# Presentation: 938876

## Status of the TRASCO Project

**Carlo Pagani**** ***INFN Milano-LASA & University of Milano *

**Oak Ridge National Lab**
**June 25-26, 2001**

**SNS-Miniworkshop**

## The TRASCO linac INFN-TC-00-23

| Source | RFQ | ISCL | High Energy SC Linac |
| --- | --- | --- | --- |
| Microwave RF Source
High current (35 mA)
80 keV | High transmission 90%
30 mA, 5 MeV | 5-100 MeV SC linac

With reentrant (or QWR) cavities

Single cavity family

8 focussing | 3 section linac:
100-190 MeV, =0.5
190-450 MeV, =0.65
450-1600 MeV, =0.85
Five(six) cell elliptical cavities
Quadrupole doublet focussing: multicavity cryostats between doublets
352.2 MHz (CERN/LEP)
704.4 MHz |

## TRASCO_AC Activities and Partners

- Source
- LNS
- Hitec
- Sistec
- Low and Intermediate Energy Section
- LNL
- Cinel
- Uni/INFN Bo
- INFN Ba
- High Energy Section
- INFN Mi
- INFN Ge
- CESI
- Saes Getters
- Zanon

## TRasco Intense Proton Source (LNS+HITEC+SISTEC)

- High intensity (several 10s mA) proton sources exist
- Chalk River
- Los Alamos
- CEA-Saclay **(Strong collaboration LNS/CEA)**
- Critical problem for ADS is the source reliability and availability
- Additional efforts with respect to state of the art are required for:
- Voltage and current stability
- Control of the low beam emittance
*Subprogram is aimed at the construction and operation of the source*

| TRIPS Goals: |  |
| --- | --- |
| Beam current | 35 mA |
| Beam emittance | 0.2  mm mrad |
| Operating voltage | 80 kV |

## TRIPS

- Design completed in 1999
- Source assembled in LNS in May 2000
- First beam of 20 mA @ 60 kV in Jan 2001
- Off-resonance microwave discharge source (2.45 GHz)
- Based on SILHI (CEA/Saclay)
- Modifications focussed on increase of reliability and availability
- TRASCO II: Optimized source with PM

## Low Energy Linac (LNL+CINEL+Ba+Bo+Na)

- The low energy linac is split in two components:
- A normal conducting **CW** Radio Frequency Quadrupole (RFQ): from 80 keV to 5 MeV
- A Superconducting linac (ISCL): from 5 MeV to 100 MeV
- /4, /2 cavities at 176 MHz or 352.2 MHz
- Reentrant cavities at 352.2 MHz

- TRASCO I: Prototype of 1/3 of the full RFQ and one of the SC cavities
- TRASCO II: full RFQ structure manifacturing

## The CW RFQ

- LANL LEDA 6.7 MeV RFQ achieved 100 mA CW (point of comparison)
- Huge engineering effort, complex design for very high current, 3 klystrons
- Different optimization procedure for TRASCO RFQ
- Limit to 1 RF source (1.3 MW CERN-LEP klystron)
- Lower design current of 30 mA (transmission of 96%)
- Peak surface electric field is 33 MV/m, 1.8 Kilpatrick limit
- Simplified engineering/manufacturing choices
- Heat dissipation in the structure ~ 600 kW total

## ISCL Linac

- The 5-100 MeV linac is made of independently phased cavities
- Re-entrant cavity geometry (single cell)
- Each SC cavity is fed by a small 15 kW solid state amplifier (Activity in LNL)
- Linac is very “tolerant” in terms of cavity failures (0.5 MeV max cav gain)
- Cavities can be designed multipactor-free
- The He vessel is integrated in the resonator in order to provide mechanical stability

- Focussing Quadrupoles

- Mechanical analysis under 1 bar He bath pressure

## Other resonator types for low energy

- A more cost effective linac can be designed with 2 gap resonators
- 1-1.5 MeV of energy gain per cavity
- In this case the linac is less tolerant to cavity failures
- Half Wave Resonators (dipole-free) and Quarter Wave Resonators (like ALPI cavities) are under analysis

- beam

## The High Energy SC Linac (MI+GE+Zanon+Saes+CESI)

- Linac Conceptual Design & Beam Dynamics (INFN)
- RF Cavity design 		Done
- All e.m., mechanical & technological fabrication aspects
- Linac design and non-linear beam dynamics		Done
- 	Two frequency options analyzed:
- 352.2 MHz (CERN LEP)
- 	*Attractive if machine is built NOW, with help of CERN infrastructures*
*Limited gradients, 4.2 K operation*
*Components are ready (RF, ancillaries, ...)*
*Long machine and huge infrastructures*
*Cheap technology (sputtering)*
- 704.4 MHz (CERN*2)
- 	More components engineering but, after TESLA achievements, more promising
- Higher gradients, 2 K operation
- Components need to be developed (RF, ...) but can be designed after TESLA/SNS
- Shorter machine and small infrastructures
- Bulk niobium cavities
- Prototypes and engineering (with partners)
- High beta single and multi cell cavity at 352.2 MHz with CERN		Done
- Low beta single cell cavity at 704.4 MHz		Done
- Cryomodule Conceptual Design		In progress

## Extension to the TRASCO program

- TRASCO II extends the program to the end of 2001
- Main goals of TRASCO II
**Source:**** **
- TRIPS-PM (permanent magnet version for further reliability)
- Beam line to the RFQ (matching section)
**Low Energy: **
- Manufacturing of the Full RFQ structure
- Engineering of the re-entrant cavity components: tuners, couplers, etc.
**High Energy:**
- Multicell cavity at 704.4 MHz (2)	**Collaboration with CEA/IN2P3**
- Engineering design of the cryomodule
- Treatment and test infrastructure in LASA
- Class 100 Clean Room
- High Pressure Rinsing station
- RF measurement infrastructure
- BCP is being set up in an external company premises

## General Linac Design

**Choices of cavity parameters**
- RF Frequency
-  values
- Determined mainly by the machine energy range and number of sections
- Number of cells
- Determined by efficient use
- How many cavities per cryomodule?
- Many: good use of space (beware of too much acceleration in one lattice cell!)
- Few: waste of space
**Cavity design provides constraints:**
- Max B surface field (and Bpeak/Eacc)
- Max E surface field (and Epeak/Eacc)
**Longitudinal beam dynamics constraints:**
- Longitudinal phase advances
- Longitudinal focussing (synch. phase)
**Beamline space inventory**

**From** 	INFN/CEA/IN2P3 Meeting
- 	LASA, Feb 23-24, 1999

## The Scaling with Frequency

- From the envelope equations, simple scaling laws with the design frequency can be derived, allowing to reproduce the same dynamics (scaling properly emittances, currents, and beamline parameters)
- higher frequency means physically smaller accelerator components
-  divide lengths by a factor 2 (=700/350)
-  use a beam physically smaller by a factor 2
- keep the same phase advances per period (the basic linac design depends on the choice of the phase advance...)
-  the phase advance per meter doubles (the cell size halves!)
-  the quadrupole gradients double, the length and bore are halved
-  the cavity gradients double
- To have the same dynamics we need to divide the emittances by a factor 2
- If we also keep the same ratio of  the emittance term to the space charge term,
-  use the same peak beam current (twice the charge in the bunch)
*In this way the envelope equation is formally the same! *Of course, the “boundary” condition at low energy is different for the two frequencies
- We did not consider the matching to the focusing channel of the previous linac section, which will be obviously different in the two cases due to the frequency transition

**From** 	INFN/CEA/IN2P3 Meeting
- 	LASA, Feb 23-24, 1999

## Linac Beam Dynamics (1 GeV TRASCO linac)

- The beam dynamics of TRASCO has been analyzed in detail
- A *multiparticle beam dynamics code* with a 3D space charge solver has been written
- Time evolution (for space charge consistency)
- Beam propagation in a z-dependent sinusoidal cavity field
- 3D Poisson solver based on a Multigrid method
- Presented at the *ICAP’98*
- Compares OK with 2D/3D Parmila versions (N. Pichoff/CEA)
*No** **substantial emittance growth**/**halo formation can be seen from simulations (up to 100.000 particles)*

- Beam Emittances

- Control of the particle distribution

**From: ****	**EPAC 2000, Vienna, June 2000

## Preliminary XADS Beamline

- In response to INFN/ENEA/Ansaldo meetings on the ADS interface, we studied the beamline for the **XADS** case:
- 600 MeV proton energy
- 6 mA beam current

- Study for the windowless solution
- Full width beam spot size on target 40 x 80 mm
- Small beam size is kept inside the last 90° bending
- Changes suggested with respect to base line XADS

## Cavity Design

- Careful analysis of the low beta cavity properties
*	**Short cavity geometry leads to peculiar problems, the cavity geometry needs to be carefully optimized*
- Electromagnetic
- Smaller volumes implies higher surface fields than electron cavities
- High surface E: field emission!  Nb quality and chemical/surface treatmens
- High surface B: thermal quenches  Nb quality
- Multipacting may be worse than electron cavities (no clear indication yet)
- Mechanical
- Different aspect ratio of the cells (long/transv)
- Mechanical stability under vacuum can be critical at low beta
- Need for stiffening in case of pulsed operation or microphonics
- Criteria/codes developed for cavity optimization have been used for
- TRASCO/352 and TRASCO/704
- Collaboration INFN/CEA/IN2P3 @ 704 (MOU)
- SNS (MOU INFN/TJNAF for SNS being signed)
- RIA (MOU INFN/MSU under definition)

## Tools for the cavity parametrization

- We built a parametric tool for the analysis of the cavity shape on the electromagnetic (and mechanical)parameters
- All RF computations are handled by SUPERFISH (no need for another code)
- Inner cell tuning is performed through the cell diameter, all the characteristic cell parameters stay constant: R, r, , d, L, Riris
- End cell tuning is performed through the wall angle inclination, ****, or distance, **d**.
-      R, L and Riris are set independently
- End groups for a 4 die cavity can be tuned using the end cell diameter (and ,d,R,L, Riris are set independently)

**From** 	SNS CCS Workshop
- 	TJNAF April 12-13, 2000

- All e.m. cavity results are stored in a database for futher parametric investigations.
- A proper file to transfer the cavity geometry to ANSYS is then generated

## Final Cavity Output

## Mechanical analysis of:

- A postprocessor reads the SFO output and builds a FEM model
- Radiation pressure calculation (Lorentz forces)
- Evaluation of the Slater coefficients
- An automated ANSYSTM procedure performs all the following calculations for 3 boundary conditions:
- Lorentz forces effects as a function of the stiffening ring radial positions
- 2 bar vacuum load on the cavity
- Tuning sensitivity (N/Hz, N/mm, Hz/mm)

- Danilo.Barni@mi.infn.it

**From** 	SNS CCS Workshop
- 	TJNAF April 12-13, 2000

**Half cell**

**Full cavity**

- Computation of the vibration eigenmodes of the “completely free” cavity
- Computation of their dependence from suitable external knobs:
- Helium vessel fixtures for the transverse modes
- Stiffening ring radius for longitudinal modes
- What is the connection Lorentz force excitation  vibrations?
- Contribution of the modes to the Lorentz forces 

## TRASCO – Cavity Prototyping

- 350 MHz cavities with CERN
- Single cell sputtered –   = 0.86
- 5 cell sputtered –   = 0.86
- Cavity integration in a LEP type cryostat – Under way at CERN
- 700 MHz Cavities with ZANON (+ Saclay & JLab)  = 0.5
- One single cell  - Built (Zanon) and Tested (Saclay) – RRR>30
- Three single cells under construction (RRR>30 & RRR>250)
- One 2-3 cell under design for fabrication optimization and stiffening prototyping
- One or two 5-cell cavities
- Arranging for chemical treatments with a local company (Delmet) – possible?
- Cryogenic RF Test Bench under Commissioning at LASA

## 350 MHz Cavities

- MOU with CERN for the fabrication and test of
- Single cell at high beta	 Done!
- 5 cell cavity at high beta	 Done!
- Extension of the contract for the insertion of the 5 cell cavity in a LEP cryostat  		on the way

## The =0.85 Cavity Produced with CERN

**The ********=0.85 ****Cavity Produced with CERN**

- Left, the cavity before the insertion of the Nb cathode in the clean room before sputtering
- Below, the cavity after chemical etching

## Five Cell Cavity Results (Q vs. Eacc)

**Results of the measurements on the TRASCO 5 cell module @ 4.5 K**

- =0.85

- The results obtained reached the original TRASCO goal!
- The limitation on the operating point of the cavity was due to the increase of the RF losses with the increasing field due to the growth of electron loading
- This limitation is exactly the same limitation experienced in the LEP cavities, *indeed the cavity performed as the best LEP cavities*

## Measurements Results and Future Work

- The next step of the joint INFN-CERN  development will be the test of the 5 cell cavity fully equipped with tuners and couplers in an accelerator-ready cryostat (a modified LEP spare cryostat)
- Here the cavity is shown in its He tank, complete with the tuner bars, before insertion in the cryomodule

- This activity was delayed till November 2000 due to the LEP-Higgs Blues
- cryomodule availability
- Current planning :
- Module completed by the end of March 2001
- Module tests (due Cryogenic Facility backlog) May-June 2001

## 700 MHz Cavities

- The 700 MHz activities are carried out in parallel with CEA/Saclay and IN2P3/Orsay, to optimise development efforts
- Milano works on prototypes of the lowest beta (0.5)
- Saclay/Orsay works on prototypes of the intermediate beta (0.65)
- The design work is **common** between the labs
- So far:
- 4 =0.5 single cell cavity have been built and 2 tested
- 3 =0.65 single cell cavity have been built and tested

## Summary of Main Cavity Parameters

| Geometrical Parameters |  |  |  |
| --- | --- | --- | --- |
| Cavity synchronous beta | 0.5 | 0.68 | 0.86 |
| Number of cells | 5 | 5 | 6 |
| Cell geom. length [mm] | 100 | 140 | 180 |
| Geometrical beta | 0.470 | 0.658 | 0.846 |
| Full Cavity Length [mm] | 900 | 1100 | 1480 |
| Iris Diameter [mm] | 80 | 90 | 100 |
| Tube at Coupler [mm] | 130 |  |  |
| Internal Wall Angle [°] | 5.5 | 8.5 | 8.5 |
| Equator Ellipse Ratio, R | 1.6 | 1 | 1 |
| Iris Ellipse Ratio, r | 1.3 | 1.3 | 1.4 |
| Full Cavity Electromagnetic Parameters |  |  |  |
| Max Epeak/Eacc | 3.59 | 2.61 | 2.36 |
| Max Bpeak/Eacc [mT/(MeV/m)] | 5.87 | 4.88 | 4.08 |
| Cell to Cell Coupling [%] | 1.34 | 1.10 | 1.28 |
| R/Q=V2/U [Ohm] | 181 | 337 | 617 |

## The =0.5 single cell cavity (Z101)

- Used **low RRR** Nb sheets: RRR> 30
- Built by Zanon (Partner)
- Treated at Saclay
- Standard BCP 1.1.2 (HF + HNO3 + H3PO4) ~  100 m removal on surface
- HPWR with ultrapure water (18 M) @ 100 bar
- Class 100 Clean Room Assembling
- Tested at CEA-Saclay *gave very good results* (given the bad Nb used!)
- The vertical insert was not arrived in Milano
- The cavity will be re-tested in Milano soon
- One other single cell with low RRR and two single cells with the “good” high RRR Nb are being built by Zanon

## Life cycle of the Z101 treated at Saclay

**Life cycle of the Z101 treated at Saclay**

**BCP**

**HPWR**

**Assembling in the insert**

## TRASCO 700 MHz:  =0.5 – Z101 Prototype

** ****Fabricated**** with ****Reactor Grade ****(RRR>30)**** Niobium**** at ZANON**
** ****Chemical Treatment and HPR at Saclay **(**no heat treatment**)
** ****Tested at Saclay at ****1.5 K**

**TRASCO 700 MHz****:****  ********=0.5 – Z101 Prototype**

## SC RF Cavity Test Facility at INFN-LASA

**The new**** insert with a **
**5 cell cavity**

**S****C ****RF Cavity Test Facility at ****INFN-****LASA**

**Class 100 ****Clean Room**

**RF Measurement Bunker**

- The old ARES (500 MHZ) Cryostat from LNF has been adapted with a new insert (ZANON) to minimize He consumption and allow fast cooldown times

**Clean Water Plant**

- A Class 100 Clean Room has been commissioned
- A 18 M clean water plant for high pressure rinsing has been installed
- High pressure rinsing (HPR) system is being installed

**Assembling of the clean room**

**The RF bunker**