CEBAF cryo requirements

J. Benesch

for Accelerator Operations

2K flow during 6 GeV run

~225 g/s with FEL dynamic load (R4XX) on, 215 g/s with FEL dynamic load off

Using R. Walker’s 665 W static+dynamic and 19 W/(g/s) for FEL, CEBAF ~190 g/s.

Preconditions for 6 GeV run

• in situ Q0 measurement with JT valves to improve

accuracy of heat load calculations

• accept higher trip rate; reduce gradient of or turn off low Q

cavities with high gradient capability

• accept higher trip rate; reduce gradients of C-50 cavities

which would otherwise require more than 168 W/zone

(MOPS limit)

Changes since 6 GeV run

• Ten cryomodules cycled to 300K. Resulting Q0s are still

being measured, but many are lower and none improved.

• Admiral replaced first 7-cell cryomodule in slot SL21.

– Three of five cavities measured so far are at half last-measured Q,

~2e9 now.

– Gradient lowered in two of these three and one other to prevent

LHe boiling.

– CM at 300K during move from FEL.

• For C25 modules, gradients at which field emission causes

arc fault every two days dropped 7% after 300K cycle.

More field emission = more heat; not yet quantified.

TN-10-008 http://www1.jlab.org/Ul/Publications/view_pub.cfm?pub_id=9288

Basic equation

P = (E2l)/(Q(r/Q))

(r/Q) shunt impedance from cavity design

l cavity length

E gradient, V/m

Q cavity quality factor Q0

example: E= 6.9 MV/m, l=0.5m, (r/Q)=960 ohms/m, Q=4.5e9

P= (6.9e6)2*0.5/(960*4.5e9)=2.38e13/4.32e12=5.5W

C100 cavities have r/Q = 1241 ohms/m, lower loss at fixed E

Cavity E and Q are distributions which must be taken into

account if any estimate is to be realistic.

Q0 distribution – C25 modules

-2.33

-1.64

-1.28

-0.67

0.0

0.67

1.28

1.64

2.33

0.5

0.8

0.2

0.05

0.01

0.95

0.99

Norm

al Q

ua

ntil

e P

lot

1e+9 3e+9 5e+9 7e+9

100.0%

99.5%

97.5%

90.0%

75.0%

50.0%

25.0%

10.0%

2.5%

0.5%

0.0%

maximum

quartile

median

quartile

minimum

8.25e+9

8.25e+9

8.25e+9

8.25e+9

5.9e+9

4.6e+9

3.4e+9

2.8e+9

1.68e+9

6.66e+8

6e+8

Quantiles

Mean

Std Dev

Std Err Mean

Upper 95% Mean

Lower 95% Mean

N

4.8042e+9

1.8277e+9

119992166

5.0406e+9

4.5678e+9

232

Moments

Q0

Distributions

Includes 29 suspect high-Q measurements capped at 8.25e9. There were only a

few this high during initial commissioning, not 10%.

Q0 distribution – C25 modules (2)

-2.33

-1.64

-1.28

-0.67

0.0

0.67

1.28

1.64

2.33

0.5

0.8

0.2

0.05

0.01

0.95

0.99

Norm

al Q

ua

ntil

e P

lot

10

20

Cou

nt

1e+9 3e+9 5e+9 7e+9

Normal(4.39e+9,1.41e+9)

Mean

Std Dev

Std Err Mean

Upper 95% Mean

Lower 95% Mean

N

4.3947e+9

1.4131e+9

99425202

4.5907e+9

4.1986e+9

202

Moments

Location

Dispersion

Type

µ

s

Parameter

4.3947e+9

1.4131e+9

Estimate

4.1986e+9

1.2874e+9

Lower 95%

4.5907e+9

1.5662e+9

Upper 95%

-2log(Likelihood) = 8948.94091039153

Parameter Estimates

Shapiro-Wilk W Test

0.991162

W

0.2558

Prob<W

Note: Ho = The data is from the Normal distribution. Small

p-values reject Ho.

Goodness-of-Fit Test

Fitted Normal

Q0

Distributions

C25 measurements less suspect high-Q values. Normal distribution.

For simulation, use mean 4.5e9, 1.4e9 partially accounting for 8.25e9 points removed

Q0 distribution – C50 modules

-2.33

-1.64

-1.28

-0.67

0.0

0.67

1.28

1.64

2.33

0.5

0.8

0.2

0.05

0.01

0.95

0.99

Norm

al Q

ua

ntil

e P

lot

1e+9 3e+9 5e+9 7e+9

100.0%

99.5%

97.5%

90.0%

75.0%

50.0%

25.0%

10.0%

2.5%

0.5%

0.0%

maximum

quartile

median

quartile

minimum

8.25e+9

8.25e+9

8.25e+9

6.18e+9

5e+9

3.75e+9

3.1e+9

2.5e+9

1.8e+9

1.4e+9

1.4e+9

Quantiles

Mean

Std Dev

Std Err Mean

Upper 95% Mean

Lower 95% Mean

N

4.1651e+9

1.537e+9

171838347

4.5072e+9

3.8231e+9

80

Moments

Q0

Distributions

Includes 4 suspect high-Q measurements capped at 8.25e9.

None were seen above 7e9 in initial commissioning.

Q0 distribution – C50 modules (2)

-2.33

-1.64

-1.28

-0.67

0.0

0.67

1.28

1.64

2.33

0.5

0.8

0.2

0.05

0.01

0.95

0.99

Norm

al Q

ua

ntil

e P

lot

5

10

15

Cou

nt

1e+9 3e+9 5e+9 7e+9

Normal(3.95e+9,1.25e+9)

Mean

Std Dev

Std Err Mean

Upper 95% Mean

Lower 95% Mean

N

3.9501e+9

1.2456e+9

142878858

4.2348e+9

3.6655e+9

76

Moments

Location

Dispersion

Type

µ

s

Parameter

3.9501e+9

1.2456e+9

Estimate

3.6655e+9

1.0742e+9

Lower 95%

4.2348e+9

1.4825e+9

Upper 95%

-2log(Likelihood) = 3397.99555909662

Parameter Estimates

Shapiro-Wilk W Test

0.977144

W

0.1862

Prob<W

Note: Ho = The data is from the Normal distribution. Small

p-values reject Ho.

Goodness-of-Fit Test

Fitted Normal

Q0

Distributions

C50 measurements less suspect high-Q values. Normal distribution.

For simulation, use mean 4.0e9, 1.3e9 partially accounting for 8.25e9 points removed

Gradients – C25 modules

-2.33

-1.64

-1.28

-0.67

0.0

0.67

1.28

1.64

2.33

0.5

0.8

0.2

0.05

0.01

0.95

0.99

Norm

al Q

ua

ntil

e P

lot

10

20

30

40

Cou

nt

3 4 5 6 7 8 9 10 11

Normal(6.90982,1.48076)

Mean

Std Dev

Std Err Mean

Upper 95% Mean

Lower 95% Mean

N

6.9098225

1.480759

0.0980657

7.1030579

6.7165872

228

Moments

Location

Dispersion

Type

µ

s

Parameter

6.9098225

1.480759

Estimate

6.7165872

1.3561741

Lower 95%

7.1030579

1.630746

Upper 95%

-2log(Likelihood) = 825.040944114034

Parameter Estimates

Shapiro-Wilk W Test

0.984320

W

0.0128*

Prob<W

Note: Ho = The data is from the Normal distribution. Small

p-values reject Ho.

Goodness-of-Fit Test

Fitted Normal

lem_gradient

Distributions

For simulation, use mean 6.9 MV/m, 1.5

Gradients – C50 modules

-2.33

-1.64

-1.28

-0.67

0.0

0.67

1.28

1.64

2.33

0.5

0.8

0.2

0.05

0.01

0.95

0.99

Norm

al Q

ua

ntil

e P

lot

5

10

Cou

nt

4 5 6 7 8 9 10 11 12 13 14

Normal(10.905,2.01554)

Mean

Std Dev

Std Err Mean

Upper 95% Mean

Lower 95% Mean

N

10.905006

2.0155435

0.2375341

11.378635

10.431376

72

Moments

Location

Dispersion

Type

µ

s

Parameter

10.905006

2.0155435

Estimate

10.431376

1.7316468

Lower 95%

11.378635

2.4116532

Upper 95%

-2log(Likelihood) = 304.255151928576

Parameter Estimates

Shapiro-Wilk W Test

0.936218

W

0.0012*

Prob<W

Note: Ho = The data is from the Normal distribution. Small

p-values reject Ho.

Goodness-of-Fit Test

Fitted Normal

lem_gradient

Distributions

Not normal, but for Monte Carlo purposes assume it is with mean 10.9 MV/m, 1.5 as for C25

Monte Carlo simulation inputs

Type G mean G Q0 mean Q0

C25 6.9 MV/m 1.5 MV/m 4.5e9 1.4e9

C50 10.9 1.5 4.0e9 1.3e9

C100 A 18 1.8 8.2e9 1.2e9

C100 B 18 1.8 7.0e9 2.0e9

• 16W/module static heat C25/50

• 50 W/module C100 includes transfer line changes but not bayonets,

15W/module or 75W/linac, per R. Ganni presentation

not included: 100W/linac as

• 2W/module electric heat allowance

• 50W/linac electric heat in three swing heat zones

Monte Carlo simulation

• Written by Arne Freyberger

• Inputs from experimental values, cryo group estimates,

cavity specifications (e.g. R/Q)

• Gradient and Q values for C25 and C50 from lem and

measurement, respectively.

• C100 scenarios agreed with SRF May 18, 2010:

– 18 MV/m, 1.8 for cases with all modules on

– 22 MV/m max

– case A: Q0 8.2e9, 1.2e9

– case B: Q0 7.0e9, 2e9

– case: one C100 off; adjust all gradient means in that

linac up to compensate

Nominal configurations

• 6 Gev injector: two C25

• 12 GeV injector: one C25, one C100

• ignore quarter

Module type 6 GeV 12 GeV

C25 32 31

C50 10 10

C100 0 11

Monte Carlo simulation – 6 GeV run

1200+67.5+2 (energy) = 1297.5 MeV

Monte Carlo simulation – 6 GeV

Monte Carlo – tweak 6 GeV

“Optimize G dist” pairs high Qs with high gradients, as we did by hand for 6 GeV run.

Experimental heat load comparable to this one. 190 g/s * 20W/g/s = 3800 W

Monte Carlo – 6 GeV tweak

Single module heat simulations

• C25 53 +/- 5 W/module

• C50 159 +/- 12 W/module

• C100 253 +/- 13 W/module (case B)

12 GeV – case A (index 1)

Includes injector CMs so 2303 MeV energy gain needed. Add 2 as before = 2341 MeV.

C50 mean gradient reduced as MeV/W lowest for these.

12 GeV – case A

12 GeV – case B (index 2)

Lower Q mean and larger for C100. 7E9 is Q spec for C100 at 19 MV/m. 2K heat from

waveguide, ~1W/kW in C50, will drive effective Q down. Experiment needed.

12 GeV – case B

12 GeV – NL case A (index 4)

NL+Injector 1203 MeV, so again 2 high. Optimistic Qs.

12 GeV – NL case B (index 5)

~300W more heat than case A due to lower, specified Q

12 GeV NL – case B less one C100 (index 6)

Heat up ~200W. Add another 50W for static load of non-functional C100 if left in place.

Fault rate doubles as C25 gradient up 10%. C100 mean gradient up 6.7%, which may not be

available. C50 gradient 11 MV/m as lem places these at max possible. 260W per C100

12 GeV – SL case B (index 8)

12 GeV – SL case B, one C100 down (index 9)

Fault rate doubles due to C25 push. C100 mean gradient up 10% to 19.8 MV/m.

Heat up ~200W. Add another 50W for static load of non-functional C100 unless pulled.

280W per active C100.

SL case Ba: JLAMP (index 10)

3281W vs 3714W, 430W savings vs SL case B. mean+2

Ten more C50s (index 3)

Fault rate falls by ~40% due to reduction in C25 module count and their lower mean

gradient. Availability improvement ~3%. Heat load about the same. Higher Q at lower

C50 gradient per commissioning measurements.

NL: ten C50, one C100 down (index 7)

Fault rate remains the same instead of doubling as before as C25 gradients unchanged.

C50 module gradients increased so heat up ~300W vs case without extra C50s. If C50 Qs

at high gradient improve in next lot of ten, heat needn’t rise.

Heat summary – 12 GeV

Index Case Linac Heat mean Sigma Mean+2

1 Optimistic Q Both 6641 120 6881

2 Specified Q Both 7176 158 7492

3* Specified Q, ten more C50 Both 7160 150 7460

4 Optimistic Q NL 3505 85 3675

5 Specified Q NL 3795 117 4029

6 Specified Q, one C100 down NL 3993 124 4241+50

7* Spec Q, ten more C50, one C100 down NL 4109 126 4361+50

8 Specified Q SL 3480 117 3714

9 Specified Q, one C100 down SL 3660 120 3900+50

10 SL JLAMP (four more C100, four fewer C25) SL 3107 87 3281

6+8 Spec Q, one NL C100 down Both 7471 165 7801

* fault rate about 60% of case above. Electric heaters not included above, 100W/linac.

Not included

• 100W/linac electric control heaters - one may view the

numbers shown as mean plus one sigma plus this heat.

• Superconducting RF gun

• Superconducting fifth pass RF separator: 50W static and

dynamic in cryounit; 50W??? 2K transfer line from SL.

CASA design assumed a conventional RF separator so

beam line is available if SRF/cryo is not cost effective.

• Error: 530W for transfer line was allocated 265W/linac

instead of 302/228 W NL/SL per Rao’s presentation. 37W

too low for NL, 37W too high for SL.

Conclusions

• NL OK in all cases

• SL OK in all cases with present FEL requirement of 665W

• SL not OK with any JLAMP case – maximum available

with four additional C100s ~1100W, 430W increase over 6

GeV run value.

• Additional C50s will reduce fault rate.

– Application of improved surface processing developed

for C100 to increase C50 Q(G) will reduce heat load.

• Additional C50s will keep fault rate from increasing 50%

with a C100 down. (Fault rate will double in linac with C100

down. Faults about equal in linacs, so overall rate up 50%.)

SL case Ba: JLAMP (index 10)

Replace nine C25 with four C100 per JLAMP proposal, leaving five SL slots empty. Heat load

260W below SL case B (mean+2 ). If this is chosen early enough, the five empty slots in the

SL need not be equipped for cryomodules, removing the 75W bayonet load too. Net savings

335W then.