* Corresponding author. Tel.: # 81-298-645626; fax: # 81- 298-645623. E-mail address: yasuhiro.miyake@kek.jp (Y. Miyake). Physica B 289}290 (2000) 666}669 Construction of the experimental set-up for ultra slow muon generation by thermal Mu ionization method at RIKEN-RAL Y. Miyake*, K. Shimomura, Y. Matsuda, R.J. Scheuermann, P. Bakule, S. Makimura, P. Strasser, S.N. Nakamura, K. Ishida, T. Matsuzaki, I. Watanabe, K. Nagamine Meson Science Laboratory (KEK-MSL), High Energy Accelerator Research Organization, Institute of Materials Structure and Science, KEK, 1-1 Oho, Tsukuba 305-0801, Japan Muon Science Laboratory, Institute of Physical and Chemical Research (RIKEN), 2-1 Wako, Saitama 351-0198, Japan Abstract At KEK-MSL we have been pursuing the Ultra Slow Muon Project, in which thermal muonium atoms (designated as Mu; consisting of a  and an e) are generated from the surface of a hot tungsten foil, placed at the primary 500 MeV proton beam line and ionized by intense lasers synchronized with the emission of Mu. However, because of the high radiation in the primary proton beam line where the present set-up is installed, a slow muon generation started not from a primary proton beam but with much higher intense surface muons is seriously required, in order to understand slow muon generation more deeply and to obtain more intense slow muons. Therefore, we are planning to perform a slow muon generation using intense surface muons, taking the advantage of the intensity of the proton beam at ISIS of 200 A being about 40 times as large as that of KEK-MSL. In this report, we are presenting a new set-up, a slow beam optics and a laser system operated at 25 Hz prepared for the generation of ultra slow muons at the RIKEN-RAL muon facility.  2000 Elsevier Science B.V. All rights reserved. Keywords: Slow muon; VUV laser; Muonium; Hydrogen 1. Target and apparatus for slow ion extraction optics The apparatus including target chamber and slow ion extraction optics will be installed at the RIKEN/RAL Port 3 experimental area. The layout of the laser system in a laser cabin and the experi- mental set-up in Port 3 is shown in Fig. 1. A high purity (99.9999%) tungsten foil of 50 m thickness (obtained from Metallwerk Plansee GmbH) is placed inside the UHV target chamber for Mu generation in vacuum [1,2]. The W foil is capable of being heated up to 3000 K by a pulsed DC current which is turned o! for 1 ms, synchronized with the arrival of the muon beam, since the mag- netic "eld caused by a DC current would have a!ected the yield of the resonantly ionized muons. The target chamber is evacuated down to 1.010 mbar at 2300 K. The tungsten target was cleaned by a surface treatment in 3.010 mbar of oxygen at 1800 K for about 10 h, and then heated 0921-4526/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 0 ) 0 0 3 0 6 - 9