Main Drift Chamber Yuanbo Chen Ihep 2001.10. Motivation (MDC IV) The BGO crystal used in L3 will be used for BES III ’ s Calorimeter. The space for MDC.

Main Drift Chamber

Yuanbo Chen

Ihep

2001.10

Motivation (MDC IV)

The BGO crystal used in L3 will be used for BES III’s Calorimeter. The space for MDC IV will be limited. In MDC IV design , some items have to be considered in the limited space:

Cell structure should be small; The height of the cell should be as small as possible,

and reduce the space between layers for setting more layers;

Since the momentum resolution is dominantly limited by the multiple scattering, a low- Z working gas and low-Z field wires are needed;

The inner part of the end-plates of the MDC IV will be designed as a multi-step to allow micro-β components at both ends, and have maximum polar angle coverage.

BES III (MDC location)

The position of micro-β in IR

• Baseline design of the drift chamber

• Expected performance• R&D program• Time schedule

MDC IV

Baseline design

General description The mechanical design Drift cell configuration and layer organization Working gas selection Low Z-field wire selection Electronics readout

General description (1) Length: 1,856 mm Outer cylinder

Thickness: 5 mm Material: Al

Inner cylinder Thickness: 1 mm Material: carbon fiber : 0.45% 0

Endplate Thickness: 25 mm Material: Al Inner section: stepped Outer section: flat

General description (2) Layer

8(first-step)+4*2(foursteps)+20(outer)

= 36 layers Sense wire

30μm , tungsten gold-plated

Field wire110μm , aluminum gold-plated

Cell Small cell configuration Total number: 5,322 Height: 12 mm

(first step)

14 mm (others) Width: 12-15 mm

Mechanical design

Multi-step endplate design (refer to CLEOIII) Cosθ=0.93 (L 18) Cosθ=0.83 (L 36) The inner diameter: 80 mm The outer diameter: 1,320 mm The length : 1,906 mm (end-plates are included) Stepped endplates: 5 steps are interconnected with

nonmagnetic steel bands via radial screw.

The structure of MDC IV

Layer organization (1)

Small cell configuration with super-layer Small cell configuration with super-layer arrangement is chosen for MDC IVarrangement is chosen for MDC IV

36 sense wire layers 8 sense wire layers: first stepped section, each layer has different number of cells. 8 sense wire layers: from second step to fifth step,every two layers have the same number of cells..

Layer organization (2)

20 sense wire layers: in the plane section,

every four layers have the same number of cells

All cells will be symmetrical at 90° Wire configuration of MDC IV (table.) The z-direction resolution: σz< 3 mm

Layer organization (3)

The Cell configuration of MDC IVlayer wire number R half width w/h

(S+F) (mm) (arc length,mm)F1 84 73 5.460387231S1 84 79 5.909186182 0. 984864F2 96 85 5.563236991S2 96 91 5.955936072 0. 992656F3 108 97 5.643231248S3 108 103 5.992297099 0. 998716F4 120 109 5.707226654S4 120 115 6.021385919 1. 003564F4 120 121 6.335545185F5 136 127 5.867386279S5 136 133 6.144585631 1. 024098F6 148 139 5.901099714S6 148 145 6.155823443 1. 025971F7 160 151 5.929756134S7 160 157 6.165375583 1. 027563F8 176 163 5.819086392S8 176 169 6.033285892 1. 005548F8 176 175 6.247485391F9 180 190 6.632251158S9 180 197 6.876597253 0. 982371F10 180 204 7.120943348S10 180 211 7.365289443 1. 052184F11 208 218 6.585261524S11 208 225 6.796714876 0. 970959F12 208 232 7.008168227S12 208 239 7.219621579 1. 031375F13 232 246 6.662343041S13 232 253 6.851921908 0. 978846F14 232 260 7.041500775S14 232 267 7.231079642 1. 033011F15 256 274 6.724971774S15 256 281 6.896777622 0. 985254F16 256 288 7.068583471S16 256 295 7.240389319 1. 034341F16 256 302 7.412195167

F17 308 318 6.48718483S17 308 325 6.629984496 0. 947141F18 308 332 6.772784162S18 308 339 6.915583828 0. 987941F19 308 346 7.058383494S19 308 353 7.201183161 1. 02874F20 308 360 7.343982827S20 308 367 7.486782493 1. 06954F20 308 374 7.629582159F21 364 382 6.593892273S21 364 389 6.71472276 0. 959246F22 364 396 6.835553246S22 364 403 6.956383733 0. 993769F23 364 410 7.07721422S23 364 417 7.198044706 1. 028292F24 364 424 7.318875193S24 364 431 7.43970568 1. 062815F24 364 438 7.560536166F25 420 446 6.672144398S25 420 453 6.776864153 0. 968123F26 420 460 6.881583908S26 420 467 6.986303663 0. 998043F27 420 474 7.091023418S27 420 481 7.195743173 1. 027963F28 420 488 7.300462928S28 420 495 7.405182683 1. 057883F28 420 502 7.509902439F29 472 510 6.789034972S29 472 517 6.882217805 0. 983174F30 472 524 6.975400638S30 472 531 7.068583471 1. 009798F31 472 538 7.161766304S31 472 545 7.254949136 1. 036421F32 472 552 7.348131969S32 472 559 7.441314802 1. 063045F32 472 566 7.534497635F33 532 574 6.779226252S33 532 581 6.861899743 0. 980271F34 532 588 6.944573234S34 532 595 7.027246725 1. 003892F35 532 602 7.109920216S35 532 609 7.192593707 1. 027513F36 532 616 7.275267198S36 532 623 7.357940689 1. 051134F36 532 630 7.44061418

Drift cell configuration Cell design of the inner layers of MDC IV

Working gas selection (1) Important factors to be considered

• X0 (radiation length)• Vd (drift velocity)• Electric stability• Availability cost

Helium is the only low-z gas condidate• Radiation length: 50times longer (≈5300m) than Argon

(≈110m)

Working gas selection (2)The properties of various He based gas mixture

Gas mixture

Ratio Radiation length

(m)

Primary (i.p./cm)

Total (i.p./cm)

Comment

He/C2H6 50/50 640 22.9 59.9 BELLE

He/iC4H10 90/10 1313 12.7 26.7 KLOE

He/iC4H10 80/20 807 21.2(20.6) (45.4) BABAR

He/CO2/

iC4H10

83/10/7 960 11.5 29.2 BABAR

He/CH4 90/10 3087 (7.0) (12.5) KLOE

He/CH4 80/20 2178 (9.1) (17.0) BTCF

He/C3H8 60/40 550 32   CLEOIII

Working gas selection (3) 60% He-40% propane gas mixture as MDC

IV working gas will be chosen (refer to CLEO III)

• Long radiation length (550m)• A drift velocity that saturates about

4 cm/μs for a relatively low electric field.

Working gas selection (4)

Working gas selection (5) The drift velocity were measured using specially constructed test

chamber.(K.K.Gan ,…,1996)

Working gas selection (6)

A Small prototype for Tau-Charm feasibility study (R&D program)

• Field wires: Al• Working gas: He/CH4 (80/20)

• Cell size: 2×2cm2

• Wire length: 1m The average spatial resolution of

155μm was obtained.

The average time resolution

Low z-field wire (1)Several kinds of light material wires have been proposed and tested.Aluminumwire has a relatively long radiation length and is a good field wire candidate. results of the long term creeping test by BTCF (tension lost <10%)

The observation result for long time creeping of 0.1mm Al wires

Low z-field wire (2)

Low z-field wire (2)

Our choices: (refer to CLEOIII)• Sense wire: 30μm gold-plated tungsten, to maximize

the drift electric field.• Field wire: 110μm aluminum, to reduce the material of

the chamber. A candidate aluminum wire with little creep has been

tested . With the proposed diameter wires, the electric field

strength at the surface of the aluminum field wires is always less than 20kv/cm, a necessary condition for avoiding radiation damage.

Electronics readout

The MDC IV has a total of 5,322 sense wires. Both the time (T) and charge (Q) information

for each wire will be read out.

Since the single wire spatial resolution is designed to be σχ ≤130μm , the time

measurement error from electronics readout ≤ 0.5 ns (20μm) is desirable ,assuming a drift

velocity of = 4 cm / μs.

The charge deposition could be measured by integrating the signal current from sense wires

with an accuracy better than the intrinsic chamber resolution of about 7%. Therefore a

charge measurement with a precision of 2 % is sufficient to match the chamber resolution.

Expected performance

Solid angle coverage Single wire spatial resolution Momentum resolution resolutiondxdE /

Solid angle coverage

As show in Fig. 2, the solid angle coverage in the Layer 18 (sense wire) is cos=0.93 and in the last layer is cos=0.83

Single wire spatial resolution Single wire spatial resolution consists of following terms:

where,

: is the contribution from the diffusion, about 60μm in our case,

: is the contribution from time measurement error of readout electronics, assumed to be 20μm here,

: is the contribution from the statistic distribution of primary ionization electron to the

From the experience of similar chambers, a single wire spatial resolution ≤130μm can be achieved.

2222itdx

dt

ix

x

Momentum resolution (1)

Where , L (lever arm) =56 cm , B ( magnetic field ) = 1.0 Tesla , (spatial resolution)=0.013 cm , N (number sampling) = 30 and ~1 .

Taking the radiation length of gas mixture , , as 550m, and assuming the wire material uniform distributed in the chamber volume, the total is =163 m. The momentum resolution from both contributions can be written as:

So the momentum resolution

can be achieved.

2.

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ptptptpos

5

720103.3)(

2

2

n

pLBpt t

xpos

pt

xppt /

0X0X

ptpt pospt %623.0)(

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ptpt pospt %7.0)(

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LXBpt smpt

Momentum resolution (2) The result from simulation

dE/dx resolution

The dE/dx resolution of CLEO III (experimental results ) is 5% (electrons),

The dE/dx resolution of the MDC IV will be about 7%.

dE/dx resolution (Simulation results)

The main performances of MDC IV are:

single wire position resolution ≤130 µm momentum resolution:

efficient tracking down below 100 Mev/c dE/dX resolution around 7% the solid angle coverage is cos=0.93 The z-direction resolution: σz< 3 mm

(

222 %)5.0(%)7.0()/( PP

R&D program

Geometry of the MDC IV chamber Cell and layer organization Track reconstruction and full simulation Cooperation with CLEO III and other

experiments Prototype making and testing

R&D program (continue)

In process: Feedthrough: Designing, making capability

investigation, Structure: Designing & Simulation with

ANYSYS, Cell : Designing & Garfield Simulation, Wire: Creeping test ,Crimping tool

investigation, Prototype : Designing & preparation.

Time schedule

items Time(year)

R&D and chamber design 1.5

Machining 1.5

Assembly and wiring 1

testing 0.5

total 4.5

The end

Thanks a lot !

ReferentsFrom [email protected] Tue Sep 25 09:56:09 2001Date: Mon, 24 Sep 2001 15:35:53 -0400 (EDT)From: [email protected]: [email protected]: Re: layer spacings

The only place that I have heard about gas cooling was in the BESS-III April

description. I recommended that you do not cool the gas. Instabilities in the cooling system could lead to rapid temperature changes of thewires which could lead to broken wires. CLEO does not cool the gas.The CLEO gas system recirculates the gas. In the process of recirculationwe remove oxygen and restore the helium to propane ratio to the

specified level. The system was built by a SLAC group, lead by Martin Perl,which is a part

of CLEO. The total cost was $250,000. I do not have a reference.

R&D:900k Endplates:5,500k Inner cylinder:30k Outer cylinder:200k Feedthrough:1,600k Wires:400k Assembly:500k Wiring:1,800k(clean room,wiring machine,manpower) High voltage boards and cables:700k Gas system:1,000k Cosmic ray test:200k Scientific exchanging and others:300k No predict:800k Total:13,930 K

Cost estimate (in RMB)

MDC4 的工作计划

2 0 0 1 2 0 0 2 2 0 0 3 2 0 0 4 2 0 0 59 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12

物理设计结构设计M.C.模拟静电学计算单元结构模拟计算定位子设计定位子试制和加工铝丝试验模型研究数据处理的准备密封胶的试验气体系统的研究气体系统的设计气体系统的加工室体的设计和计算台阶的机械模型室体的加工拉丝方法的研究拉丝机的设计拉丝机的加工高压和信号引出研究高压和信号板的设计高压和信号板的加工清洁间的准备予应力的准备调装和拉丝的准备室体调装和清洁拉丝和测量宇宙线试验