# Presentation: 551114

## Accelerator Physics

- _Accelerator Physics_

**Petr Ostroumov (ANL)**
**March 15 , 2005**

- Proton Driver Director's Review

- March 15-17, 2005

## Outline

**Basic concepts for the Linac design **
**Choice of lattice parameters**
**High-intensity beam physics**
**Detailed design and simulations**
**R&D issues**
**Conclusion**

- Proton Driver Director's Review

- March 15-17, 2005

## 8-GeV Linac conceptual design

**GOAL: Design 8-GeV high-power linac in a cost-effective manner**
**Apply ILC-style cavities above ~1.2 GeV **
**Feed multiple cavities from one klystron**
**Develop and use S-ILC cavities (beta=0.81) in the energy range ~400 MeV-1.2 GeV **
**Select sub-harmonic frequency for the front end: 1/4. Motivation: multi-spoke cavities are developed at ~345-350 MHz. Requires 30% less number of cavities compared to 433 MHz option. Klystrons are available from JHF developments.**
**No need in SRF cavities below 15 MeV: use 21 RT-TSR  with very high shunt impedance. Power distribution is similar to those for SRF cavities**

- Proton Driver Director's Review

- March 15-17, 2005

## Linac conceptual design (cont’d)

**325 MHz SSR, DSR and TSR from 15 MeV to ~400 MeV **
**Apply SC solenoid focusing  to obtain compact lattice in the front end including MEBT**
**JHF-SNS-style RFQ delivers axial-symmetric 3 MeV beam **
**MEBT consists of  2 re-bunchers and a chopper. Smooth axial-symmetric focusing mitigates beam halo formation**
**Beam matching between the cryostats: adjust parameters of outermost elements (solenoid fields, rf phase)**
**Frequency transition 1:4 at ~400 MeV, matching in **
**    ****(********, ********W)-plane is provided by 90******** “bunch rotation” **
**Avoid beam losses due to H-minus stripping **

- Proton Driver Director's Review

- March 15-17, 2005

## Linac Structure

- 325 MHz  1300 MHz	 	1300 MHz

- Major Linac Sections
- Front end     Squeezed ILC-style 	ILS-style

- Proton Driver Director's Review

- March 15-17, 2005

## MEBT, Linac entrance, 28 mA

- Chopper

- Proton Driver Director's Review

- March 15-17, 2005

## RT-TSR, f=325 MHz

**Shunt Impedance: 160 M********/m  -  80 M********/m****IH structure application for heavy ions: ****GSI, LMU (Munich), CERN-ISOLDA, TRIUMF-ISAC, several Labs in Japan**

- Proton Driver Director's Review

- March 15-17, 2005

## Energy gain per resonator vs distance

- Proton Driver Director's Review

- March 15-17, 2005

## Stability Diagram (transverse motion)

- Unstable due to
- parametric resonance

- Linac operating tunes (black dots)
- Stable for all particles
- inside the separatrix

- Defocusing Factor

- Proton Driver Director's Review

- March 15-17, 2005

## Defocusing Factor vs Energy

- Beam Energy (MeV)

**S-ILC: 6 cavities/period**
**ILC:   16 cavities/period**

**S-ILC: 4 cavities/period**
**ILC:     8 cavities/period**
**Upper Limit for **
**Defocusing Factor **

- Defocusing factor

- Proton Driver Director's Review

- March 15-17, 2005

## Focusing lattice

| Section | Lattice | Length, m |
| --- | --- | --- |
| RT-TSR | S+C
S=solenoid, C=cavity | 0.4
0.6 |
| SSR | S+C  | 0.6 |
| DSR | S+CC  | 1.4 |
| TSR | F+C+D+C
F=Fquad, D=Dquad | 2.9 |
| S-ILC | F+CC+D+CC  | 5.3 |
| ILC | F+CCCC+D+CCCC
F+CCCCCCCC+D+CCCCCCCC | 12 (W<2.5GeV)
24 (W>2.5GeV) |

- Proton Driver Director's Review

- March 15-17, 2005

## High intensity beam physics   

**“****Current independent” lattice (Developed at LANL for ATP, SNS ...)**
- Smooth kT0 and kL0 – avoid ‘jumps’ in the transition, very important in the SC linac
**Space charge and higher order internal resonances**
- Beam matching in the transitions
- Parameters should be close to equipartitioning
- Avoid obvious resonance T0 = 90
- Watch for higher order resonances (Hoffman’s Chart)
- Final verification by multi-particle simulations
**Front End**
- The length of focusing period should be minimized: SC solenoids provide shortest focusing period
**Analyze HOM and avoid excessive power losses on cavity walls**

- Proton Driver Director's Review

- March 15-17, 2005

## RMS analysis: wavenumebrs of T- and L-oscillations

- Proton Driver Director's Review

- March 15-17, 2005

## RMS analysis: Phase advance

- Proton Driver Director's Review

- March 15-17, 2005

## Detailed design and simulation

** ****RFQ design;**
**Linac design on the base of rms equations (TRACE 3D, TRACK-fitting)**
**Simulations with the codes PARMILA, IMPACT (in progress) and TRACK**
**End-to-end simulations: TRACK**
**All fields are 3-D, resonator’s fields - MWS, solenoid fields - EMS**
**Most time-consuming work is beam matching in the transitions  between different sections and cryostats**

- Proton Driver Director's Review

- March 15-17, 2005

## End-to-end BD simulations (20K particles)

- aperture

- Beam current: 30 mA-RFQ, 28 mA - Linac

- Proton Driver Director's Review

- March 15-17, 2005

## End-to-end BD simulations, Log scale

- Beam current: 30 mA-RFQ, 28 mA - Linac

- aperture

-     RFQ  MEBT RT-TSR  SSR,DSR  TSR

- S-ILC, ILC

- Proton Driver Director's Review

- March 15-17, 2005

## Phase width (deg) along the linac

- Beam current: 30 mA-RFQ, 28 mA - Linac

- Proton Driver Director's Review

- March 15-17, 2005

## The same “tune”, 10 mA, 0 mA

-       10 mA-RFQ entrance			Zero current

- Proton Driver Director's Review

- March 15-17, 2005

## Emittance growth

**Emittance growth is almost negligible as soon as beam is matched carefully.**

- 30 mA (28 mA)

- 10 mA (9.3 mA)

- Proton Driver Director's Review

- March 15-17, 2005

## Phase space plots of 8-GeV beam

**Beam current 9.3 mA**

- Proton Driver Director's Review

- March 15-17, 2005

##  R&D issues

**Develop optimized design of the linac**
**Error studies **
**Study of different options of the linac to provide the most cost-effective design. **
- Example: frequency transition energy (110 MeV vs 400 MeV)
**Detailed studies of HOM in all ILC-style cavities and in TSRs**
**Iterate beam dynamics studies with hardware development**
**Some code development work is required **
- fitting in realistic fields
- support many different types of lattice structure
- include feedback loops of rf field for error simulations
**Apply different codes for BD simulations **
**High-statistics simulations**

- Proton Driver Director's Review

- March 15-17, 2005

## CONCLUSIONS

**Beam physics in the driver is predictable. Most problems are similar to the SNS and can be solved during R&D phase**
**New approach in hadron Linacs - “Pulsed SC Front End”-provides high-quality beams**
**Extremely high accelerating gradients require shorter focusing periods. It is recommended to keep peak surface fields in the S-ILC section below 50 MV/m**
**The concept of “current-independent” tune similar to those developed for the SNS works well for the Proton Driver: the same “30-mA tune” is good for all beam currents in the range from 0 to 30 mA**
**R&D work is required to eliminate uncertainties and provide cost-effective design and construction of the Linac **

- Proton Driver Director's Review

- March 15-17, 2005