LINAC4 Meeting

LINAC4 Meeting

Status of the future CERN H- RF ion source

Th. Meinschad / AB-ABP-HSL

Introduction (volume source /H- production / optimisation ) Collaboration – STATUS The DESY source (information) CERN concept (possible designs / compensation / RF) LEBT (simulations / emittance growth: RS) What do we have to expect ? What has to be done ! Time Schedule

Linac4 Meeting, Th. Meinschad, 2nd May 2006

Contents


RF driven volume source: plasma production

Inductively coupled plasma generated by 2 MHz RF. The curling E-field is concentrated inside the solenoidal antenna loops with the highest ionizing field close to the antenna. Well suited for producing plasma in a large volume, which can be easily confined with a multicusp magnetic field.Other industrial applications: coating, etching …

rot E = - dB/dt describes a curling electrical field generated by a changing magnetic field in the absence of charge. Such a B-field can be produced with an alternating current i=i0cos(wt).


RF driven volume source: H- formation

D. Moehs: Proton Driver Requirements, May 2004

2: dissociative attachment

H- destruction

ALSO surface processes in the DESY source: recombinative desorption: H* + H* + wall H2(”) + wall

1:


Plasma ParametersnH2 ~ 1014 – 1015 cm-3

ne ~ 1012 – 1013 cm-3

TH_ ~ 0. 35 -1.4eV / 0.03-0.11eV

Te ~ 2eV / 15eV

RF driven volume source: E & M fields

Filter Field: ~ 200 Gauss

Cusp Field: ~ 2500 GaussPermanent Magnets (SmCo, NdFeB)Cooling ! (50kW RF/50mA H-/ 1% df / 500Watts)

Bacal et al.: IEEE Trans. on Plasma Science Vol. 33, No. 6

Solution: Tandem Source separation: DTe

-1/2

pressure ~ mTorrhydrogen flux ~ 1 - 10 sccm

emittance !


RF driven volume source: external antenna

Sputtering problems on the Porcelain coated antenna external antenna DESY and later SNS longer lifetime

R. F. Welton, RSI 75, 2004

In 2002 J. Peters (DESY) introduced the RF source with an external antenna to the H- community (Proc. EPAC 2002, p: 1727 – 1729).

SNS power upgrade (94mA, 1.23ms, 60Hz) similar to SPL requ.


H- Source Collaboration - STATUS

DESY wanted to develop the collaboration to a prime example for further collaborations (other research labs are also interested) 1st proposal from DESY arrived, CERN sent a improved version back if both partners agree upon the collaboration paper, the technical annex can be attacked (details of the collaboration) – maybe critical ! Constant improvement of the source new tech. drawings

(e.g.: spectrometer, biased plasma electrode … )

Technical drawings (up to date) in digitized version (IDEAS) Equipment: Ignition Source & Piezo Gas Valve Small (defined) amount of manpower basically no other costs for CERN

Content of the Collaboration – what CERN gets !

Information – why a delay:


RF driven volume source: DESY type

DESY RF source

Current: 40 mA (54 mA!) Pulse length: 0.1 ms Repetition rate: 5 Hz Duty Factor: 0.05 % Extraction: 35 kV ε90%n,rms: 0.25 mm mrad Caesium: free Lifetime: 25000 hours

RF volume source with the best performance !(surface & volume)

10 cm



plasma chamber (Al2O3)

RF coil (water flushed)

VESPEL jacketwith SmCo bars – multicusp configuration



H- correction

e- deflectionspace for e-dump

spectrometer (steel)water cooled

steel boxes with NdFeB insidelinings to shape the field


RF driven volume source: DESY setup

pump

HV cage (35kV), inside

HV cage (35kV), outside

source body

RF input, from coupling box

piezo valve & ignition source

coupling box (matching, HV insulation)


RF driven volume source: CERN concept I

source bucket (modified)

HV insulation & vacuumon 60kV platform

side view

DESY source bucket (1:1)

wall

Main issues:cost – use what is available, pumping connectionsas close to the 1st LEBT solenoid as possible


RF driven volume source: CERN concepts II

Pumps outside the HV cagePumps outside the HV cage600mm insulator

Pumps inside the HV cageSmall corona ring (230mm)


RF driven volume source: CERN concept (elec.)

2 HV platforms (post-acc) active OR passive compensation RF Generator (on ground) Coupling box (matching & HV isolation 2 CERN pumping stations (30 m3/h scroll & 500l/s TMP) on a 60kV platform 2 (50Hz) isolation transformer 2 racks on Teflon bars

Base area: 3.0 x 2.8 m2 !! Schematics of the HV cage (passive compensation)

Preliminary !


RF driven volume source: compensation

H- pulse / measured at DESY !19.3kW forward / 1.2kW ref.

38mA peak/ 3 ms

Active / Passive compensation / Energy spread

passive: voltage droop over 0.4ms: 720V / 2.6 F, 200Factive: ~0V, 1.2F, 100F, complicated !

“unofficial” collaboration withSNS, FNAL: long pulse / emittance


RF driven volume source: RF Amplifier

RF Generator (M. Paoluzzi): (SPL specs)1.8-2.2MHz, rep. rate: 1-60Hz, pulsed, pulse length: 0.2-2ms, 1-100kW peak power, sine wave, low distortion level, high pulse stability

A RF generator (~2MHz, 50, ~1-2kV ~20-30A peak) produces a RF signal, which is used to heat the Hydrogen plasma. The generator is coupled to the RF coil (L ~ H, some ohms at 2MHz) via an impedance matching network. The RF power is coupled into the plasma inductively (transformer model).

Problem: RF isolation transformer2 MHz for 100kV, df: 12%


RF driven volume source: facts & problems

DESY RF source


What do we have to expect ?


DESY RF source


CERN RF source (3MeVTCC)

Current: +40 mA Pulse length: 0.4 ms Repetition rate: 1 Hz Duty Factor: 0.04 % Extraction: 95 kV ε90%n,rms: growth Caesium: free Lifetime:


Emittance growth due to post-acceleration !


DESY RF source



Current: +40 mA Pulse length: 0.4 ms Repetition rate: 1 Hz Duty Factor: 0.04 % Extraction: 95 kV ε90%n,rms: growth Caesium: free Lifetime:

CERN RF source (LINAC4)

Current: 80mA Pulse length: 0.4 ms Repetition rate: 2 Hz Duty Factor: 0.08 % Extraction: 95 kV ε90%n,rms: growth Caesium: X Lifetime:


Problems due to high current requirement !


RF driven volume source: TASKS

DESY RF source



Current: +40 mA Pulse length: 0.4 ms Repetition rate: 1 Hz Duty Factor: 0.04 % Extraction: 95 kV ε90%n,rms: growth (+33%)Caesium: free Lifetime:

CERN RF source (LINAC4)

Current: 80mA Pulse length: 0.4 ms Repetition rate: 2 Hz Duty Factor: 0.08 % Extraction: 95 kV ε90%n,rms: growth (+6%)Caesium: X Lifetime:

Technical drawings (DESY)

Implementation (final design, CERN)

Construction (company)

RF Generator (RF)

Equipment (CERN)

LEBT (low cost)

Installation (HSL)

Pressure Test (end 2006)

HV Test (HSL)

Plasma Test (HSL)

Commissioning (HSL)

LEBT design (low growth)


RF driven volume source: Time schedule

LINAC4 Meeting

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