General Design of C-ADS Accelerator Physics Zhihui Li On behalf of IHEP-IMP Joint Accelerator Physics Group of C-ADS Institute of High Energy Physics

Outline Introduction Design philosophy Design status of each part. Roadmap of C-ADS. Specifications for the C-ADS driver Linac. Layout of C-ADS linac Design philosophy Measures to maintain high reliability. Cavity types and lattice structure. Frequency of the two injectors Beam dynamics. Design status of each part. Summary

Road map of C-ADS project

Main specifications of the C-ADS driver linac Particle Proton Energy 1.5 GeV Current 10 mA Beam power 15 MW Frequency 162.5/325/650 MHz Duty factor 100 % Beam Loss <1 (0.3) W/m Beam trips/year <25000 <2500 <25 1s<t<10s 10s<t<5m t>5m

Superconducting Linac if preferred for C-ADS accelerator Characters of C-ADS accelerator. Low beam loss. High reliability. CW operation S.C. Linac is preferred. High power efficiency. Linear trajectory. Large aperture. Independent powered short cavity.

Progress on C-ADS Linac physical design Started at 2010.06 at IHEP and IMP. IHEP: Frequency 352MHz, spoke cavity, 40mA in dynamics design, 10mA in engineering design. IMP: S.C. CH cavity. 2010.08: 325MHz, 10mA in dynamics design, checked with 20mA. C-ADS project was really launched at the beginning of 2011. 2011.03, the IHEP-IMP Joint accelerator physics group. 2011.04, first Experts’ review meeting on C-ADS physics design. 3 schemes for injector I and main linac by IHEP. 325MHz (RFQ (3.0MeV)+spoke (0.12, 0.21, 0.4) )+650 MHz elliptical (0.63, 0.82) 325MHz (RFQ (3.0MeV)+R.T. CH (6MeV)+spoke (0.14, 0.33) ) +650MHz elliptical (0.63, 0.82) . 162.5MHz (RFQ (2.5MeV)+HWR(0.09) )+325MHz spoke (0.21, 0.4) +650MHz elliptical (0.63, 0.82) 2 schemes for injector II by IMP 325 MHz (RFQ(3.0MeV) +S.C. CH ) 162.5 MHz (RFQ (2.5 MeV) + HWR (0.09) )

Layout of the C-ADS linac Main linac

Design philosophy

Fault tolerance design to maintain high reliability and availability The accelerator design needs to have some capabilities of functioning with a number of faulty components, meeting the nominal operational goals (energy, current and stability). Automated procedures of the accelerator control system need to guarantee the prompt detection of faulty components and consequent machine retune in a short time, with no (or very short) beam interruptions. Local compensation-for main linac (Energy>10MeV) “Hot stand by” spare – injector (Energy<10 MeV).

Local compensation-for main linac (Energy>10MeV) Details will be presented by Dr. Fang Yan! Application conditions: Short independently powered cavities. Energy great than 10 MeV. Why local compensation? Fast retuning; Several components failure happen! Considered components Cavity Coupler, LLRF, power amplifier, cavity, … Solenoid and quadrupole. Parameters setting 30% of margin for RF cavity is reserved for compensation Study strategy Failure happen at beginning, middle and end of each section; Study of beam behaviors after local rematching. Results: Works for main linac.

Cavities in the main Linac Spoke or HWR? HWR: lower cost, more compact; Higher Bpeak/Eacc 650MHz or 1.3GHz for elliptical cavity? 650MHZ Larger aperture More efficient One less frequency jump Should we re-optimize the cavities （2 types）to reduce the peak magnetic field in the compensation mode, to below 70 or 80 mT?

Cavities in the main accelerator Cavity type b Energy (MeV) # of Cavity /CM Lattice Spoke021 0.14-0.24 10-34 30/5 RSR Spoke040 0.24-0.54 34-178 72/9 RRSRR Ellip063 0.54-0.69 178-367 28/7 RRRRT Ellip082 0.69-0.93 367-1500 80/16 RRRRRT Total length: ~310 m Total number of cavities: 210

Lattice design Good lattice design Focusing elements Economic. Beam dynamics: Combining good acceleration and efficiency. Meeting reliability requirements. Immune to important beam instabilities and small emittance growth. Less sensitive to errors. Less stringent to hardware. Economic. Technical feasibility. Focusing elements Defocusing effect of SC cavities at low energy. Spoke sections: S.C. solenoid Saving longitudinal space. Efficient at low energy. Elliptical sections: Warm quadrupoles. Design principles Phase advance per cell: <900. keep phase advance per meters adiabatically changing along linac. Ratio of transverse and longitudinal phase advance satisfy the equipartition condition.

Lattice design Parameter settings: I.Gonin et. all, proceedings of IPAC10 Parameter settings: reference design of SSR0 of Project-X. Cavity: cavity length (EM design)+117 mm one both sides. Solenoid: effective length + 75 mm on both sides. 100 mm for BPM. 800 mm for transition between crymodules. Another 100 mm is left if two cavities are adjacent. 75

Lattice design 500 mm is left between two cavities. Coupler, HOM damper; Prevent cross-talk between adjacent cavities;

Lattice design For the injector, compact lattice because of low velocity! For the main linac: About 400 mm drift space is reserved in both sides of each focusing period! Periodic property can be maintained within same sections even at the segmentation point. Benefits the local compensation.

Frequency of the injectors Beam dynamic. From the viewpoint of beam dynamics in main linac: 325 MHz favored. Acceleration structure: RFQ: 162.5MHz : larger section -> reduce heat density. larger aperture 325MHz: LEDA 973 ADS RFQ in IHEP Superconducting structure 162.5MHz: HWR 325MHz: spoke 325MHz RFQ+spoke injector I 162.5MHz RFQ+HWR injector II

Beam dynamics Very strong space charge effects even at 10 mA! High intensity beam dynamics design recipes should be applied in design!

Possible instabilities Parametric resonance driven by Transverse - longitudinal coupling Stable condition: sl0<1.7st0. Transverse mismatch instability Stable condition: st0<900. Longitudinal mismatch instability Stable condition: sl0<900. Emittance exchange Resonance free region in the Hoffman chart; Equipartition design: Beam collective instabilities HOM induced instabilities

Principles in beam dynamics design Design recipes Phase advance in all planes below 90 degree; Approximate equipartitionning design; Large apertures to avoid losses; Emittance ratios close to 1 (in our case: 0.8, decided by RFQ); Goals: Envelope smooth; Phase advance per meter smooth; Emittance growth minimized;

Phase advance settings Acceleration gradient is limited by the longitudinal phase advance. Longitudinal phase advance limitations. Phase advance law in our design.

Development status of each part

Design status of Injector I Two candidates of superconducting section scheme need to be decided: Spoke 011T solution – high-beta cavity to accelerate low-beta particle. Spoke 012 solution. Details will be presented in the following talk

Design status of Injector II ECR LEBT RFQ 4-5m MEBT SC-segment HWR C.M. 2*Sole. 4-5parts . FDF-B-FDF-B 35keV 2.1MeV 2.1-10MeV =0.087 =0.067 g~0.09 option A1 A2 B Length of cell 630 mm Number of cell 16 7？ Number of cavities 7 Number of solenoids 18 6 Focusing period SR SRR SR？ Total length 11.2 m Cryomodules 2 1 Emittance growth (0.99) 10(t)/6.1(l) % Emittance growth (RMS) 3.2(t)/2.0(l) Basic frequency is 162.5 MHz Ion source extraction voltage is 35 kV Extraction energy of RFQ is 2.1 MeV HWR is the main road to develop CH cavity will be R&D

Design status of Injector II The details of Injector II design will be presented By Prof. Yuan He.

Design status of the main linac The base line is determined. 4 kinds of cavities. Total number of cavities: 210. Total length: 310 m. Intensive beam dynamics study is performed. Approximated equipartitioning. Design with different emittance ratios. Local compensation study. Error analysis. Focused on emittance growth control. Details will be presented by Dr. Fang Yan.

Summary A baseline design for the main linac has been chosen for the review. Fault tolerance design. Local compensation in main linac. “hot-stand-by” spare for Injectors. Two injectors. With different frequency: 325MHz and 162.5MHz. RFQ: dynamics and structure design progress well. Superconducting section: both have more than one proposals and need to be decided. Works to be done. Integration of injector and main linac, front-to-end simulations should be done to prove the performance of the design. Comparison study of different lattice design. Commissioning and operation modes study for the linac in phases. Beam instabilities study ……

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