Design for the Control and Data-Acquisition System for the TAMA300 300m
Laser Interferometer
Norihiko Kamikubota
National Laboratory for High Energy Physics (KEK), 1-1 Oho, Tsukuba, Ibaraki 305, Japan
Nobuyuki Kanda
Institute for Cosmic Ray Research (ICRR), Univ. of Tokyo, 3-2-1 Midori-cho, Tanashi,Tokyo 188, JapanEi-ichi Mizuno
The Institute of Space and Astronautical Science (ISAS), 3-1-1 Yoshinodai, Sagamihara, Kanagawa
229, Japan
Masatake Ohashi, Ryutaro Takahashi, Toshitaka Yamazaki
National Astronomical Observatory (NAO), 2-21-1 Osawa, Mitaka, Tokyo 181, JapanAbstract
A five-year project, “TAMA300”, was started in 1995. The purpose of the project is to construct a 300m laserinterferometer in Tokyo to search for gravitational waves. The studies of the control and the data-acquisition system for
TAMA300 have been carried out and a conceptual design is presented. We are evaluating an EPICS system for devices
which are well distributed along the interferometer arms and need to be supervised at a rate of 1–100 Hz. We also needa data-acquisition system with high-speed ADCs to record 14 interferometer signals at the rate of 20 kHz. In addition,
we are investigating a scheme to merge the signals from both the EPICS and the data-acquisition systems into a raw-dataarchiver. The scheme includes a data server to provide sampled data for online analysis.

I. Introduction
Although the existence of gravitational waves is predicted by the general theory of relativity, there has so far been no
direct observation. Much effort has been put at many places in the world into the direct detection of gravitational waves.
Recent interest has been concentrated on long-baseline laser interferometers [1]. Virgo (the French-Italian project toconstruct a laser interferometer with 3-km arms in Pisa [2]) and LIGO (two interferometers with 4-km arms in Washingtonand Louisiana [6], [7]) are typical examples, which are now under construction and are expected to make their firstobservations in 2000 or 2001. In Japan, a five-year project, “TAMA300” (Tokyo Advanced Medium-scale Antenna), wasstarted in 1995.
The aim of the TAMA300 project is to construct a 300-meter laser interferometer in Tokyo [9]. Though the TAMA300 has
a shorter baseline compared with the other km-size interferometers and accordingly less sensitivity, it has two significantadvantages. First, the operation of TAMA300 is expected to start in 1998, which is earlier than other projects. Second,
the location of TAMA300 in Asia is quite important to complete the world-wide coverage with gravitational antennas,
since coincidence studies between separated interferometers are necessary to determine both the direction and phase of
the arriving gravitational waves.
Some studies concerning the control and data-acquisition system for large interferometers have already been carried out.
The Virgo group has studied control, monitoring and data taking systems [3], [4] as well as a simulation code [5]. For
the LIGO project, a system called CDS (Control and Data System) has been developed to control interferometers and tomanage various data [8]. We also carried out early studies of interferometer control systems in 1991 [10], [11].
In order to develop a control and data-acquisition system for TAMA300, we started a collaboration between NAO, KEK,ISAS and ICRR in 1994. The primary aims of the system are as follows:a) data acquisition for interferometer signals with a 20-kHz sampling rateb) remote control, monitoring and data logging of interferometer devicesc) online pre-analysis for gravitational-wave candidates.
Although the systems used for offline analysis and the simulation of gravitational signals are also of interest, they will be
discussed elsewhere in the future.

II. Signals to be recorded
As a first step, we discuss the signals to be recorded (or at least monitored). Signals can be divided into two groups:
The first group contains the high-rate signals. Interferometer signals, laser signals and signals related to online analysis
belong to this group. Since the shapes of gravitational waves may have a structure with components of up to a few kHz,
we have set the sampling frequency at 20 kHz. As given in Table I, 14 signals are planned to be recorded.
The second group contains the low-rate signals. The major part of the second group contains signals related to mirrors.
Alignment control signals to keep the mirrors stable against seismic noise and the signals of the mirror positions will berecorded at a rate of 100 Hz. Signals from vacuum controllers and from environmental monitors are also included in thisgroup. Those will be recorded at a rate of 1 Hz or lower. A summary of the signals belonging to the second group is also
given in Table I.
The total amount of signals is estimated to be 600 kbytes per second. The major contribution comes from the high-rate
signals.
Table I

List of signals to be recorded with the TAMA300 gravitational-wave antenna.
signal categoryinterferometerinterferometer feedback

laser

online analysis
mirror control

mirror isolation

environment
vacuum
GPS monitor

signal namemain signal
visibility
mainbeam splitter
recycling mirror
mode cleaner
power
frequency stability
visibility
hmatched filter
main(4deg.freedom)
recycling(4deg.freedom)
mode cleaner(4deg.freedom)main(5deg.freedom)
recycling(5deg.freedom)
mode cleaner(5deg.freedom)
beam splitter(5deg.freedom)seismic noise, acoustic noise, etc.
temperature, etc.
vacuum status
valve statusclock

sampling
20kHz
20kHz
20kHz
20kHz
20kHz
20kHz
20kHz
20kHz
20kHz
20kHz
20kHz
100Hz
100Hz
100Hz
100Hz
100Hz
100Hz
100Hz
100Hz
1Hz
1Hz
1Hz
1Hz

channels
1ch
1ch
2ch
1ch
1ch
1ch
1ch
1ch
1ch
1ch
3ch
4ch
1ch
2ch
4ch
1ch
2ch
1ch
30ch
100ch
20ch
50ch
2ch

III. Proposed system for control and data acquisition
A. EPICS for low-rate signals
Since most of the signal sources are well spread along the interferometer arms, it is obvious that a network-oriented
control and data-acquisition system is necessary. In addition, we do not have much manpower and have only three years
remaining to complete the project. We have thus looked for a platform on which to develop our own system, and havefound that EPICS (Experimental Physics and Industrial Control System) [12] seems to be the best choice among several
commercial products and public-domain tools.
We have installed an EPICS test bench at ISAS and are now evaluating its performance with dummy signals. At present,the EPICS seems to satisfy our requirements for low-rate signals. The proposed system consists of a few Unix workstations, X-terminals and roughly ten VME-bus computers, which are connected through a network to each other. We
expect EPICS to be an easy supervisor of the low-rate signals.
B. High-rate data acquisition
It is not easy to collect high-rate signals with EPICS, mainly due to network capacity. Since all of the high-rate signals
are localized near to the central control room in our case, we have looked for another high-rate data-acquisition system.
At present, we are interested in a commercial data-recorder with VXI-ADC modules and an archiver. A serious problem
is that we need to record signals continuously. In order not to interrupt an observation, we require an intelligent raw-datastorage, such as a tape-robot. In addition, we must decide on the archiver media among several candidates such as tapes(DAT, Exabyte, DLT, etc.) or removable disks. Since progress in this field is very fast, we will leave the final decision
until 1997, which is one year prior to the start of observations.
C. Event builder and Data server
We need an “event builder” to merge both the high-rate and low-rate signals together. As shown in Figure 1, the event
builder is in charge of creating a data package, called an “event packet”, every two seconds, which contains the raw
data of both the high-rate and low-rate signals. Each event packet exists in memory for roughly 10 seconds and is thenoverwritten with a new one. During this interval it remains in memory and is transferred into a raw-data archiver. The datatransfer from the high-rate data-acquisition system to the archiver is made through a dedicated high-speed communication
channel.
An event packet is used as a basic unit during the various data treatment, including the online and offline analysis. For
easier handling of the data, the size of one packet has been designed to be on the order of 1 MB. It may include an
additional header, such as a time stamp, a serial number, and so on, for later analysis1 . The detailed structure of a packet
is to be determined in the future.
The data server is also shown in Figure 1. Its role is to provide the latest data for an online analysis. Sampled packets,as many as the CPU power allows, are copied into the files on large scratch disks. The size of the disks is roughly 400
GB in total, so as to keep the data for one week.
We are investigating a physical scheme to realize the mechanism mentioned above. The most promising idea is to use
a reflective memory in order to share on-memory packets with many nodes, including the high-rate data-acquisition, theevent builder and the data server. A feasibility study is in progress.
D. Network
The network is an essential part of our system. We have the idea of dividing it into a few segments. We will install at
least two networks along each arm. One will be an FDDI network having a sufficiently high capacity for data transfer for
the EPICS system. This network will be used only for data transfer. Another is the popular Ethernet, which is to be usedfor very low-rate data transfer, such as the vacuum-monitoring signals, and for general purposes, including X-window
protocols. In order to avoid troubles caused by lightning during the summer season, optical isolation is to be introduced.
E. Schedule
The schedule of the TAMA300 project for the next 5 years is summarized in Table II. The time limit for completing thecontrol and data-acquisition system is 1998.
1 Early consideration was found in [13].

Table II

Schedule for developing the system for TAMA300.
Year
1995
1996
1997
1998
1999

Goal(s) for each year
Evaluation of EPICS with a test benchConstruct the EPICS Supervisory system for low-rate signals
Install network environment
Construct the data-acquisition system for high-rate signals
Install systems for actual observation and analysis
Short observations for performance check
Start the continuous observation for gravitational waves

IV. Acknowledgement
We wish to thank Dr. Kazuro Furukawa and Dr. Yujiro Ogawa for various discussions and suggestions. We also express
our thanks to our colleagues in the TAMA300 group for kind encouragement. The present work is supported by a Grant
in Aid of Scientific Research, Ministry of Education, Science, Sports and Culture, Japan.

References[1] For instance, K.S. Thorne, Proc. of the Snowmass 95 summer Study on Particle and Nuclear Astrophysics andCosmology, August 1995, (World Scientific, 1995), in press[2] A. Vilenkin, Phys. Rev. D24(1981)2082[3] Virgo final conceptual design (1992), chapter VI and chapter VII[4] Virgo note PJT93-16[5] B. Mours and I. Wingerter-Seez, Proc. the Sixth Marcel Grossmann Meeting on General Relativity (MG6), Kyoto,June 1991, (World Scientific, 1992) p.1576-1578[6] A. Abramovici et.al., Science 256(1992)p.325-333[7] S.E. Whitcomb, Proc. of the Fourth Int’l Symp. on Particles, Strings and Cosmology (PASCOS94), New York, May1994, (World Scientific, 1995) p.300-307[8] private communication, http://www.ligo.caltech.edu/LIGO_web/overview/CDS.ps[9] K. Tsubono, Proc. First E. Amaldi Conf. on Gravitational Wave Experiments, Frascati(Rome), June 1994, (WorldScientific, 1995) p.112-114[10] N. Kamikubota, K. Furukawa, K. Nakahara, Y. Ogawa and A. Asami, Proc. the Sixth Marcel Grossmann Meetingon General Relativity (MG6), Kyoto, June 1991, (World Scientific, 1992) p.1480-1482[11] N. Kamikubota, K. Furukawa, K. Nakahara and I. Abe, Proc. Int’l Conf. on Accelerator and Large Experimental
Physics Control Systems (ICALEPCS’91), Tsukuba, November 1991, KEK Proceedings 92-15, p.318-321[12] For instance, http://epics.aps.anl.gov/asd/controls/epics/h̃ome.html[13] J.R. Shuttleworth, Univ. Coll Cardiff, private communication

1.mirror control
2.environments (vacuum,temperature, seismicnoise)
3...

ADC

1.main signal frominterferometer2.optics servo controls
3...

ADC

low-rate signals
1~100 Hz sampling(20 kbytes/sec)

ADC

high-rate signals
20 kHz sampling(560 kbytes/sec)

high-rate
data aquisition

VMEVMEVMEVME(VXI/VME)

event builder
EPICS
1.merge both datahigh-speed
communication
channellow-rate data

1.environment monitor
2.online analysis(FFT, matched filter)3...

on memory
event packets#01
0:00:00-02#02
0:00:02-04#03
0:00:04-06

sampled packets#04
0:00:06-08.
.
.

data serverhigh-speed
communication
channelraw-data archive

1.~400GB disks
2.keep 1week data

large scratch
disks

X-terminals for end-users

Figure. 1. Schematic view of the data flows between the high-rate data-acquisition, the EPICS, the event builder, thedata server, and the raw-data archiver.