Review 09/2010 page

RF System for Electron Collider RingRF System for Electron Collider Ring

Haipeng Wangfor the team of R. Rimmer and F. Marhauser, SRF Institute

and

Y. Zhang, G. Krafft and S. Derbenev, CASA

Review 09/2010 page

Medium Energy EIC Top Layout

Three compact rings:• 3 to 11 GeV electron• Up to 12 GeV/c proton (warm)• Up to 60 GeV/c proton (cold)

Review 09/2010 page

Electron collider ring figure 8 layout

3

MEIC collider ring134.989 m

R=57.495 m

60°

379.609 m

20.000 m

239.167 m

dipole magnet bending radius m 57.495 57.495average beam current A 3 0.13electron beam energy GeV 5 11synchrotron radiation power per ring MW 3.85 3.91energy loss per turn MeV 1.28 30.07radiation power per unit arc length kW/m 5.331 5.411figure 8 circumference m 1000 1000electron revolution frequency kHz 299.79 299.79RF harmonic number 2496 2496RF cavity's frequency MHz 748.50 748.50revolution time ms 3.3356 3.3356bunch spacing m 0.401 0.401

RF insertion

Low energyHigh current

High energyLow current

Straights cross angle deg 60.000Circumference m 1000.000

Arc radius m 57.495Figure 8 width m 134.989Figure 8 length m 379.609Straight length m 239.167

Insertion straight length m 20.000Dipole compacting factor % 60

Review 09/2010 page

Electron Beam Stacking Structure for 5GeV

4

<3.3 ps(<1 mm)0.4 pC

1.334 ns (40 cm)

0.750 GHz

10-turn injection 33.3 μs (4 pC)

40 ms (~5 times radiation

damping)25 Hz

40 s (1000 bunch trains), average current=3 A

Microscopic bunch duty factor 2.47x10-3 average current=0.3 mA

Macroscopic bunch duty factor 8.33x10-4

From CEBAF SRF Linac

Stored beam in collider ring

revolution time=3.33 μs, 2501 bunches per ring

Review 09/2010 page

Existing RF systems in storage rings: normal conducting

5

BESSY

PEP-II

Two examples

Rimmer and Allen etc

Marhauser and Weihreter etc

Review 09/2010 page

Existing RF systems in storage rings: superconducting

6

Two examples

CESR-III B-cell

KEKB-TRISTANFuruya and Akai etc.

Padamsee and Chojnacki etc

Design Parameters Units Original CESR-III, Cornell Univ. Original KEKB, Japan

cavity parameters CESR-III Cavity KEKB-HER cavity

frequency MHz 499.765 509number of cell 1 1

R/Q = Ueff^2/(w*W) Ohm 89.0 93.0R/Q/cell Ohm 89.0 93.0

material independent geometry factor G = Rs*Q0 Ohm 270.0 250.0R/Q*G Ohm 24030 23250

acitve length m 0.3 0.243insertion length m 2.86 3.01

operating temperature Kelvin 4.2 4.2

BCS surface resistance RBCS nΩ 97.2 100.8

residual surface resistance assumed Rres nΩ 13.0 13.0

total surface resistance Rs nΩ 110.2 113.8Q0 5.0E+08 2.2E+09

shunt impedance (R=Ueff^2/P) MΩ 4.5E+04 2.0E+05input power (total losses) kW 324.9 571.2Pcavity (surface losses) kW 0.00761 0.00079Pbeam (beam loading) kW 320.00 562.50

Pbeam (beam loading on crest) kW 324.9 571.2average beam current A 0.55 1.4

minimum gap voltage required kV 581.8 401.8accelerating gradient MV/m 1.97 1.68

Qext matched Q0/(1+Pbeam/Pcavity) 2.00E+05 8.90E+04coupling factor (Q0/Qext) 2.50E+03 2.47E+04

total radiated power MW 1.28 4.50energy loss per turn MeV 2.33 3.21

beam energy GeV 5.3 8rf effective accelerating voltage MV 2.33 3.21

synchronous phase, 0 is on crest deg 10 10rf peak voltage required MV 2.363 3.264

number of cavities needed   4 8insertion length m 11.440 24.080

straigh section length in storage ring m

Preliminary Cost Exercise from BNL per Jim Rose 2008costs per cavity $ $1,200,000

total investment costs + RF power $ $3,395,000total investment costs (cavities only) $ $4,800,000

total costs (w/o power bill) $13,580,000cryoplant $

RF to AC power per year $

operational costs per year $ could favor SRF after 5-10 years could favor SRF after 5-10 years

Review 09/2010 page

Synchrotron radiation power

RF system in storage ring: Technology of choice

7

High CurrentLow Energy

High EnergyLow Current

Klystron power

Power coupler and RF window

Beam excited HOMs

HOM damping by waveguide or coaxial coupler

Liquid heliumCooling, 4.2K

DI water cooling<300K

High gradient for CW

Bunch head-tail instability

Large beam aperture

ceramics

ferrites

Low RF Frequency

Low gradientfor CW

Normal conducting cavity

RF acceleration

Low broadband and narrow band HOM impedance cavity

)()(

)()/(108575.8

4435 mAI

m

GeVEGeVmPrad

Superconducting cavity

Warm HOM windows and loads

<600kW for CW RF power

Beam loading control

Review 09/2010 page

Design Parameters Units MEIC3 MEIC4cavity parameters BESSY type cavity scaled BESSY type cavity scaled

frequency MHz 748.5 748.5number of cell 1 1

R/Q = Ueff^2/(w*W) Ohm 230.8 230.8R/Q/cell Ohm 230.8 230.8

material independent geometry factor G = Rs*Q0 Ohm 234.0 234.0

R/Q*G Ohm 54007 54007acitve length m 0.2 0.155

insertion length m 0.333 0.333operating temperature Kelvin >300 >300

BCS surface resistance RBCS nΩ n/a n/a

residual surface resistance assumed Rres nΩ n/a n/a

total surface resistance Rs nΩ n/a n/a

Q0 30000 30000shunt impedance (R=Ueff^2/P) MΩ 6.92 6.92

input power (total losses) kW 551 549Pcavity (surface losses) kW 333.196 3.913Pbeam (beam loading) kW 197.457 493.775

Pbeam (beam loading on crest) kW 217.869 544.821average beam current A 0.13 3

minimum gap voltage required kV 1518.9 164.6accelerating gradient MV/m 10.84 1.17

Qext matched Q0/(1+Pbeam/Pcavity) 1.81E+04 2.14E+02coupling factor (Q0/Qext) 1.65E+00 1.40E+02

total radiated power MW 6.52 6.42energy loss per turn MeV 50.12 2.14

beam energy GeV 11 5rf effective accelerating voltage MV 50.124 2.140

synchronous phase, 0 is on crest deg 25 25rf peak voltage required MV 55.305 2.361

number of cavities needed 33 13insertion length m 11.0 4.3

straigh section length in storage ring m 20.000 20.000Preliminary Cost Exercise

costs per cavity $total investment costs + RF power $

total investment costs (cavities only) $total costs (w/o power bill)

cryoplant $RF to AC power per year $operational costs per year $

Scaled RF system for MEIC Electron ring: normal conducting

8

BESSY:<100kWEacc=6MV/mConditioned up to 30kW CW in 5 days.

11GeV 5GeV

Marhauser and Weihreter

Review 09/2010 page

Design Parameters Units MEIC1 MEIC2cavity parameters CESR Cavity Scaled, high energy CESR Cavity Scaled, low energy

frequency MHz 748.5 748.5number of cell 1 1

R/Q = Ueff^2/(w*W) Ohm 89 89R/Q/cell Ohm 89.0 89.0

material independent geometry factor G = Rs*Q0 Ohm 270.0 270.0

R/Q*G Ohm 24030 24030acitve length m 0.2 0.2

insertion length m 1.91 1.91operating temperature Kelvin 4.2 4.2

BCS surface resistance RBCS nΩ 218.0 218.0

residual surface resistance assumed Rres nΩ 13.0 13.0

total surface resistance Rs nΩ 231.01 231.0

Q0 1.17E+09 1.17E+09shunt impedance (R=Ueff^2/P) MΩ 1.04E+05 1.04E+05

input power (total losses) kW 513.7 544.8Pcavity (surface losses) kW 0.12323 0.00026Pbeam (beam loading) kW 465.43 493.78

Pbeam (beam loading on crest) kW 513.5 544.8average beam current A 0.13 3

minimum gap voltage required kV 3580.3 164.6accelerating gradient MV/m 19.73 0.91

Qext matched Q0/(1+Pbeam/Pcavity) 2.80E+05 5.59E+02coupling factor (Q0/Qext) 4.17E+03 2.09E+06

total radiated power MW 6.52 6.42energy loss per turn MeV 50.12 2.14

beam energy GeV 11 5rf effective accelerating voltage MV 50.12 2.14

synchronous phase, 0 is on crest deg 25 25rf peak voltage required MV 55.305 2.361

number of cavities needed 14 13insertion length m 26.734 24.825

straigh section length in storage ring m 20.000 20.000Preliminary Cost Exercise from BNL per Jim Rose 2008

costs per cavity $ $1,200,000total investment costs + RF power $ $3,395,000

total investment costs (cavities only) $ $29,789,600total costs (w/o power bill) $84,279,742

cryoplant $RF to AC power per year $operational costs per year $ could favor SRF after 5-10 years

Scaled RF system for MEIC electron ring: superconducting

9

11GeV 5GeV

JLab High Current 750MHz, 5-cell, 1A cavity

Only single-cell is preferred due to a heavy HOM damping requirement in storage ring,But space is limited.

Rimmer and Wang etc

Review 09/2010 page

Initial HOM Analysis: beam current excitation

10

FFT

S. H. Kim and H.Wang

•Time averaged HOM power normalized to R/Q (W/= Amp2) is current square drive term. It has no information of the cavity but with assumed HOM damping Qext. • For example, if we have a HOM resonated at 2.25GHz with R/Q of 10 and Q external of 100 , we have 1kW HOM power from the beam in this mode.• When we design a high current cavity, we have to avoid HOM frequencies sitting on the beam excitation resonances.H. Wang etc PAC2005 TPPT086.

Review 09/2010 page

Initial HOM damping analysis: Impedance and HOM power

11

BESSY CWCT copper cavity impedance measurement sMarhauser and Weihreter, EPAC 2004

Impedance scaling from BESSY NC RF cavity in same shape but in different frequency scale:• monopole modes around 2.25 GHz have to be avoid by either changing the cavity shape (safe to park) or damping totally with Qext< 100, otherwise 50kW (on resonance HOM power will come out to the HOM loads.• Following is an example (H. Wang etc PAC 2005) for JLab High Current 5-cell cavity design to avoid HOM resonance by choosing different cavity shapes.

0

36

72

108

144

180

2.90 2.92 2.94 2.96 2.98 3.00 3.02 3.04 3.06 3.08 3.1010-1

100

101

102

103

104

105

106

light cone line

R/Q/cell=1.25(/cell)

JLab-LL Re-entrant JLab-LL-modified ILC-LL Rounded Pillbox Spherical Section

Frequency f (GHz)

Pha

se A

dvan

ce

(de

g)

P=120(W/)*1.25(/cell)*5(cell)=750W

1A, 750MHz CW laser, Qext

=10^4 1A, 750MHz CW laser, Q

ext=10^3

TM030 mode

Tim

e A

vera

ged

HO

M P

ower

/ (R

/Q)

(W/

)

Review 09/2010 page

MEIC electron ring RF system Summary: Pros and Cons

12

SCRF favors to High Energy, Low Current Operation NCRF favors to Low Energy, High Current Operation