CryoUpdate

Alan BrossMICE Tracker Phone Meeting

September 8, 2006

Status

Essentially all the parts have arrived We are still having problems with the brazing of the studs

Cracking of the invar envelop has caused leaks to develop “Work-in-Progress”

It was decided to reassemble the system with the new cassette (112), MICE cassette #3 and reassemble but this time try to flow the indium ribbons that sits between the copper thermal links and the VLPC cassette invar envelop and do not attempt stud brazing for now. The flow was accomplished with heat from a heat gun and/or iron using a dummy cassette in the cassette space.

This process yielding promising results (visually) Good apparent contact between the thermal link and the invar

It was decided to proceed to full assembly and then cooldown

Cooldown

From Russ The cryostat now appears to be as cold as it is going to get.  I am a bit puzzled by the temperatures.    The upper thermal link is running a few Kelvin warmer and

with more gradient than previous operations.  T4(stage 1) = 49.2 K and T3 (near envelope) = 58.6 K.  The delta T

across the link is 9.3 K now versus 7.6 K in Jan. 06 and 6.7 K in April 05.  The temperature gradient indicates that the upper link is taking out 20% more heat (watts) than previous operating periods.

– This is usually a GOOD sign! 

The lower thermal link temperatures are 1.7 Kelvin warmer but have the same gradient as previous operations. 

T1(stage 2) = 7.12 K and T2 (near envelope) = 7.26 K.  The delta T = 0.14 K.  For comparison in April 05, T1 = 5.27 K and T2 = 5.40 K.  In Jan. 06, T1=5.40 K and T2 = 5.54 K.

7k is too warm for good operation (will be worse @ 60Hz)

Cooldown II

MICE cryostat cooldowns

0

50

100

150

200

250

300

350

0 5 10 15 20 25 30

Time (hrs)

Te

mp

era

ture

(K

elv

in)

9_5_06 T1 9_5_06 T3 4_28_05 T1 4_28_05 T3 4_20_05 T1 4_20_05 T3

T1 is on stage 2 coldheadT3 is on upper thermal link near envelope

Cooldown III

MICE cryostat cooldowns

0

5

10

15

20

25

30

0 5 10 15 20 25 30

Time (hrs)

Te

mp

era

ture

(K

elv

in)

9_5_06 T1 9_5_06 T3 4_28_05 T1 4_28_05 T3 4_20_05 T1 4_20_05 T3

T1 is on stage 2 coldheadT3 is on upper thermal link near envelope

Won’t Make It

Next Step

READ OUT CASSETTE TEMPERATURES! Maybe this will help illuminate what is going on Possible problems include

Bad thermal link to the cryo-cooler head Cryo-cooler malfunction High heat leak in new cassette (112) Bolts loosened ????

This will not speed things up

And So It Goes