# Presentation: 051947

## Experimental results in 150MeV proton FFAG

- M. Aiba (KEK)
- For KEK FFAG Gr.

**ISS@KEK, Jan. 06**

**Notes:**
I would like to talk about experimental results in 150MeV proton FFAG. I’m Masamitsu Aiba from KEK.

## Contents

- Purpose of 150MeV FFAG project
- Machine parameters
- _COD correction and resonance crossing_
- _Hardware improvement in RF system_
- _Beam extraction with 100Hz operation_
- Summary

**Notes:**
They are contents of my talk. As experimental results I will show you COD correction and resonance crossing, hardware improvement in RF system and beam extraction with 100Hz operation. 

## Purpose of 150MeV FFAG

- To establish a prototype FFAG for various applications.
- Beam extraction from FFAG for the first time
- Rapid cycling
- Test experiments for applications using extracted beam

**Notes:**
Purpose of this project is to establish a prototype FFAG for various applications such as medical application.  For this purpose we have some important subjects. The first is beam extraction because of no beam extraction from FFAG before this machine. The second is rapid cycling. Rapid cycling is one of big features of FFAG. So we want to demonstrate it. The third is test experiments for applications using extracted beam. Actually some experiments using extracted beam are planned. Also we believe our experimental results are helpful for the electron model and further muon FFAG.

## Machine parameters

**Notes:**
This is a design parameter table and a picture of the machine. The machine is in the east counter hall of KEK. It is a radial type scaling FFAG with triplet lattice. Number of cell is 12. There are twelve identical magnet. K-value is 7.6. Maximum energy is 150MeV, Radius is about 5m. Betatron tunes are about 3.7 for horizontal and 1.3 for vertical. Maximum field is about 1.6T. 

## COD:Source & Correction scheme

- RF cores disturb fringing field.
- Additional two dipoles to correct COD.

**Notes:**
In the beam commissioning, we found a problem of COD. The biggest source of COD was RF cavity at the straight section, that is, RF cores absorb and disturb fringing field and COD is excited. In order to correct COD, we put additional two dipole magnets nearby RF cavity. Now we can control COD with this scheme. 

## Resonance crossing (3x=11)

- Horizontal tune changes from ~3.6 to ~3.8
- Characteristics of crossing 3x=11
- Non structure resonance excited by COD & feed down.
- Crossing near injection energy.
-      Injection septum determines horizontal aperture.

**Notes:**
Without this COD correction, there was considerable beam loss due to resonance crossing. In this machine horizontal tune changes from about 3.6 to 3.8, then horizontal tune crosses third integer resonance during acceleration. Third integer resonance of 3Nx=11 is a non-structure resonance excited by COD and feed down effect. The crossing point is near injection energy. Then injection septum determines horizontal aperture and beam loss will be observed if we have a considerable emittance growth.

## Crossing direction dependence

- Phase space topology with dominant nonlinearlity

- 1.(a)→(e)

- “Emittance growth”
-              (150MeV FFAG)

- 2.(e) →(a)

- “Particle trapping”

-  (distance from resonance)

- 〇

- (Proposed by A.W.Chao & M.Month)

**Notes:**
In scaling FFAG,  magnetic field has octupole components. Then an affection of resonance crossing depends on crossing direction. This is phase space topology near third integer resonance. The parameter xi is proportional to the distance from resonance, that is, tune is on resonance when xi is zero. When tune crosses in the direction of (a) to (e), some particles will be trapped by islands, islands mean these closed area and trapped particles will be transported to larger amplitude and finally they will be lost. This picture is called  particle trapping and it was proposed by Chao and Month. On the other hand, when tune crosses in the direction of (e) to (a), beam emittance will grow because islands initially being at large amplitude come close and disturb beam particles and finally disappears. In our machine, tune crosses in this direction.

## “Emittance growth”

- “Emittance growth”

- “Particle trapping”

**Notes:**
This slide shows simulation results describing the direction dependence. Left side figures are particles in phase space before crossing and right side figures are after crossing. We can see the difference due to crossing direction.

## Experiment data

- Crossing point

- Beam intensity during acceleration

- Black:Suitable dipole
-            correction

- Red:70% dipole
-          correction

**Notes:**
This figure shows experimental data of beam intensity during acceleration. The horizontal axis is time and vertical axis is beam intensity.Black points are obtained data when correction dipole is excited with suitable strength. And when we reduced dipole excitation 30% intentionally,  clear signal of beam loss was observed. At present, resonance crossing is not a problem as long as COD is corrected.

## Hardware improvement in RF system

- Enhancement of RF system:

- RF voltage:   ~5kVpp          ~12kVpp
- Rapid cycling has become possible.

**Notes:**
We made hardware improvement in RF system. We changed Anode power supply and main amplifier during summer shutdown of last year. With new power supply and amplifier, RF voltage is increased from 5kVpp to 12kVpp. Then rapid cycling has become possible.

## Beam extraction

- Fast extraction with kicker and septum
- Try to realize 100% extraction efficiency

- Top and side drawings of the septum magnet

**Notes:**
Next topic is beam extraction. The extraction scheme is fast extraction with kicker and septum. This is top and side drawing of the septum magnet. It is pulse-septum and thickness of septum is only less than 3mm. We are trying to realize 100% extraction efficiency with this thin septum.   

## Beam extraction experiment(1)

- Beam separation with kicker

- Circulating beam

- Separated beam
- with kicker

- 5mm

**Notes:**
First, we measured beam separation with kicker as shown in this figure. Horizontal axis is machine radius and vertical axis is signal of scraper, I mean vertical axis is proportional to the number of particle hitting the scraper. The scraper position can be changed and These signals were obtained by changing scraper position. This is circulating beam and this is separated beam with kicker. We can see clearly that the beam orbit is separated by kicker. 

## Beam extraction experiment(2)

- Experiment set up

**Notes:**
After that, we excited the extraction septum magnet. Then we set fluorescent screen at the extraction beam line like this figure and also set CCD camera.
Here. I show you 

## Summary

- COD and resonance crossing has been overcome.
- Improvements in RF system to realize rapid cycling.
- 100Hz operation was successful.
-    Basic accelerator R&D studies has been completed.

- 150MeV proton FFAG has been developed to be
- a prototype of FFAG for various applications.

- Experimentally,

**Notes:**
As described above, basic ~