production of 400 mirrors with high vuv - SLAC - Stanford University

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.SLAC-PUB-5199 April 1990

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(El

z

PRODUCTION OF 400 MIRRORS WITH HIGH REFLECTIVITY FOR USE IN THE SLD CERENKOV RING IMAGING DETECTOR*

-.

VUV

K. Abe,’ P. Antilogus, D. Astoq2 A. Bean,’ T. Bienz,’ F. Bird,2(a) D. Caldwell, P. Co~le,~ D. Co~ne,~ P. Datte,3(b) J. Dubosq3 W. Dunwoodie,2 P. Gagnon: D. Hale,3 G. Hallewell,2 K. Hasegawa,’ M. Hilton,3(c) J. Hubeq3 P. Jacques5 R. A. Johnsoq6 H. Kawahara,2 Y, Kwoq2 D. W. G. S. Leith,2 A. Lq3 J. Martinez,’ L. Mathys,3 S. McHugh,3 R. Morrisoq3 D. Muller,2 T. Nagarnine,2 M. Nussbarq6 T. PaveL2 R. P1an0,~ B. Ratcliff, P. Rensing,2 A. K. S. Santha,’ D. Schultq2 S. Shapiro,2 A. Shoup,’ C. Sirnopoulos,2 E. Solodov,2(d) P. Stamer,5 I. Stockdahq6 F. Suekane,’ N. Togq2 J. Va’vrq2 J. S. Whitaker,7 D. A. Willianq4 S. H. Williams,2 M. Witherell,3 R. J. Wilson,7 S. Yellin,” and H. Yuta’

THE SLD

CRID

COLLABORATION

-‘Department

of Physics, Tohoku University, Aramaki, Sendai 980, Japan 2Stanjord Linear Accelerator Center, Stanford University, Stanford, CA 94309, USA ‘Department of Physics, University of California, Santa Barbara, CA 93106, USA 4Santa Cruz Institute for Particle Physics, University of California, Santa Crux, CA 95064, USA 5Serin Phy sa‘cs Laboratory, Rutgers University, PO Box 849, Piscataway, NJ 08855, USA 6Department of Physics, University of Cincinnati, Cincinnati, OH 45221, USA 7Department of Physics, Boston University, Boston, MA 02215, USA

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Submitted

to Nuclear Instruments

and Methods B.

*

Work supported by Department of Energy contract DE-ACO3-76SFO0515; and National Science Foundation grants PHY88-13669 and PHY88-13018. (a) Present address: EP Division, CERN, CH1211, Geneva 23, Switzerland. (b) Present address: Texas Accelerator Center, 2319 Timberloch Drive, The Woodlands, TX 77380, USA. (c) Permanent address: Applied Magnetics Company, Goleta, CA 93117. (d)

Permanent address:

Institute

of Nuclear

Physics,

Novosibirsk,

630090,

USSR.

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_-

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ABSTRACT

The Stanford

Large Detector

for experimental

particle

physics detection

at the

c SLAC Linear Collider contains a Cerenkov Ring Imaging Detector -.

CRID

mirrors

production

process, the quality

control

of the mirrors

The industrial

produced,

and the results of

of at least 80% for light at 160 nm and 85% for light in the

180-230 nm wavelength

range has been achieved in the production

size of 30 by 30 cm. imply

that

the light

and mirror-shape

mirror

An average reflectivity

incident

reflectivity

and installed.

(VUV)

measurements ._

produced

The barrel

the vacuum ultraviolet

of a typical

.-

have been successfully

(CRID).

The surface roughness loss due to scattering

light and the angular error due to shape distortion

2

accuracy are described.

of over 400 mirrors

and optical

distortion

is a few percent

of the

is less than 1 mrad.

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.-

1. INTRODUCTION

_*

A large Cerenkov Ring Imaging Detector (GRID)’ y2 is currently to be included

-.

detection

in the Stanford

at the SLAC

Linear

Large Detector Collider

(SLC).

barrel and two endcaps, as shown in fig. l(a).

under construction

for experimental This CRID

particle

physics

consists of a cylindrical

This device is capable of determining

the actual radius of the Cerenkov ring associated with each charged particle along with a momentum

measurement,

In a gas ring imaging charged particle -

provides particle

detector 3y4 the Cerenkov

traveling

through

the radiator

focus a ring image onto the photosensitive - ‘detector consists of Time Projection tetrakis[dimethylamine]ethylene the photocathode

mixed

windows that are transparent -

identification.

light emitted

medium

by a relativistic

is reflected

by a mirror

detector plane. The single-photon

with an ionization

the drift

gas.

to VUV light.

The TPCs

threshold (drift

to

position

Chambers (TPCs) with the photosensitive

(TMAE,

with

which,

additive

of 5.4 eV) as

boxes) use quartz

This apparatus permits the reconstruction

in three dimensions of the position where the photon ionized a TMAE molecule. ” The angle of Cerenkov radiation emission, from which the velocity of the relativistic particle

can be determined,

by the photodetector

includes both liquid and gas radiators,

long drift boxes of the TPC type containing

and proportional

chambers with charge division

barrel half is divided associated liquid of 5 mirrors

the ring image as registered

for all the photons associated with a given charged particle.

The SLD barrel CRID mirrors,

is found by reconstructing

into 10 azimuthal

radiators

as the photocathode,

readout, as shown in fig. l(b).

sectors which contain 2 drift

and 20 mirrors.

and all of the 10 mirrors

gaseous TMAE

spherical focusing

Each drift

3

boxes and their

box detects light from 2 rows

have a unique shape.

contains a total of 400 spherical mirrors.

Each

The SLD barrel CRID

3?he gas radiator c

emitted

is only transparent

the photocathode -.

perfluoro-n-pentane5

below 220 nm. the constraint mirrors

efficiency

of a reasonable

light

is

165 nm, whereas

only at wavelengths

of photons

as possible within

cost, it was necessary to require the reflectivity

of the

to be not less than 85% for light in the range of 180-220 nm.

of error:

with

chromatic

geometric,

which

geometric

aberration

and momentum

contribution

spatial reconstruction of mirrors

A total completed

the CRID the mirrors

by the contributions

in the gas radiator,

of the mirrors

from optical uncertainty

of 472 mirror

and reasonable

of California,

vessel. We describe the mirror

The mirror scattering

but

error of less than fl

mrad

a small

and surface

are difficult

to maintain

as

in large

cost. 430 were coated,

Santa Barbara

production

and the results obtained

substrate

scattering,

work are not as demanding

(UCSB)

that best met our acceptance criteria

Substrate

multiple

to the allowed overall photoelectron

of which

2. MIRROR 2.1 Mirror

measurement,

for ring imaging

substrates,

by the University

produced,

from five separate sources

of about l-2 mm 3 . The focal properties

telescope -mirror,

with thin mirrors

angle of a particle

of 479 mm and 508 mm ensured

distortions

which are suitable

The 400 mirrors

measures the Cerenkov

smearing. 6 The angular reflection

those for an astronomical quantities

the CRID

is determined

for the two focal lengths

CRID.

quantum

the Cerenkov

longer than

In order to detect as large a number

from the gas radiator

quality

in which

of wavelengths

h as a significant

(TMAE)

The accuracy

-

for light

(C5F12)

of VUV

were successfully for the SLD barrel

have been installed

process, the quality

into

control

of

reflectivity.

SUBSTRATE

Manufacturing was required

to a few percent of the incident

to have a surface finish light.

4

This requirement

which

would

limit

is due to the small

number _-

of photons

was required

produced,

typically

10 or so. In addition,

to give an angular reflection

error of

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Wavelength Fig. 8

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