Physics design on the main linac IHEP Physics design on the main linac Yan Fang, Li Zhihui C-ADS accelerator Physics Group Institute of High Energy Physics September 19, 2011

Outline Design philosophy The main linac lattice design: IHEP Outline Design philosophy The main linac lattice design: The acceptance of each section Simulation results Summary Outlook

IHEP C-ADS configuration（325/650 MHz) —RFQ + Spoke*+Spoke021+ Spoke040+ Ellip063+ Ellip082 10MeV Injector I spoke021 spoke040 ellip063 ellip082 Injector II Main linac

The design philosophy IHEP Equipartitioning design; The zero current phase advance in all three planes remains below 90 to avoid envelope resonance ; Smaller longitudinal emittance than transverse emittance to get more accelerating efficiency of the cavity; Long drift at both end of the period to avoid cryomodule separation causing emittance growth; Derated cavity nominal gradient for compensation in case any one cavity is lost; Using triplets instead of doublets in the elliptical section; For intersection matching we keep the phase advance per meter smooth.

Equipartitioning design IHEP Equipartitioning design Theoretical tune depression of each section tune depression 10mA 20mA Transverse Longitudinal Entra. exit Spoke021 0.76 0.77 0.79 0.8 0.64 0.65 0.67 0.69 Spoke040 0.80 0.83 0.73 Ellip063 0.74 0.81 0.86 0.62 0.70 Ellip082 0.84 0.95 0.92 Tune depression bigger than 0.71: Emittance dominated! Tune depression smaller than 0.71: Space charge dominated!

For the equipartitioning design: IHEP For the equipartitioning design: From the chart in the previous slide the theoretically tune depression is very close in our design: Then we keep zero current phase advance ratio constant to satisfy equipartitioning design approximately:

Emittance ratio choices IHEP Emittance ratio choices We investigated three emittance ratio cases: Case 1: Small emittance growth; Case 2: Better accelerating efficiency than case 1; Case 3: Emittance growth is small too, but hard to achieve such a small longitudinal emittance ; * Noted: Keep transverse emittance constant:

Main linac design on the basis of emittance ratio of 1.3 (case 1) IHEP Main linac design on the basis of emittance ratio of 1.3 (case 1)

Main linac design on the basis of emittance ratio of 1.3 (case 1) IHEP Main linac design on the basis of emittance ratio of 1.3 (case 1) Norm. RMS emittance growth are: 2% / 4% / 3.5% ( x/y/z) respectively.

Main linac design on the basis of emittance ratio of 0.7 (case 3) IHEP Main linac design on the basis of emittance ratio of 0.7 (case 3)

Main linac design on the basis of emittance ratio of 0.7 (case 3) IHEP Main linac design on the basis of emittance ratio of 0.7 (case 3) Norm. RMS emittance growth are: 4.9% / 3.7% / 3.9% ( x/y/z) respectively.

Main linac design on the basis of emittance ratio of 0.85 IHEP Main linac design on the basis of emittance ratio of 0.85

Main linac design on the basis of emittance ratio of 0.85 IHEP Main linac design on the basis of emittance ratio of 0.85 Normalized RMS emittance growth(x/y/z): 2.16% / 1.77% / 7.45%

IHEP 0.85 in our design We adopted kz/kx=1.33 (1/0.75: the red line) instead of 1.18 (1/0.85)

IHEP Main linac design on the basis of emittance ratio of 0.85, but keep kx/kz=0.75

IHEP Main linac design on the basis of emittance ratio of 0.85, but keep kx/kz=0.75 Normalized RMS emittance growth(x/y/z): 2.5% / 4.2% / 2.1%

Outline Design philosophy The main linac lattice design: IHEP Outline Design philosophy The main linac lattice design: The acceptance of each section Simulation results Summary Outlook

IHEP Lattice design Which is determined mainly under the condition that the zero phase advance per period is less than 90 degree both transversely and longitudinally.

IHEP IHEP Spoke021 period The lattice including 2 cavities and one solenoid: A 117mm is remained in each side of the cavity for tuner and bellows; The effective length of the solenoid is 150mm and 75mm in each side is remained for the flange and necessary shielding; An 100mm space in between solenoid and cavity is remained for the cold BPM. 400mm at both side of the period to accommodate possible cryomodule separation. 40mm 250mm

Spoke040 period IHEP IHEP The lattice including 4 cavities and one solenoid: An additional 100mm in between the cavities is allotted for the bellows and tuner of the two cavities. 60mm 380mm

Schematic figure of ellip063 cavity IHEP Schematic figure of ellip063 cavity

IHEP Ellip063 period The inter cavity distance, 500mm is allotted here to accommodate both the main power coupler and HOM coupler in case is needed. This number is determined according to ESS design: the inter cavity distance for ESS design is 400mm.* * Quoted from: M.Eshraqi et al, Proceedings of HB2010, Morschach, Switzerland.

IHEP Ellip082 period

Phase advance evolution along each section IHEP Phase advance evolution along each section

Phase advance per meter along main linac IHEP Phase advance per meter along main linac

How do we determine the space needed in between the cavity & solenoid! IHEP How do we determine the space needed in between the cavity & solenoid!

Project-X SSR0 lattice IHEP A117mm is allotted in between the cavity and solenoid. Courtesy of FNAL Project-X: T. Khabiboulline, S. Barbanotti, I Gonin, N. Solyak, I. Terechkine and V. Yakovlev et al, “CW RF system of the project-X accelerator front end”, proceedings of LINAC2010, Tsukuba, Japan. 117mm

Project-X lattice period IHEP Project-X lattice period Sol. Effective length: Leff=100mm Extension length: Lext=95/2=47.5mm Leff Lext Courtesy of FNAL Project-X: T. Khabiboulline, S. Barbanotti, I Gonin, N. Solyak, I. Terechkine and V. Yakovlev et al, “CW RF system of the project-X accelerator front end”, Proceedings of LINAC2010, Tsukuba, Japan.

FRIB β=0.045 section lattice IHEP FRIB β=0.045 section lattice Sol. Effective length: Leff=200mm Extension length: Lext=(352-200)/2 =76mm Leff Lext

Outline Design philosophy The main linac lattice design: IHEP Outline Design philosophy The main linac lattice design: The acceptance of each section Simulation results Summary Outlook

How do we determine the Synchronous phase? IHEP How do we determine the Synchronous phase? Which is mainly decided under the condition that the acceptance emittance ratio bigger than 10.

Acceptance of spoke021( φ:-30°) Longitudinal transverse Acceptance emittance ratio:9 Acceptance emittance ratio:6.6

Acceptance of spoke040 ( φ:-23°) Longitudinal transverse Acceptance emittance ratio:>10 Acceptance emittance ratio:>10

Acceptance of ellip063 ( φ:-15°) Longitudinal Transverse Acceptance emittance ratio:>10 Acceptance emittance ratio:>10

Acceptance of ellip082 ( φ:-12°) Longitudinal Transverse Acceptance emittance ratio:>10 Acceptance emittance ratio:>10

Conditions & Conclusions IHEP Conditions & Conclusions Beam is assumed to be lost if the energy spread is bigger than 10%; (Question: is it reasonable?) Conclusions: Longitudinally, try to keep the acceptance emittance ratio bigger than 10 (Question: is it necessary?) ; The longitudinal acceptance emittance ratio of spoke021 section is smaller than 9, but it’s a trade off between acceleration efficiency & big acceptance; Transverse: the acceptance is 6.6 times of the emittance in the spoke02 section, but the beam tube radius is 8-10 times of the RMS beam size (Question: is it enough?).

Outline Design philosophy The main linac lattice design: IHEP Outline Design philosophy The main linac lattice design: The acceptance of each section Simulation results Summary Outlook

Conditions & Specifications IHEP Conditions & Specifications Input Energy : 10MeV Average current: 10mA The normalized RMS emittance: εnt=0.252πmm.mad=0.21(1+20%) πmm.mad , εnl=0.2136πmm.mad=0.065x(1+20%) πdeg.MeV εl/εt=0.848 * Note: the emittance growth is assumed to be 20% increase from the exit of RFQ to the entrance of the main linac. 6D Gaussian distribution: (truncated at ±3σ) 100000 particles used for the simulation.

Envelope evolution of the main linac IHEP Envelope evolution of the main linac

emittance evolution of the main linac IHEP emittance evolution of the main linac Normalized RMS emittance growth(x/y/z): 2.5% / 4.2% / 2.1%

Sync. phase evolution of the main linac IHEP Sync. phase evolution of the main linac

Phase advance ratio & tune depression IHEP Phase advance ratio & tune depression Transv. phase Adv over long. phase Adv

IHEP Halo & phase space @1.5GeV

Energy gain (total: 210 cavities) IHEP Energy gain (total: 210 cavities) No:16*5=80 375-1498MeV Spoke cavity number: 102 No: 7*4=28 185-375MeV No:18*4=72 36.4 -185MeV Ellipse cavity number: 108 No:15*2=30 10-36.4MeV

Increased the current up to 20mA IHEP Increased the current up to 20mA

Increase the current up to 20mA IHEP Increase the current up to 20mA Normalized RMS emittance growth(x/y/z): 8.5% / 11.6% / 11%

The general layout of main linac current design Section spoke021 spoke040 ellip063 ellip082 Input energy(MeV) 10 36.6 185 378 Output energy(MeV) 1498 Geometry Beta 0.21 0.40 0.63 0.82 Cavity type 2 5 Number of cavities 30 72 28 80 Focusing type solenoid triplet Cavity per period 4 Synchronous phase (deg) -30° -23°to -30° -15° -12° period length(m) 2.168 3.8 7.3756 9.62 Section length(m) 32.52 68.4 51.6 153.88 Eacc (MV/m) ≤6.87 ≤ 5.26 7.9 9.75 Nominal Ep (MV/m) 25 35

Focusing devices of main linac IHEP Focusing devices of main linac FOCUSING DEVICES spoke021 spoke040 ellip063 ellip082 Focusing type solenoid triplet Aperture (mm) 50 70 Field Range (T) 2.4 to 3.2 3.2 to 5.2 Gradient Range (T/m) 6.8 to 14.1 5.8 to 15.1

summary The emittance ratio after RFQ is ; IHEP summary The emittance ratio after RFQ is ; The zero current phase advance ratio is kept constant along the whole linac with ; The acceptance emittance ratio is bigger than 10 except spoke021 section (a tradeoff between acceptance and acceleration efficiency); The total cavity needed acceleration from 10MeV to 1.5GeV is 210 cavities; The total length of the main linac is around 306 m; The RMS normalized emittance growth are: 2.5% / 4.2% / 2.1% respectively.

IHEP Outlook When we match the intersection the absolute value of sync. phase are changed smaller than nominal setting, in the next step we need to keep the sync. phase below the nominal setting; Further optimization of cavity parameter optimization; Different lattice design comparing; Compensation study; Error analysis; HOM analysis; ………

That’s all! Thank you for your attention! IHEP That’s all! Thank you for your attention!