prototype

Development of Photomultipliers

Photomultiplers(PMTs) available in liquid Xe are being developed in collaboraion with Hamamatsu Photonics Inc. There are two working version now. One is R6041Q, which has been used during studies with the small prototype and proved to operate stably in liquid Xe for long term. The other one is R5900-06 using the same photocathode material with R6041Q. The package of R5900-06 is the same one as R5900 listed in the catalogue of Hamamatsu. Specifications of these PMTs are summarised in the following table.

	R6041Q	R5900-06
PMT size	57mmφ	27.7mm x 27.7mm
Photo-Cathode material	Rb-Cs-Sb	Rb-Cs-Sb
Size of effective area	46mmφ	18mm x 18mm
Q.E. at normal temperature	10%-15%	10%-15%
Dynode type	Metal channel	Metal channel
Number of stages	12	10
Typical H.V.	1000V	800V
Current amplification	1 x 10⁶	2.0 x 10⁶

These two types employ metal channel dynode structure in order to reduce the lengths of PMTS. With micromachining technology closed proximity assembly of these thin electrodes has been achived. The schematical view of the struture is shown in Fig.1.

Fig.1 : Schematical view of metal channel dynode

R6041Q: Drawing and Voltage Divider Circuit

r5900-06: Drawing and Voltage Divider Circuit Amount of material used in R6041Q and the holder is listed in the following table.

PMT	Material	Weight[g]	Radius
Window	Quartz	15.1	27.5mm
Stem	Glass	32.8	22.6mm
Dynode	SUS	12 x 2.02	25.5mm
Base	G10	8.0	22.4mm
Tube	SUS	6.4	----

HOLDER	Material	Thickness
holder	G10	29 mm
Spacer	Acrylic	11 mm
Backend	Acrylic	5 mm

Modified version of R6041Q is under development. This version employs new metal chanel dynode stucture with more efficient collection efficiency. It is expected that transmission efficiency will increase without changing other parts of the PMT. Another version is also investigated. That is different from the compact PMT such as R6041Q and R5900-06, but uses a tradistional glass-tube resulting in higher quantum efficiency and transmission probability. The expected performance estimated with simulation by Hamamatsu are summarized in the following table.

	R6041Q	R6041Q-mod1	R7281Q
PMT length	32 mm	32 mm	80 mm
Outer diameter	57 mmφ	57 mmφ	51 mmφ
Effective area	41 mmφ	41 mmφ	46 mmφ
Q.E. at 200nm	10% TYP	10% TYP	20% TYP
Transmission efficiency	64% TYP	79% TYP	90% TYP
TTS	0.75ns TYP	0.75ns TYP	9.7ns TYP

In 2002 the situation developed. Hamamatsu adopted K-Cs-Sb photocathode instead of Rb-Cs-Sb. In addition it has an aluminum strip pattern to acquire 1.5 times higher QE than the previous ones. Quantum efficiencies as a function of wave length are shown in the follwing figure.

S. Mihara Feb 18th, 2004