BES III Main Drift Chamber

MDC groupYuanbo Chen

June 5,2002, Beijing

  General consideration The main functions are:

1. Precise momentum measurement accuracy, with particular emphasis on minimizing the effects of multiple Coulomb scattering;

2. Adequate dE/ dx resolution for particle identification; Short tracks from interaction point can be reconstructed;

3. Charged particle trigger can be realized;

4. Maximum-possible solid angle subtended in the barrel region ( ～ 90%4 π Str.)

General consideration The drift chamber must be : 1. In the limited space, arrange more readout layers,and less m

aterials inside;2. To have a possible big solid angle, the end-plates of the drift

chamber should be adopted a special shape;3. Have enough accuracy for wire location; 4. Obtain good hit efficiency, a uniform time-to-distance relati

on and a uniform dE/dx collection region. 5. For the trigger requirement, the drift cell number in one laye

r should have good symmetry alignment, and super-layer arrangement will be adopted.

General consideration The inner diameter of the drift chamber is limited t

o 118 mm by the beam pipe and the assembly procedure for the interaction quadrupole. The physical outer diameter is 1600 mm to satisfy the physical requirements. The length is 2400 mm for the outer polar angle at .

The drift chamber is a most inner sub-detector of BESIII detector. It is designed in two parts, inner chamber and outer chamber. The consideration is that the inner chamber can be replaced if needed.

830.cos

MDC structure design.

  The drift cell Small cell construction ( square cell ). Average cell half height is 6 mm in the inner

chamber; 7mm for the outer chamber. Width / height of the cell is nearly equal. Two kinds of wires are selected for the drift

chamber, the sense wire is 30μm Gold-plated tungsten and the field wire is 110μm gold-plated aluminum wire.

The drift cell

The position resolution/drift distance(CLEOIII)

The layer arrangement There are altogether 47 sense wire layers in the drift chamber, 8 layers in the

inner chamber and 39 layers in the outer chamber. The stereo wire layers are necessary to provide longitudinal measurements in

the drift chamber. For measuring the small incident angle particles, 8 layers are stereo layers in the inner chamber, and 20 stereo layers in the outer chamber. There are 19 axial layers in the outer chamber for trigger and reconstruction.

The axial layers and stereo layers are arranged alternately according the super-layers.

All cells in the inner chamber will be symmetrical in 45 °. All cells in the outer chamber will be symmetrical in 11.25 ° except stepped

range. All cells in the stepped range are symmetrical in 22.5 °(30°). The axial layer will have to start at a small angle with the X-axis.

The layer arrangement

The layer arrangementF24 436. 3 384 7.14 7 78. 422 1. 953 1. 766 3. 813F25 443 448 6.21 6.7S25 449. 4 448 6.3 6.4 0. 984F26 455. 8 448 6.39 6.4S26 462. 3 448 6.48 6.5 0. 997F27 468. 8 448 6.57 6.5S27 475. 5 448 6.67 6.7 0. 996F28 482. 2 448 6.76 6.7S28 489. 1 448 6.86 6.9 0. 994F28 496 448 6.96 6.9F29 502. 9 448 7.05 6.9 91. 564 2. 28 2. 088 3. 265S29 510 448 7.15 7.1 1. 007 92. 857 2. 312 2. 118 3. 22F30 517. 1 448 7.25 7.1 94. 15 2. 344 2. 147 3. 176S30 524. 4 448 7.35 7.3 1. 007 95. 479 2. 377 2. 178 3. 132F31 531. 7 448 7.46 7.3 96. 808 2. 41 2. 208 3. 089S31 539. 2 448 7.56 7.5 1. 008 98. 173 2. 444 2. 239 3. 046F32 546. 7 448 7.67 7.5 99. 539 2. 478 2. 27 3. 004S32 554. 4 448 7.78 7.7 1. 01 100. 94 2. 513 2. 302 2. 962F33 561. 8 512 6.89 7.4 89. 531 2. 229 1. 786 3. 34S33 568. 8 512 6.98 7 0. 997 90. 647 2. 257 1. 809 3. 299F34 575. 8 512 7.07 7 91. 762 2. 285 1. 831 3. 258S34 583 512 7.15 7.2 0. 993 92. 91 2. 313 1. 854 3. 218F35 590. 2 512 7.24 7.2 94. 057 2. 342 1. 877 3. 179S35 597. 5 512 7.33 7.3 1. 004 95. 221 2. 371 1. 9 3. 14F36 604. 8 512 7.42 7.3 96. 384 2. 4 1. 923 3. 102S36 612. 3 512 7.51 7.5 1. 001 97. 579 2. 429 1. 947 3. 064F37 619. 5 576 6.76 7.2 87. 776 2. 186 1. 557 3. 406S37 626. 4 576 6.83 6.9 0. 99 88. 754 2. 21 1. 574 3. 369F38 633. 3 576 6.91 6.9 89. 732 2. 234 1. 591 3. 332S38 640. 3 576 6.98 7 0. 997 90. 724 2. 259 1. 609 3. 296F39 647. 3 576 7.06 7 91. 715 2. 284 1. 626 3. 26S39 654. 4 576 7.14 7.1 1. 006 92. 721 2. 309 1. 644 3. 225F40 661. 5 576 7.22 7.1 93. 727 2. 334 1. 662 3. 19S40 668. 8 576 7.3 7.3 1 94. 762 2. 359 1. 68 3. 155F40 676. 1 576 7.38 7.3 95. 796 2. 385 1. 699 3. 121F41 682. 9 640 6.7 6.8S41 689. 7 640 6.77 6.8 0. 996F42 696. 5 640 6.84 6.8S42 703. 4 640 6.91 6.9 1.001F43 710. 3 640 6.97 6.9S43 717. 4 640 7.04 7.1 0. 992F44 724. 5 640 7.11 7.1S44 731. 7 640 7.18 7.2 0. 997F45 738. 9 640 7.25 7.2S45 746. 2 640 7.33 7.3 1.004F46 753. 5 640 7.4 7.3S46 760. 9 640 7.47 7.4 1. 009F47 768. 3 640 7.54 7.4S47 775. 9 640 7.62 7.6 1.003F47 783. 5 640 7.69 7.6信号丝:9096,场丝29800,共38896

layer R Wire N half width H(mm) w/h a ε δ σ z(mm) (F+S) (arc l ,mm) (mm) (degree) (mm) (mm)

F1 77. 5 80 6.09 30. 239 2. 331 1. 489 3. 194S1 84 80 6.6 6.5 1. 015 32. 775 2. 526 1. 614 2. 947F2 90. 1 96 5.9 6.1 29. 354 2. 203 1. 203 3. 379S2 96. 3 96 6.3 6.2 1. 016 31. 374 2. 355 1. 286 3. 162F3 102. 3 112 5.74 6 28. 601 2. 092 1. 004 3. 559S3 108. 3 112 6.08 6 1. 013 30. 279 2. 215 1. 063 3. 362F4 114. 1 128 5.6 5.8 27. 934 1. 992 0. 858 3. 737S4 120 128 5.89 5.9 0. 998 29. 379 2. 095 0. 902 3. 553F5 125. 8 144 5.49 5.8 27. 391 1. 906 0. 748 3. 906S5 131. 5 144 5.74 5.7 1. 007 28. 632 1. 993 0. 782 3. 737F6 137. 2 144 5.99 5.7 29. 873 2. 03 0. 815 3. 669S6 143. 4 144 6.26 6.2 1. 01 31. 223 2. 121 0. 852 3. 51F7 149. 4 160 5.87 6 29. 288 1. 944 0. 719 3. 831S7 155. 5 160 6.11 6.1 1. 002 30. 483 2. 023 0. 749 3. 68F8 161. 5 176 5.77 6 28. 789 1. 867 0. 643 3. 987S8 167. 5 176 5.98 6 0. 997 29. 859 1. 937 0. 667 3. 844F8 173. 5 176 6.19 6 30. 929 2. 006 0. 691 3. 711F9 204. 5 192 6.69 31S9 211. 4 192 6.92 6.9 1. 003F10 218. 3 192 7.14 6.9S10 225. 6 192 7.38 7.3 1. 011F11 232. 7 224 6.53 7.1S11 239. 5 224 6.72 6.8 0. 988F12 246. 4 224 6.91 6.9S12 253. 5 224 7.11 7.1 1. 001F13 260. 6 256 6.4 7.1S13 267. 3 256 6.56 6.7 0. 979F14 274. 1 256 6.73 6.8S14 281. 1 256 6.9 7 0. 986F15 288. 1 288 6.29 7S15 294. 5 288 6.42 6.4 1.003F16 301. 2 288 6.57 6.7S16 308 288 6.72 6.8 0. 988F16 314. 8 288 6.87 6.8F17 327. 5 320 6.43 12.7 70. 598 1. 758 1. 908 4. 235S17 334. 1 320 6.56 6.6 0. 994 72. 02 1. 794 1. 946 4. 152F18 340. 7 320 6.69 6.6 73. 443 1. 829 1. 985 4. 071S18 347. 5 320 6.82 6.8 1. 003 74. 909 1. 865 2. 024 3. 992F19 354. 3 320 6.96 6.8 76. 375 1. 902 2. 064 3. 915S19 361. 4 320 7.1 7.1 1 77. 905 1. 94 2. 105 3. 838F20 368. 5 320 7.24 7.1 79. 436 1. 978 2. 147 3. 764S20 375. 8 320 7.38 7.3 1. 011 81. 009 2. 017 2. 189 3. 691F21 382. 7 384 6.26 6.9 68. 788 1. 713 1. 549 4. 347S21 389. 1 384 6.37 6.4 0. 995 69. 938 1. 742 1. 575 4. 275F22 395. 5 384 6.47 6.4 71. 089 1. 77 1. 6 4. 206S22 402. 1 384 6.58 6.6 0. 997 72. 275 1. 8 1. 627 4. 137F23 408. 7 384 6.69 6.6 73. 461 1. 829 1. 654 4. 07S23 415. 5 384 6.8 6.8 1 74. 684 1. 86 1. 681 4. 004F24 422. 3 384 6.91 6.8 75. 906 1. 89 1. 709 3. 939S24 429. 3 384 7.02 7 1. 003 77. 164 1. 922 1. 737 3. 875

Low Z working gas The helium gas is only low Z working gas. It has a

radiation length about 50 times longer (≈ 5300 m) than Argon gas (110m) ;

We chose 60%He-40% propane gas mixture , same as CLEOIII.

Low Z field wire 110 μm gold-plated Aluminum wire. California Fine Wire, Al5056, 0.75 μm Au,

Ni flash, “ultra-finish”

The feedthrough design The design of the feedthrough is referenced the feedthrough use

d in CLEO III drift chamber. Three parts:

1. The outer side is insulating bush for high voltage insulation;

2. The middle part is copper tube for inner tube location and a connector of high voltage;

3. The inner part is small tube for wire fixing, copper for sense wire and aluminum for field wire.

The cramping method will be used to fix wire in the inner tube.  The material of the insulating bush is Vectra A130, a kind of liq

uid crystal copolyester.

The feedthrough design

  The mechanical design (Inner chamber )

To reduce materials ,the inner chamber is designed as an open cylinder, no outer skin. All wire tension in the inner chamber will be transferred to the inner skin.

It will be a whole chamber after the inner chamber is connected to the outer chamber. However, the deformation caused by wire tension in the inner chamber and the outer chamber will not be the same. It has to be considered in the design, and attention should also be paid to the helium gas leakage. The optimum connection design will be done based on the ANALYSIS simulation.

Inner chamber

The mechanical design (Outer chamber )

The inner radius of the outer chamber is to 198 mm, the outside radius is 810 mm. The length of the inner skin of the outer chamber is 1180 mm, the length of the outer skin of the outer chamber is 2400 mm. The polar angle is COSθ= 0.93, and a large acceptance of COSθ=0.83 in last sense wire layer.

An inner skin of the outer chamber is necessary to conquer the deformation in the inner radius. In order to reduce materials in the working range, the thickness should be as thinner as possible. The thickness of the inner skin will be 0.5 mm carbon fiber according to the calculation. The thickness of the outer skin, made of aluminum (Al 5056), is 10 mm (the TOF detector will be banded on the surface of the outer skin).

Outer chamber

The multi-step endplate The endplate of the outer chamber is separated to two parts,

one is the multi-steps, and an inclined plane. The design of the multi-step part has to guarantee the polar

angle in COSθ= 0.93 , to accommodate the interaction quadrupole, and to have space for cables.

The stepped endplate is a set 4 aluminum rings interconnected with nonmagnetic steel bands via radial screws. Every ring is for holding 2 sense wire layers.

The multi-step endplate

The inclined plane endplate The another part of the endplate is design to inclined plane,

by reason of reducing deformation caused by wire tension. The inclined plane is processed from a whole aluminum plate (Al-5056). It will be processed to some mini -steps to guarantee all feedthroughs are located in parallel with Z axis.

The thickness of the endplate is 25 mm.

The inclined plane endplate

inner support ring

Radius=810mm

Radius=310mm

chamber gas volume this side

Structural analysis of the drift chamber axial stability analysis of inner cylinder (she

ll) stability safety factor is ：

So the inner cylinder is steady enough.

428356

8310105.

.

T

Tcr

  Analysis of outer chamber The max deformation of outside of endplate is

2.44mm is excessive than 1mm. What we should do for reducing the deformation is to add the inner cylinder support to endplate

Analysis of outer chamber

Inner skin is 0.5mmMaximal deformation in axial direction is 0.985mm 。 Inner skin is 0.8mm

Maximal deformation in axial direction is 0.919mm 。

The drift chamber wiring inner chamber:

It is simple to stretch wires in the inner chamber, because there is no outer skin. During the wiring procedure, the inner chamber will be installed on a rolling support.

There will have 40,000 wires for the inner chamber and the outer chamber.

The total wire tension is nearly 8.5 ton. To guarantee a uniform wire tension in the chamber, pre-

stress method will be used in the wiring.

The drift chamber wiring The outer chamber will be set up in vertical

for wiring. There is a special support to hold the outer chamber. The chamber can be rotated as needed during wiring. The support is showed in the figure.

The outer chamber wiring

High voltage system A positive high voltage will be connected to the

sense wire to form a drift field in the drift cell. An RC low pass filter is used for each supply at

the drift chamber end plate before distribution to the chamber wires.

High voltage power supply system

Principle diagram of the high voltage power supply system

The electronics readout The BES III drift chamber has total of 9096 sense wires, time

( T ) and electric charge ( Q) information of each sense wire will be read out.

Since the single wire spatial resolution is designed to be , the time measurement error from electronics readout <1 ns is desirable, assuming a drift velocity of 3.8cm/μs.

The charge deposition could be measured by integrating the signal from sense wire with the accuracy better than the intrinsic resolution of about 6%. Therefore a charge measurement with a precision of 2% is sufficient to match the chamber resolution.

m130

Expected performances Solid angle coverage The solid angle coverage in the layer 17 (sense wire) is

and in the last sense wire layer is .830.cos

930.cos

Single wire spatial resolution

The single wire Z-direction resolution According to the experience formula, , L is the

half length of the wire, D is the movement of the stereo wire along the circle. There are 28 layers of stereo wires in the chamber, of each layer is listed in the table.

Z resolution is decided by stereo wire layers. From TRACKERR the Z resolution of the chamber ≤3mm.

xz DL )/(2

Momentum resolution

Where , L (lever arm) = 80 cm , B ( magnetic field ) = 1.0

Tesla , x (spatial resolution)=0.013 cm , N (number

sampling) = 40 and ppt/ ~1 .

Taking the radiation length of gas mixture , 0X, as 640

m[1], and assuming the wire material uniform distributed in

the chamber volume, the total 0X is =184.5 m. The

momentum resolution from both contributions can be written

as:

  Momentum resolution The TRACKERR program was developed by Barba drift chamber gro

up to quickly simulate the performances of the chamber. The momentum resolution of BES III drift chamber was simulated by the TRACKERR , , at 1Gev/c,

%.510t

pt

p

The dE/ dX resolution From the calculation, is 4.7% for the 1.2 cm long sample, and

is 4.5% for the 1.4 cm long sample in He/C3H8 (60/40) gas mixture. In the 1.2 cm long sample, 3 π / K and π / p separation momentum is 0.80 GeV/ c with 1.35 GeV/c respectively. In the 1.4 cm long sample, 3 π / K and π / p separation momentum is 0.81 GeV/ c with 1.40 GeV/ c respectively.

The dE/ dX resolution is expected to be 6-7%.

The dE/ dX resolution

( a) Calculated probable energy loss as a function of P , in 1.2 cm sample length. (b) The particle identification capability.

mpE

(a) Calculated probable energy loss as a function of P ,in 1.4 cm sample length. (b) The particle identification capability.

mpE

The R & D programs Geometry of the drift chamber. According to the measurement of the MIcr

o-β, with references to the endplate of CLEO III drift chamber, BES III drift chamber structural design will be done ,and all factors will be more detail studied.

Cell and layer organization. The optimum ratio of field wires to sense wires , cell size , type of layers -axial and stereo and the arrangement will be evaluated before a final design is chosen.

Track reconstruction and full simulation are needed. Cooperation with CLEO III and BELLE experiments. We will make the wi

dest possible use of successful technology to design our drift chamber. This is important to reduce the R&D time and to perfect drift chamber structural design and manufacture.

Prototypes & beam test.

Progress plan

The end

Thanks a lot!

Radiation Length 0.5 mm carbon fiber ( =0.222m) ~0.225%

800 mm (radius) ( =184.5 m) ~ 0.43%

10 mm outer cylinder( =0.089 m) ~ 11.23%

0X 0X

0X 0X

0X 0X

The parameters of wires

wire category

Material

Diameter( μ m) Linear density( g/ m)

Sense wire

Gold-plate

tungsten wire

30 13.6345×10-3

Field wire

gold-plate

aluminum

wire

110 28.18×10-3

Low Z working gasThe different He

Gas mixture

Ratio

Radiation

length(m)

Primary(i.p./cm)

Total(i.p./cm)

Comment

He/C2H6 50/5 640 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

Low Z working gas

1. 5

2. 0

2. 5

3. 0

3. 5

4. 0

4. 5

0 1 2 3 4 5 6 7E/ P (V/ cm Torr)．

Dri

ft v

elo

city

(cm

/us)

100

150

200

0 1 2 3 4 5 6 7

E/ P (V/ cm Torr)．

Longitudin

al d

iffusi

on p

er

cm (

um

)

0

5

10

15

20

25

30

35

0 1 2 3 4 5 6 7E/ P (V/ cm Torr)．

Lore

ntz

angle

( d

egre

es)

Low Z working gas

Electrons drift line (from field wires)

Electrons drift line(from the cell)

Electrical field X-T relation

Low Z field wire Fig. shows the creeping result from the Al wire using in the CLEO III

drift chamber.

Low Z field wire Several kinds of light material wires have been proposed

and tested. Aluminum wire has a relatively long radiation length and is a good field wire candidate. CLEO II reported that a long-term creeping effect of partial tempered 5056-Al field wire was observed (less than 15% tension reduction). Several other experiments like BELLE, BABAR, and KLOE have also reported their measurements on the creeping of this kind of wires .

The thickness of the endplate is 25 mm, and the material is aluminum Al-2024. The joint space is limited by half width of the cell (7 mm), so the thickness of steel bands will be limited to 1.5 mm. The multi-step endplate is a challenge to the mechanical manufacture.

The drift chamber assembling The outer chamber endplate installation

The assembling accuracy of the multiple steps will directly affect the wire position accuracy in the chamber. The tolerance of wire holes in every ring is 25μm. For the demand of the single wire position, all wire hole position tolerance should be below 60μm. A method has to be studied to guarantee the assembling accuracy of multiple steps.

The drift chamber assembling The inner chamber endplate installation The endplate of the inner chamber is processed

from a whole aluminum plate, and all wire holes are finished in a digital mechanical center, the hole tolerance could be controlled at 25μm. Because there is no outer skin for the inner chamber, two endplates are only jointed with the inner skin. It is a key point to guarantee two endplates will be paralleled in 250μm and the concentricity will be less than 100μm in a limited connection area.