitch of the thick-foil GEM is 80 μm with a hole diameter of 40 μm, and a thickness of the insulator is 100 µm. The maximum effective gain in a 70%-30% mixture of argon and carbon dioxide reaches 3×104 at voltage of 750 V between GEM electrodes. No significant gain increase or decrease was observed during 24 hours test in which applied high voltage was ramped up and down frequently. The measured gain stability was less than 4%. An accelerated test of the high voltage ramp up and down for two years LEO operations were carried out. During the 6500 times voltage ramp up and down, the GEM kept its gain within 4% variation and no unexpected behavior was observed.

Low-mass dilepton production through transport processes in a quark-gluon plasma

We attempt to understand the low-mass dielectron enhancement observed by PHENIX Collaboration at Relativistic Heavy Ion Collider (RHIC) by transport peak in the spectral function. On the basis of the second-order formalism of relativistic dissipative hydrodynamics, we parameterize the spectral function in low-frequency and long-wavelength region by two transport coefficients, electric diffusion coefficient

Simulation study for Forward Calorimater in LHC-ALICE experiment

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Development of a pipelined ADC chip for the gas electron multiplier readout

and relaxation time

Development of gas electron multipliers with Resistive Kapton electrodes

\tau_{\rm J}

Development of a Time Projection Chamber (TPC) using Gas Electron Multiplier (GEM) for use as an active target

, and compared our theoretical dielectron spectra with the experimental data. We study spectrum of dielectrons produced in relativistic heavy ion collisions by using the profile of matter evolution under full (3+1)-dimensional hydrodynamics. We find that the experimental data require the diffusion coefficient to be

Nuclear Media Effects on Production and Decay of Vector Meson Studied in 12 GeV p+A Interaction

D\geq 2/T