# Presentation: 775598

## CERN Plans for High Intensity Proton Linacs

- Motivations
- Baseline Scenario (SPL, Linac4)
- R&D Programme
- Roadmap

- Maurizio Vretenar,   CERN AB/RF

**CERN Plans for High Intensity Proton Linacs**

## Motivations – The LEP RF

-   The LEP Collider at CERN was decommissioned in 2000
-   The 352 MHz RF equipment (SC cavities, cryostats, klystrons, waveguides, circulators, etc.) is now available for future projects (46 1-MW klystrons, 288 SC cavities, 6-km of waveguides,  etc.)
-   352 MHz is an almost ideal frequency for a linear accelerator...

- The LEP klystron

- Storage of the LEP
- cavities in the ISR tunnel

## Motivations – Demands for higher intensity

** **already with the present approved programme, CERN will 	lack protons from the year 2007:  LHC, CNGS 	(Neutrinos), ISOLDE (Radioactive Ions).
-  CERN users have already ambitious upgrade plans that 	are calling for even higher intensities               	(LHC upgrade, Neutrino Superbeam, EURISOL).
-  an upgrade of the injectors is the only way to provide 	more proton intensity, preparing at the same time 	an interesting future for CERN after the LHC.
-  a high-energy linac is the favorite candidate to achieve 	higher intensities *(no instabilities, long pulses, high **	**repetition rates, simple to operate, ...)*

## Example – The 3 neutrino roads

***1. “conventional” way from pion decay:  Accelerator, target and decay channel at CERN ******→ 400 kt detector in the Frejus tunnel (130 km)***

***2. from muon decay after ******	******muon acceleration ******	******→ Neutrino Factory ******	******(far detector)***

## The 3rd neutrino road

***3. From beta-decay of radioactive ions (after production and acceleration) →***
***	******to far detector ******	******	******	******(BETA-BEAMS)***

## Baseline Design - The SPL

*** SPL = Superconducting Proton Linac**
***A concept for improving the performance of the proton beams at CERN, ultimately based on a high-energy Superconducting Linear Accelerator***

**Baseline Design:**
***2.2 GeV, H-, 50 Hz, ***
***4 MW on target***
***     ******2 main users:***
- high brightness beam to LHC through the PS
- – high intensity beam to neutrino-RIB physics via accumulator/compressor rings in the ISR tunnel

## The SPL Working Group

- - Conceptual Design of the SPL, a High Power Superconducting Proton
- 	Linac at CERN Ed. M. Vretenar, CERN 2000-012
- - K. Bongardt et al., Progress in the Design of the SPL, EPAC 2002
- - SPL web site: *http://ps-div.web.cern.ch/ps-div/SPL_SG/*

**REFERENCES**

## SPL Design - Basics

**Design** principles:
**** 352 MHz frequency (LEP) for all the linac (standard RF, easy long. matching)
**** start room-temperature, go to SC as soon as possible
**** trade-off between current and pulse length (best compromise SC/RT)

**Basic** parameters
**** Energy >2 GeV (PS injection,  production)
**** Max. repetition rate 50 Hz (limit for SC
- 			cavities)
**** Beam power 4 MW (limit of target technology)

**Notes:**
RT part is about 10%, SC is 90%  -  RT more complex

## SPL Design - Parameters

- chopping

## SPL Design - Layout

**SPL Design - Layout**

- 55 cryostats,
- 33 from LEP, 22 using components
- (68 total available)

- 49 klystrons
- (44 used in LEP)** **

**Note**:
- no more unmodified LEP cavities are used in the SPL design, for a 87 m shorter linac** **

## SPL Design – Layout on site

**SPL Design – Layout on site**

## SPL R&D guidelines

- The SPL R&D programme is funded inside the CERN R&D plan (2001-2008)
- The goal is to concentrate effort on strategic items (with associated priorities):

- Requiring limited resources (inside SPL R&D budget)
- Essential / critical to the project
- Where CERN competence/experience is particularly valuable
- With a maximum of collaboration/exchanges with other labs
- Useful for any upgrade of the CERN injectors → priority to
- 	the low-energy part.

**Notes:**
The main idea is to grow a garden of competences, much more than to start building tomorrow an SPL as designed here. Long/medium term vision

## SPL Design – R&D topics

**SPL Design – R&D topics**

**H- source, 25 mA**
**14% duty cycle**

**Fast chopper**
**(2 ns transition time)**

**Cell Coupled Drift Tube Linac**

**new SC cavities: ********=0.52, 0.7, 0.8**

**Development of a new Low Level RF for linacs**

**Beam dynamics studies aiming at minimising losses**

**Vibrations of SC cavities: analysis, compensation schemes.**

**RF system: pulsing of**
**LEP klystrons**

**DTL test with CEA Saclay**

**Halo diagnostics, dump and collimation for MEBT**

**Notes:**
Identify strategic items and establish a list of priorities: 2. Essential/critical to the project / 4. Where collaboration/exchanges with are labs are possible / 3. Where CERN competence is valuable / 1. With limited use of resources / 5. Useful for our linacs

## R&D topics: the chopper structure and driver

**CERN Chopper structure ***(F. Caspers)* **:**
- Alumina substrate, reduced width
- Prototypes tested (attenuation and dispersion)
- Can stand beam losses

- Only 1 _fast_ chopper (2 ns rise/fall time)
- Placed inside quadrupoles
- Double 100 meander

**Driver amplifier**
- (HF prototype):
-  2.2 ns rise-fall time
- achieved (10%-90%)
-  ± 500 V
*(M. Paoluzzi)*

- 40 ns

- Chopper: Travelling-wave RF deflector (meander line) at 3 MeV

## The MEBT (chopper line)

- a. 2 chopper plates inside quadrupoles
- b. 3 bunch rotating cavities
- c. Valves, diagnostics, collimation, halo measurement device
- -  all in 3.6 m
- -  minimising emittance growth (~25%)

- MEBT (chopper line) at 3MeV
*under construction at CERN*

- Status (5/2003):
*quads recuperated from old CERN lines, bunchers at execution drawings, chopper 1 (prototype) in construction, dump and diagnostics being designed.*

## Chopper Dump

**The chopper dump (target)**
- 				*(L. Bruno)*
- - designed for 14% duty (3.3 kW)
- - copper core shrink-fit into a water-cooled Cu/Al2O3 jacket
- - can be rotated (if needed)
- - makes a good collimator
- - not expensive

## Beam Shape & Halo Monitor

**BSHM:**
*      **(M. Hori, K. Hanke)*
***Gated time-resolved ***
***beam profile monitor***
- - empty buckets
- - halo characterisation
- Secondary e- emission from a carbon foil
- Phosphor screen with optical fibres
- Gated photomultiplier for high sensitivity
- Integration on a CCD camera for profile

## R&D : the DTL test stand

- CERN 50 kW amplifier

- DTL model (CEA-Saclay)

**Test stand in **
**for 352 MHz linac**
**structures **
- 50 kW CW, 100 kW pulse

- 2002: tested the IPHI  DTL model
- (3 drift tubes, 5 MeV, CW, electromagnets)
- mech. design close to CERN Linac2

## R&D topics – the CCDTL

**From 40 MeV (up to 120 MeV)**
**the Alvarez can be replaced by a **
***Cell-Coupled Drift Tube Linac:***

- 1. Quadrupoles outside drift tubes: simpler
-     cooling, access/replacement, alignment
- 2. Less expensive structure than DTL
- 3. Same real estate shunt impedance
- 4. Continuous focusing lattice
- 5. Stabilised structure (/2 mode)
- 6. One resonator/klystron

- drift tube

- quadrupole housing

- coupling cell

- Full scale CCDTL prototype
- (2 half cells + 1 coupling cell, cooled)
- in construction at CERN,
- RF power tests in April 2004.

## R&D topics – low  SC cavities

- The =0.7 4-cell prototype

-  CERN technique of Nb/Cu sputtering
-  excellent thermal and mechanical stability
- 	(important for pulsed systems)
-  lower material cost, large apertures, released
- 	tolerances, 4.5 K operation with Q = 109

-  Bulk Nb or mixed technique for
- =0.52 (one 100 kW tetrode per cavity)

*(E. Chiaveri, R. Losito)*

## R&D topics - vibrations

**Effect on field **
**regulation**

**Effect on**
**the beam**

**  ****vector sum feedback can compensate only      ****	****for vibration amplitudes below 40 Hz**
**  ****possible remedies: piezos and/or high power**
**      ****	****phase and amplitude modulators**
**	*****(prototype ordered - H. Frischholz)***** **

**+ possible chaotic effects**
***(J. T******ü******ckmantel)***

## R&D topics - Low Level RF

**Need of a modern RF Low Level, to be tested on the CERN Linacs**
*	**Development of a prototype I/Q servo-system (T. Rohlev)*

- 1.  Built on a single VME card
- 2.  All processing done in a single FPGA
- 3.  Digital I/Q Modulator
- 4.  3 input / 1 output channels

- The board is now finished and under test.

## R&D topics – pulsing of LEP klystrons

**Mod anode driver**

**   ****LEP power supplies and klystrons are capable to operate in pulsed mode after minor modifications**
**      ****up to 12 klystrons can be connected to one LEP power supply**

**14/05/2001 - H. Frischholz**

## R&D topics – loss management

- For *hands-on maintenance* loss < 1 W/m

- For the *SPL*, 10 nA/m (10-6/m) @ 100 MeV,
- 	       0.5 nA/m (10-7/m) @ 2 GeV

- Present Linac2 loss level (transfer line):  25W/80m = 0.3 W/m
- 				          (but hot spots at > 1 W/m !)

- Mechanism of beam loss in the SPL:
- H- stripping ****** **< 0.01 W/m in quads for an off-axis beam
- Residual gas ****** **< 0.03 W/m @ 10-8 mbar, 2 GeV (but 0.25 W/m @ 10-7)
- Halo scraping ****** **more delicate, requires:
- 						 large apertures (SC is good!)
- 						 careful beam dynamics design

## R&D topics – beam dynamics

****  Control *rms emittance growth* and *loss from the outer halo* by avoiding
- 					parametric resonances

****  Selection of the working point (phase advances) on the Hofmann’s chart

*(F. Gerigk)*

**+ **Careful matching      (50Mpart simulations with IMPACT at NERSC, Berkeley)

**Notes:**
Hofmann’s chart: in the plane of tune depression (in x) vs. focusing ratio (long. over transv. Phase advance) plot analytically calculated emittance growth ratios

## R&D topics – after the linac...

- Transfer lines, collimation (= *scrape away halo particles *_*before*_* the accumulator*), etc.

**Accumulator/Collector**
**scheme *****(PDAC study***
***group) *****for NuFact**

- Two Rings in the ISR Tunnel
- Accumulator:
*3.3 ****s burst of *
*144 bunches at*
*44 MHz*
- Compressor:
*Bunch length *
*reduced to 3 ns*

## Roadmap

- Build the front-end in collaboration with IPHI

- Build the room-temperature part to inject at 150 MeV into the Booster
- (RF from LEP, hall and infrastructure available).

- Build the complete SPL

- 2006
- 2008
- 2010
- 2012
- 2014

- funded

## Stage 1: putting together the 3 MeV front-end

- A 352 MHz CW RFQ at 3 MeV, 100 mA is in construction at CEA-Saclay
- Formal agreement CERN/CEA-IN2P3:
- 2005: test of the RFQ at Saclay (p, CW, 100 mA)
- from 2006: installation of the RFQ at CERN (max. 14%, 40 mA, p&H-)
-          IPHI=Injecteur de Protons Haute Intensité (CEA+IN2P3)

- The 1st RFQ module (1m) after brazing and the layout of the Saclay test stand.

## The 3 MeV line at CERN

- At CERN, the IPHI RFQ will be used at lower current (→ only 1 klystron)
- and tested with the CERN-made chopper line (MEBT) from 2006.
- Tests will start with protons, and then with H- from the ECR source
- 		under development (or from another source)

- CERN p+
- or H- source

- MEBT

- klystron

- First test with proton,
- then with H- source
- + IPHI RFQ
- + CERN chopper line
- + Diagnostics line

## Stage 2 – The Linac4

*Relaxed parameters*
*Space and infrastructure  available in the PS South Hall*
*RF from LEP (klystrons, waveguides, etc. - already stored).*

- Build in a preliminary stage the room temperature section (120/150 MeV) of the SPL as new injector for the CERN Booster.
- → Increase of Booster intensity (p/pulse) by a factor ~2 as compared to 	present proton injection at 50 MeV + increased brightness.

- 4th linac built at CERN → Linac4

## Linac4

*Take only the **room temperature** part of the SPL (120 MeV) **	*
*and install it in the PS **South Hall**, to inject H- into the **PS** **Booster*
*	**	**	*    > *twice the number of protons/pulse in the PSB  **(5 10**13**)*

- 120 MeV, 80m, 16 LEP klystrons

## Linac4 in the PS Hall 

- 72 m

- to inflector & PSB

## European Integration

**** Some funding for accelerator research can come from the European Union, but the condition is to integrate programmes between EU laboratories.
****** **Established (2003) the HIPPI Joint Research Activity (HIPPI=High Intensity Pulsed Proton Injectors)
****** **Bid to EU in the 6th FW Programme, inside CARE (Coordinated Accelerator Research in Europe)
****** **HIPPI = 8 laboratories (CEA, CERN, FZJ, GSI, IAP-FU, INFN-Mi, IN2P3, RAL) joining efforts in the R&D for pulsed linacs 3-200 MeV (RT and SC), for the design of new injectors for 3 laboratories: CERN, GSI, RAL.
****** **An answer to the bid is expected for June-September 03.

## CONCLUSIONS

- More than a project, the SPL (Superconducting Proton Linac)
- is a roadmap for an evolution of the CERN complex towards
- higher proton intensity and brightness, as a viable alternative
- for the future after the LHC and for an LHC upgrade.

-  But of course first of all we have to work hard to finish the LHC !

- And without forgetting that the SPL (and CLIC)
- are the seeds of the CERN future !