# Presentation: 666119

## 
Ion Source and Injector Experiments at the HIF/VNL

J. W. Kwan, D. Baca, E. Henestroza, J. Kapica, F. M. Bieniosek, W.L. Waldron, J.-L. Vay, S. Yu, LBNLG.A. Westenskow, D. P. Grote, E. Halaxa, LLNLI. Haber, Univ. of MarylandL. Grisham, PPPL

HIF Symposium, Princeton, NJJune 7, 2004

**Ion Source and Injector Experiments ****at the HIF/VNL**
**J. W. Kwan, D. Baca, E. Henestroza, J. Kapica, F. M. Bieniosek, ****W.L. Waldron, J.-L. Vay, S. Yu, LBNL****G.A. Westenskow, D. P. Grote, E. Halaxa, LLNL****I. Haber, Univ. of Maryland****L. Grisham, PPPL**
- HIF Symposium, Princeton, NJJune 7, 2004

## This talk is dedicated to the amazing Cicada

**In the hope that the ****HIF symposium 2021, Princeton, NJ**
**will tell the story of ****heavy ion beams achieving fusion**

## A summary of main experiments

| Experiment | Purpose | Facility |
| --- | --- | --- |
| Large diameter ion diode | Study large beam optics and benchmark simulation | STS-500 |
| RF plasma source | Prepare source for Merging Beamlets | STS-100 |
| Merging Beamlets  | High average current density (J) injector | STS-500 |
| Negative ions | Check if Cl- is applicable for HIF | STS-100 |
| Accel-decel injection | High line charge density () beam for solenoid focusing | NDCX |
| Al-Si source development | Long and short pulse length for special applications  | STS-50 |

## Experiments on STS-500 to study beam optics

- 500 kV, 17 s pulse, 1.0 s rise time

## Experimental Apparatus 

**10-cm diameter K+ Al-Si source with Pierce electrode**

**For Beam Imaging, use:**
**Kapton**
**100 ********m Alumina scintillator**

**Faraday cup with electron suppressor using a honeycomb bottom**

**Slit scanners: 2 mils, 17.8 cm apart**

## Good agreement between experimental results and simulation predictions

**Good agreement between experimental results and simulation predictions**

- _Experimental results_

_**150 kV**__**48A heater**_

**Emittance taken here**

- 10 cm source, 21 cm diode gap,Space charge limited mode

## The emission-limited under-dense beam did not show much aberration

## Aperturing the large beam

**Aperturing the large beam**

- _7.5 cm aperture_

- aperture

| Aperture | Beam fraction | Norm. emittance | Brightness ratio |
| --- | --- | --- | --- |
| None | 100% | 0.60 | 1 |
| 7.5 cm | 55% | 0.152 | 8.6 |
| 5.0 cm | 25% | 0.048 | 39 |

- Brightness comparison

## The apertured beam showed no aberrations

**Optical image from the alumina scintillator taken with a gated camera**

**Integrated current density profile (compares to a slit cup measurement)**

**7.5 cm aperture**

## Time-dependent adaptive-mesh simulation shows how to achieve a fast rise time

**Red--expt. data;****black--simulation**

**Time-dependent adaptive-mesh simulation shows how to achieve a fast rise time**

- _Current at Faraday cup_

-    The current pulse rises faster than the applied voltage pulse.
-    Capacitive coupling softens the signal rise time.
-    One dimensional theoretical model:
-    Example: 50ns/350ns

- _Applied Diode Voltage_

## Merging high density beamlets is an innovative approach to build compact multi-beam HIF injector

-    Achieve high current, _and_ high average current density
-    Minimize the injector and matching section size for a    compact multi-beam HIF driver system

## WARP-3D simulation to study emittance growth

- 39.9 m

- 0.5 m past column

- 1.9 m

- 4.1 m

**91 beamlets (each semi-Gaussian, 0.006 A, 0.003 π-mm-mrad, 160k particles),  1.2-1.6 MeV, 1024x1024, 1 cm/step**
**After the beamlets are merged, the emittances settle down at about 1.0 pi-mm-mrad.**
**Emittance is optimized if the number of beamlets is large and the beamlets are slight converging, but only weakly dependent on the emittance of each beamlet. **

- 4.1 m

- 1.9 m

- _Configuration               Phase_

## Testing Plasma Source on STS-100

_**Testing Plasma Source on STS-100**_

**RF-driven 26 cm diam. multi-cusp source inside ceramic insulator**

**500********s, 20kW, ~ 10 MHz Compact RF oscillator**

## Characterization of the RF plasma source

**18 kW of 13 MHz RF,****multicusp Argon plasma source at optimum pressure of 2 mTorr**

**Multi-aperture extracts****61 beamlets at 100 mA/cm****2**** using high gradient insulator**

**Einzel lens to focus beamlets and examine charge exchange loss**

## RF plasma source beamlets results

**Achieve 100 mA/cm****2**

**90% Ar****+**

**< 0.5% low energy component**

- _Electrostatic energy analyser_

## Full Gradient test on STS-500 will begin this month

**Full Gradient test on STS-500 will begin this month**

**This experiment will confirm full current density, its uniformity, and voltage gradient across vacuum gap.**

## Merging Beamlets test will begin in September

**Apparatus is full scale in dimension, but****1/4 scale in voltage,****so 1/8 in current.**
**The experiment will study emittance growth physics, beam matching parameters, and beam halos.**
**Success in this experiment will establish the basis for building a (future) driver-scale injector.**

## Negative ion beams is an innovative idea in response to the gas and electrons problem

**Avoid the problem of electrons being trapped in positive ion beams**
**No charge exchange problem to cause energy dispersion **
**Low ion temperature for both negative and positive halogen ions**
**Can be efficiently converted to atomic neutrals by laser photo-detachment, if this can be of advantage to the final focusing at the fusion chamber.**

## Negative ion sources for HIF Drivers

- We have already demonstrated 45 mA/cm2 of pure Cl- ions with relatively low co-extracted electrons (7:1) from a single aperture.
- Current density scaled almost linearly with RF power (12.56 MHz).
- Current density of Cl+ ~ 1.3 x Cl-.
- A new experiment will run on STS-100 this summer to examine the negative ion production from a large source, measure emittance, and form an array of beamlets.

## The accel-decel injector is an innovation to meet our HEDP challenge: build a low energy high current driver to hit target

**At 3.3 mC/m, the HEDP   ******** is > 10****x**** the present HCX experiment.**
**Longitudinal emittance can coupling to transverse emittance**
**Possible compression limit when the bunch’s forward kinetic energy becomes comparable to the beam potential.**

**The accel-decel injector is an innovation to meet our HEDP challenge: build a low energy high current driver to hit target**

**In an accel-decel injector, a long pulse is compressed when decelerates into a solenoid, the Super-High ******** (line charge density) bunch is then accelerated without expansion.  **

******= I/v**

*The situation is similar to loading passengers into a roller coaster train.*

**10A x 100ns****= 0.3m x 3.3 ********C/m**

## A proof-of-principle Super-High  experiment 

- 60 cm solenoid located 5 cm from ground plate
- (winding:7.7cm ID, 9.2 cm OD,1 Mega Amp-Turn)

- Bz/100(Tesla)

- 30 kV

- 0 kV

- -220 kV

- -35 kV

- -55 kV

**A proof-of-principle Super-High ******** experiment **

- K+ Gun (using Al-Si source)

- E.H.20.MAY.04

**NDCX-1**

## Conclusion

**Several ion source/injector experiments at the HIF/VNL are aimed at:****-- supporting on-going HIF needs, ****-- developing future HIF driver, ****-- innovative concepts (high J, high ********, fast rise, ****	****negative ions)**
**In response to funding difficulty, the injector test facility at LLNL is scheduled to terminate in March 2004.  **
**We hope STS-100 can be moved to LBNL to continue ion source development. **

## What is unchanged is the constantly changing direction.What is certain is the permanently uncertain state.

_**After Thought**_