TRIAC Progress Report - KEK

charge-up, we modified the structure of the holes and the surface of the electrode.
Table 2-8 shows a summary of such modifications together with observed
pulse-height shifts under various injection rates of particles with the energy of about 1
MeV/nucleon. THGEM #1 indicates the THGEM previously developed in Ref. 2-25,
which has an insulator rim of 100 µm in width around a hole. THGEM #2 has no rim
and the gain shift was suppressed to be less than 12 % under the 4 He injection rate of
10 4 pps. However, a discharge often occurred in several hours from the beginning of the
injection, and the gain became unstable once the discharge occurred. In order to avoid
the discharge, the diameter of the hole of THGEM#3 was reduced to be smaller than of
THGEM#2.
Table 2-8. Summary of modified THGEMs together with pulse height shifts at various injection
rates. THGEM#1 indicates the previously developed THGEM [2-25]. THGEM#2 has no rim on the
hole of 500 µm in diameter. The diameter of the hole of THGEM#3 was smaller than for
THGEM#2. The surface of copper electrodes was coated with gold for THGEM#4. ‘n/a’ indicates
not-measured.
Pulse
height
THGEM# #1 #2 #3 #4
Hole diameter [µm] 300 500 300 300
Rim yes no no no
Hole pitch [µm] 700 700 700 700
Electrode surface Au Cu Cu Au
4 He (E = 5.4 MeV, 10 0 pps ) 100 a few n/a n/a
4 He (E = 5.4MeV, 10 4 pps ) n/a 12 1~5 n/a
shift (%) 12 C (E = 13.2 MeV, 10 5 pps) n/a n/a 8 < 3
Fig. 2-43. Pulse-height shifts under the 12 C-beam injection rate from 400 pps to 10 5 pps using
THGEM #3 (left panel) and THGEM #4 (right panel). The horizontal axis indicates time from the
beginning of the beam injection.
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