# Presentation: 940932

## Neutralized compression and focusing of an intense ion beam for target heating experiments

- J.E. Coleman, D. Ogata, Dept. of Nuclear Engineering, UC Berkeley, Berkeley, CA 94720, USA.
- P.A. Seidl, P.K. Roy, LBNL, Berkeley, CA 94720, USA.
- E.P. Gilson, A.B. Sefkow, PPPL, New Jersey 08543, USA.
- D.R. Welch, Voss Scientific, Albuquerque, NM 87108, USA.

## Neutralized Drift Compression Experiment (NDCX)

**Neutralized Drift Compression Experiment (NDCX)**

_***Outline***_
- Objectives
- Fundamental physics
- Experimental layout
- Measurements of beam
- Axial compression
- Transverse focusing
- Simultaneous focusing

## Neutralized compression and focusing experiment objectives

**Demonstrate capabilities for WDM experiments**
**Control beam envelope****	****	****	****	****         **
**Demonstrate effective neutralization of the beam space-charge****	****	****	****	****	****         **
**Control velocity tilt on beam**
**  ****Effects of net defocusing****	****	****	****         **
**  ****Effects of field imperfections****	****	****	**
**Understand limitations on minimal spot size**
**  ****Emittance****	****	****	****	****	**
**  ****Aberrations**
**Effectively measure longitudinal phase space and temperature**

## Warm Dense Matter Target Experiments

**WDM is that region in temperature (T) - density (********) space: ****	****	****	****	****	****(.1 eV < T < 10 eV and .1 ********o**** < ********o**** < 10 ********o****)**
**Not described as normal condensed matter **
**Not described by weakly coupled plasma theory**
**Additional System Requirements**
**t****LTE**** << ****t****pulse**** << t****hydro**** = ********z / c****s**

**- strong coupling parameter**
**V****ii ****- interaction energy between particles**
**T - kinetic energy**

**Warm Dense Matter Target Experiments**

**A - heat slowly**
**B - heat rapidly**
**C - shock heat and compress**

**A**

**C**

**B**

- solid

- vapor

- 2 phase mixture

- (courtesy R. Lee, LLNL)

**Aluminum**

**WDM**

- liquid

- (courtesy R. More, NIFS and LBNL)

**WDM**

## Neutralizing the space charge provides the ability to focus K+ ion beams to a smaller spot

**High K = 7 x 10****-4****	****    ****I****beam**** = 28 mA****	****E****beam**** = 300 keV**

**Initial Beam Radius**

- r0

**Beam Convergence Angle**

- = ao’

**Envelope equation for a drifting beam**

- (P.K. Roy Dec. 2003)

## The neutralized K+ ion beam bunch is longitudinally compressed using a velocity tilt

*z**o*

**In****itial Pulse Length**

**Velocity Tilt**

**Longitudinal Velocity**
**Spread**

**Compression Ratio**

**The neutralized K****+**** ion beam bunch is longitudinally compressed using a velocity tilt**

- Injector

- 4 Quadrupole Magnets

- Induction
- Bunching
- Module

- Plasma Column

- Experiment
- LSP Calculation

- Experiment
- LSP Calculation

**Longitudinal Compression**

**Velocity of compressing beam**

**Focal length**

*f*

**Notes:**
3D parallel Lsp particle-in-cell (PIC) code using a fully kinetic energy-conserving algorithm.  (Large Scale Plasmas)

 T. P. Hughes, S. S. Yu, and  R. E. Clark, Physics Review ST-AB 2, 110401 (1999); D. R. Welch, D. V. Rose, B. V. Oliver, and R. E. Clark, Nuclear Instruments & Methods in Physics Research A 464, 134 (2001). Lsp is a software product of Mission Research Corporation, Albuquerque, NM ().

## 4-solenoid transport, Induction Bunching Module, and neutralization column 

**413 cm**

**Emitter**
**surface**

**Pierce **
**cone**

**Extractor **
**plate**

**Suppression electrodes**
**and aperture**

**Diagnostic **
**box**

**Suppression**
** ****electrode**

**Diagnostic **
**box**

**129 cm**

**Induction**
**Bunching **
**Module**

**FEPS**

**FCAPS**

**4-solenoid transport, Induction Bunching Module, and neutralization column **

**2.6, 1.4, 0.6, 2.3 T**

**Envelope before tilt**
**a(281) = 15 mm**
**a’(281) = -30 mrad**

**26-mA**
**300-keV**
**K****+**** ion beam**

**Solenoid Tune**

**Beam envelope**

## Two different plasma sources used to neutralize the beam space charge

**Two different plasma sources used to neutralize the beam space charge**

_**Ferro-electric plasma source (FEPS)**_

_**Filtered cathodic arc plasma source (FCAPS)**_

**BaTi ceramic rings**

**Al cathode**

**Filter Coil**

**n****e-**** ~ 10****10**** cm****-3**

**n****e-**** ~ 10****14**** cm****-3**

## A monochromatic 300 kV, 3 s pulse was extracted for these experiments

**A monochromatic 300 kV, 3 ********s pulse was extracted for these experiments**

**Improved**
**Velocity**
**Tilt**

- Beam space charge must be
- neutralized to diagnose at
- the end of drift section

## Velocity tilt has a time dependent defocusing effect which causes a chromatic aberration

**15 % velocity tilt**

**Velocity tilt has a time dependent defocusing effect which causes a chromatic aberration**

**50**
**0**
**-50**

**Voltage (kV)**

**10****5**
**5 x 10****4**
**0**
**-5 x 10****4**
**-10****5**

**Axial velocity (m/s)**

**0           50        100        150       200**
**Time (ns)**

**0           50        100        150       200**
**Time (ns)**

**Before tilt**
**a(281) = 15 mm**
**a’(281) = -30 mrad**

**Change in envelope angle**

**Ideal velocity tilt**

**Beam envelope**

## Scans in energy demonstrate tuning the beam to axial focus

**Energy (keV)**

**Compression Ratios: >100 ± 10 %**

**FWHM (ns): 2.4 ± 0.8**

## Pinhole Faraday cup measures fast time response in a plasma environment

**Pinhole Faraday cup measur****es**** fast t****ime response in a plasma environment**

**Pinhole Faraday cup**

**Front plate**
**Middle plate (-)**
**Collector (+)**

**RC time constant**

- C = oA/d

- A: area of collector (31.67 cm2)
- d: plate distance (1 mm)
- R: 50  transmission line

**t****RC ****~ 1.3 ns**
**t****meas**** ≤ 1 ns**** **

**Two consecut****ive plates used to screen out plasma particles.**
**Measured ion current reduced by a factor of 40.**

## Phototube measures beam induced light emission with sub ns resolution

- Gated input to driver

- Pulse to shutter

- Ferro-electric shutter
- (in front of photo tube)

- Signal monitor

- SHV bias from power supply

**Phototube setup**

- Displaytech driver

**Phototube measur****es beam induced light emission with sub ns resolution**

**Phototube construction**
- Units in mm

- Input Pulse

- Driver Output

- (shown open)

## Phototube (PT) and fast Faraday cup (FFC) measurements complement each other well

**Phototube (PT) and fast Faraday cup (FFC) measurements complement each other well**

**<Q> = 80.7 ± 5.4 nC**
**<Q> = 75.5 ± 5.0 nC**

**FFC**

**<Vdt> = 17.4 ± 0.5 nV s**

**PT**

**FWHM (ns): ****1.72****, ****1.94**

## Spread in axial compression is due to velocity tilt jitter

**Spread in axial compression is due to velocity tilt jitter**

**5 ns Jitter**

**For 30 shots**
**10 ns Jitter**
**Total V s ± 5 %**

******V = ****I****deal - actual**

- Compressed
- Pulse Width

## Fourth solenoid tweaked to optimize simultaneous focus

**10 ns gates**

**	****Best case**
**a = 4.4 mm   FWHM = 5.18 mm**
**b = 3.99 mm FWHM = 4.69 mm**

**a(281) = 15 mm**
**a’(281) = -30 mrad**

******B = 200 G ~ ********a’ = 1 mrad **

## Time scans demonstrate simultaneous focus

**	****Best case**
**a = 4.4 mm  FWHM = 5.18 mm**
**b = 3.99 mm FWHM = 4.69 mm**

**FWHM (ns): ****1.72****, ****1.94**

**n****K+**** ~ 10****11**** cm****-3     ****2.3 x 10****-3**** J/cm****2**

## Optical diagnostics to measure simultaneous focus 

- Photo tube

- 135 mm Nikkor lens for CCD Camera

- Ferro-electric shutter

- 50% transmitting and 50% reflecting mirror

**Optical diagnostics to measure simultaneous focus **

- improved optics for increasing light collection
- efficiency for phototube and
- CCD Camera

- First attempt to simultaneously measure
- Axial compression and J(x,y)  => **S/N too low**

- Vacuum

- Vacuum

- Camera

- Phototube

- Phototube

- 50% transmitting and 50% reflecting mirror

## Conclusions

**Demonstrate capabilities for WDM experiments**
**Control beam envelope****	****	****	****	****        ****√**
**Demonstrate effective neutralization of the beam space-charge****	****	****	****	****	****         ****	****        ****√**
**Control velocity tilt on beam**
**  ****Effects of net defocusing****	****	****	****         ****	****         ****√**
**  ****Effects of field imperfections****	****	****	****         ****√**
**Understand limitations on minimal spot size**
**  ****Emittance****	****	****	****	****	****         ****√**
**  ****Aberrations****	****	****	****	****	****         ****√**
**Effectively measure longitudinal phase space and temperature**

## End

**End**

## Extras

**Extras**

## Electrostatic energy analyzer provides measurements of 2-D longitudinal phase space and temperature

**1-d Maxwellian Beam**
**Gaussian **

**Electrostatic energy analyzer provides**** measurements of 2-D longitudinal phase space and temperature**

***l*****1**

***l*****2**

**M = f/(g-*****l*****1****)**

**f****2**** = (*****l*****1****-g)(*****l*****2****-g)**

**Resolution**

**Magnifcation**

**Longitudinal Phase Space**

**First Aperture**

**Entrance Slit**
**Width: w**

**Deflector Gap: d**

**Radius: a**

**Diagnostic**

**Entrance**
**Slit**

**Outer**
**Deflector**

**I****nner**
**Deflector**

**Term****i****nat****i****ng**
**Electrode**

**Diagnostic**

**Term****i****nat****i****ng**
**Electrode**

**Second **
**Aperture**

## Advantages of using ions
Uniform heating and energy deposition of large volumes.
No shocks, No x-ray or e- preheat.
tLTE << tpulse << thydro.

**Simple target example: ****Al Foil**** of solid or “foam” metal**

- (dE/dX figure from L.C Northcliffe and R.F.Schilling, Nuclear Data Tables, **A7**, 233 (1970))

**E****entrance ****= 1.0 MeV/amu**
**E****peak ****= 0.6 MeV/amu**
**E****exit**** = 0.4 MeV/amu**
******dE/dx)/(dE/dx) ≈ 0.05**

**Advantages of using ions**
**Uniform**** heating and energy deposition of large volumes.**
**No shocks, No x-ray or e****-**** preheat.**
**t****LTE**** << ****t****pulse**** << t****hydro****.**

**Enter foil**

**Exit foil**

**Neon Ion beam **

**Strategy: Operating at the Bragg Peak**

******dE**

**dx**

****** ********T**

- (courtesy J.J. Barnard, LLNL and LBNL)

## A new bunching module will increase the voltage amplitude and voltage ramp duration

**14 --> 20 induction cores ****--> higher voltage amplitude & ********V********t**

**Gap geometry is flexible; opportunity to optimize.**

- V (kV)

- 250x compression (model)

- 60x compression measured, modeled

- 125x compression (model)

**Notes:**
core is driven by a thyratron-switched modulator.  Because the modulator for each core can be designed to produce different waveforms and can be triggered independently, a variety of waveforms can be produced at the acceleration gap using the 14 discrete building blocks. 

## 4-Solenoid Transport, NDCX tune, Induction Bunching Module, and neutralization column 

**4-Solenoid Transport, NDCX tune, Induction Bunching Module, and neutralization column **

**Camera /**
**Photo tube**

**Faraday cup**
**4 in square scintillator**
**Horizontally & Vertically Driven Slits and Slit-Cups**

**Diagnostic Box 2**

**Diagnostic Box 1**

**4 cm fast Faraday cup (FFC)**
**4 cm Scintillator**

**2.6 T****	****1.4 T****	**** 0.6 T        2.3 T**

## For WDM experiments, simultaneous longitudinal compression and transverse focusing must be demonstrated

**For WDM experiments, simultaneous longitudinal compression and transverse focusing must be demonstrated**

- 7.5 mr 13.5 mr

- Net defocusing in gap due to energy change, Er

*Angle at entrance to bunching module*

**Experiment**

**LSP Calculation**

- (m)

- (m)

- z (m)

- B (T)

**2.6  1.4   0.6  2.3**

**Notes:**
Space charge couples transverse & longitudinal  dimensions

## Initial measurements of axial focus

**	****070314**
**Energy (keV): ****300****, ****301**
**Compression Ratios: ****65****, ****132**
**FWHM (ns): ****4.07****, ****1.42**

- Later measurements with FFC and **Both** plasma sources were confounded by FCAPS plasma

## Phototube (PT) demonstrates method of neutralization is not critical for axial focus

- Due to loss of light a compression ratio cannot be resolved from the PT but only inferred

**250 keV**

**350 keV**

- From FFC

## Time scans demonstrate simultaneous focus

**	****Best case**
**a = 4.4 mm  FWHM = 5.18 mm**
**b = 3.99 mm FWHM = 4.69 mm**

**5.085 us****	****	****        5.095 us****	****                  5.105 us**

**All 10 ns gates**