Hamamatsu R7525HA: outer conductive coating with insulating sleeveCC: convex-concave window 0.5-0.6 mm thick (standard

plano-concave: 1mm center, 6.1 mm edge)μ: soft mu-metal shield wrap2700 units3 month lead time ARO200 units/month delivery rate

Each Total

R7525 HA $246.41 665 k$

R7525 HA-μ $265.55 717 k$

R7525 CC-HA $360.29 973 k$

R7525 CC-HA-μ $ 377.64 1020 k$

Neutrons on Glass• PMT window materials (silica and

borosilicate) were studied in a reactor and compared with other data

• 6 x 1012 n/cm2• 4.1 x 1013 n/cm2(Hamamatsu

points at 14 MeV, red)• 2.5 x 1014 n/cm2(Hamamatsu

points at 14 MeV, blue)• 6 x 1014 n/cm2

– Expected total neutron fluence at the PMTs is 2.5 x 1012 n/cm2 in 10 years (E>100 keV 1.6x1012, E>20 MeV 5.1x1011)

– Expect transmission loss of a few percent over ten years;

– not a problem.

40

50

60

70

80

90

100

390 410 430 450 470 490 510 530 550 570 590 610 630 650 670 690

Boro 0 n

Boro 6 x 10̂ 12 n

Boro 6 x 10̂ 14 n

Quartz 0 n

Quartz 6 x 10̂ 12 n

Quartz 6 x 10̂ 14 n

Is Boron in Window a problem?• B10

5 + n10 -> Li7

3+42+2.792 MeV (gnd state) 6%

• B105 + n1

0 -> *Li73+4

2+2.310 MeV (ex state) 94%

• E = 1.47 MeV ELi = 0.84 MeV

• The natural abundance of B105 is 19.8 %

• Alpha particle ranges out in ~450 m

• *Li gives out 0.43 MeV gamma with ~ 10-13 sec

• For thermal neutrons (< 0.025 eV), ~ 3840 b

• At PMT location, n ~ 10 kHz/cm2

• d/dt = n A D N ~ 1000 /sec, E = 1.47 MeV

• Tmax ~ 2 mec222 ~ 0.8 keV

• R ~ 0.7 T 1.7 ~ 88 nm

• Cook all of these numbers with simulation and get

– Alphas produced in glass = 1000 /sec

– Alphas entering photocathode = 226 /sec

– Electrons entering PMT/ = 18

– Electrons with E<100 eV / = 12

• Conclusion is that there will be ~0.02 alphas per event per HF side with a mean energy of 12 GeV. This is not a problem and verified with MC.

Radiation Backgrounds around PMTs• This problem has been recently revisited and the present shielding system looks OK (20

cm steel, 18 cm polyethylene, 2 cm aluminum). The holes (~2.5 cm dia.) for the light guides are included in the these calculations. The charged hadrons and neutrons are ~100 Hz/cm2. The photon rate is higher at 10000 and we are trying to do something about that.

• The PMT window is a potential source for Cherenkov radiation from charged particles. – 2x1010 ch/cm2 for 10 years give ~10-5 PMTs/xing. If 20 pe/PMT (1-3 mm thick window), 2x10-4

pe/(xing PMT)– If an isolated particle hits a PMT window, it would represent ~80 GeV.

Other Issues

• Scintillation of the PMT window is only a concern if the dose rate is >0.03 rad/sec. For HF, the estimate is 0.00002 rad/sec (factor of 1000 less).

• Ambient He partial pressure in air (0.53 Pa) will not be a problem with borosilicate window. Partial pressure will change 10 times in 10 years but will remain below the danger level by a factor of ~50000.

• Nitrogen gas will be circulated inside the ROBox against He leak from cryogenics and temperature fluctuations (+/- 2 degrees should not be a problem).

HammamatsuItem Specifications R7525

Anode current vs. cathode position

+- 20%, 3mm spot +- 30%, 3mm spot

Gain 105 at 75% VKA(max 105 at 80% VKA

Single pe resolution 50% or better 65% or better

Stability +-3% within any 48 hour OK after 10 hr. warmup

Envelope Opaque and conductive Graphite +PVC

Window Planer or convex Convex cost + 50%

Samples are on hand

PhotonisItem Specification XP2960 XP3182

Pc diameter 22-28 mm 23 mm 21 mm

Gain 104-105 2x104-2x106 105-106

Transit time <25ns preferred

19 ns 33 ns

Pe resolution 50% or better 70% 70%

Convex-concave window is not available.Samples are being sent.

Electron Tube

Two candidates, D843WSB and D844WSB, meet all preliminary specifications, with no exceptions noted. Final data sheets not yet in hand.

Both tubes come with 1 mm convex-concave windows of uv-transmitting glass.

843 longer with better linearity range and lower after each pulse.

844 shorter with better rise time and transit time.Samples are being sent

Lifetime - I

• Aging is suspected to be dependent on the total accumulated charge. Charge rate is not relevant at 10 micro amps average anode current.

3600 C(~40%)

360 C(~10%)

180 CSAFE

Iave = 0.1 mA

Lifetime - II

260 C(~15%)

26 C

• These estimates are based on 0.25 pe/GeV and gain of 4x104 for ten calendar years.

• There does not seem to be a drastic problem with PMT aging based on what we know now.

• The gain loss is recoverable by voltage increase.

Magnetic Field• The external magnetic field around the ROBox region is small (<0.0023 T).

Therefore it is not difficult to magnetically shield the PMTs to satisfactory levels.

• Shielding factor = 3t/4r ~3000 for the mu-shield and there is another factor of 4 from the soft iron tube around the PMTs which results in the effective suppression factor of 12000.

Rise Time

0

0.5

1

1.5

2

2.5

3

3.5

700 900 1100 1300 1500

High Voltage (Volts)

Ris

e T

ime

(ns)

ZC9957

ZC9903

ZC9900

ZC9898

D843WSB

D844WSB

Transit Time

0

5

10

15

20

25

30

600 800 1000 1200 1400 1600

High Voltage (Volts)

Tra

nsi

t T

ime

(ns) ZC9957

ZC9903

ZC9900

ZC9898

D843WSB

D844WSB

Pulse Width

0

1

2

3

4

5

6

7

8

9

600 800 1000 1200 1400 1600

High Voltage (Volts)

Pu

lse

Wid

th (

ns

)

W ZC9957W ZC9903W ZC9900W ZC9898W D843WSBW D844WSB

Anode Currents

0.1

1

10

100

1000

600 800 1000 1200 1400 1600

Voltage (V)

mic

ro A

mp ZC9903

ZC9900

ZC9957

ZC9898

D843WSB

Hamamatsu gain

1000

10000

100000

1000000

10000000

600 800 1000 1200 1400 1600

Voltage (V)

gai

n

ZC9957

ZC9903

ZC9900

ZC9898