# Presentation: 570573

## Opportunities for Beam Physics R&D 
@ the DUV-FEL 

X.J. Wang for DUV-FEL Team
National Synchrotron Light Source

Presented at the DUV FEL 
Accelerator and FEL Physics Workshop 
February 19 - 20, 2004

**Brookhaven Science Associates****U.S. Department of Energy**

**Opportunities for Beam Physics R&D **
**@ the DUV-FEL**
**X.J. Wang for DUV-FEL Team**
**National Synchrotron Light Source**
***Presented at the DUV FEL ***
***Accelerator and FEL Physics Workshop ***
***February 19 - 20, 2004***

**Notes:**
Good Morning!
Dave just presented a beautiful picture of what coherent X-ray can do for the science, he also out the major issues or challenges on the way to realize the coherent X-ray sources. In my talk, I would like to present a picture how DUV-FEL can help to over come those challenges.

## Outline

**Introduction - DUV-FEL and Future Light Sources**
**Beam Physics R&D Opportunities at the DUV-FEL**
**  ****1. Transverse and Longitudinal Emittance Optimization.**
**  ****2. Bunch Compression and Related Beam Physics.**
**  ****3. Timing Jitter and Multi-laser Synchronization.**
**  ****4. Beam instrumentation for Ultra-short High-brightness Electron Beam.**
**  ****5. Other sources: Coherent THz, Atto-second Electron Bunches.**
**Challenges and Summary**

**Notes:**
Here is the outline of my talk.
I will give you a brief introduction of the FEL, specially sing-pass high gain FEL.
After the introduction, I will discuss the DUV-FEL facility, and its major components.
The core of this talk is about the performance of the DUV-FEL, I will present experiment data of the FEL.
The DUV-FEL operation, and NSLS infra-structure to support potential users will also be discussed.

## Introduction

-  DOE Basic Energy Science Advisor Committee (BESAC) Subcommittee in its 20-Year Basic Energy Sciences Facilities Roadmap recommended:
-  “...development in the following areas be a priority: electron gun technology, detector technologies, cutting edge end stations, automation, robotics, energy recovery linacs (ERLs) and superconducting short period undulators.”
-   The BESAC subcommittee further elucidated:
- “The critical enabling technology to advance linac-based light sources is the electron gun. At low repetition rates, the present RF photocathode technology generates 1 mm-mrad normalized emittance bunches with a charge of a nanocoulomb at 100 Hz repetition rates.”

## Greenfield FEL @BESAC

## Timing jitter effects - Laser  e- beam (FEL) Interaction

## Slide 6

## e-

**The timing jitter between the laser (FEL) and e-beam *****is  ******the arriving time jitter of the e-beam relative to the pump laser*****.  Furthermore we can assume the photocathode RF gun laser and the pump laser originate from the same laser,  now the timing jitter is the traveling time jitter of the electron beam only **

**e****-**

- Pump

## DUV-FEL and XFEL

**DUV-FEL and XFEL**

##  Photoinjector Optimization

**6-D performance – smaller emittance and shorter bunch.**
**Flexibility.**
- Photoinjector consists of:
**RF gun.**
**Laser, optical transport and shaping.**
**Emittance compensation magnet.**
**Photocathode.**
**Beam instrumentation.**
**Operating principle.**

## RF Photoinjector Theory

-  Are all emittances uncorrelated?
**K-J.’s theory:**
**Emittance growth (Reiser):**

## VISA Gain Optimization

**VISA Gain Optimization**

## Thermal Emittance

- Electrons are emitted with a kinetic energy *E**k*

- laser spot assumed uniform

- with radius *r*

- Example of measurement for Cu-cathode

***(Courtesy of W. Graves)***

- Linear fit gives *E**k*=0.43 eV

- Nonlinear fit gives rf=3.1+/-0.5,
***cu*=4.73+/-0.04 eV*, *and *E**k*=0.40 eV

- ICFA/BD Sardinia July 2002

## Possible Photocathode RF Gun Test Stand and Femto-second Electron Diffraction

## Emittance Optimization by Programmable Laser Control

- Longitudinal pulse control:
- Transverse profile control
- Microlens array
- Adaptive Optics
- Phase Plate

## Ultra-Short Bunch Generation

- P. Emma of SLAC

## Beam Physics During the Bunch Compression

**1. Seeding a controllable amount of modulation in  RF-gun drive laser****	**
- Measurement and analysis of modulation in electron bunch
-  Comparison with model (PARMELA-
- ELEGANT)
**2. Possible experiments on emittance growth for different charge and compression.**

**t [ps]**

## Femto-second Kilo-Ampere Beam Generation by Longitudinal Emittance Compensation

**Boost Linac**

## Electron Beam Bunch Length and Emittance Along the Linac

## Timing Jitter and Multi-laser Synchronization

- Laser as RF source.
- Re-generate HGHG
- Linac Modulator Stabilization.
- Timing Jitter characterization:
-  Experimental characterization Gun, linac, chicane on timing jitter.
- Multi-laser synchronization

## Phase Jitter Measured between Laser 

- Phase Jitter Measured between Laser
- Oscillator and RF Drive

- Each plot consists of histograms of 8 second duration of a mixer-based phase error measurement. Left plot is for laser oscillator and RF synthesizer driven from same crystal, on right laser output pulses are filtered to drive RF directly.In each plot the outside histograms are data taken by programming+/- 3 degree
- and +/- 2 degree steps, respectively, in the RF path  for calibration.

## e-

**e****-**

- Pump

**        ****To reduce the jitter between electron beam and laser, we need reduce the ****energy jitter**** of the electron beam. Energy jitter can be:**
**Timing jitter between the laser and RF.**
**RF power jitter.**

## Timing Jitter Due to Energy Fluctuation

- For 5 MeV beam through 1 meter, 10-3 energy jitter will lead to 30 fs arrive time jitter. Similar jitter will be generated inside the RF gun,  RF gun energy stability better than 10-4 is required.

## Jitter in the Magnetic Bunch Compressor

**The path length jitter due to the phase jitter can be estimated by**:(RAUBENHEIMER et al, PAC 93)

**For ****σ****z0 ****= 2ps, ******** = 70, ********=200 fs, ********z < 7 fs!!**

## Two-Stage Compression Used for Stability

- late arrival,
- higher energy,
- less chirp

**Two-Stage Compression Used for Stability**

- P. Emma SLAC

## Is  Ti:Sapp Laser a Good Choice for Photoinjector? No!

**Is  Ti:Sapp Laser a Good Choice for Photoinjector? ****No****!**

##  200 fs Yb:glass oscillator

- 1.051	136	      150
- 1.047	117	      177
- Timing jitter: 200fs (FW, detector limited)

** ****200 fs Yb:glass oscillator**

## Possible Beam Instrumentation R&D for Ultra-short High-brightness Electron Beam

**High-resolution beam profile monitors.**
**fs Electro-Optic bunch length monitor.**
**Beam based alignment.**
**fs resolution timing jitter monitor.**

## Jitter Measurement Technique Based on HGHG

- e-beam

- e-beam pulse length

## Possible Jitter Measurement Techniques – RF 

- e-

## Other Sources R&D at the DUV-FEL

- .

- 

- =

- 5

- 5

- a

- s

- 

- =

- 1

- 2

- 0

- a

- s

- Peak current, A

- Peak current, A

**THz Output Optimization**

**Atto-second Bunches by IFEL**

## Challenges

-     To realize the full potential of the DUV-FEL, following challenges needs to overcome:
**1.Funding to support the user program, both beam physics and chemical science.**
**2.Your help to outline the experimental program.**
**3.Your participation can make it successful!**
**     **

## Summary

**    ****DUV-FEL is a unique facility in the world, it can, and it should play critical role in both FEL R&D and beam physics.**
**  ****1. Transverse and Longitudinal Emittance Optimization.**
**  ****2. Bunch Compression and Related Beam Physics.**
**  ****3. Timing Jitter and Multi-laser Synchronization.**
**  ****4. Beam instrumentation for Ultra-short High-brightness Electron Beam.**
**  ****5. Other sources: Coherent THz, Atto-second Electron Bunches.**