CCR Status, 1/31/2012

Top Level Requirements• Deliver properly configured periodic train of bunches to cooling

channel at appropriate repetition rate– 54 MeV– Few mm-mrad– 0.01% x ~ 1 cm – 2 nC– Rep rate of 750 MHz/N, N=1,10,100…

• Manage stray power deposition, instabilities; preserve beam quality

• Recover itVery similar to FEL requirements (but with longitudinal phase space

rotated 90o)

Implementation Requirements

• System configuration/geometry consistent with MEIC collider– 2 x 30 m 2 kG solenoids; figure X layout– ½ m vertical separation

Perform design exercise to explore technology boundaries and beam dynamical limitations

Design ParametersParameter ValueInjection energy (momentum) pinj (MeV/c)

5

Injected longitudinal emittance ez (as used Figure 3, allows for 2x degradation; keV-psec)

80

RMS injected bunch length sl (psec) 5RMS injected energy spread sdp/p 0.003Linac on-crest energy gan (MeV) 50.4Full energy (momentum) pfull (MeV/c) 54Acceleration phase (deg) -13o (ahead of crest)Recovery phase (deg) 166o (ahead of trough)Decompression arc compactions (m) M56

T566

W5666

1.615-3.93253

Dechirper on-crest energy gain (MeV) 1.8Dechirper phase (deg) 90o (descending portion of waveform)RMS bunch length sl at CCR (cm; psec)

1; 33

RMS energy relative spread sdp/p at CCR

<10-4

CCR compaction (m) M56

0 (isochronous)Dechirper on-crest energy gain (MeV) 1.8Dechirper phase (deg) -90o (ascending portion of waveform)Decompression arc compactions (m) M56

T566

W5666

2.24250

Energy at dump (MeV) 5.3

System Configuration

• Three options– 750 MHz ERL (high risk source)– 75 MHz ERL (moderate risk source & beam transfer, high

risk beam-beam interaction)– 7.5 MHz ERL (high risk beam transfer)

• All three use common cooling channel geometry• All three use similar beam transfer system – Single DC dipole for 750 MHz ERL– Pair of RF separators/single septum for 75 MHz ERL– Pair of ultrafast kickers/single septum for 7.5 MHz ERL

System Layout

injector

dump

cooling solenoids

rechirper

dechirper

recirculation/decompression transport

recovery/recompression transport

CCR

ERLbeam

exchange system

ERL Characteristics• 4 five-cell 750 MHz SRF cavities

– Existing JLab high current design• Longitudinal aspect ratio at CCR imposes some degree of

gymnastics– Harmonic RF problematic– Chirp/compress/dechirp before injection

• Use transport system compactions for linear/nonlinear compensation– Chirp/decompress/energy compress during recovery

• Use transport system compactions for linear/nonlinear compensation

• Betatron matching between/amongst functional modules

Longitudinal Match – 1 cm

Longitudinal Match – 2 cm

Betatron Matching (1 cm)

CCR Concept• Use common figure-8 layout for all 3 ERL options• 2 x 30 m 20 kG cooling solenoids– Round beam matched to cooling channels

• FODO arcs, asymmetric chicane vertical steps– Compactions cancel isochronous transport

• Betatron matching between/amongst segments• Beam transfer: 2 x 90 FODO cells– Single dipole at center in 750 MHz ERL option– RFS/fast kickers at ends, septum in center in 75, 7.5 MHz ERL

option)• Cf. CEBAF beam distribution system

CCR layout• Figure 8, 30 m solenoids, ½ m vertical

separation

CCR Optics

Rudimentary S2E: Injector to CCR

CCR: 1000(+) particles x 100 turns• Added a few outliers to probe aperture

Rudimentary S2E: CCR to Dump

Cheats, Swindles, Things Left Undone

• Matching to/from CCR “figurative”– Simply set ERL match to 1 m into/out of exchange

dipole/septum; adjusted using Twiss matrix into/out of CCR & started simulation in middle of central quad in beam exchange section

Still have to construct details of transfer for each case…

• Path lengths not properly set– ½ lRF for full ERL– Multi-turn CCR needs to be multiple of lRF

• Haven’t started sensitivity/aberration analyses– Matching poorly optimized

Now, the bad news…

• 2 nC x 54 MeV is nontrivial…• CW MHz, rep rate, nsec-rise/fall time kickers

nontrivial