Low alpha mode for SPEAR3 and a potential THz beamline

Transcription

1 Low alpha mode for SPEAR3 and a potential THz beamline X. Huang For the SSRL Accelerator Team 3/4/00 Future Light Source Workshop X. Huang

2 Outline The low-alpha mode for SPEAR3 Potential for a THz beamline Chicane THz source THz power calculation Parameter Circumference Beam energy Emittance For SPEAR3 34 m 3 GeV Momentum spread 0.00 Momentum compaction factor Rf frequency Rf voltage 8 nm (achromat) 0 nm (low emitx) (low emitx) (achromat) MHz 3. MV Beam current 00 ma (500mA) 3/4/00 Future Light Source Workshop X. Huang

3 Reasons to go low-alpha Shorter bunches short X-ray pulses CSR in THz regime Bunch length T E / E E f h rev / e V U / 4 rf 0 E C E q I 3 I I4 / Ways to get short bunches: () Reduce beam energy () Increase rf voltage (3) Increase rf frequecy (4) Reduce momentum compaction factor - alpha 3/4/00 Future Light Source Workshop X. Huang 3

4 SPEAR3 low alpha optics First and second order momentum compaction factors: C D x0 C ds Dx D' x0 ds, QFC, QF D x (m m) 0.6 achromat 0.4 low emittance 0 0. low alpha S( (m) 5 The need to control : bucket height 3/ to maintain normal rf buckets x,y (m) 000 is required for SPEAR S (m) Response matrix for chromaticities Cx C y I(SF) I(SD 3 3 ) We have to run with a negative Cx 3/4/00 Future Light Source Workshop X. Huang 4

5 Implementation of the low alpha optics Sextupole SF is set to minimize Chromaticity [- x, 0.5 y].5 x 0-5 Two calibrated low alpha lattice: /, /59, Adjust QFC to get lower alpha =.0739e e-004 QFC [A] QFC (ma) Injection is more sensitive to rf frequency and injected beam timing error. After LOCO measurement and then orbit correction. 3/4/00 Future Light Source Workshop X. Huang 5

6 . Synchrotron tune measurements Nadji et al, NIMA (996) Measurements of alpha nu 4 (E/heVcoss s ) x I = 0 SF alpha f (MHz) rf nu 4 (E/heVcoss s ) 0 x I = 0 SF alpha0/ f (MHz) rf x 0-3 Longitudinal motion driven by rf noise, not an intentional excitation.. Orbit offset from rf frequency change. xidi D i ignore <D D >/<D ^>=.50 for low alpha lattice, delta< x (mm) model meas - Fit for, spos (m) 3/4/00 Future Light Source Workshop X. Huang 6

7 Short bunches observed 0.0 khz bunch length [ps, rms] khz 3.6 khz 6kHz.6.50 khz 0.50 khz single bunch current [ma] 4 f f s s, o 4 I I.7 I =3.8mA, = 6.8ps, f s0 =0.8 khz Streak camera measurement by J. Corbett, et al 3/4/00 Future Light Source Workshop X. Huang 7

8 Orbit stability Better longitudinal l phase stability in low alpha mode Horizontal orbit stability is worse, but can be kept under control by fast orbit feedback. 4 mm FOFB on FOFB on for /340 lattice 0 mm 3/4/00 Future Light Source Workshop X. Huang 8

9 Lifetime Lifetime is 30 hrs at 00 ma, alpha/, dominated by Touschek lifetime. A positive 3 (=0.05) helps stabilize the beam (Y. Shoji, NewSUBARU). 3/4/00 Future Light Source Workshop X. Huang 9

10 Timing experiment User interests in low alpha mode ps rms beam for a user group in several experimental sessions. THz? 3/4/00 Future Light Source Workshop X. Huang 0

11 Plan for a THz beamline Edge radiation or dipole radiation? Parameter Value The chicane dipole source Bending radius 45 m Incoherent synchrotron radiation flux Bending angle 66.7 mrad Source point Aperture 5 x 5 mrad 0.3 mm Consideration for bending radius Opening angle of SR Shielding of vacuum chamber THz flux Horizontal size of first mirror cost cutoff flux h / 3 h We need to optimize the design (not done yet) Calculated with SRW 3/4/00 Future Light Source Workshop X. Huang

12 Calculation of THz power Considerations: Incoherent THz flux CSR amplification factor Single g bunch current limit Equilibrium distribution Vacuum chamber shielding at the port Current bunch length scaling law (for SPEAR3): I[ ma] [ps] I[ ma] [ps] 7 /3.354 F. Sannibale model with /5 J. Corbett measurement Hassinski eq. with free space CSR F(k=0.9)=3.3 (FSSR) y=i(s) no ormalized SPEAR3, sigma0= ps, ma FSSR PPSR g() N SPEAR3, sigma0= ps, ma FSSR 0 4 PPSR x=s/ z / (mm - ) 3/4/00 Future Light Source Workshop X. Huang

13 Shielding y=i(s) norm malized SPEAR3, sigma0=.7 ps, 0.07 ma FSSR PPSR x=s/ z N g() SPEAR3, sigma0=.7 ps, 0.07 ma FSSR PPSR / (mm - ) Assume chamber height 5 mm R.A. Bosch, NIMA 48 (00) 3/4/00 Future Light Source Workshop X. Huang 3

14 THz power flux, PPSR total power, PPSR flux (Watts/c cm - ) Power (Wa att) 0 - ps ps.4 ps wavenumber (/mm) Flux through a 5 x 5 mrad aperture wavenumber (/mm) ps.7 ps.4 ps Ttl Total power through hthe aperture Integration is numerically over data points shown on the left plot.. The measured current-bunch length scaling law is used. Parallel plate shielding model is used to calculate bunch shape deformation. The total THz power is 44 mw for the ps mode, mainly from wavelengths between 3 mm and 0.5 mm. The power can reach 300 mw for longer bunch modes, but concentrated in longer wavelengths. 3/4/00 Future Light Source Workshop X. Huang 4

15 Summary Low alpha mode for SPEAR3 was developed and is deliverable to users. A plan for a THz beamline is in its early stage. Questions: Scaling law Single bunch current limit it may be -4 times higher h than assumed. CSR impedance with shielding 3/4/00 Future Light Source Workshop X. Huang 5