Beam Jitter Measurement& Emittance Calculation

Jong Min Yoon

Cornell University

A0 Photoinjector

Mentor : Victor Scarpine & Jinhao Ruan

Outline

A0 Photoinjector Beam Jitter Measurement

Definition of jitter Significance of the jitter measurement Principles of measurement Experimental Setup

Emittance Calculation of Multi-Slit Method Definition of emittance Multi-Slit method Program demonstration

A0 Photoinjector

Electron Beam Parameters

Typically 10 bunches/RF pulse(81.25 MHz) 1 Hz repetition rate Laser energy 16 mJ/pulse @ 263nm <5nC/bunch (have had >12 nC in the past) 4 MeV gun output energy 16 MeV total energy Dp/p ≈ 0.3%@ 16MeV (1nC) Bunch length ≈ 2 mm (1nC) z ≈ 120 mm-mrad (RMS @ 1nC) x,y≈4 mm-mrad (RMS @ 1nC)

1 sec

10μs

81.25

Beam Jitter Measurement

What is Jitter?Ideal Situation

All electron bunches travels at a uniform interval

81.25 MHz or 1/81.25 µs

What is Jitter?Real Situation

The interval is somewhat irregularThis irregularity is called Jitter – in time domain

or Phase Noise – in frequency domain

81.25 MHz or 1/81.25 µs

Why Measuring the Jitter?

The stability of experiments carried out with A0 photoinjector depends sensitively on precise synchronization between the electron beam and other components in A0 photoinjector.

Jitter measurement is the first step to build a precise arrival-time monitor of electron bunches.

Principle of the Beam Phase Monitor

81.25 MHz

Compact ultra-high precision beam phase monitor system, Florian Löhl, FLS 2006, May 16th, 2006

Oscilloscope

Schematic Diagram of Experimental Setup

Schematic Diagram of Experimental Setup

Beam Pick-up

Courtesy of MDI, DESY

Schematic Diagram of Experimental Setup

Nanoseconds Delay Line

3.4ns

Nanoseconds Delay Line

3.5ns

Nanoseconds Delay Line

3.6ns

Amplitude Change along with the Delay Time

Time-of-Arrival to Modulation Voltage

Change in bunch time-of-arrival have difference voltages when laser pulse arrives time mapped into laser modulation.

Compact ultra-high precision beam phase monitor system, Florian Löhl, FLS 2006, May 16th, 2006

Amplitude Change along with the Delay Time

Amplitude Change along with the Delay Time

Slope : -17.715mV/ps

At 3.57ns, sigma of amplitude fluctuation = 51.8mV- Corresponding jitter = 2.924ps

The precision of our setup is not good enough – we want sub 1 ps

Emittance Calculation of Multi-Slit method

Electron Beam Line

What is Emittance?

ɛ = Area in x, x’ plane occupied by beam particles divided by π

Emittance

Along a beamline, the shape of beam ellipse in x, x’ plane changes, But the area πɛ remains constant

Why measuring it?

We can know beam half width, beam half divergence, and whether beam is converging or diverging.

Emittance is one of key parameters for overall performance of an accelerator Luminosity of colliders for particle physics Brightness of synchrotron radiation sources Wavelength range of free electron lasers Resolution of fixed target experiments

Multi-Slit Method

'xx L

Program Demonstration

Conclusion

Jitter measurement First step to build a precise arrival-time monitor of electron

bunches. Principle and setup of measurement are explained. Right now ~2ps precision

Emittance Calculation One of the important beam parameters Multi-slit method Semi-automatic program

References

Ray Fliller III, “Advanced Accelerator R&D at the A0 Photoinjector,” FNAL, February 5, 2008

F. Loehl, et al., “A sub-100 fs electron bunch arrival time monitor system for FLASH,” PAC 2006, Edinburgh, Scotland, 26-30 June, 2006

H. Braun, “Emittance Diagnostics,” CAS Beam diagnostic, Dourdan, 2 June 2008

Special Thanks to…

Victor Scarpine Jinhao Ruan Roger, Erik, and Jean Fermilab IPM program All other interns