‘multi-pass-droplet’ experiment

Operated by JSA for the U.S. Department of Energy

Muons, Inc.Multi-Pass Arc Experiment Meeting, October 28, 2011

‘Multi-pass-Droplet’ Experiment

1

Why multi-pass arcs? Recent development of Dogbone RLAs Alex 15 min.

Proof-of-principle optics for a two-pass arc Vasiliy 15 min.

Scaled super-cell test with electrons Yves 25 min.

Discussion All 20 min.

Why?

How?

What?

????

Kevin Beard, Alex Bogacz, Vasiliy Morozov, Yves Roblin

Discussion



Why multi-pass arcs?

Recent development of Dogbone RLAs

2

Alex Bogacz



A Decade of Muon RLAs

Racetrack RLA – NF Study I (2000) (Bogacz/Lebedev)

Switchyard (single bend, horizontal)

Individual energy return Arcs for recirculation

Dogbone RLA – NF Study II (2005) (Bogacz)

Better separation of passes

Compact arcs, saving on beamlines

Simultaneous acceleration of both charge species

Increasing number of passes (ISS/IDS-NF):

Bi-sected linac Optics (2006) (Bogacz)

Ramped linac quads (2007) (Johnson)

Reducing number of return Arcs – Multi-pass Arcs (IDS-NF):

Non-scaling FFAG arcs with sextupoles (2008) (Trbojevic/Bogacz/Wang)

Linear Non-scaling FFAG arcs (2010) (Morozov)

Arcs based on combined function magnets (2011) (Morozov)

3



Racetrack vs ‘Dogbone’ RLA

E/2

E/2

E

E

E

the droplets can be reduced in size according to the required energy

better orbit separation at linac’s end ~ energy difference between consecutive passes (2E)

allows both charges to traverse the Linac in the same direction (more uniform focusing profile)

both charge signs can be made to follow a Figure-8 path (suppression of depolarization effects)

4



Dogbone RLA – IDS

244 MeV 900 MeV

0.9 GeV 3.6 GeV

86 m0.6 GeV/pass

5



Pre-Linac and RLA I to RLA II …

3 GeV

1.8 GeV

1.2 GeV

3.6 GeV

244 MeV

900 MeV

2.4 GeV

6



Injection/Extraction Chicane

FODO lattice:

900/900 (h/v) betatron phase adv. per cell

7



Droplet Arcs

top view

side view

2.4 GeV1.2 GeV

1.2 GeV

2.4 GeV

1 m

8



(out = in and out = -in , matched to the linacs)

Mirror-symmetric ‘Droplet’ Arc – Optics

10 cells indisp. sup. cells out

2 empty transition cells

disp. sup. cells out

2 empty transition cells

130.6180

20

0

3-3

BE

TA

_X&

Y[m

]

DIS

P_

X&

Y[m

]

BETA_X BETA_Y DISP_X DISP_Y

2 vertical steps 2 vertical steps

9



Switchyard - Arc 1 and 3

1.2 GeV

1.2 GeV

2.4 GeV

10



Switchyard - Arc 1 and 3

2.4 GeV1.2 GeV

1.2 GeV

11



78.91030

150

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


39.91030

150

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


Multi-pass Linac Optics – Bi-sected Linac

1-pass, 1200-1800 MeV

‘half pass’ , 900-1200 MeV initial phase adv/cell 90 deg. scaling quads with energy

mirror symmetric quads in the linac

quad gradient

quad gradient

6 meter 90 deg. FODO cells17 MV/m RF, 2 cell cavities

12



Multi-pass bi-sected linac Optics

389.3020

300

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


1.2 GeV0.9 GeV 3.0 GeV2.4 GeV1.8 GeV 3.6 GeV

Arc 4Arc 3Arc 2Arc 1

x = 3.2 m y = 6.0 mx =-1.1 y =1.5 x,y → x,y

xy → xy

x,y → x,y

xy → xy

x,y → x,y

xy → xy

x,y → x,y

xy → xy

x = 6.3 m y = 7.9 mx =-1.2 y =1.3

x = 7.9 m y = 8.7 mx =-0.8 y =1.3

x = 13.0 m y = 14.4 mx =-1.2 y =1.5

quad grad.

length

13



254.6510

100

0

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


254.6510

100

0

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


‘Fixed’ vs ‘Pulsed’ linac Optics (8-pass)

Pulsed

Fixed

14



‘Dogbone’ RLA with 2-pass Arcs

15



A Decade of Muon RLAs

Racetrack RLA – NF Study I (2000) (Bogacz/Lebedev)

Switchyard (single bend, horizontal)

Individual energy return Arcs for recirculation

Dogbone RLA – NF Study II (2005) (Bogacz)

Better separation of passes

Compact arcs, saving on beamlines

Simultaneous acceleration of both charge species

Increasing number of passes (ISS/IDS-NF):

Bi-sected linac Optics (2006) (Bogacz)

Ramped linac quads (2007) (Johnson)

Reducing number of return Arcs – Multi-pass Arcs (IDS-NF):Reducing number of return Arcs – Multi-pass Arcs (IDS-NF):

Non-scaling FFAG arcs with sextupoles (2008) Non-scaling FFAG arcs with sextupoles (2008) ((Trbojevic/Bogacz/WangTrbojevic/Bogacz/Wang))

Linear Non-scaling FFAG arcs (2010) Linear Non-scaling FFAG arcs (2010) ((MorozovMorozov))

Arcs based on combined function magnets (2011) Arcs based on combined function magnets (2011) ((MorozovMorozov))

16



2-pass ‘Droplet’ Arc

* Trajectories are shown to scale

B 1 .7 Tesla

G 28 Tesla/m

17

Dipole and quadrupole field components of the remaining magnets adjusted so that at both momenta

Each super-cell has periodic solutions for the orbit and the Twiss functions

At the cell’s entrance and exit, periodic orbit offset, dispersion and their slopes are all zero

Vasiliy Morozov



Proof-of-principle optics for a two-pass arc

18

Vasiliy Morozov



RLA with Two-Pass Arcs

244 MeV

0.6 GeV/pass3.6 GeV

0.9 GeV

146 m

79 m

2 GeV/pass

264 m

12.6 GeV

Two or potentially more regular droplet arcs replaced by one multi-pass arc

Simplified scheme

No need for a complicated switchyard

Compactness

More efficient use of RF by maximizing the number of passes

Potentially cheaper

Potential for other applications

79 m

RLA with FFAG Arcs

Alex Bogacz

19



60

300

simple closing of geometrywhen using similar cells

= 41.3 m

C = 302.4 m

Schematic Layout of a Two-Pass FFAG Arc

20



Non-Linear FFAG: 1.2 GeV/c Linear Optics of Unit Cell

Combined-function bending magnets are used

1.2 GeV/c orbit goes through magnet centersLinear optics controlled by quadrupole gradients in symmetric 3-magnet cellDispersion compensated in each 3-magnet cell

3-magnet cell

MAD-X (PTC)

in + out + in = in

21



sextupole and octupole components

Non-Linear FFAG: 2.4 GeV/c Linear Optics of Unit Cell

Unit cell composed symmetrically of three 3-magnet cellsOff-center periodic orbitOrbit offset and dispersion are compensated by symmetrically introducing sextupole and octupole field components in the center magnets of 3-magnet cells

symmetric unit cell

MAD-X (PTC)

22



Cell Matching1.2 GeV/c 2.4 GeV/c

outward inward outward inward

23



Issues with Non-Linear FFAG Arcs

Small dynamic aperture and momentum acceptance

Compensation of non-linear effects is complicated

Matching to linac is difficult

Hard to control the orbit lengths and therefore the difference in the times of flight of the two momenta

Combined function magnets with precise control of field components up to octupole

24



Two-Pass Linear FFAG Arcs

Same concept as with the non-linear FFAG arcs

Droplet arcs composed of symmetric FFAG cells

Each cell has periodic solution for the orbit and the Twiss functions

For both energies, at the cell’s entrance and exit:

Offset and angle of the periodic orbit are zero

Alpha functions are zero

Dispersion and its slope are zero

Outward and inward bending cells are automatically matched

25



Two-Pass Linear FFAG Arcs

Combined function magnets with dipole and quadrupole field components only

Much greater dynamic aperture expected than in the non-linear case

Easier to adjust the pass length and the time of flight for each energy

Easier to control the beta-function and dispersion values

Initial beta-function values chosen to simplify matching to linac

Much simpler practical implementation without non-linear fields

More elements are used in each unit cell to satisfy the diverse requirements and provide enough flexibility in the orbit control

26



Linear FFAG: Linear Optics of Unit Cell Initial conditions set; orbit, dispersion and -function slopes zero at the centerPath lengths adjusted to give time of flight difference of one period of RF1.2 GeV/c 2.4 GeV/c

27



Dynamic Aperture

28



Design Based on Linear Combined-Function Magnets

Same concept as the linear FFAG design

Linear combined-function magnets

Droplet arc composed of symmetric super cells

Each super-cell has periodic solutions for the orbit and the Twiss functions

At the cell’s entrance and exit, periodic orbit offset, dispersion and their slopes are all zero

Two cells bending in the same or opposite directions automatically matched at both momenta

First few magnets of the super cell have dipole field component only, serving as spreader/recombiner

Both dipole and quadrupole field components of the remaining magnets used as parameters to meet the constraints

Synchronization with linac accomplished using path-length adjusting chicanes and/or vertical beam bypasses

29



Advantages of New Arc Design

All the advantages of a linear FFAG at a greater compactness

Alternating in-out-in or out-in-out pattern no longer required

Variation of the bending angles increases the number of available parameters and reduces the number of magnets required

Reduced orbit excursion

Spreader/recombiner incorporated into the arc design

Large dynamic aperture and momentum acceptance expected

Simple linear combined-function magnet design

30



60

300

C = 117.6 m

Arc Layout

Still simple closing of arc geometry when using similar super cells

1.2 / 2.4 GeV/c arc design used as an illustration can be scaled/optimized for other momenta preserving the factor of 2 momentum ratio of the two passes

B 1 .7 Tesla

G 28 Tesla/m

31



Super-Cell Optics for P2 / P1 = 2P 2xP

32



Droplet Arc Spreader/Recombiner

First few magnets of the super cell have dipole field component only, serving as Spreader/Recombiner


33



Two 2-Pass Arc Switchyard

Two 2-pass arcs

Lower momentum arc is the most challenging because of the highest momentum ratio; have a solution but still plenty of room for optimization


34



Future Studies and Optimization Paths

Lower momentum ratio

In case of a race-track design or in the inner droplet super cells, quadrupole field component can be used in the super-cell’s first magnets

Introduce sextupole component in the spreader/recombiner to control orbit deviation

Study the possibility of more than two passes

Study sextupole compensation of chromatic effects

Study error sensitivity

Tracking using realistic field maps

35



Scaled super-cell test with electrons

36

Yves Roblin



goal of the project

•Validate the concept of combined function magnet return arcs

•Demonstrate feasibility, establish leadership

•The scaled down test is a fertile ground for beam physics:• Dynamic aperture,•Effect of non linearities,•Tunability,•Envelope control,•Exploring the range of momenta that can be transported•Etc..etc..

37



Closed orbit in cell

20cm aperture

38



scope

Build a fully functional half-cell (first phase) and eventually a full arc using electrons rather than muons.

Use this arc to characterize and demonstrate the concept for the MAP program

Great teaching tool. Can partner with local universities (ODU Beam physics program)

39



feasibility

Electron is 206 times lighter than muon. We only need a few MeV to 10’s of MeV to carry out the tests. Canonical 2.4 GeV/c lattice requires 11.6 MeV/c electrons.

Real arc will have superconducting magnets. We can build small normal conducting magnets in house to test the concept (more about this later)

We have the expertise with electron beams and can deliver the needed beam

We have the room at JLAB (see next slides) for testing a half cell, maybe even a full cell and later a full arc.

40



Testing a Half-Cell with Electrons

Cell with 12 combined function magnets bending a totalof 30 degrees.

Each magnet is a dipole+quad+sextupole.L=50cm, aperture=20cm

Need instrumentation between each magnet (beam position monitors and means of measuring beam profile at some locations)

Low current is adequate.5 to 40 MeV/c of electron beam is good

41



Footprint of the apparatus

Full cell

About 8x3 meters on floor for the half cell.

42



Possible Locations at Jefferson Lab

Where 0L07 spectrometer is.

In a Hall after setting up CEBAF in energy recovery mode to get aLow energy beam. Good option if one want to test a bigger device.

In the test lab !! Using the injector group test gun along with a cavity to bring beam to 5 MeV. Maybe some paperwork involved..

43



Magnet specifications

Aperture of 20 cm, length of 50 cm.

The real thing will have to provide around 1.8 Tesla.

Our prototype only needs to put out 1.8/206 or about 87 Gauss.

These magnets can be easily (maybe??) made in house.

44



Printed Circuit design(cont)

And it works..

Phys. Rev. ST Accel. Beams 3, 122401 (2000)

45



Printed Circuit design

BackFront

That’s a quad !

46



Full scaled down simulation of RLA with return arcs

Eventually two of these return arcs can be build.

A small recirculating linac would accelerate from 11.6 GeV to 46.4 GeV/c over several recirculations.

This would be a full scaled down test of the neutrino factoryand/or muon colliders.

47

‘multi-pass-droplet’ experiment

Documents